Effect of Synthetic Somatotropin Release Inhibiting Factor on the Increase in Plasma Growth Hormone Elicited by L-Dopa in the Dog

Synthetic somatotropin release inhibiting factor (SRIF, GIF, somatostatin) was given to 6 adult male mongrel dogs in an intravenous loading dose of 500 fig followed by a 1-hr infusion(30 µig/kg); 15 min after the start of the infusion L-dopa was injected intravenously. SRIF completely suppressed the increase in plasma growth hormone evoked by L-dopa. In 3 dogs, simultaneous administration of SRIF and L-dopa also caused no increase in plasma growth hormone. Plasma growth hormone levels increased within 30 min after discontinuation of the SRIF and L-dopa infusion, but failed to rise 45 min after termination of an infusion of SRIF alone. (Endocrinology95: 943, 1974)