Hormonal consequences of subcutaneous 6-methoxy-2-benzoxazolinone pellets or injections in prepubertal male and female rats

Abstract

Prepubertal 27-day-old female rats maintained in a 14L:10D cycle (lights on 06:00 h) were injected s.c. at 13:00 h with saline or 2, 20 or 200 μg 6-methoxy-2-benzoxazolinone (6-MBOA) and killed 25-27 h later. No significant differences in body, pituitary or ovarian weight were noted. Differences in uterine weight (mg/100 g body weight) and in circulating free thyroxine index fit the pattern of a reduction after the lower doses with reversal of this effect after the highest dose. A dose-related rise in plasma prolactin concentration was accompanied by a significant increase in pituitary prolactin at the lowest (2 μg) dose. When 27-day-old prepubertal male and female rats maintained in a 14L:10D cycle were implanted with a beeswax pellet or a wax pellet that contained 100 μg or 1 mg 6-MBOA and killed 3 days later between 14:00 and 16:00 h, body and absolute ventral prostate weights (but not weights of other accessory organs, testes or relative ventral prostate weights) in males were lower. Pituitary (but not plasma) prolactin concentrations were higher after the lower dose compared to the controls; pituitary and plasma values of LH and FSH were unchanged. In females, reproductive variables were unchanged except for a reduction of pituitary prolactin after the 1 mg dose. Triiodothyronine and its free index were elevated after the higher dose in males and the lower dose in females. The free thyroxine index appeared raised after the larger dose only in males. The present results do not suggest a strong role of 6-MBOA in augmenting reproductive function in prepubertal laboratory rats over a period of 1-3 days at the doses used.