Effect of 24‐Hour Somatostatin Infusion on Glucose Homeostasis and on the Levels of Somatomedin A and Pancreatic and Thyroid Hormones in Man

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Abstract
To investigate whether somatostatin plays a role in the regulation of thyroid hormone secretion the effects of a prolonged somatostatin infusion on insulin and glucagon levels were compared with its effect on T4 (thyroxine), T3 (triiodothyronine), r (reverse) T3 and TSH [thyrotropin]. The serum levels of somatomedin A were determined. Saline was infused in control experiments. Cyclic somatostatin was given as an i.v. bolus of 200 .mu.g followed by a constant rate infusion of 50 .mu.g/h during 24 h. Somatostatin suppressed basal insulin and glucagon levels as well as insulin responses to meals but did not influence somatomedin A levels. T4 and T3 decreased during the 1st h, whether somatostatin was given or not. Thereafter, T4 and T3 remained stable in the control experiments, while they continued to decrease slowly when somatostatin was added. The suppressive effect of somatostatin was significant 11 h (P < 0.05) and 24 h (P < 0.005) after the onset of the infusion. rT3 and TSH were not suppressed by somatostatin. The fact that basal TSH did not decrease, favors the idea that the suppression of T4 and T3 was mainly due to a direct inhibitory effect of somatostatin on the thyroid gland. The observation that a low dose of somatostatin decreases peripheral T4 and T3 levels supports the idea that somatostatin plays a role in the regulation of thyroid hormone secretion.