Effects of an organophosphate pesticide, quinalphos, on the hypothalamo-pituitary-gonadal axis in adult male rats

The effects of chronic sub-lethal doses (7-14 mg kg(-1) a day for 15 days) of quinalphos were evaluated in adult male rats for changes in testicular m orphology, circulatory concentrations of hormones (LH, FSH, prolactin and t estosterone), activities of acetylcholinesterase (AChE) and angiotensin con verting enzyme (ACE) as well as metabolism of biogenic amines (dopamine, no radrenaline and 5-hydroxytryptamine (5-HT)) in the hypothalamus and pituita ry. Hormones were assayed by radioimmunoassay or chemiluminescent immunoass ay (testosterone). The enzymes were estimated after spectrophotometry and t he biogenic amines by HPLC-electrochemistry. Sub-lethal chronic administrat ion of quinalphos resulted in: decreased testicular mass and AChE activity in central as well as peripheral organs; increased serum LH, FSH, prolactin and testosterone concentrations; decreased pituitary or increased testicul ar ACE activity; severe disruption of spermatogenesis with increasing doses of pesticide; and no significant effects on dopamine, noradrenaline or 5-H T concentrations in the hypothalamus or pituitary. Administration of oestra diol (50 mu g per rat a day) during pesticide treatment resulted in: a sign ificant decrease in the mass of the testis and accessory sex organs; decrea ses in serum LH, FSH, testosterone concentrations; an increase in prolactin concentration; and a decrease in dopamine or an increase in noradrenaline and 5-HT in the hypothalamus or pituitary. Oestradiol had a marked effect: in pesticide-treated animals, the pesticide effects were significantly reve rsed. This indicates that in pesticide toxicity, the hypothalamopituitary-g onadal axis is operational. Since many of the observed pesticide effects co uld be inhibited by oestradiol, it is suggested that the pesticide acts dir ectly on the gonadotrophins. in conclusion, quinalphos decreases fertility in adult male rats by affecting the pituitary gonadotrophins.