Failure of fasting and changes in plasma metabolites to affect spontaneous fluctuations in plasma concentrations of ovine placental lactogen.

The relationships between plasma concentrations of energy substrates and placental lactogen (PL) were investigated in pregnant ewes. In successive hourly samples of plasma PL, concentrations varied by +/- 30% but were not related to general activity or feeding of the ewes or the time of day. Fasting ewes for 72 h did not alter the pattern or the mean PL titres. Insulin-induced acute hypoglycaemia, hyperglycaemia and decreases or increases in free fatty acids (FFA) all failed to alter PL levels significantly during 5-h post-treatment periods. These experiments demonstrate that PL secretion in the ewe fluctuates markedly and is unaffected by changes in plasma glucose FFA concentrations.