Sexual dimorphism of inactive renin in rat plasma

The plasma concentration of inactive renin was higher (p less than 0.002) in male (0.48 Goldblatt units (GU)/l, range 0.28-0.67 GU/l; n = 20) than in female rats (0.19 GU/l, range 0.09-0.30 GU/l; n = 20). This new finding indicates a sexual dimorphism of inactive plasma renin similar to that recently reported in mice and humans. Castration of male rats (n = 10) decreased (p less than 0.01) inactive plasma renin from 0.45 GU/l (range 0.22-0.65 GU/l) to 0.26 GU/l (range 0.15-0.37 GU/l) over a period of seven weeks. Similarly, inactive renin decreased (p less than 0.01) from 0.50 GU/l (range 0.28-0.67 GU/l) to 0.30 GU/l (range 0.19-0.47 GU/l) during treatment with the anti-androgen flutamide (n = 10). In castrated male rats (n = 10), inactive plasma renin was unaffected of substitution with testosterone. In intact female rats (n = 10), inactive renin increased (p less than 0.05) from 0.18 GU/l (range 0.12-0.30 GU/l) to 0.27 GU/l (range 0.15-0.40 GU/L) during testosterone treatment. Our findings indicate that androgens may be involved in the regulation of the plasma concentration of inactive renin in rats, but also suggest that other factors may be of importance.