Maintenance of the Corpus Luteum of Early Pregnancy in the Ewe. I. Luteotropic Properties of Embryonic Homogenates

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Abstract
Experiments were carried out to examine the luteotropic properties of embryonic homogenates in ewes. Homogenates prepared from embryos collected 14-15 days postcoitum were infused into the uterine lumen of cycling ewes (n = 4) from Days 12 through 18 postestrus. Four control ewes received isotonic saline only. Embryonic homogenate, infused at a rate of 3 embryonic equivalents/24 h, prolonged the lifespan of corpora lutea through Day 18 postestrus. Mean serum progesterone levels on Days 16, 17 and 18 were 2.2 ± 0.5 ng/ml (±SEM), 2.0 ± 0.4 ng/ml and 1.6 ± 0.4 ng/ml in the treatment group and 0.33 ± 0.29 ng/ml 0.04 ± 0.01 ng/ml and 0.06 ± 0.01 ng/ml in the control group. Luteal weights on Day 18 were 626 ± 22 mg in the treatment group and 194 ± 46 mg in the control group. To determine if the luteotropic property of embryonic homogenate was due to the presence of LH or prolactin-like molecules, we examined embryonic protein in sensitive radioreceptor assays for these hormones. However, 100 µg of embryonic protein had no activity in either the LH-hCG or prolactin radioreceptor assay. In a second study, 100 µg of embryonic protein had no effect on synthesis of progesterone or cAMP in dispersed ovine luteal cells, either alone or in combination with LH and/or prolactin. Synthesis of both progesterone and cAMP could be stimulated in these cells by NIH-LH-S19. The data indicate that homogenates of 14-15-day-old embryos are capable of prolonging luteal function when infused into the uterine lumen, but the effect does not appear to be exerted via an LH or prolactin-like molecule.