Influence of catecholamines on gonadotropin secretion in goldfish, Carassius auratus.

Serum gonadotropin (GtH) concentrations in female goldfish were measured before and at various times after intraperitoneal injection of drugs altering catecholamine synthesis and neural activities. Reserpine, a depleter of neurotransmitter stores, elevated serum GtH levels compared to controls, suggesting the general involvement of neurotransmitters in altering GtH release. 6-Hydroxydopamine, a catecholaminergic neurotoxin, increased serum GtH concentration, suggesting that catecholaminergic neurons inhibit GtH release. Blocking of L-DOPA and dopamine synthesis by alpha-methyl-para-tyrosine and carbidopa, respectively, but not norepinephrine by diethyldithiocarbamate, raised serum GtH values above those of controls. Injections of an alpha-agonist, clonidine, also increased serum GtH concentrations. These results suggest the existence of an inhibitory dopaminergic and a stimulatory alpha-adrenergic influence on GtH release in goldfish.