Influence of cerebroventricular injection of dopamine on plasma prolactin and LH levels of postlaying and broody turkey hens.

Dopamine (DA), a well-known inhibitor of prolactin secretion in mammals, was injected into the third cerebroventricle of turkey hens in two distinct physiological states. Nonbroody postlaying turkeys had preinjection plasma prolactin (Prl) levels of about 68 ng/ml. Prolactin levels were significantly elevated 20 and 40 min after intraventricular injection of 10 micrograms of dopamine and then returned to basal levels. Incubating turkey hens, in contrast, showed the typical hyperprolactinemia characteristic of this physiological state. Mean preinjection Prl levels ranged from about 1290 to 1860 ng/ml. Injection of 10 or 30 micrograms of dopamine neither increased nor decreased plasma Prl levels over the 120-min time course of this experiment. Plasma luteinizing hormone (LH) levels were increased in nonbroody postlaying hens within 40 min after intraventricular injection of 10 micrograms of DA and then declined. Levels in vehicle-injected hens did not change significantly up to 120 min after injection. Dopamine injection had no effect on LH levels of broody turkey hens. These data clearly show that DA is not an inhibitor of Prl secretion in nonlaying turkeys with moderate Prl levels and in fact it appears to stimulate its release.