Plasma insulin and growth hormone concentrations in pregnant sheep II: post-absorptive levels in mid- and late pregnancy.

The pregnant ewe compensates the reduced carbohydrate availability in late pregnancy by increased fat combustion. The purpose of the present study was to examine the adaptation of plasma growth hormone (GH) and insulin levels to this change in energy substrate metabolism. Two groups of ewes were bled in the post-absorptive state at different stages of pregnancy. One group (7 animals) was fed adequately throughout pregnancy, while the other received a maintenance ration for non-pregnant sheep (28 animals). Plasma GH increased from averages from 2-3 to 8-14 ng/ml during the last month before lambing. Shearing of the wool combined with a cold stress resulted in a clearly detectable peak in plasma GH in the underfed sheep. No significant difference in plasms GH attributable to differences in diet could be detected in late pregnancy. Plasma insulin decreased steadily the last 5 weeks towards lambing, most in mothers with 3 lambs. Plasma free fatty levels (FFA) increased the last 2 months of pregnancy, most in the underfed sheep. GH and FFA were positively correlated (r= 0.50 and 0.30 in the two groups). It is concluded that the adaptation of the maternal metabolism to reduced carbohydrate - and eventually energy-availability in late pregnancy included lowering of insulin and enhancement of plasms GH levels. These adaptations were detectable under the present conditions the last 5-6 weeks before term.