Within-day variations in the composition of maternal and fetal plasma from catheterised ewes fed once daily or at hourly intervals during late pregnancy.

Within-day variations in the concentrations of glucose, fructose, lactate, urea, insulin, thyroxine, corticosteroids and individual amino acids in maternal and fetal plasma from 12 Scottish Blackface ewes between 125 and 134 days of pregnancy were examined during a period of six days. In six ewes maintained on an adequate diet given at hourly intervals the concentrations of almost all the plasma constituents remained within the limits of analytical error during the period of observation. The advantages of this method of feeding in attaining the 'steady state' commonly required for kinetic experiments using isotopically labelled metabolites are discussed. In six ewes given similar rations but fed once daily substantial postprandial changes occurred in both maternal and fetal plasma composition and persisted for at least 15 hours after feeding. In maternal plasma the concentrations of glucose, lactate, insulin, thyroxine, alanine, glutamic acid, glutamine and asparagine increased after feeding and the concentrations of urea, glycine, taurine, citrulline and the essential amino acids decreased. Changes in fetal plasma were generally similar but some differences from maternal plasma, mainly in the timing and duration of postprandial changes, suggested that fetal plasma composition was primarily affected by factors within the fetus. Only six amino acids gave significant correlations between their maternal and fetal plasma concentrations. It is suggested that maternal effects on fetal amino acid metabolism and possibly protein turnover are imposed indirectly through an autonomous fetal endocrine response stimulated in part by variations in the supply of glucose from the mother.