STEADY-STATE LUTEINIZING-HORMONE RECEPTOR MESSENGER-RIBONUCLEIC-ACID LEVELS AND ENDOTHELIAL-CELL COMPOSITION IN BOVINE NORMAL-LIVED AND SHORT-LIVED CORPORA-LUTEA

The short-lived corpus luteum (CL) contributes to reproductive ineffic iency during the postpartum period in beef cows. The cause for the ear ly demise of the short-lived CL is not fully understood but is believe d to involve a premature release of prostaglandin F-2 alpha. The objec tives of this study were to evaluate norgestomet-hCG-induced normal-li ved CL and hCG-induced shortlived CL in postpartum cows with respect t o serum progesterone (P-4) and 13,14-dihydro-15-keto, prostaglandin F- 2 alpha (PGFM) concentrations and luteal LH receptor (LH-R) concentrat ions, LH-R mRNA levels, and vascularity. Although serum P-4 profiles f rom the time of hCG administration (Day 0) until luteectomy (Day 6, 7, or 8) were similar between CL life span groups, PGFM concentrations w ere elevated (p < 0.05) on Day 8 in cows expected to have short-lived CL compared to normal-lived CL. The LH-R concentrations were similar b etween normal- and shortlived CL on all days measured. Irrespective of luteal life span and day of luteectomy, all CL possessed a 4.4-kb LH- R transcript. Actin-normalized LH-R mRNA levels were similar between n ormal- and short-lived CL on Days 6 and 7; however, Day 8 shortlived C L contained less (p < 0.05) LH-R mRNA than Day 8 normal-lived CL. Alth ough the area of luteal tissue occupied by capillaries in normal- and short-lived CL was similar on Days 6 and 7, the area occupied by capil laries in short-lived CL was lower (p < 0.05) than that for normal-liv ed CL on Day 8. Collectively, these results indicate that there is a d ecrease in steady-state LH-R mRNA and a reduction in luteal vascularit y in CL expected to be short-lived. These changes occur concomitantly with a rise in serum PCFM, but prior to a decline in serum P-4.