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Copyright 1982 by Academic Press, Inc. "Afitferf in U.S.A. .
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037226
SL
Inhalation Exposure of Rats to Vapors of 1-Nitropropane at 100 ppm
Travis B, Griffin, Arthur a. Stein, and Frederick Coulston Coulslon International Corporation, White Sands Research Center. 2512 Christina Place.
Alamogordo. New Mexico 88310
Reprinted from Ecotoxicology and Environmental Safety, Volume 6, No. 3, June 1982 Copyright 1982 by Academic Press, Inc. Printed in V.S.A.
SL 037227
ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 6, 268-2S2 (1982)
Inhalation Exposure of Rats to Vapors of 1-Nitropropane at 100 ppm
Travis B. Griffin, Arthur A. Stein, and Frederick Coulston
SL 037228
ECOTOXICOLOCY AND ENVIRONMENTAL SAFETY 6, 268-282 (1982)
Inhalation Exposure of Rats to Vapors of 1-Nitropropane at 100 ppm
Travis B. Griffin, Arthur A. Stein, and Frederick Coulston
Coulston International Corporation, White Santis Research Center, 2512 Christina Place, Alamogordo, New Mexico 88310
Received March 12, 1982
Male and female Long-Evans rats were exposed by inhalation to vapors of 1 -nitropropane at 100 ppm. The animals were exposed 7 hr per day, 5 days per week for periods up to 21W months. Groups of rats were killed after 1, 3, 12, and 18 months of exposure and additional groups of exposed rats were removed from the exposure chamber after 3 and 12 months and held under nonexposure conditions for the remainder of the study. All animals remaining alive were killed 2116 months after the start of the study. The results of gross necropsies of the animals did not disclose any effects of exposure to 1 nitropropane on any of the organs or tissues. There were no histopathologic effects on the liver and, in particular, no induction of hepatocarcinomas. No effects were observed on final body weights or the weights of liver, kidney, or brain. There were no effects on serum chemistry or hematology.
INTRODUCTION
1-Nitropropane is one of a mixture of nitroparaffins produced from the vaporphase nitration of propane and purified by distillation. It is used as a propellant fuel, gasoline additive, solvent, and in chemical synthesis.
The nitroparaffins are moderately toxic by oral intake, but the potential for toxic effects resulting from inhalation is of greater significance because of the possibility of exposures in industrial uses. Recent studies by inhalation have emphasized the effects on rats of subchronic exposures (Lewis et ai, 1979) and chronic exposures (Griffin et al., 1980, 1981) to 2-nitropropane. These studies showed that if the concentration of 2-nitropropane is high enough (100 ppm or higher) severe hepatotoxicity results and continued exposure of the damaged liver to the chemical can lead to the formation of hepatocarcinomas. Neither hepatotoxicity nor the formation of hepatocarcinomas are a consequence of the exposure of rats to lower concentrations (25 ppm) of 2-nitropropane,
In the present report, the study of the potential effects of chronic exposures to nitroparaffins was extended to 1-nitropropane (1-NP). Rats were exposed to vapors of 1-NP at 100 ppm in a study which lasted for about 21 months. The animals were exposed 7 hr per day, 5 days per week. Clinical laboratory examinations were conducted on groups of animals sacrificed at interim time intervals of 1, 3, 12, and 18 months, as well as at the terminal sacrifice.
METHODS AND MATERIALS
Animals. Five hundred BLU:(LE) BR Long-Evans rats, 250 males and 250 females, were obtained from the Blue Spruce Farms, Altamont, New York. The
0147-6S13/82/030268-15S02.00/0 Copyright C 1982 by Academic Press. Inc.
All rights of reproduction in any form reserved.
268
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INHALATION OF 1-NP AT 100 ppm
269
animals were divided into an exposure group consisting of 125 males and 125 females and a control group also consisting of 125 male and 125 female rats. The animals were individually housed in galvanized iron cages.
Test substance. The 1-nitropropane utilized in this study was identified as NIPAR S-10, LNB-62425, DR-5 obtained from International Minerals and Chem ical Corporation.
Chamber operations. The test group was exposed to vapors of 1-nitropropane at 100 ppm for 7 hr per day, 5 days per week. To minimize oral exposure to 1-NP, which could occur through absorption of the compound in the diet, food and water were removed when the animals were placed in the exposure chamber. After the 7-hr exposure period, the cages were removed from the chamber and the water bottles and food cups were replaced in their respective cages. Food and water were similarly removed from the cages of the Control animals during the exposure period. The control animals were housed in a room having environmental conditions similar to those in the exposure chamber.
