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'-guanylylimidodiphosphate, 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, althoug prostaglandin I₂ stimulated insulin secreton in cultures of the benign tumour. The in vitro responsiveness of the adenylate cylase to glucagon did not correlate closely with the effect of glucagon on insulin secretion in vivo.