Adenylate Cyclase Responsiveness of Human Insulinomas

Adenylate cyclase activity was assayed in a crude particulate fraction of one benign and one malignant human insulinoma. Adenylate cyclase of both tumours responded to 5'-guanylyl-imidodiphosphate, sodium fluoride, glucagon and prostaglandin E2, and in addition the adenylate cyclase of the benign tumour responded to isoprenaline. Glucose and prostaglandin I2 (prostacyclin) did not stimulate the adenylate cyclase in either tumour, although prostaglandin I2 stimulated insulin secretion in cultures of the benign tumour. The in vitro responsiveness of the adenylate cyclase to glucagon did not correlate closely with the effect of glucagon on insulin secretion in vivo.