The stimulatory and inhibitory effects of dopamine on prolactin secretion in the turkey.

Dopamine (DA) was infused into the third ventricle of anesthetized laying turkey hens at various concentrations to determine its effect on both basal prolactin (PRL) levels and ongoing electrically induced PRL secretion. The infusion of DA at rates of 1.0 or 10.0 nmol/min resulted in dose dependent increases in plasma PRL. These infusions had no inhibitory effect on electrically stimulated PRL release. The infusion of DA at 100.0 or 500.0 nmol/min caused no stimulation of PRL secretion and totally inhibited the PRL response elicited by electrical stimulation of the medial preoptic nucleus. These results show that dopaminergic influences are involved in both stimulating and inhibiting avian PRL secretion and suggest possible biphasic actions of DA within the brain.