Insulin, dexamethasone and their interactions in the control of glucose metabolism in adipose tissue from lactating and nonlactating sheep.

1. Lactation results in decreased glucose and acetate utilization and increased lactate output by sheep adipose tissue. 2. The ability of insulin to stimulate acetate uptake was lost in adipose tissue from lactating sheep, whereas both the response and the sensitivity (ED50) for insulin for stimulation of glucose conversion into products other than lactate were decreased. These impairments were partly restored by prolonged incubation of adipose tissue for 48 h. 3. The ability of insulin to stimulate lactate output was not altered by lactation. 4. Dexamethasone inhibited glucose uptake, lactate output and glycerol output in adipose tissue from both non-lactating and lactating sheep, with an ED50 of about 1 nM. Dexamethasone inhibited acetate uptake by adipose tissue from non-lactating sheep, but this effect was not observed with adipose tissue from lactating sheep. 5. Dexamethasone inhibited the stimulation of glucose uptake at all concentrations of insulin used; the effect varied with insulin concentration and resulted in an accentuation of the insulin dose-response curve. The insulin dose-response curve in the presence of dexamethasone was muted during lactation. 6. The overall effect of these adaptations is to ensure that glucose and acetate utilization by adipose tissue after an insulin surge is diminished during lactation.