ROLE OF SERUM NONSUPPRESSIBLE INSULIN-LIKE ACTIVITY (NSILA) IN COMPENSATORY RENAL GROWTH

Abstract

The nonsuppressible insulin-like activity (NSILA) of serum is defined as the insulin-like activity measured in insulin bioassays that is not suppressed by addition of insulin antiserum. The major part of serum NSILA is attributable to a 90,000 MW trace protein which was recently purified. This study was designed to evaluate the role of serum NSILA in compensatory renal growth (CRG). Two normal and 6 hypophysectomized groups of male rats were studied; 14 days following hypophysectomy, unilateral nephrectomy was performed in 1 normal control group and 5 hypophysectomized groups. Daily hormone replacement was begun 1 day prior to nephrectomy in 4 hypophysectomized groups and continued for 15 days at which time CRG was assessed. Replacement hormone therapy consisted of growth hormone (GH), thyrotropin (TSH), ACTH, partially purified NSILA and various hormone combinations. CRG was quantitated by reference to control relationships of body weight to kidney dry weight analyzed by linear regression in both normal and hypophysectomized animals. Hypophysectomy failed to suppress CRG, and GH replacement alone did not affect the response. GH, ACTH and TSH, when given together, significantly potentiated CRG above the normal control response by 7.6% (P < .01). NSILA replacement had no effect on food consumption or body weight change, but resulted in a significant (P < .05) inhibition of CRG. These results support the possibility of an inhibitor of CRG and focus on the complex interrelationships of the humoral modulation of this response.