The Response of Large and Small Luteal Cells from the Pregnant Rat to Substrates and Secretagogues1

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Abstract
Large (> 22 .mu.m) and small (12-21 .mu.m) luteal cells from Day 8 pregnant rats were separated by elutriation after enzyme dissociation. Aliquots of cells were incubated for 4 h at 37.degree.C in Medium 199 alone (control) or with medium containing dibutyryl cyclic adenosine 3'',5''-monophosphate (cAMP) at 0.5 mM or 5 mM; rat luteinizing hormone (LH) at doses of 1, 10, 100, or 1000 ng/ml; 10 .mu.g/ml 25-OH-cholesterol; or 10 ng/ml testosterone. Production of progesterone, testosterone, and estradiol was measured by radioimmunoassay. Both cell types showed a similar increase in estradiol synthesis when stimulated with LH (1 .mu.g/ml) or dibutyryl cAMP (5 mM); however, large luteal cells aromatized exogenous testerone, whereas small luteal cells did not. Large luteal cells produced increased amounts of progesterone at lower doses of dibutyryl cAMP (0.5 mM) and LH (10 ng/ml), compared to small cells, which required 5 mM dibutyryl cAMP or 1 .mu.g/ml LH for minimal stimulation. Dibutyryl in both cell types was enhanced by 25-OH-cholesterol. These results suggest that the two cell types differ functionally with respect to steroidogenesis during pregnancy, and that the large luteal cells appear to be primary site of progesterone and estradiol production at this stage of pregnancy.