PRIMING EFFECT OF LUTEINIZING HORMONE RELEASING FACTOR IN VITRO: ROLE OF PROTEIN SYNTHESIS, CONTRACTILE ELEMENTS, Ca2+ AND CYCLIC AMP

Abstract

The mechanism of the priming effect of luteinizing hormone releasing factor (LH-RF) upon gonadotrophin secretion was studied using short-term incubation of hemipituitary glands from pro-oestrous rats. The dependence of the priming, but not the LH releasing action of LH-RF on protein synthesis in pituitary tissue was confirmed. Cytochalasin B failed to affect the first response to LH-RF, but abolished the priming effect, suggesting that the integrity of cellular microfilaments was essential. Colchicine and vinblastine did not modify the response to LH-RF. Neither inhibitors of DNA nor the inhibitor of RNA polymerase II, α-amanitin, significantly affected the priming action of LH-RF. Normal extracellular concentrations of Ca²⁺ were necessary for gonadotrophin release, but the priming effect was not significantly affected by low extracellular Ca²⁺ and could not be elicited by raising intracellular Ca²⁺ concentrations. Adenosine 3′:5′-cyclic phosphate did not appear to act as a second messenger for either the gonadotrophin releasing or the priming action of LH-RF.