Differences in the ability of reserpine and chlorpromazine to block ovulation throughout the estrous cycle of the rat

Abstract

Abstract Rats with a 4‐day estrous cycle were given a single dose of reserpine (62.5, 125, 500, 1000 or 2000 μg/kg body wt) or chlorpromazine (1, 2.5 or 5 mg/kg body wt) at 13.00 h on the days of estrus, diestrus 1, diestrus 2 or proestrus and were autopsied on the next expected day of estrus. The doses of reserpine (in μg/kg body wt) necessary to block ovulation during the cycle were 500 at estrus, 62.5 at diestrus 1, 500 at diestrus 2 and 2000 at proestrus, and for chlorpromazine (in μg/kg body wt) 2.5 on diestrus 1 and diestrus 2 and 1 in proestrus. On estrus, at 13.00 h, chlorpromazine was ineffective to block ovulation. A single dose of reserpine (125 μg/kg) or chlorpromazine (2.5 mg/kg) was given at estrus, diestrus 1 or diestrus 2 at 09.00, 13.00, 17.00 or 21.00 h, autopsy again being performed on the next expected day of estrus. The ability of reserpine to block ovulation begins at 17.00 on estrus, reaches its maximum throughout diestrus 1 and disappears at diestrus 2. Chlorpromazine ability to block ovulation appeared to have a circadian rhythm on diestrus 1 and diestrus 2, with a maximum at 13.00 and a minimum at 21.00 h, and no effect on estrus. Hormone replacement (human chorionic gonadotrophin) on diestrus 1, diestrus 2 and proestrus re‐established ovulation in rats whose ovulation was blocked by reserpine on diestrus 1 (125 μg/kg) and had no effect when the replacement was done only on diestrus 1 or diestrus 2. Rats blocked with chlorpromazine (1 mg/kg) on proestrus ovulated 24 hrs after the next expected day of estrus. The weight of the ovaries diminished in almost all rats treated with chlorpromazine, while the effects of reserpine depend on the dose used and the day of the cycle considered. Results obtained in these experiments suggest that the dopaminergic system susceptible to blocking by chlorpromazine, stimulates gonadotrophin control secretion on diestrus 1, diestrus 2 and proestrus. On diestrus 1 and diestrus 2, a circadian rhythm control system linked to dopaminergic system might exist. Blockade induced by reserpine might be related to changes observed in the hypothalamus content of norepinephrine throughout the estrus cycle, and also to the blockade on ovarian innervation exerted by reserpine.