RECEPTOR-MEDIATED STIMULATORY EFFECT OF ATRIAL-NATRIURETIC-FACTOR, BRAIN NATRIURETIC PEPTIDE, AND C-TYPE NATRIURETIC PEPTIDE ON TESTOSTERONE PRODUCTION IN PURIFIED MOUSE LEYDIG-CELLS - ACTIVATION OF CHOLESTEROL SIDE-CHAIN CLEAVAGE ENZYME

We have investigated the mechanisms by which different natriuretic peptides stimulate steroidogenesis in purified mouse Leydig cells. In addition to atrial natriuretic factor (ANF), we show that brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) also stimulate testosterone production in these cells. Testosterone production was increased dramatically to 14-fold with ANF (EC50 = 0.3 nm) and 15-fold with BNP (EC50 = 0.2 nm); however, the CNP-stimulated level of testosterone production was only 2.5-fold compared with controls. ANF and BNP enhanced the stimulatory effect of LH on testosterone production. The C-ANF(4-23) (a truncated form of ANF) had no effect on testosterone production in these cells. ANF, BNP, and CNP stimulated the production of intermediate precursors of testosterone biosynthesis, which included progesterone, 17alpha-hydroxy progesterone, androstenedione, pregnenolone, 17alpha-hydroxy pregnenolone, and dehydroepiandrosterone sulfate. The conversion of pregnenolone and progesterone to testosterone was also significantly enhanced after treatment of Leydig cells with these peptides. All three natriuretic peptides (ANF, BNP, and CNP) stimulated the activity of particulate guanylate cyclase by 8.4-, 8.5-, and 4.8-fold and the accumulation of intracellular cGMP by 52-, 58-, and 19-fold, respectively. The cGMP inhibitor LY83583 attenuated both the generation of cGMP as well as testosterone in response to these natriuretic peptides, suggesting the involvement of cGMP as a second messenger. Leydig cells were found to contain high affinity and low capacity binding sites for ANF [dissociation constant (K(d)), 2.0 x 10(-10) m; maximum binding capacity (B(max)). 20 fmol/1 x 10(5) cells], BNP (K(d), 2.2 x 10(-10) m; B(max), 19 fmol/1 x 10(5) cells), and CNP (K(d), 3.1 x 10(-10) m; B(max), 8.6 fmol/1 x 10(5) cells). The results presented here document that a family of different natriuretic peptides stimulates Leydig cell steroidogenesis in receptor-mediated fashion, beginning at the cholesterol side-chain cleavage enzyme. The data also show that these peptide hormones induce testosterone production in mouse Leydig cells by involving both DELTA4- and DELTA5-pathways of steroidogenesis.