SEXUAL DIMORPHISM OF URINE ANGIOTENSINOGEN EXCRETION IN THE RAT

To determine the source of angiotensinogen excreted in urine, urine an giotensinogen was measured in male and female rats during growth. Angi otensinogen in 24-hr urine, measured by direct radioimmunoassay with a ntibody against rat angiotensinogen, increased fourfold in males betwe en the ages of 5 and 7 weeks, whereas no significant changes were obse rved in females or castrated males. Plasma levels of angiotensinogen, in contrast, showed no significant differences between these groups at any age. Castration of adult males caused a significant reduction of urinary angiotensinogen after 4 weeks. Consecutive s.c. administration of 17 alpha-methyltestosterone for 3 weeks in castrated males resulte d in a threefold increase in the urinary excretion of angiotensinogen, as well as a twofold increase in the renal expression of angiotensino gen messenger RNA (mRNA). Renal levels of angiotensinogen mRNA in inta ct adult males were about threefold higher than those in females and c astrated males, whereas there were no significant differences in hepat ic angiotensinogen mRNA between these animals. These results suggest t hat the sexual differences in the urinary excretion of angiotensinogen are primarily due to the androgen-dependent dimorphic expression of a ngiotensinogen mRNA in the kidney; thus, levels of angiotensinogen in urine might reflect intrarenal production.