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LH receptors in ovine corpora lutea in relation to various physiological states and effects PGF-2 on LH-induced steroidogenesis in vitro

Summary. The LH binding properties (determined using tritiated methylated LH) and the in-vitro steroidogenic activity of CL from ewes in the oestrous cycle or early pregnancy (Day 18) were compared.

No significant alteration in the K_d values was observed. However, the number of sites was maximal at Day 10 of the cycle and in early pregnant animals which had not been pregnant for at least 3 months (dry ewes). Non-lactating or suckling ewes had half the numbers of binding sites. The increase of the number of receptor sites was accompanied by a steroidogenic response at lower LH concentration.

During incubation or superfusion for 5 h, a refractoriness to LH stimulation appeared after 1 h with high LH concentrations and after 3 h with low concentrations. The opposite effect of the addition of indomethacin or PGF-2 suggests the intervention of PGs in this phenomenon.