Further Evidence that Prolactin Does not Affect Gonadotropin Release at Pituitary Level

Summary

In a primary monolayer cell culture of the anterior pituitary from mature male rats the effects of exogenous rPrl (rPrl exog.) and endogenously secreted rPrl (rPrl endog.) on basal and LHRH stimulated LH secretion were investigated. In pilot studies basal Prl- and LH secretion as well as influence of various LHRH concentrations (10^-1-10⁺³ng/ml) on Prl- and LH release were observed. The influence of exogenous rPrl was studied at various concentrations (50-500 ng/ml) and with preincubation periods of 2 hrs and 6 hrs before starting LHRH stimulation. The dopamine agonist bromocriptine and the dopamine antagonist sulpirid were preferentially used to prove physiologic function of the cell system presented.

Basal LH secretion started after a delay of 3 hrs, whereas basal Prl secretion began immediately showing a linear rise for 9 hrs. LHRH stimulation resulted in a non-linear dose and time dependent LH secretion. LHRH showed no influence on endogenous Prl (rPrl endog.) secretion of the mammotroph cells.

Exogenous Prl (rPrl exog.) did not affect spontaneous Prl release excluding ultra short loop inhibition in this cell system. Furthermore, exogenous Prl had no effect on either basal or LHRH stimulated LH secretion even after a preincubation period of up to 6 hrs and at concentrations generally observed for prolactin secreting tumors.

Bromocriptine suppressed endogenous Prl release and did not affect LH secretion. Sulpirid had no influence on either Prl or LH secretion.

The present data supply further evidence that there is no direct interaction between Prl and LH secretion at the pituitary level. Autoregulation of Prl release (ultra short loop inhibition) could not be demonstrated in this cell system.

Key-Words

Prolactin - LH - Anterior Pituitary Monolayer Cell Cultures - Male Rat