Effects of dopamine and serotonin on concentrations of luteinizing hormone and estradiol-17 beta in plasma of cycling ewes.

Abstract

Effects of 0, 0.66 and 6.6 micrograms/kg per min of dopamine (DA) and of 0, 0.06 and 0.66 micrograms/kg per min of serotonin (5-HT) on secretion of luteinizing hormone (LH), estradiol-17 beta and progesterone were examined in ewes during luteal regression and the follicular phase. Onset of luteolysis was synchronized with two injections of 7.5 mg prostaglandin F2 alpha (PGF2 alpha) (i.m.) given 3 h apart in ewes which were 12-14 days postestrus. Ewes were infused intravenously with DA, 5-HT or a combination of DA and 5-HT for a 60-h period beginning at the time of the first PGF2 alpha injection. Neither DA nor 5-HT influenced the decrease in plasma concentrations of progesterone following PGF2 alpha. Effects of DA and 5-HT on tonic secretion of LH changed during the infusion. During the first 12 h, increasing doses of DA depressed and increasing doses of 5-HT increased mean concentrations of LH in plasma in a linear manner (DA, P less than 0.01; 5-HT, P less than 0.05). Between 16 and 34 h, 6.6 micrograms/kg per min of DA continued to suppress LH, however, 5-HT was no longer stimulatory to secretion of LH. DA was unable to inhibit secretion of LH after 40 h. Also, between 0 and 34 h, concentrations of estradiol-17 beta in plasma were decreased by infusion of DA (P less than 0.01). Interval from PGF2 alpha to onset of the preovulatory surge of LH, magnitude of the surge and duration of the surge were not altered by infusion of either DA or 5-HT.