Somatostatin-28 inhibits thyroid-stimulating hormone release in man

The effects of an equimolar (1,8 nmol/kg body weight) infusion of somatostatin-28 (SS-28) and somatostatin-14 (SS-14) on the thyroid-stimulating hormone (TSH) response to a combined pituitary function test consisting of 200 micrograms thyrotrophin-releasing hormone (TRH) as well as 100 micrograms luteinizing hormone-releasing hormone (LH-RH) and insulin 0.1 U/kg were compared in 5 normal men. SS-28 significantly inhibited the TSH response to TRH compared with the control infusion. SS-14 was ineffective in 1 subject but overall did not differ significantly from SS-28. In 1 of the subjects the inhibitory effects of SS-28 on the TSH response was determined at three different doses of SS-28. In this subject SS-28 was found to be approximately 16 times more potent than SS-14 in the inhibition of TSH release. Suppression of TSH by SS-28 adds further support for a hormonal role for the peptide.