Summary. Immature rats and adult hamsters were killed on Days 2,4 or 8 of pregnancy (Day 1 = sperm positive vaginal smear). Dispersed luteal cells (5 × 104 cells) were incubated for 2 h in the absence or presence of graded doses of ovine LH. In the absence of LH, incubation of rat luteal cells compared to hamster cells produced about 3–6-fold as much progesterone, 26–66 times as much 20α-dihydroprogesterone and about the same amounts of 17α-hydroxyprogesterone. For the rat, 1 ng LH was the minimal dose which stimulated synthesis of progesterone and 17α-hydroxyprogesterone by luteal cells on Days 2 and 4 whereas 10 ng LH stimulated maximal production of progesterone by Day-8 luteal cells. As pregnancy progressed from Day 2 to Day 8, there was an inverse relationship between the levels of progesterone and 20α-dihydroprogesterone accumulated by rat luteal cells. For the hamster, 1 ng LH significantly stimulated accumulation of progesterone and 17α-hydroxyprogesterone by Day-2 luteal cells but not by Day-4 or Day-8 cells. Hamster luteal cells on Day 4 produced the highest levels of progesterone in response to 10 or 100 ng LH, with a maximal rate of accumulation by Day-8 cells with 10 ng LH.
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