The effect of fatty acid infusion on growth hormone secretion in the ovine fetus: evidence for immaturity of pituitary responsiveness in utero.

The fetal growth hormone response to a 2-h intravenous infusion of a free fatty acid emulsion, Intralipid, was studied in the late gestation ovine fetus. Fetuses received low, medium or high dose Intralipid infusions for 2 h. Low dose infusions (0.5-0.7 ml/kg, n = 3) produced no significant changes in growth hormone concentrations. Both medium (2.0-4.0 ml/kg, n = 6) and high (4.1-6.0 ml/kg, n = 4) dose infusions elicited a significant decrease (P less than 0.01) in fetal growth hormone concentrations. At the high dose, growth hormone concentrations comparable to those seen in newborn lambs (28.5 +/- 10.6 ng/ml), were observed. Such an inhibition of growth hormone has not previously been seen in fetuses. To determine the possible mechanism of this effect, studies of the fetal growth hormone response to growth hormone releasing factor and somatostatin in the presence of Intralipid were undertaken. During control studies with growth hormone releasing factor alone, there was a significant (P less than 0.05) increase in fetal growth hormone levels within 20 min of administering the growth hormone releasing factor bolus (0.1 microgram/kg, n = 5). Intralipid infusion (2.0-4.0 ml/kg, n = 4), inhibited the response to growth hormone releasing factor. In control studies with somatostatin infusion (50 micrograms/kg bolus followed by 50 micrograms/kg infusion for 2 h, n = 3), there was a significant (P less than 0.005) but partial decrease in growth hormone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)