Chlordimeform-induced alterations in endocrine regulation within the male rat reproductive system

The acaricide chlordimeform has been reported to have adverse effects in mammals that may be mediated by an interaction with alpha-adrenergic receptors. Since the hormonal signals involved in the regulation of reproductive function are themselves under hypothalamic adrenergic control, the present study was designed to investigate the effects of acute exposure to this compound on the hypothalamic-pituitary-testicular axis. Male rats given two intraperitoneal injections of chlordimeform-HCl (20 or 50 mg/kg) spaced 12 hr apart showed 24-hr declines in serum gonadotropins at 50 mg/kg that were paralleled by a drop in testosterone. These changes returned to control levels by 96 hr. Thyroid-stimulating hormone exhibited a dose-response decline that was accompanied by a similar decrease in serum thyroid hormone levels. The norepinephrine-stimulated secretion in vitro of gonadotropin-releasing hormone from hypothalamic explants was suppressed at the higher dose, while LH release from pituitary fragments in culture was unaffected. Although measurements of the in vitro release of other pituitary hormones suggest that there could be some direct pituitary effects of the compound, it appears likely that chlordimeform is able to influence endocrine regulation adversely within the reproductive system by interfering with hypothalamic alpha-adrenergic activity.