Degradation of Luteinizing Hormone-Releasing Hormone by Rat Pituitary Plasma Membrane Associated Enzymes

Abstract

The hypothalamic decapeptide luteinizing hormone-releasing hormone (LHRH) is known to be inactivated by peptidases present at its site of synthesis and release, the hypothalamus (1–8), at its target organ, the pituitary (3,9–16), as well as in other locations such as in brain (3,17,18), kidney and liver (19,20,21), in serum and plasma (22,23). Little is known about the mechanism of action of these enzymes and their physiological significance is still uncertain. Since the stimulation of gonadotropin secretion from the pituitary gland is initiated by specific binding of LHRH to plasma membrane receptors (11,24), the presence of membrane-bound, LHRH degrading enzymes (11,14) may be of potential significance. These peptidases may be involved in the mechanism of action of LHRH, by regulating the amount and duration of action of the decapeptide at its receptor site. The elucidation of the degradation products of LHRH, the design of analogs modified at the site of cleavage and determination of their resistance to enzymatic degradation can provide a better insight into the mode of action of these peptidases. Investigation of a possible relation between LHRH at the receptor site and the enzymatic activity may provide evidence for the involvement of these enzymes in the regulation of LHRH action.