Somatostatin-28 inhibits LHRH-stimulated gonadotrophin secretion in man

The LH and FSH responses to 100 micrograms LHRH in a combined pituitary stimulation test were compared to five normal men during infusions of somatostatin-28 (SS-28) and somatostatin (SS-14) and during control infusions of haemacel. SS-28 and SS-14 were administered in equimolar concentrations of 1.8 nmol/kg body weight over 210 min and LHRH was injected as a bolus at 120 min after commencement of the infusion. SS-28 significantly reduced both LH and FSH responses to LHRH compared with control infusions. SS-14 did not significantly alter the FSH response but caused a significant reduction in the LH concentration 75 and 90 min after LHRH injection. These findings demonstrate that SS-28 has distinct biological activity in addition to its role as a putative precursor of SS-14. Inhibition of gonadotropin hormone secretion by SS-14 and SS-28 suggest that these hypothalamic peptides may play a part in the regulation of LH and FSH secretion.