SOMATOSTATIN AND INSULIN-SECRETION IN MAN .2. THE EFFECT OF THEOPHYLLINE

The effect of theophylline, a drug that increases the intracellular concentrations of cyclic AMP by inhibiting phosphodiesterase activity was evaluated, on somatostatin (SRIF)-mediated inhibition of insulin secretion in man. Acute insulin response (AIR) to i.v. glucose (mean change 3-10 min) was almost totally suppressed by SRIF (500 .mu.g/h) and glucose utilization was reduced (P < 0.0001). These SRIF-induced decreases failed to be eliminated by a concurrent theophylline infusion (100 mg as a loading dose followed by a constant infusion of 5 mg/min). Theophylline alone resulted in a significant increase in both AIR (P < 0.01) and glucose removal rates (P < 0.05). The data apparently disprove the involvement of the phosphodiesterase enzymes in the inhibitory action of SRIF on glucose-induced insulin secretion in man.