The exposure chamber was 8 feet wide, 8 feet high, and 12 feet long, with controlled temperature and humidity, modified to permit introduction of the 1-NP vapors. The effluent from the vapor generator was injected into a section of the chamber containing circulating fans which mixed the effluent with air from the intake air duct. This fan circulated air within the entire exposure chamber itself and thereby maintained uniform air mixtures. An exhaust blower removed air from the chamber at a constant rate. It was operated at a velocity sufficient to provide 15 air changes per hour in the exposure chamber.
The vapor generator was maintained in a thermostated water bath at a tem perature of 45C. Vapors were generated by bubbling purified nitrogen through liquid 1-NP in an all-glass vessel. The vapor of 1-NP and nitrogen were then introduced into the mixing chamber prior to their transfer to the exposure chamber.
The concentration of 1-NP vapors in the exposure chamber was monitored by frequent sampling. Routinely at least three air samples were obtained daily: one at 30 min after the chamber was started, another after 3 hr, and the third after 5 hr. The air sample was removed from the chamber by means of an air-sampling pump operating with a limiting orifice to control flow rate of air through it. The air from the chamber was withdrawn through two glass impingers aligned in series, filled with ethyl acetate, and immersed in an ice bath. Prior to usage each sampling train, including the two ethyl acetate-filled impingers, the limiting orifice, and the sampling pump, was calibrated using a spirometer as the primary standard.
After a suitable sampling period, the contents of the impingers were transferred to a volumetric flask and a known quantity of 2-nitropropane (2-NP) was added as an internal standard. After dilution to volume, an aliquot was injected into a gas chromatograph and compared with a standard containing the same concen tration of 2-NP and a known concentration of 1-NP. Gas chromatographic con ditions were as follows:
column: 6 ft glass packed with 10% Carbowax 20M on 80/100-mesh Chromosorb W-AW and maintained at 90C;
injection port: 150C, flame ionization detector: 300C. Necropsy. Ten male and ten female rats from both the exposed and control
SL 037230
270
griffin, stein, and coulston
TABLE 1
Weekly Mean Concentrations of 1-Nitropropane in Atmosphere of Exposure Chamber Expressed as ppm
Week
Concn
Week
Concn
Week
Concn
Week
Concn
1 104 21 104 41 102 61
2 97 22 101 42 101 62
3 104 23 103 43
99 63
4 94 24 103 44 99 64
5 105 25 105 45
98 65
6 94 26 103 46 98 66
7 92 27 100 47 101 67
8 106 28
99 48
95 68
9 103 29 100 49 101 69
10 101 30 102 50
99 70
11 102 31 110 51 100 71
12 99 32 100 52 99 72
13 100 33 102 53 102 73
14 102 34 103 54 104 74
15 108 35 101 55 100 75
16 101 36
96 56
99 76
17 98 37 98 57 100 77
18 100 38 102 58
98 78
19 101 39 100 59
97 79
20 100 40 102 60
96 80
100 103 103 102 102 103 103 101 100 99 100 99 102 101 99 98 99 101 101 99
Note. Average 1 SD = 101 3.
groups were killed after 1, 3, 12, and 18 months of exposure to 1-nitropropane. Also, at 3 and 12 months, 10 males and 10 females were removed from the exposed group and thereafter maintained under nonexposure conditions. All animals re maining alive were sacrificed 21 Vi months after exposure was initiated. A complete necropsy was performed on each animal killed at the end of each study period or whenever a rat became moribund or was found dead. All tissues and organs were examined during the necropsy, but special care was given to examination of the liver, the suspected target organ.
Microscopy. Representative sections from 26 organs, as well as samples from all gross pathology, were taken for microscopic preparations from each animal. The tissues were fixed in 10% formalin, processed on a Technicon auto tissue processor, embedded in paraffin, cut at 5 /im thickness, and stained with hema toxylin and eosin.
Clinical chemistry and hematology. At the time of necropsy blood samples via the aorta were obtained for clinical chemistry and hematology. Serum samples were used for determinations of the following: glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), isocitric dehydrogenase (ICDH), total bilirubin, total protein, creatinine, urea nitrogen (BUN), sodium, and potas sium. Hematologic examination included measurements of the following: methemoglobin, hemoglobin, packed cell volume (hematocrit), red blood cell count, white blood cell count, and prothrombin time.
