RELATIONSHIP OF CIRCULATING STEROID-HORMONES, LUTEAL LUTEINIZING-HORMONE RECEPTOR AND PROGESTERONE CONCENTRATION, AND EMBRYONIC MORTALITY DURING EARLY EMBRYOGENESIS IN THE DOMESTIC CAT

Serum hormones, corpus luteum (CL) progesterone, and CL LH receptors w ere characterized and interrelated to ovarian follicle and CL number a nd preimplantation embryo quality/survival in the cat, Blood samples w ere collected from queens ovariohysterectomized at 64 (n = 7), 76 (n = 11), 100 (n = 8), 124 (n = 7), 148 (n = 6), or 480 (n = 8) h after fi rst copulation (3-times-daily matings on Days 2 and 3 of estrus). Ovar ian CL were enucleated, weighed, and bisected; one hemi-CL was assayed for progesterone and the other for LH receptors, Serum was assessed f or estradiol-17 beta and progesterone. Serum estradiol-17 beta concent rations did not return (p > 0.05) to baseline (similar to 20 pg/ml) un til 124 h after first copulation, whereas serum progesterone began to increase (> 1 ng/ml) by 76 h, was elevated (p < 0.05) by 124 h, and co ntinued to rise thereafter. Serum progesterone was highly correlated w ith CL mass and LH receptor and progesterone concentration (range, r = 0.69-0.82; p < 0.01). CL progesterone and LH receptor concentrations were similar (p > 0.05) at 64 and 76 h, and both increased (p < 0.05) at subsequent time intervals and were correlated closely (r = 0.65; p < 0.01), Although ovarian CL were distinct and well organized by 64 h, pronounced elevations in serum progesterone and CL LH receptors and p rogesterone did not occur until at least 36 h later. The rapid increas e in serum progesterone concentrations between 100 and 148 h was relat ed to accelerated LH receptor synthesis and CL progesterone production and not entirely to enhanced CL growth. There were few discernible di fferences in hormonal and luteal traits between queens with viable emb ryos or high implantation rates and females with degenerate embryos, u nfertilized oocytes, or poor implantation, with one consistent excepti on, Queens with poor fertility in the 64-, 76-, and 100-h groups had h igher (p < 0.05) CL progesterone concentrations than cats with viable embryos, suggesting that altered follicular dynamics (perhaps prematur e luteinization) adversely impacted oocyte/embryo quality. In summary, there is a direct and significant relationship between circulating pr ogesterone, CL mass, and CL progesterone/LH receptors during preimplan tation embryogenesis in the domestic cat, The temporal kinetics of the se events are remarkably similar among mated females and, with the pos sible exception of CL progesterone, appear unrelated to embryonic viab ility.