Control of gonadotropin release in the Atlantic croaker (Micropogonias undulatus): evidence for lack of dopaminergic inhibition.

Gonadotropin (GTH) secretion is known to be under inhibitory dopaminergic control in several species of fish. To investigate whether this is also the case in the Atlantic croaker (Micropogonias undulatus), juvenile and adult croaker were treated with a gonadotropin-releasing hormone analog (des-Gly10D-Ala6Pro9 n ethylamide luteinizing hormone-releasing hormone (LHRHa), 1-100 ng/g body wt) in combination with various dopaminergic drugs (1-20 mg/kg body wt). None of the dopamine antagonists tested, metoclopramide, pimozide, haloperidol, and domperidone, were able to increase plasma GTH levels above those induced by treatment with LHRHa alone and in some cases the gonadotropin response to LHRHa was reduced. The dopamine agonists bromocriptine and apomorphine either had no effect on the normal response to LHRHa or increased it. None of the drugs tested had any detectable effect on GTH levels in the absence of LHRHa. These results provide evidence for a lack of dopaminergic inhibition in the control of GTH secretion in the Atlantic croaker.