SL 037231
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271
TABLE 2 Body Weights of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 21 Yi months exposed
3 months exposed/ 18 Vi months recovery*
12 months exposed/ 9Vi months recovery*
381 32(10) 509 42 (10) 655 65 (10) 674 62 (10) 671 94 (60)
367 31 (10) 484 48 (10) 580 78(10) 651 101 (10) 629 74 (27)
247 40(10) 300 26 (10) 341 42 (10)
428 67 (10) 397 80 (59)
219 20(10) 288 19 (10) 333 34 (10) 349 28 (10) 413 70 (28)
755 105 (4)
381 42 (4)
636 41 (6)
357 66 (8)
Note. Values shown are means 1 SD and are expressed as grams. The number of animals is shown in parentheses.
"Compare with 21Vi-month controls.
RESULTS
Conditions of exposure. Weekly means of the concentration of vapors of 1nitropropane in the atmosphere of the exposure chamber are presented in Table 1. The average of these weekly means was 101 ppm of 1-NP, which, at the ambient conditions of 1350 m of altitude and 21 C, is equivalent to 320 mg/m3.
TABLE 3 Liver Weight of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 21 Vi months exposed
3 months exposed/ 18Vi months recovery*
12 months exposed/ 9V4 months recovery*
13.8 6.5 (10) 13.1 1.5 (10) 8.8 1.2 (10) 8.0 1.0 (10) 16.7 1.5 (10) 15.2 2.2 (10) 10.0 1.2(10) 9.5 0.9 (10) 16.1 3.0 (10) 13.8 2.8 (10) 8.4 1.2 (10) 8.7 1.2 (10)
19.5 3.0(10) 14.9 3.3 (10) 12.3 1.2 (10) 8.7 1.3 (10) 15.7 3.0 (60) 16.0 2.6 (27) 10.4 2.5 (59) 10.9 2.5 (28)
16.7 1.9 (4)
10.0 1.7 (4)
15.5 0.8 (6)
10.1 1.4 (8)
Note. Values shown are means 1 SD and are expressed as grams. The number of animals is shown in parentheses.
"Compare with 21W-month controls.
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GRIFFIN, STEIN, AND COULSTON
TABLE 4 Kidney Weights of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2ltd months exposed
3 months exposed/ 1814 months recovery*
12 months exposed/ 914 months recovery"
2.86 0.19 (10) 3.57 0.25 (10) 3.69 0.48 (10) 4.87 dt 1.81 (10) 4.27 0.85 (59)
2.84 0.42 (10) 3.38 0.43 (10) 3.47 0.43 (10) 4.00 0.93(10) 4.83 1.26 (24)
1.90 0,13 (10) 2.05 0.30 (10) 2.17 0.29 (10) 2.68 0.20 (10) 2.60 0.38 (58)
1.74 0.20 (10) 2.05 0.10 (10) 2.29 0.24 (10) 2.47 0.36 (10) 2.94 0.56 (27)
4.10 0.53 (4)
2.36 0.29 (4)
3.78 0.29 (6)
2.50 0.54 (4)
Note. Values shown are means 1 SD and are expressed as grams. The number of animals is shown in parentheses. * Compare with 21V6month controls.
Necropsy. Examination of tissues and organs at the time of necropsy did not disclose any effects of exposure to 1-NP. With particular regard to the liver, there were only very infrequent findings of apparent abnormalities and these findings were equally distributed among control and exposed groups of male and female rats. Grossly, there was no evidence of any change caused by 1-NP in either sex.
Microscopy. Sections of all tissues and any gross abnormalities of each rat were examined microscopically. In general, no microscopic changes attributable to the
TABLE 5 Brain Weights of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 914 months recovery"
2.01 0.10 (10) 2.01 0.07 (10) 2.12 0.10 (10) 2,17 0.24(10) 2.27 0.14(10) 2.25 0.07 (10) 2.25 0.17 (10) 2.23 0.11 (10) 2.21 0.31 (59) 2.27 0.35 (26)
1.85 0.04 (10) 1.95 0.07 (10) 2.15 0.12 (10) 2.07 0.10 (10) 1.97 0.29 (57)
1.83 0.14 (10) 1.95 0.11 GO) 2.23 0.66(10) 2.02 0.10 (10) 2.00 0.10 (28)
2.24 0.08 (4)
1.94 0.15 (4)
2.25 0.11 (6)
1.93 0.07 (8)
Note. Values shown are 1 SD and are expressed as grams. The number of animals is shown in parentheses. 'Compare with 2!46-month controls.
