The effects of progesterone on glucose and lactate metabolism in ovariectomized sheep

In nine samples from four ovariectomized sheep the mean plasma concentration of progesterone was 0.19 +/- 0.04 ng/ml. After the subcutaneous implantation of 3 x 375 mg of progesterone in silicone rubber the concentration rose to 3.8 +/- 0.51 ng/ml at 48 h and fell steadily to 1.5 ng/ml at 21 days. Removal of the implants caused a reduction to pre-implantation values by 48 h. The increased concentration of circulating progesterone after implantation had no significant effect on the concentration of glucose in plasma, its total entry rate, irreversible loss or on plasma lactate concentration. Glucose recycling increased from 0.13 +/- 0.05 to 0.38 +/- 0.12 mg min-1 kg-1 (P less than 0.05). Lactate entry rate fell from 1.68 +/- 0.16 to 1.12 +/- 0.10 mg min-1 kg-1 (P less than 0.02). The total net formation of lactate from glucose fell from 0.56 +/- 0.05 to 0.41 +/- 0.08 mg min-1 kg-1 (P less than 0.05). The production of lactate from non-glucose substrates fell from 1.15 +/- 0.11 to 0.70 +/- 0.04 mg min-1 kg-1 (P less than 0.02). The utilization of lactate for purposes other than glucose synthesis fell from 1.50 +/- 0.14 to 0.97 +/- 0.09 mg min-1 kg-1 (P less than 0.05). The results support the view that progesterone produces an increase in glucose recycling by pathways involving compounds other than lactate.