Nutritional control of respiratory and other muscular activities in relation to plasma prostaglandin E in the fetal sheep

The effects of nutrient availability on fetal plasma prostaglandin E (PGE) concentrations, on fetal breathing movements and electromyographic (EMG) activities of fetal nuchal and forelimb muscles were investigated in pregnant ewes by varying dietary intake and by manipulation of fetal plasma glucose concentration. The incidence of fetal breathing movements (06.00-10.00 h) decreased with increasing gestational age while fetal arterial concentrations of plasma PGE increased significantly over the same period of gestation. Maternal fasting for 48 h reduced the incidence of fetal breathing movements and the amount of nuchal EMG activity (06.00-10.00 h) in animals older than 130 days but had no effect earlier in gestation. No changes in forelimb EMG activity were observed during fasting at any gestational age. Plasma PGE levels increased significantly during fasts begun both before and after 130 days of gestation. When data from fed and fasted states were combined for all fetuses, irrespective of gestational age, there was a significant inverse correlation between fetal breathing movements incidence and plasma PGE concentration in utero. This relationship was even more pronounced when the fetuses were considered individually. Insulin infusions induced hypoglycaemia, an increase in fetal plasma PGE concentration and a significant reduction in the incidence of fetal breathing movements at all ages. Glucose infusions of fetal breathing movements only after 130 days and had no effect on plasma PGE levels in utero at any gestational age. Neither insulin nor glucose infusions altered the EMG activities of the nuchal and forelimb muscles. The results show that glucose availability is an important factor in determining the incidence of fetal breathing movements in utero and indicate that nutritionally induced changes in fetal breathing movements are mediated in part by PGE. They also suggest that PGE is a physiological regulator of fetal breathing movements in the sheep during late gestation.