1?
SL 037233
vaJJ4Mt4
UUtnMUUuuvUVliUVlJ
INHALATION OF 1-NP AT 100 ppm
273
TABLE 6
Liver Weight Relative to Body Weight of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 21 Vi months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 914 months recovery"
3.60 0.20 (10) 3.28 0.30 (10) 2.44 0.27 (10)
2.89 0.41 (10) 2.40 0.48 (60)
3.57 0.30(10) 3.14 0.35 (10) 2.38 0.38 (10) 2.42 1.15(10) 2.57 0.51 (27)
0
2.22 0.12 (4)
2.26 0.16 (5)
3.59 0.38 (10) 3.34 0.20 (10) 2.46 0.26 (10) :2.91 0.39 (10) 2.76 0.49 (59)
3.63 0.32 (10) 3.30 0.19 (10) 2.62 0.25 (10) 2.51 0.45 (10) 2.77 0.50 (28)
2.66 0.54 (4)
2.75 0.31 (8)
Note. Values shown are means 1 SD and are expressed as percentages. The number of animals is shown in parentheses.
'Compare with 21^-month controls.
inhalation of 1-NP were observed in any of the rats. At this time, only the micro scopic examination of the livers will be reported and the other findings will be reported in detail later. There was no evidence of chemical injury to the livers of rats exposed to 100 ppm of 1-NP even when the exposure was extended to 21'A
TABLE 7
Liver Weight Relative to Brain Weight of Rats Exposed to 1-Nitropropane AT 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed ! 2 months exposed 18 months exposed 2VA months exposed
3 months exposed/ lS'A months recovery"
12 months exposed/ 914 months recovery"
683 67 (10) 649 63 (10) 476 63 (10) 437 55 (10) 786 64 (10) 703 103 (10) 510 48 (10) 489 51 (10) 709 134 (10) 613 122 (10) 391 58 (10) 411 91 (10) 868 125 (10) 668 141 (10) 440 79 (10) 432 63(10) 705 113 (59) 711 137 (26) 539 88 (58) 567 96 (28)
744 58 (4)
523 115 (4)
690 33 (6)
522 69(8)
Note, Values shown are means 1 SD and are expressed as percentages. The number of animals is shown in parentheses.
"Compare with 21 W-month controls.
SL 03723*
274
GRIFFIN, STEIN, AND COULSTON
Serum GOT in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1816 months recovery"
12 months exposed/ 9V4 months recovery"
211 41 (10) 98 16 (10) 103 28 (9) 115 35 (10) 107 31 (11)
205 56 (10) 69 14 (10) 115 92 (10) 102 23 (10) 94 26 (10)
146 35 (10) 89 11 (10) 78 25 (10) 88 19 (10) 104 27 (11)
122 42 (9) 73 10(10) 49 13 (9) 105 34 (10) 120 28 (9)
74 36 (4)
95 26 (4)
81 22 (6)
85 21 (8)
Note. Values shown are means 1 SD and are expressed as IU/liter. The number of animals is shown in parentheses.
"Compare with 21!6-month controls.
months. No hepatocarcinomas were found in any animals in the study of 1-NP at 100 ppm.
There were few incidences of liver vacuolization and a number of parenchymal abscesses among animals that were found dead or sacrificed moribund during the
TABLE 9 Serum GPT in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 motnhs exposed 12 months exposed 18 months exposed 21H months exposed
3 months exposed/ 18V4 months recovery"
12 months exposed/ 9Vt months recovery"
19 3(10)
46 11 (10) 36 18(9) 38 19 (10) 23 9(11)
16 3(10) 52 16(10) 26 12 (9) 24 4(10) 20 7(10)
19 10 (10) 31 5(10) 27 14 (10) 27 6(10) 23 8(11)
15 3 00) 33 10(10) 22 16(9) 25 8(10) 25 6(9)
23 11 (4)
24 10(4)
23 9 (6)
29 17(8)
Note. Values shown are means 1 SD and are expressed as IU/liter. The number of animals is shown in parentheses.
"Compare with 2H6-month controls.
