Histochemical observations on the lipid changes in rat corpora lutea during various reproductive states after treatment with exogenous hormones.

Lipid changes were studied histochemically in rat CL during the oestrous cycle, pregnancy and lactation after treatment with oestradiol benzoate (EB), LH and prolactin. A single injection of 50 mug EB given on any day during the first half of the oestrous cycle, pregnancy and lactation caused a heavy accumulation of lipid droplets, which consisted mainly of cholesterol and/or its esters, triglycerides and some phospholipids. If the treatment with EB was followed by a single injection of 20 i.u. prolactin, droplet accumulation either did not occur, or was greatly reduced. During the second half of pregnancy, a massive accumulation of cholesterol- and triglyceride-positive lipid droplets occurred in the CL of untreated rats, and prolactin was equally effective in reducing, or preventing the storage of cholesterol-positive lipid droplets. Prolactin was more effective if two injections of 10 i.u. were given daily after an interval of 11 to 12 hr. No appreciable lipid change in the CL was caused by injection of 100 mug LH on any day during the first half of the oestrous cycle and pregnancy, but during lactation the same amount caused a heavy accumulation of lipid droplets, consisting mainly of cholesterol and/or its esters, triglycerides and very little phospholipid. Persisting CL of pregnancy and cyclic CL seen during lactation and pregnancy, respectively, were unresponsive to exogenous hormones, apparently due to ageing as no lipid changes occurred in the CL after hormonal treatment. The results are discussed in relation to previous histochemical and biochemical studies and suggest that both LH and prolactin regulate the lipid and cholesterol metabolism in the luteal cells of the rat.