Effect of synthetic thyrotrophin releasing hormone on thyrotrophin and prolactin concentractions in the peripheral plasma of the pregnant ewe, lamb fetus and neonatal lamb.

Synthetic thyrotrophin releasing hormone (TRH) has been administered to pregnant ewes, chronically catheterised fetuses in the latter stages of gestation, and to newborn lambs. Both the pregnant ewe and her fetus showed marked rises in TSH and prolactin concentrations after administration of TRH. The placenta was impermeable to TRH, TSH and prolactin in both directions. The sheep fetus near term and the newborn lamb both demonstrated a considerable reserve of secretory capacity for TSH and prolactin.