DIFFERENTIAL EXPRESSION AND AUTORADIOGRAPHIC LOCALIZATION OF ATRIAL-NATRIURETIC-PEPTIDE RECEPTOR IN SPONTANEOUSLY HYPERTENSIVE AND NORMOTENSIVE RAT TESTES - DIMINUTION OF TESTOSTERONE IN HYPERTENSION

Previous studies have shown that the diuretic hormone atrial natriuret ic peptide (ANP) also regulates the steroidogenic responsiveness in is olated Leydig cells from mouse and rat testes. In the present study, w e examined the distribution of specific receptors for ANP and C-type n atriuretic peptide (CNP) in the testicular compartments of 12-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). We used an in vitro autoradiographic procedure on slide-mounted frozen testic ular sections to localize the receptors of the natriuretic peptide hor mone family using I-125-ANP and I-125-CNP as radioligands. A high leve l of specific I-125-ANP binding sites was localized largely in the Ley dig cells of the interstitial compartment; other testicular cells were not significantly labeled. On the other hand, no significant differen ce was observed in I-125-CNP binding sites in the testicular cells of SHR and WKY. Semiquantitative analysis of the binding sites indicated that the density of I-125-ANP receptor binding in Leydig cells of WKY testis was ninefold higher than in those of SHR testis. A moderate lev el of I-125-ANP binding was also observed in seminiferous tubules, par ticularly in the spermatids of both SHR and WKY. I-125-ANP binding in WKY spermatids was approximately 2.5-fold higher than in SHR spermatid s. Northern blot analysis showed that mRNA specific for guanylyl cycla se type A (Npra) was expressed at approximately twofold higher levels in WKY than in SHR testis. ANP(1 x 10(-8) mol/L) stimulated fourfold t o fivefold increased levels of testosterone production in isolated Ley dig cells from normotensive WKY compared with those from SHR. These fi ndings support a new physiological role of ANP in Leydig cells, in whi ch a functional relationship seems to exist between testicular ANP rec eptor expression and testosterone production and the state of hyperten sion in SHR.