THE INFLUENCE OF HYPOPHYSECTOMY ON NSILA CONCENTRATIONS IN THE DOG: EVIDENCE FOR PARTIALLY PITUITARY-INDEPENDENT REGULATION

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Abstract
Non-suppressible insulin-like activity (NSILA) was determined in 5 dogs before and after hypophysectomy. All NSILA determinations were carried out on serum samples after acidic Sephadex G-50 chromatography by 2 different assay systems, i.e., a bioassay and a protein binding assay. The levels of NSILA decreased significantly after hypophysectomy and returned to near normal levels after 2 wk. T3 [triiodothyronine], T4 [thyroxine] and cortisol levels were drastically reduced during the entire period of the experiment. Several GH [growth hormone] determinations after hypophysectomy revealed very low levels. Insulin-induced hypoglycemia failed to provoke a rise of GH levels as late as 4 mo. after hypophysectomy. The pituitary gland cannot be the site of synthesis of NSILA. NSILA concentrations in the dog are maintained at a near normal level in the presence of very low GH and thyroid hormone concentrations, so that these latter hormones do not appear to be the only regulatory factors concerned in NSILA synthesis.