Hypertension associated with decreased testosterone levels in natriuretic peptide receptor-A gene-knockout and gene-duplicated mutant mouse models

Mice lacking the gene (Npr1) encoding the natriuretic peptide receptor A (N PRA) have hypertension with elevated blood pressure and cardiac hypertrophy . In particular, Nprl gene-deficient male mice exhibit lethal vascular even ts similar to those seen in untreated human hypertensive patients. Serum te stosterone levels tend to be lower in hypertensive male humans than in norm al males without hypertension, but the genetic basis for this tendency rema ins unknown. To determine whether Npr1 gene function affects the testostero ne level, we measured serum testosterone in male hypertensive mice lacking a functional Nprl gene, wild-type animals with two copies, and the gene-dup licated littermates expressing four copies of the gene. In the Nprl gene-kn ockout (zero-copy) mice, the serum testosterone level was 62% lower than th at in the two-copy control mice (80 +/- 10 us. 120 +/- 14 ng/ml, respective ly; P < 0.005). Serum testosterone in the four-copy mice was 144% (P < 0.00 5) of that in the two-copy wild-type control mice. To investigate the role of NPRA in testicular steroidogenesis, me analyzed atrial natriuretic pepti de (ANP)-dependent guanylyl cyclase activation, accumulation of intracellul ar cGMP, and testosterone production in purified primary Leydig cells from animals with zero, two, or four copies of the Nprl gene. Leydig cells lacki ng the Npr1 gene did not show ANP-stimulated guanylyl cyclase activation or cGMP accumulation and had no ANP-dependent testosterone production. ANP st imulation of Leydig cells from the four-copy males elicited a a-fold greate r production of cGMP compared to that in the two-copy wild-type counterpart s (260 +/- 12 vs. 126 +/- 7 pmol/1 x 10(6) cells; P < 0.001). Similarly, AN P-dependent testosterone production in Leydig cells was nearly twice as hig h in four-copy mice as in two-copy wild-type controls (561 +/- 18 us. 325 /- 11 ng/l x 10(6) cells; P < 0.001). ANP-dependent guanylyl cyclase activa tion and production of cGMP in Leydig cells increased progressively with th e number of Npr1 gene copies. Our results establish the existence of an alt ernate mechanism for testicular steroidogenesis that is stimulated by NPRA- dependent cGMP signaling, in addition to that mediated by gonadotropins, vi a a cAMP pathway. These findings demonstrate the role of Npr1 gene function in the maintenance of serum testosterone levels and testicular steroidogen esis and provide a genetic link between hypertension associated with decrea sed NPRA and low testosterone levels.