Effect of Posterior Pituitary Extracts on Urine Formation and Glomerular Circulation in the Frog

Abstract

Pituitrin can exert a protective action against dehydration in the frog Rana pipiens. This is accomplished by a reduction in the rate of urine formation. Pituitrin can also inhibit diuresis produced by the injn. of water or Ringer''s soln. Pitocin is approx. 10 times as active as pitressin in inhibiting water diuresis. Urine output and exogenous creatinine excretion are proportional over a wide range of rates. The rate of urine formation appears to be controlled by variations in glomerular filtration rate. Pituitrin can inhibit water diuresis by reducing glomerular filtration as measured by creatinine clearance. This effect is this one of glomerular antidiuresis similar to that known to occur in reptiles. By direct observation it was found that pitocin is as effective as pituitrin in causing constriction of the afferent glomerular arteriole and that pitressin is much less effective. It is concluded that the oxytocic fraction exerts a specific glomerular antidiuretic effect in this species by means of constriction of the afferent glomerular arteriole and the resultant reduction in glomerular filtration.