Developmental aspects of the renal kallikrein-like activity in fetal and newborn lambs.

The ontogeny of the renal kallikrein-like activity and the interrelationships between this enzyme and the renin-angiotensin-aldosterone and prostaglandin systems were studied in 43 chronically catheterized sheep fetuses between 104 and 142 days of gestation (term, 145 days) and in 8 chronically catheterized newborn lambs between 5 and 23 days of age. Urinary kallikrein (UKall) excretion rate expressed in absolute values (mEU/hr) or corrected for kidney weight (mEU X hr-1 X gKW-1) or glomerular filtration (mEU X hr-1 X ml GFR-1) increased significantly during fetal maturation and after birth. The rise in UKall during fetal and newborn life was not dependent on an increase in urinary flow rate (r = 0.06). The increase in fetal UKall (mEU X hr-1 X gKW-1) correlated closely with the rise in plasma aldosterone concentration for values above 35 pg/ml (r = 0.72, P less than 0.001). A significant negative correlation was found between UKall (mEU X hr-1 X gKW-1) and log of individual urinary sodium excretion values (r = -0.78, P less than 0.001). No correlation was found between UKall and urinary prostaglandins (PGE, PGF2 alpha) excretion during fetal and newborn life, but UKall correlated closely with the rise in renal blood flow during maturation (r = 0.87, P less than 0.001). The present data suggest that aldosterone is an important regulator of UKall release early during development. It is also suggested that conceptional age is an important factor which may modulate the renal sensitivity to aldosterone-stimulated UKall excretion.