I
1
I
037235
INHALATION OF 1-NP AT 100 ppm
275
TABLE 10 Serum ICDH in Rats Exposed to I-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 914 months recovery"
14 5(10) 46 13 (10) 42 41 (9) 18 5(7) 20 15 (11)
8 3(10) 61 38 (10) 22 14 (9) 12 3(10) 14 4(10)
14 4(10) 23 11 (10) 10 5(9) 17 12 (10) 16 6(11)
12 5(10) 12 5(8) 9 7(8) 13 8(10) 25 20 (8)
15 14 (4)
15 3 (3)
11+5 (6)
1 1 5(7)
Note. Values shown are means 1 SD and are expressed as IU/liter. The number of animals is shown in parentheses.
'Compare with 2114-month controls.
study. Affected animals were in both control and exposed groups. These findings were apparently due to an intercurrent systemic infection among these animals and they were not associated with exposure to 1-NP.
Body and organ weights. At the time of necropsy final body weights and weights of liver, kidney, and brain were obtained. Group means of these weights are pre-
TABLE 11 Serum Total Bilirubin in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 914 months recovery"
0.4 0.1 (10) 0.3 0.3 (10) 0.7 0.4 (9) 0.6 0.2 (10) 0.7 0.1 (11)
0.3 0.1 (10) 0.2 0.1 (10) 0.5 0.1 (10) 0.4 0.1 (10) 0.7 0.2 (10)
0.2 0.1 (10) 0.3 0.1 (10) 0.6 0.1 (10) 0.5 0.2 (10) 0.9 0.8 (11)
0.2 0.1 (10) 0.3 0.1 (10) 0.5 0.1 (9) 0.5 0.3 (10) 0.5 0.2 (10)
0.6 0.2 (10)
0.9 0.3 (4)
0.7 0.1 (6)
0.9 0.3 (8)
Note. Values shown are means 1 SD and are expressed as mg/deciliter. The number of animals is shown in parentheses.
" Compare with 2114-month controls.
SL 037236
276
GRIFFIN, STEIN, AND COULSTON
TABLE 12 Serum Total Protein in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery1
12 months exposed/ 914 months recovery
5.1 0.2 (10) 7.6 0.9 (10) 6.3 0.2 (9) 5.8 0.7 (10) 5.7 0.4(10)
5.0 0.2 (10) 7.4 0.5 (10) 6.0 0.3 (10) 5.7 0.3 (10) 5.6 0.4 (10)
6.5 0.3 (10) 6.3 0.5 (10) 7.2 0.6 (10) 6.5 0.4 (10) 6.7 0.5 (11)
6.4 0.3 (10) 6.0 0.6 (9) 7.3 0.4 (9) 6.5 0.3 (10) 6.6 0.9 (10)
5.6 0.3 (4)
7.1 0.5 (4)
6.1 0.3 (6)
7.3 0.6 (8)
Note. Values shown are means 1 SD and are expressed as g/deciliter. The number of animals is shown in parentheses.
'Compare with 2114-month controls.
sented in Tables 2-5, respectively. It should be noted that in these tables and those that follow presenting the results of serum chemistry and hematology, the "number of animals" shown in parentheses represents the number of animals for which data was utilized to calculate the statistical values. In some cases this was the same as the number of animals in the subgroup, but in other cases, e.g., when samples could
TABLE 13 Serum Creatinine in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2144 months exposed
3 months exposed/ 1844 months recovery
12 months exposed/ 944 months recovery
0.6 0.1 (10) 0.7 0.2 (10) 0.9 0.2 (9) 1.1 0.3 (10) 1.0 0.2 (11)
0.6 0.1 (10) 0.6 0.1 (10) 0.9 0.1 (10) 1.1 0.8 (10) 1.6 1.2 (10)
0.7 0.1 (10) 0.6 0.1 (10) 0.8 0.2 (10) 0.9 0.3(10) 1.1 0.2(11)
0.7 0.1 (10) 0.6 0.2 (10) 0.7 0.1 (9) 0.9 0.1 (10) 1.1 0.2(10)
0.8 0.3 (4)
0.9 0.1 (4)
1.1 0.5 (6)
0.9 0.2 (8)
Note. Values shown are means 1 SD and are expressed as mg/deciliter. The number of animals is shown in parentheses.
'Compare with 2114-month controls.
