Abstract for RACB20103, RACB20104, RACB20105, RACB20106, and RACB20203

The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.

Summary

The purpose of this study was to examine the sensitivity of the pubertal assay to an estrogen (Methoxychlor), anti-androgen (Vinclozolin and Flutamide), and a thyroid-active agent (Phenobarbital) in intact juvenile/peripubertal male and female rats. Fifty-five time-mated female (F0) Sprague Dawley Rats were received from Charles River Laboratories and allowed to litter at TherImmune. After weaning on Postnatal Day (PND) 21, 135 F1 males and 135 F1 females were assigned to male and female cohort studies, respectively. The F1 males were dosed with corn oil (0 mg/kg), or the test articles: Phenobarbital (25, 50, and 100 mg/kg/day), Vinclozolin (10, 30, and 100 mg/kg/day), or Flutamide (25 and 50 mg/kg/day), once daily via oral gavage from PND 23-53/54. The F1 females were dosed with corn oil (0 mg/kg), or the test articles: Ethinyl Estradiol (0.0025 and 0.0050 mg/kg/day), Methoxychlor (12.5, 25, and 50 mg/kg/day), or Phenobarbital (25, 50 and 100 mg/kg/day), once daily via oral gavage from PND 22-42/43.

Parameters evaluated include mortality and clinical observations, body weights, day of preputial separation, day of vaginal opening, estrous cyclicity, gross pathology, organ weights and histopathology.

Males
Test Article	Concentration (mg/kg/day)	Body Weight	Age of Preputial Separation	Organ Weights	Histology
Phenobarbital	25	-	-	⇑liver	-
	50	-	-	⇑liver	-
	100	⇓	⇑	⇑liver ⇓pituitary	-
Vinclozolin	10	-	⇑	-	-
	30	-	⇑	⇓repro. organs ⇑ testis,	-
	100	-	⇑	⇓repro. organs ⇑ testis	-
Flutamide	25	-	⇑	⇓repro. organs ⇑ testis, ⇓ kidneys	-
	50	-	⇑	⇓repro. organs ⇑ testis, ⇓ kidneys, ⇑adrenal glands	testis lesions

- = no effect; ⇑ = higher than control means; ⇓ = lower than control means
repro. = reproductive

Females
Test Article	Concentration (mg/kg/day)	Age at Vaginal Opening	Age at First Estrus	Irregular Estrous Cycles	Organ Weights
Phenobarbital	25	-	-	-	⇑liver ⇑ adrenal
	50	-	-	-	⇑ liver ⇑ adrenal
	100	⇑	-	-	⇑ liver ⇑ adrenal ⇓ thyroid
Methoxychlor	12.5	⇓	⇓	-	-
	25	⇓	⇓	X	-
	50	⇓	⇓	X	⇓ liver ⇓ ovary ⇓ pituitary
Ethinyl Estradiol	0.0025	-	-	-	⇑adrenal
	0.005	⇓	⇓	X	⇑adrenal

- = no effect; ⇑ = higher than control means; ⇓ = lower than control means; X =present
repro. = reproductive

The lowest observable effect level (LOEL) for an endocrine effect was 25 mg/kg/day for Flutamide, 10 mg/kg/day for Vinclozolin, 100 mg/kg/day for Phenobarbital, 12.5 mg/kg/day for Methoxychlor, and 0.005 mg/kg/day for Ethinyl Estradiol.

NTIS # PB2004-105924