The effect of dopamine on the release of prolactin in sheep with lesions of the hypothetical centre producing prolactin inhibiting factor (PIF).

It has been demonstrated in our previous papers that in the anterior part of medial basal hypothalamus (AM BH) in sheep a stimulating, while in the caudal part of MBH (CMBH) an inhibiting centre of prolactin release are situated. These results suggested that CMBH might be the site of PIF production and prompted us to investigate the effect of dopamine (DA) on the concentration of prolactin in the peripheral blood (p.bl.) in animals in which CMBH had been previously lesioned and this concentration was very high. Microinfusion of L-dopamine into the third cerebral ventricle (c.v.) or into the internal maxillary artery in intact as well as in lesioned lactating ewes depressed distinctly the prolactin level in the p.bl. This action of DA suggests that in the CMBH exists dopaminergic system which itself plays an inhibitory role in the control of prolactin release without involvement of PIF.