Effect of short term intravenous infusion of noradrenaline on energy metabolism in shorn and unshorn pregnant sheep

Abstract

The effect of a three hour intravenous noradrenaline (NA) infusion, at a dose of 0.8 micrograms min-1 kg-1 bodyweight, on energy metabolism was studied in five pairs of shorn and unshorn pregnant ewes. The concentration of oxygen and carbon dioxide in blood was significantly higher in shorn animals during saline infusion, but this difference between shorn and unshorn groups was removed by NA infusion. Significant increases in the plasma concentrations of glucose, lactate, non-esterified fatty acids (NEFA), 3-hydroxybutyrate and glycerol occurred in both shorn and unshorn animals during NA infusion. There was a 48 per cent larger rise in the plasma NEFA concentration during NA infusion in the unshorn group, suggesting that the lipolytic effect of exogenous NA is greater in these animals. NA infusion had no effect on the plasma concentration of thyroid hormones in both groups of ewes, while growth hormone levels fell and cortisol increased in all animals. The plasma insulin concentration was significantly reduced during NA treatment in the unshorn group, but was unchanged in shorn animals. These results may be a consequence of sympathetic activity already being elevated in shorn ewes due to chronic exposure to an environmental temperature below the thermoneutral zone.