Effects of catecholaminergic agonists and antagonists on serum gonadotropin concentrations and ovulation in goldfish: evidence for specificity of dopamine inhibition of gonadotropin secretion.
The elevated serum gonadotropin (GtH) levels in goldfish receiving two injections of des Gly10, [D-Ala6] LH-RH ethylamide (LH-RH-A), given 12-hr apart, were reduced by apomorphine, a dopamine agonist, injected at either the first or the second LH-RH-A injection. Serum GtH concentrations in goldfish given two injections of LH-RH-A at a 3-hr interval were also depressed by bromocriptine, a specific D-2 dopamine receptor agonist, administered simultaneously with both LH-RH-A injections. Injections of dopamine antagonists, pimozide or metoclopramide (a specific D-2 antagonist) caused increased serum GtH concentrations in normal goldfish, but no changes were found following injections of the alpha-adrenergic antagonist phentolamine, the beta-adrenergic antagonist propranolol, or the sympathomimetic agent octopamine. Injection of pimozide or metoclopramide at the time of the second of two LH-RH-A injections given at an interval of 12 hr potentiated the LH-RH-A-induced increase in serum GtH concentrations; injections of phentolamine, propranolol, or octopamine did not alter the response to LH-RH-A. Injections of pimozide or metoclopramide also increased the frequency of ovulation in LH-RH-A-injected gravid female goldfish. These results suggest that stimulation of dopamine receptors can block the potentiating effect of multiple injections of GtH-releasing hormone, as well as ongoing LH-RH-A-stimulated release. The results also indicate that the dopamine inhibition of GtH secretion is specific and may be mediated by receptors resembling the D-2 type receptors in mammals.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001971:Bromocriptine / Q000494:pharmacology; D003530:Cyprinidae / Q000097:blood*; D004298:Dopamine / Q000502:physiology*; D005260:Female; D006054:Goldfish / Q000097:blood*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology; D006062:Gonadotropins / Q000097:blood*; D008787:Metoclopramide / Q000494:pharmacology; D009655:Octopamine / Q000494:pharmacology; D010060:Ovulation / Q000187:drug effects*; D010646:Phentolamine / Q000494:pharmacology; D010868:Pimozide / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology
D006062:Gonadotropins; D009655:Octopamine; D010868:Pimozide; D007987:Gonadotropin-Releasing Hormone; D001971:Bromocriptine; C010661:surfagon; D011433:Propranolol; D008787:Metoclopramide; D001058:Apomorphine; D004298:Dopamine; D010646:Phentolamine