Suppression of Basal Insulin Secretion by Adrenalin in Normal Man and in Patients with Insulinomas

Basal insulin secretion has been thought to be via a different mechanism from stimulated insulin secretion, partly because it is not similarly suppressed by adrenalin. However, adrenalin normally causes hyperglycaemia, but if it is infused while the plasma glucose is kept constant there is marked suppression of insulin secretion. Sympathetic stimulation modulates basal insulin secretion, and alpha adrenergic blockade impaired the suppression of insulin secretion in response to hypoglycaemia. Four of five benign insulinomas had marked suppression of insulin secretion by adrenalin, but one malignant and one benign insulionoma had little suppression. Both had a raised proportion of their basal plasma insulin as proinsulin, and the impaired suppression of secretion by adrenalin probably signified an undifferentiated tumour.