Renal renin activity in rats bearing a mammotropic tumor secreting growth hormone (GH) and prolactin or injected with GH

The effect of GH and prolactin on renin levels in the kidney is not yet well defined. Use has been made of a mammotropic pituitary tumor (MtT W10) which secretes large quantities of GH and prolactin, to study this problem. Renal renin content was measured in the kidney cortex of female rats of W/FU strain after 5 wk of tumor growth. Renin levels were significantly decreased (10±2 ng angiotensin per mg kidney cortex in tumor implanted rats versus 41±9 for controls). Indices of juxtaglomerular granulation were also lower whereas sodium consumption and plasma levels of sodium were identical in the 2 groups. The ultrastructure of zona glomerulosa cells was also identical in both groups. In a second experiment Sprague Dawley female rats, mononephrectomized and drinking 1% NaCl solutions, were injected s.c. for 17 days with 8 mg of GH per day. A significant decrease in renal renin content and indices of juxtaglomerular granulation, similar to those of the tumor bearing rats, was seen in these animals. Plasma sodium levels were identical in control and GH treated rats. GH induced no changes in the width or ultrastructure of zona glomerulosa; the ultrastructure of zona fasciculata was also indistinguishable from that of the controls. Thus, GH may have a direct effect on renal renin not involving alterations of sodium balance.