Plasma growth hormone and thyroxine levels in the chronically catheterised pig foetus and the effect of thyrotrophin releasing hormone.

The circulating levels of growth hormone and thyroxine during the last 2 weeks of gestation, and the effect of thyrotrophin releasing hormone on their secretion, has been examined in 13 chronically catheterised pig foetuses. Porcine growth hormone, measured by homologous radioimmunoassay, in the foetal plasma was found to average 83.5 +/- 10.3 ng/ml, while thyroxine levels were 92.9 +/- 4.1 nmol/l. There was no change in thyroxine or growth hormone levels with gestational age. Injection of 5 micrograms TRH produced a marked increase in plasma growth hormone levels (+194 +/- 51 ng/ml) but no change in thyroxine was observed. Injection of saline and subsequent blood sampling had no effect on the levels of either growth hormone or thyroxine.