The Inhibitory Effect of Dopamine Agonists on LH Release in Women¹

Abstract

Our demonstration of an inhibitory effect of dopamine on LH release prompted us to examine whether a similar action exists for dopamine agonists, such as L-dopa and 2-bromo-alpha-ergocryptine (CB-154). Following the administration of L-dopa (0.5 g, orally) to 6 normal women in the early follicular phase, a significant fall in mean LH levels after 1 h which lasted for 5 h was observed (P less than 0.00005). This was followed by a significant rebound above basal levels between the 7th and 10th h (P less than 0.00005). The expected fall in mean PRL levels which lasted for 4 h (P less than 0.00001) was followed by a significant rebound above basal levels after the 6th h (P less than 0.00001)). There was no significant change in mean FSH levels. Following the administration of CB-154 (2.5 mg. orally) to 6 women with hyperprolactinemic amenorrhea, there was also a significant fall in LH levels (P less than 0.00001) and in FSH levels (P less than 0.00001) from 5 h until the study ended at 10 h. The anticipated PRL suppression was also observed and persisted for the duration of the 10 h study. The demonstration of an inhibitory effect of L-dopa and CB-154 on LH release adds further support to the role of dopaminergic control of pituitary LH secretion.

Suppression of luteal function in dogs by luteinizing hormone antiserum and by bromocriptine

“…The daily dosage of bromocriptine used in the present study (OT mg/kg/dog) was similar to the dose ( 1 mg/dog) previously demonstrated to reduce serum prolactin concentrations in dogs to 25% of preinjection levels after a single injection (Reimers et al, 1978). The effects of bromo¬ criptine could have involved changes in secretion of hormones other than prolactin, including decreased LH secretion (Lachelin et al, 1977;Shaban & Terranova, 1986 (Okkens et al, 1985). The abortions in bromocriptine-treated bitches after declines in progesterone to < 2 ng/ml correspond to abortions under similar con¬ ditions during induction of luteolysis by administration of prostaglandin F-2a (Concannon & Hansel, 1977).…”

Evidence for prolactin as the main luteotrophic factor in the cyclic dog

“…The dosage of bromocriptine in our study was high enough to cause a significant reduction of prolactin, but not so high as to affect the general health of the dogs thereby excluding the possibility that the function of the corpus luteum was influenced by other factors. High doses of bromocriptine decrease the LH secretion in women and rats (8,20). In our experiment there was no significant difference in the mean LH levels before and during treatment, indicating that bromocriptine, in the dosage used, did not affect the LH secretion during the luteal period in the dog.…”

Inhibition of ovarian function in subordinate female marmoset monkeys (Callithrix jacchus jacchus)

“…This explanation would be in accordance with the lower prolactin levels found in subordinates in 4 out of the 10 groups when compared with the dominant female (Table 3). Increased dopamine turn-over is also known to suppress LH secretion (LeBlanc, Lachelin, Abu-Fadil & Yen, 1976;Lachelin, LeBlanc & Yen, 1977;Fuxe et ai, 1976;Judd, Rakoff & Yen, 1978;McNeilly, 1980) (1978). Since oestrogen blocks dopamine at its receptor (Labrie, Baulieu, Caron & Raymond, 1978), ovariectomy followed by oestrogen treatment of the subordinate talapoins and reduced oestrogen levels of the subordinate marmosets might contribute directly to the dissimilar prolactin findings in these two species of monkey.…”