Effect of exogenous glucagon on pituitary polypeptide hormone release

Abstract

Anterior pituitary hormone secretion following administration of crystalline glucagon was studied in three phases, i.e., after subcutaneous injection, after intravenous injection, and after intravenous injection during constant glucose infusion. Although changes in serum glucose and plasma insulin levels were predictable, significant increases did not occur in the mean levels of plasma cortisol, serum growth hormone, serum luteinizing hormone, or serum thyrotropin. Only nine of the 24 subjects had increased cortisol levels, and ten had growth hormone responses. The timing and the magnitude of these responses were inconsistent but correlated well with the glucose nadir. Only seven of the 13 subjects who developed stressful stimuli (nausea and/ or hypoglycemic manifestations) had hormonal changes. When four of the responsive subjects were restudied during constant glucose infusion, their hormonal levels were unaffected and stressful symptoms did not occur. These data suggest that glucagon does not directly influence polypeptide hormone release from the pituitary gland. Hormonal responses appear to be secondary to changes in serum glucose and/or nonspecific stress.