Effect of TRH, TSH, and LH-RH on plasma thyroxine and triiodothyronine in the lesser snow goose (Anser caerulescens caerulescens) and plasma thyroxine in the Rouen duck (Anas platyrhynchos)

Abstract

The effect of TRH, TSH, and LH-RH on plasma thyroxine (T4) and triiodothyronine (T3) levels was studied in the lesser snow goose (Anser caerulescens c.) and on plasma T4 in the Rouen duck (Anas platyrhychos). LH-RH when given in doses sufficient to stimulate LH release demonstrated no thyrotrophic activity. TRH increased plasma T4 levels in the geese by 96% to 52 ng/mL within 20 min of treatment and levels remained high for up to 1 h. Return of plasma T4 levels to base-line levels appeared to take 80 to 90 min. TSH resulted in similar increases in plasma T4 within 15 min of treatment and produced maximum levels of 42 ng/mL in the male and 30 ng/mL in the female (329 and 266% increases, respectively). Peak plasma T3 levels lagged behind T4 peaks providing evidence that at least part of the T3 is foimed by peripheral monodeiodination of T4. The response of plasma T4 to TSH in the duck was similar to that in the geese although base-line levels were higher.