Somatostatin immunoneutralization stimulates thyroid function in fowl.

Abstract

The influence of somatostatin on thyroid function has been examined in immature domestic fowl passively immunized with somatostatin antiserum. Plasma thyroxine (T4) and tri-iodothyronine (T3) concentrations were markedly increased within 10 min of antisomatostatin administration and remained raised for at least 5 h. The increases in the T3 and T4 concentrations following somatostatin immunoneutralization were directly related to the volume of antisera administered. The increase in the T3 concentration exceeded the increase in the T4 concentration, resulting in a T3 : T4 ratio greater than unity. While the raised T4 concentration began to decline 30 min after antisomatostatin administration, raised T3 concentrations were sustained for at least 2 h, and further increased the plasma T3 : T4 ratio. These results demonstrate that somatostatin immunoneutralization stimulates thyroid function in fowl. The magnitude and rapidity of the thyroidal responses to somatostatin immunoneutralization suggests that they occur independently of the hypothalamic-pituitary-thyroid axis. Somatostatin appears to exert a tonic inhibitory control on avian thyroid function, possibly by effects mediated at the thyroid gland to inhibit T4 release and by peripheral effects to suppress the conversion of T4 and T3.