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INHALATION OF 1-NP AT 100 ppm
277
TABLE 14 Serum Urea Nitrogen (BUN) in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2116 months exposed
3 months exposed/ 1816 months recovery
12 months exposed/ 916 months recovery
23 3 (10) 25 2(10) 29 6 (9) 30 13 (10) 27 10 (11)
18 2(10) 21 4 (10) 23 4(10) 20 2(9) 29 12 (8)
23 2 (10) 18 4 (10) 24 5 (10) 21 7 (10)
28 8 (11)
22 5 (10) 14 2 (9) 18 2 (9) 21 4 (10) 23 3 (10)
23 8 (4)
20 2 (4)
22 4 (6)
21 4(8)
Note. Values shown are means 1 SD and arc expressed as mg/deciliter. The number of animals is shown in parentheses.
Compare with 2116-month controls.
not be obtained from all animals, the number is less. One set of animals was excluded from the tables. These were the animals which were found dead or sac rificed moribund during the study and which were of widely differing ages and for which clinical laboratory data usually were not available.
TABLE 15 . Serum Sodium in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2116 months exposed
3 months exposed/ 1816 months recovery
12 months exposed/ 916 months recovery
146 1 (10) 140 1 (10) 137 2 (7) 142 2 (10) 144 2(11)
144 2 (10) 139 2 (10) 137 2(10) 142 1 (9) 143 1 (10)
146 3 (10) 138 2 (9) 135 2 (10) 140 2 (10) 142 2 (11)
146 2 (10) 137 2 (9) 133 4 (7)
140 2 (10) 142 1 (10)
142 1 (4)
142 1 (4)
144 4 (6)
142 3 (8)
Note. Values shown are means 1 SD and are expressed as meq/litcr. The number of animals is shown in parentheses.
" Compare with 21V6-month controls.
037238
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GRIFFIN, STEIN, AND COULSTON
TABLE 16
Serum Potassium in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 9Vi months recovery"
4.6 0.3 (10) 5.4 0.6 (10) 4.9 0.3 (7) 5.8 1.7 (10) 5.4 0.5 (11)
4.5 + 0.2(10) 5.1 0.6(10)
5.3 0.5 (10) 5.3 1.0 (10) 5.4 0.9 (10)
4.1 0.3 (10) 4.4 0.4 (9) 4.6 0.3 (10) 4.5 0.7 (10) 4.9 0.4(11)
4.1 0.2(10) 4.3 0.5 (9) 4.3 0.4 (7) 4.6 0.3 (10) 5.1 0.7 (10)
4.8 0.2 (4)
5.4 1.9 (4)
5.0 0.6 (6)
4.7 0.6 (8)
Note. Values shown are means 1 SD and are expressed as imeq/liter. The number of animals is shown in parentheses.
"Compare with 2114-month controls.
Growth appeared normal for both sexes and only inconsistent differences were seen in body weights between control and exposed groups. The slightly lower body weights of males exposed 12 months is considered to be an anomaly in view of the remaining data. The slightly increased weights of males exposed 3 months and recovered 18V4 months is also considered anomalous and likely due to the small sample size.
TABLE 17 Methemoglobin in Blood of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery"
12 months exposed/ 914 months recovery"
25 20 (9) 24 14 (9) 16 10(9) 36 8 (9) 120 73 (10)
32 25 (10) 30 22 (10) 22 19(10) 49 7(10) 70 37(10)
13 8(10) 38 15 (10) 17 15 (10) 36 13 (10) 74 72 (9)
29 20 (7) 49 23 (7) 22 11 (10) 29 12(12) 46 45 (10)
29 12 (4)
19 12 (3)
43 14 (6)
50 62 (8)
Note, Values shown arc means 1 SD and are expressed as mg/deciliter. The number of animals is shown in parentheses.
'Compare with 21V4-month controls.
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TABLE 18 Hemoglobin in Blood of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 21`A months exposed
3 months exposed/ 18 Vi months recovery0
12 months exposed/ 9lA months recovery*
14.0 0.4 (8) 14.0 1.0 (10) 14.2 0.5 (10) 14.3 1.0 (10)
16.2 1.0(10) 15.5 0.9 (10) 14.2 0.9 (10) 13.4+ 1.3 (8) 15.4 0.6 (9) 15.0 0.9 (10) 15.6 0.5 (10) 15.6 0.7 (10) 15.6 3.4 (9) 16.8 1.6 (10) 16.4 0.7 (10) 16.4 + 2.1 (10) 16.7 0.6 (10) 1.6.0 1.7 (10) 18.1 2.1 (10) 16.5 2.5 (10)
14.3 4.8 (4)
16.5 (3)
18.5 2.7 (6)
17.4 1.3 (7)
Note. Values shown arc means 1 SD and are expressed as g/deciliter. The number of animals is shown in parentheses.
