THE EFFECT OF OXYTOCIN ON PROGESTERONE SECRETION AND OF PGF2-ALPHA ON OXYTOCIN SECRETION FROM BOVINE LUTEAL AND GRANULOSA-CELLS IN CULTURE

Oxytocin had a variable effect on progesterone output from hCG-stimulated bovine luteal cells cultured for 12 h in vitro. In two out of eight experiments high doses of oxytocin (> 10-9 M) inhibited progesterone output, whereas in a further four experiments progesterone release was stimulated by oxytocin at a range of concentrations from 10-10 to 10-6 M. When luteinized granulosa cells were used, oxytocin (10-9 to 10-6 M) tended to stimulate progesterone output, but in a few cases inhibition was also observed. Oxytocin release from isolated mid-cycle luteal cells declined rapidly during the first 3 h in culture, and the cells had released nearly their entire store of oxytocin within 12 h. Nevertheless, in some experiments, low concentrations of oxytocin could still be measured in the medium after 120 h. The amount of oxytocin released during culture exceeded the concentration present in the luteal cells at the start of each experiment, suggesting that a limited amount of synthesis and/or processing was occurring in vitro. The release pattern of oxytocin was not influenced by the presence of serum or hCG in the medium. The addition of PGF2α during long-term cultures decreased oxytocin output in two out of three experiments. © 1990.