Alpha 2-adrenoceptor-mediated inhibition of prolactin release in suckling- or fenfluramine-induced hyperprolactinemia.
It has recently been shown that the specific and selective alpha 2-antagonist idazoxan (IDZ) displays prolactin-lowering activity on hyperprolactinemia induced in the rat either by suckling or serotonergic drugs. In an attempt better to understand the role of alpha 2-adrenoceptors under the above conditions, experiments were carried out to compare the effects of IDZ with that of the classic alpha 2-antagonist yohimbine (YOH), and also of the alpha 2-agonists clonidine (CLO) and B-HT 920, on prolactin (PRL) release during lactation and in hyperprolactinemia induced in male rats by the serotonergic drug fenfluramine (FEN). In lactating rats, both alpha 2-agonists decreased PRL release; this effect was enhanced by prior separation of the animals from their pups for several hours. A decrease of plasma PRL levels was also induced by IDZ but not by YOH, which tended further to increase hyperprolactinemia. In male rats treated with FEN, IDZ and CLO, a significant decrease of plasma PRL was produced, but YOH further enhanced PRL secretion. It is concluded that the alpha 2-agonists tested and also the alpha 2-antagonist IDZ display a unique inhibitory activity on PRL release during suckling or serotonergic-induced hyperprolactinemia.
Laboratory of Normal and Pathological Physiology, State University of Ghent, Belgium.
P
P
Navarra
W
W
Eechaute
P
P
Preziosi
E
E
Lacroix
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000833:Animals, Suckling / Q000378:metabolism; D005260:Female; D005277:Fenfluramine / Q000494:pharmacology*; D006966:Hyperprolactinemia / Q000097:blood / Q000139:chemically induced*; D007774:Lactation / Q000187:drug effects; D008297:Male; D011388:Prolactin / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D005277:Fenfluramine; D011388:Prolactin