G. S. Kledzik

Reinitiation of Estrous Cycles in Old Constant-Estrous Rats by Central-Acting Drugs

Daily injections of epinephrine, 1-dopa, or iproniazid for 25 days into 20- to 23-month-old constant estrous Sprague-Dawley rats initiated regular estrous cycles in most rats. On termination of treatm

Effects of Haloperidol on Serum and Pituitary Prolactin, LH and FSH, and Hypothalamic PIF and LRF

A single s.c. injection of haloperidol into ratson the morning of proestrus produced up to a 22-fold increase in serum prolactin and a significant increase in pituitary prolactin concentration. There was a significant decrease in serum LH and FSH levels and a complete block of spontaneous ovulation. Haloperidol significantly reduced hypothalamic PIF and LRF activities. The anti-ovulatory effect of haloperidol was overcome by the administration of exogenous LH. Haloperidol directly inhibited prolactin and LH release by the pituitary in vitro. These results suggest that the increased release and synthesis of pituitary prolactin by haloperidol is mediated by a decrease in hypothalamic PIF activity, and the reduction in release of LH by a decrease in hypothalamic LRF activity and perhaps also by a direct inhibitory action on the pituitary.

Effects of estrogen and testosterone on specific prolactin binding in the kidneys and adrenals of rats

Abstract The effects of estradiol benzoate in the female rat, testosterone propionate in the male rat, and castration in both sexes on specific prolactin binding sites in the particulate membranes of the kidneys and adrenals were studied. Castration resulted in a significant increase in PRL binding activity in the kidneys of both males and females, and in a significant increase in PRL binding activity in the adrenals of the females. The increase in PRL binding with castration and the decrease seen with testosterone treatment were similar in both immature and mature rats. Progesterone administration to castrate females failed to alter PRL binding in both tissues. The present results suggest that estrogen and testosterone participate in the PRL osmoregulatory system in the rat.

Reinitiation of Estrous Cycles in Light-Induced Constant Estrous Female Rats by Drugs

Summary Light induced constant estrous female rats were injected daily with central acting drugs that either increased or decreased brain catecholamines or serotonin or altered levels of both amines. Only the combination of L-dopa and p-chloroamphet-amine (PCA) was effective in reinitiating regular estrous cycles in the rats while still under constant light. Nine of 15 rats so treated with PCA and L-dopa in the first experiment showed at least 2 consecutive cycles, and 22 of 30 rats in a second experiment showed 3 consecutive cycles. Serum LH was observed from 10 AM to 6 PM on the day of proestrus in the 22 cycling rats of the second experiment. Rats showing LH peaks ovulated by the next day. These results suggest that constant light induces a deficiency of catecholamines and an excess of serotonin in the hypothalamus, thereby preventing normal LH release.