'Compare with 2IW-month controls.
There was no effect of exposure of the rats on the weights of liver, kidney, or brain. At 18 months there was a greater mean liver weight among the control males. This is considered to have no significance with regard to exposure to 1-NP. No effects were observed on kidney or brain.
TABLE 19
Packed Cell Volume (Hematocrit) of Blood of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2114 months exposed
3 months exposed/ 1814 months recovery*
12 months exposed/ 914 months recovery*
43 2 (9) 45 1 (10) 46 1 (9) 44 3 (9) 44 + 2(10)
42 2 (10) 45 1 (10) 45 3 (10) 44 3 (10) 42 5 (10)
42 1 (10) 42 + 2 (10) 45 1 (10) 43 2 (10) 43 2 (10)
42 2 (10) 42+3 (8) 45 2 (10) 43 + 5 (10) 44 8 (10)
45 1 (4)
43 (3)
46 1 (5)
46 3 (7)
Note. Values shown arc means 1 SD and arc expressed as percentages. The number of animals is shown in parentheses.
* Compare with 21Vi-month controls.
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TABLE 20 Red Blood Cell Counts of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
/Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2116 months exposed
3 months exposed/ 1816 months recovery*
12 months exposed/ 916 months recovery"
4.9 0.7 (9) 6.3 0.5 (10) 7.3 0.4 (9) 5.7 0.7 (9) 5.5 0.9 (10)
4.5 0.5 (10) , 3,3, 0.5 (10) 6.2 0.4 (10) f 5.3 0.3 (10) 7.7 0.6 (10) 6.9 0.3 (10) 6.1 1.9 (10) > 7.5 0.7 (10) 5.6 0.8 (10) 5.8 1.0(10)
3.5 0.9 (10) 6.3 1.2 (8) 7.3 0.4(10) 7.9 1.4(10) 5.6 1.4 (10)
5.2 0.2 (4)
4.0 (3)
5.3 0.9 (6)
4.4 1.3 (7)
Note. Values shown are means 1 SD and are expressed as cells per cubic millimeter X 106. The number of animals is shown in parentheses.
* Compare with 2116-month controls.
In order to examine further the possibility of an effect on the liver weights of exposed rats, the liver weights, relative to body weights and relative to brain weights, were calculated and the results are shown in Tables 6 and 7. Because of the uni formity of brain weights, the comparisons of ratios of liver weights brain weights
TABLE 21 White Blood Cell Counts of Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed ^months exposed 18 months exposed 2116 months exposed
3 months exposed/ 1816 months recovery*
12 months exposed/ 916 months recovery*
4.0 0.4 (9) 5.1 1.0 (10) 3.7 0.8 (9) 3.0 1.6 (9) 3.6 1.8 (10)
6.0 0.8 (10) 3.6 0.6 (10) 5.8 1.2 (10) 4.1 1.0 (10) 4.0 0.9 (10) .3.1 1.0(10) 3.7 1.4 (10) 3.1 2.8 (10) 5.2 3.0 (10) 2.2 0.6 (10)
3.6 0.8 (10) 3.1 0.9 (8) 2.9 0.9 (10) 3.7 2.1 (10) 2.1 0.6 (10)
3.7 1.0 (4)
2.8 (3)
3.5 1.7 (6)
1.8 1.0 (7)
Note. Values shown are means 1 SD and are expressed as cells per cubic millimeter X 10J. The number of animals is shown in parentheses.
* Compare with 2116-month controls.
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TABLE 22
- Prothrombin Time in Rats Exposed to 1-Nitropropane at 100 ppm
Males
Females
Controls
Exposed
Controls
Exposed
1 month exposed 3 months exposed 12 months exposed 18 months exposed 2ltt-months exposed
16.3 2.4 (9) 15.6 0.9 (10) 11.6 1.3 (8) 11.7 1.2 (9)
15.4 2.6 (4) 15.2 2.4 (10) 13.4 2.3 (9) 16.0
(3)
12.1 1.6 (9) 12.8 2.1 (10) 11.3 0.7 (10) 12.8 2.0 (10)
20.1 6.3 (9) 17.1 5.3 (10) 15.0 0.9 (9) 17.0 5.4 (9)
13.7 2.0 (10) 12.9 1.9 (9) 15.0 2.0 (10) 12.8 12.6 (10)
3 months exposed/ 1816 months recovery4
"V 12.9 0.9 (4)
13.5 2.1 (5)
12 months exposed/ 916 months recovery4
16.1 5.0 (5)
15.0 (3)
Note. Values shown arc means 1 SD and are expressed as seconds. The number of animals is shown in parentheses.
