Somatostatin inhibits thyroid function in fowl

Plasma concentrations of thyroxine (T4) and triiodothyronine (T3) were marginally (less than 25%) lowered 10 and 60 min, respectively, following somatostatin (SRIF) administration (at doses of 10-30 micrograms/kg) in immature domestic fowl. When plasma iodothyronine levels were elevated by the administration of anti-SRIF (1.0 ml/kg) 10 min prior to SRIF challenge, the inhibitory effect of SRIF on T4 and T3 concentrations was greatly augmented. The relative reduction in the T3 concentration was greater than the decline in the T4 level, resulting in a decline in the T3:T4 ratio. These data indicate that SRIF inhibits thyroid function in fowl, possibly by direct effects on the thyroid gland and by effects on the peripheral conversion of T4 to T3.