Functional status of the peri-partum bovine corpus luteum

Abstract Thirteen cows, Experiment I, were injected at 1 h post-partum with saline ( n =4) or Human Chorionic Gonadotropin, (HCG) ( n =9). Eleven additional cows, Experiment II, were ovariectomized (ovx) unilaterally at 10 days pre-partum ( n =4) or 4 h post-partum ( n =7) to remove the only corpus luteum (CL). These ovx post-partum animals ( n =7) were also injected as part of Experiment I with saline ( n =2) or HCG ( n =5). All CL were sliced and incubated in media alone and with LH, tritium-labeled-pregnenolone ( 3 HP 5 ) or both. Blood samples were collected pre- and post-injection, Experiment I and pre- and post-surgery, Experiment II. Plasma and media samples were analyzed for progesterone (P 4 ) by radioimmunoassay. Media samples with 3 HP 5 were chromatographed for determination of P 5 conversion to P 4 . No significant differences ( P > 0.1) between P 4 profiles for saline or HCG treated animals were observed. Pre- and post-partum CL slices were able to convert P 5 to P 4 . Post-partum CL slices were unresponsive to LH whereas pre-partum slices responded. These data indicate the decline in luteal function peri-partum is probably not due to withdrawal of gonadotropin support.