CHARACTERIZATION OF A SOLUBLE LHRH-DEGRADING ACTIVITY IN THE RAT VENTRAL PROSTATE

Recent evidence supports the hypothesis of a direct action of LHRH at the level of the prostate. Since peptidases able to degrade the hormon e are present in several LHRH target structures, it was deemed of inte rest to investigate whether the prostate of adult normal male rats mig ht possess LHRH degrading activities (LHRH-DA). Through the use of RP- HPLC, it has been observed that LHRH-DA is present in the soluble frac tion of the rat ventral prostate homogenate, and is able to hydrolyze synthetic LHRH and to generate fragments 1-3 and 1-5 of the decapeptid e. The degradation of [pGlu-H-3]LHRH is inhibited by LHRH itself, and affected by several LHRH agonists and antagonists with different kinet ics and potencies. TRH, the enkephalin analog [D-Ala(2)-D-Leu(5)]enkep halin and rat prolactin do not inhibit the degradation of [pGlu-H-3]LH RH by the soluble fraction of prostate homogenate; on the contrary, th is is inhibited by graded doses of somatostatin. The prostatic LHRH-DA is also inhibited, in a dose dependent manner, by bacitracin, serine protease inhibitors (diisopropylfluorophosphate and phenylmethansulfon ylfluoride), the metal chelating agent EDTA, HgCl2, and dithiothreitol . No inhibitory effect on [pGlu-H-3]LHRH hydrolysis was observed after incubation of the prostatic extract in the presence of captopril. The prostatic LHRH-DA seems to be different from that present in other ti ssues of the rat (e.g., hypothalamus, pituitary, gonads), and to be de creased by castration performed 3 weeks before. These results suggest that (1) an LHRH-DA is found in the soluble fraction of rat prostate h omogenate; (2) this enzymatic activity exhibits the characteristics of a metallo- and thiol-dependent neutral endopeptidase; (3) it appears to be different from similar hydrolytic activities found in other tiss ues; and (4) it is influenced by the hormonal milieu, since castration causes a significant decrease of its activity. (C) 1993 Wiley-Liss, I nc.