Influence of Pituitary Stalk Section on Growth Hormone, Insulin and TSH Secretion in Women with Metastatic Breast Cancer

Abstract

The effect of pituitary stalk section on growth hormone secretion, insulin secretion and carbohydrate tolerance was studied in 13 women with advanced metastatic breast cancer. Plasma immunoreactive growth hormone concentrations were measured during standard insulin tolerance tests in 8 women preoperatively and 12 women postoperatively. Glucose disappearance rates (K_g), plasma growth hormone and insulin concentrations were measured after the rapid intravenous administration of glucose in 5 women preoperatively and 9 women postoperatively. In addition, the acute effect of stalk section on thyroidal discharge rate was studied in one patient. Measurable growth hormone levels in the fasting state were found on one or more occasions in 4 out of 8 patients studied during the early postoperative period. None of the 5 patients studied 8 months or longer after surgery had detectable levels of growth hormone under basal conditions. Peak preoperative growth hormone responses to insulin were between 22 and 115 ng/ml, with 2 patients showing exaggerated and prolonged responses. Postoperatively, the responses to insulin were either abolished or markedly attenuated. The responses which did occur had peak values which coincided in time with those of the preoperative tests. These responses progressively diminished in the 3 patients who were tested at successive time intervals after stalk section. Preoperative growth hormone responses to rapid iv glucose were about ⅓ the magnitude of the insulin responses. Both early and late peak values were observed. Five of the 8 patients tested postoperatively in this manner had growth hormone responses during the early hyperglycemic phase of the test but no late responses were observed. The mean fasting blood sugar of the group as a whole postoperatively was significantly lower than preoperatively (0.025<p<0.05). Paired comparisons revealed an accelerated glucose disappearance postoperatively in 3 out of 4 patients. Fasting hypoglycemia developed postoperatively in one patient who was hyperinsulinemic preoperatively. Lowering of the fasting blood sugar and improvement of glucose tolerance following stalk section, when it occurred, may have been due to decreased growth hormone secretion since these changes could not be explained by the alterations in plasma insulin levels. Stalk section caused an immediate decrease in the thyroidal discharge rate, but a slower rate of discharge continued for 4 days, suggesting that TSH was released from existing storage sites in the pituitary gland.