An extended one-generation reproductive toxicity test of 1,2,4-Triazol-5-one (NTO) in rats

Abstract

Nitrotriazolone (1,2,4-triazol-5-one; NTO), an insensitive, energetic material used in explosive formulations, induced testicular toxicity and oligospermia in repeated-dose oral toxicity tests in rats. To evaluate whether NTO produces additional reproductive and developmental effects, a modified extended one-generation reproductive toxicity test was conducted. Rats were provided ad libitum access to NTO in drinking water at 0-, 144-, 720-, or 3600-mg/L NTO. Treatment of the parental generation began 2 (females) and 4 (males) wk premating and continued until weaning of litters. Direct dosing of offspring (F1) occurred from weaning through puberty. Pups were counted and weighed on postnatal day (PND) 0/1. Anogenital distance (AGD) was measured on PND 4 and males were examined for presence of nipples on PND 13. F1 offspring were examined daily for attainment of puberty. NTO did not markedly affect measures of fertility, including mating indices, gestation index, litter size, and sex ratio. Seminiferous tubule degeneration or atrophy was observed in P1 and F1 3600-mg/L NTO males. F1 males in the 3600 mg/L group exhibited reduced reproductive organ mass (testes, epididymides, and accessory sex organs). Nipple retention was increased in NTO exposed F1 males compared to controls. Attainment of puberty was delayed by 2.6 d in the 3600-mg/L NTO-exposed males relative to controls. Comparison of the effects of NTO with those of antiandrogens suggests absence of malformations of the genital tract in NTO-exposed males. This study supports previous findings indicating that NTO is a testicular toxicant with male developmental effects that may be secondary to testicular toxicity.

Characterization of the Testicular Toxicity of 3-Nitro-1,2,4-Triazol-5-One and 2,4-Dinitroanisole in Rats (Rattus norvegicus)

“…Although the pattern of morphological changes previously observed following exposure to NTO was consistent with low testosterone levels, 12,13 that pattern was not observed in the current study. Here, diffuse loss of pachytene/zygotene spermatocytes and step 1 to 19 spermatids was noted in tubules at all stages (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) of the cycle for both NTO-and DNAN-exposed rats. This was accompanied by Sertoli cell degeneration marked by cytoplasm vacuolization and rarefaction (lacey cytoplasm).…”

“…12,13 In peripubertal rats given 250 mg/kg/d NTO and F1 generation rats given 3,600 mg/L NTO, the testes exhibited degenerative changes characteristic of low testosterone levels, including degeneration of pachytene spermatocytes and depletion or absence of elongating spermatids. 12,13 Additionally, the weight of accessory sex organs (ie, seminal vesicles and lateral prostate), which are the most sensitive indicator of reduced testosterone as they integrate changes in androgen levels over time, 19 was reduced in both studies. These studies suggest that NTO-induced reproductive toxicity is mediated by reduced androgenic tone, the most common hormonal cause of altered male reproductive morphology.…”

“…This may be reflective of the high variability (30 fold) in point measurements of testosterone 20 rather than an absence of effect, as serum testosterone levels have previously failed to demonstrate an effect when effects were noted in accessory sex organs. 12,13 Intratesticular testosterone levels can be 40-fold to 250-fold higher than serum testosterone levels in rats and man, respectively, but the relationship between serum and intratesticular levels is not constant. [22][23][24] Intratesticular testosterone supports development of pachytene spermatocytes and germ cells through stage VII by controlling secretion of proteins from Sertoli cells 25 ; however, spermatogenesis can be maintained by 5% to 10% of normal intratesticular testosterone levels.…”

“…The dose factor levels were set at 50 and 100 mg/kg/d DNAN, 500 mg/kg/d NTO, and corn oil vehicle control, based on results from previous studies conducted in rats. [10][11][12][13] Following an acclimatization period, rats were stratified by body mass and randomly distributed to 1 of 16 treatment groups (5 rats/group). Dosing suspensions were administered via oral gavage using a stainless steel 16 G Â 2 in gavage needle at approximately the same time daily for 1 to 14 days based on time course grouping.…”

“…11 In reproductive and developmental studies, degenerative changes characteristic of low testosterone levels (ie, degeneration of pachytene spermatocytes and depletion or absence of elongating spermatids) were observed in the testes of peripubertal rats given 250 mg/kg/d NTO and F1 generation rats given 3,600 mg/L NTO. 12,13 The prolonged duration of these studies, however, resulted in progressive absence of germ cell stages due to maturation depletion and precluded identification of the initial site of injury and the target site of testicular toxicity.…”