Relaxin,Oxytocin,and Prostaglandin Effects on Progesterone Secretion from Bovine Luteal Cells during Different Stages of Gestation 1

Abstract

Abstract

To determine the effects of relaxin, oxytocin, and prostaglandin F_2α on progesterone secretion, bovine luteal cells from different stages of gestation were dispersed in Medium 199 with 200 units/ml penicillin, 1.0% kanamycin, 0.5% bovine serum albumin, and 400 units/ml collagenase. Cells (10⁵) were cultured in 400 μl of Dulbecco's modified Eagle's medium and Ham's F-12 medium containing fetal bovine serum and antibiotics, in Falcon multiwell plates, in a humidified environment of 95% O₂ and 5% CO₂ at 37°C. Cells were cultured for 24 hr without treatment and thereafter with medium-hormone replacement every 24 hr. Progesterone was quantified from unextracted media by radioimmunoassay. Basal progesterone secretion after 24 hr was 1.81 ± 0.14, 1.76 ± 0.17, 0.54 ± 0.49, and 0.57 ± 0.21 pg/ml per viable luteal cell from 145-, 165-, 185-, and 240-day-old corpora lutea, respectively. Basal progesterone secretion increased (P < 0.05) with time in culture. Relaxin induced a dose-dependent (>100 ng/ml) increase in progesterone release, compared with the controls. Oxytocin and prostaglandin F_2α induced greater release (P < 0.05) of progesterone than relaxin at all stages of gestation, but progesterone release was dependent on the stage of gestation and the duration in culture. Luteinizing hormone (100 ng/ml) stimulated whereas 17β-estradiol (50 ng/ml) inhibited progesterone secretion by luteal cells at all stages of gestation examined. Relaxin obliterated the prostaglandin- and oxytocin-induced progesterone secretion by bovine luteal cells from 145 to 214 days of gestation. Thus, relaxin, cloprostenol, and oxytocin regulate progesterone production by cultured bovine luteal cells, but hormone secretion was dependent on the stage of gestation.