4 Compare with 21 Vi-month controls.
yields a sensitive measure of changes in liver weights during experimental condi tions. There was no effect demonstrated by these two relative measures of liver weights of rats exposed to I-NP. (Note: the anomalously high liver weights in control males at 18 months is also reflected in the relative weights.) This lack of effect on liver weights is particularly significant, since liver weights are known to be increased in rats exposed to 2-nitropropane.
Serum chemistry. The results of examinations of serum chemistry are shown in Tables 8-16. None of these measurements disclosed any evidence of an effect of exposure of the rats to 1-NP.
Hematology. The results of hematology studies are shown in Tables 16-22. None of these studies showed an effect of exposure to 1-NP.
Comparison of results obtained on the two groups of animals exposed for either three months or twelve months, and then removed for recovery, with results from other groups did not reveal any effects of exposure to 1-NP.
DISCUSSION
In a previous publication (Griffin et al., 1980) a review was made of the necessary time course and concentration effect of 2-nitropropane required to induce severe damage to hepatic parenchyma as an essential step in the induction of hepatic carcinoma in the rat. By contrast, 1-nitropropane, even at a high concentration and even when the exposure is continued to near the lifetime of the experimental animal, does not cause chemical injury to the liver and does not induce hepatocarcinoma. At a concentration of 100 ppm, hepatocarcinomas are induced in animals exposed to 2-NP, but not 1-NP. One is hard pressed even to find any evidence of exposure of the rats to 1-NP. Body weights and organ weights, including liver weights, were
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GRIFFIN, STEIN, AND COULSTON
unchanged by exposure to 1-NP. There were no effects on clinical pathology and no histopathologic effects on the liver.
Damage to the liver parenchymal cells is an essential precursor to the induction of hepatocarcinoma in the rat with 2-NP. Hepatocellular carcinomas induced by 2-NP only occur when the degree of exposure is sufficient to cause severe hepatotoxicity. We believe that the cellular proliferative response is due to intense hyperregeneration following the severe damage to the hepatic cells. Under these conditions, with 2-NP, it is not possible for the cellular regeneration processes to overcome the toxic effect of the chemicals to the liver cells. Some of the new emerging regenerated hepatic cells become autonomous, leading to neoplasia.
We are presently studying other doses of 2-NP in great detail. Twenty-five ppm 2-NP produced no toxicity to the parenchymal cell of the liver and therefore no cellular proliferative resjibnse and, consequently, no carcinomas. On the other hand, at 100 ppm and 200 ppm 2-NP hepatocarcinomas and metastates were observed.
The fact that with 1-NP no liver parenchymal cell toxicity and no hepatocellular carcinomas were observed gives credence to the theory that we have stated in the past concerning the relationship between exposure and degree of liver cell damage and carcinogenic potential.
CONCLUSIONS
The following conclusions can be made from this study of inhalation exposure of rats to 1-nitropropane at 100 ppm.
1. No gross or microscopic effects on tissues or organs were observed. 2. No histopathologic changes or induction of hepatocarcinomas were observed in any of the exposed rats. 3. No effect on total body weights or on the weights of liver, kidney, or brain were recorded. 4. There was no effect on serum chemistry or hematology. 5. There was no effect on the appearance and behavior of the rats.
REFERENCES
Lewis, T. R., Ulrich, C. E., andBusey, W. M. (1979). Subchronic inhalation toxicity of nitromethane and 2-nitropropane. J. Environ. Pathol. Toxicol. 2, 233-249.
Griffin, T. B., Coulston, F., and Stein, A. A. (1980). Chronic inhalation exposure of rats to vapors of 2-nitropropane at 2S ppm. Ecotoxicol. Environ Safety 4, 267-281.
Griffin, T. B., Stein, A. A., and Coulston, F. (1981). Histologic study of tissues and organs from rats exposed to vapors of 2-nitropropane at 25 ppm. Ecotoxicol. Environ Safety 4, 194-201,
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