Luteinizing hormone response to oxytocin is steroid-dependent

Oxytocin-induced LH release from dispersed rat anterior pituitary cells in vitro was shown to be dependent on the steroidal environment. Preincubation of anterior pituitary cells with estradiol for 48 h enhanced the subsequent LH response to oxytocin (p less than 0.001). Maximal sensitization was observed with estradiol at 1 nM. Release of LH induced by oxytocin was inhibited in the presence of progesterone or to a greater extent in the presence of equimolar testosterone. Complete suppression of oxytocin-induced LH secretion occurred with 1 nM progesterone. Incubation of hemipituitaries with oxytocin revealed that the pituitary was sensitive in vitro to oxytocin at proestrus (p less than 0.05) but not at other stages of the cycle. The results indicate that there is altered sensitivity to oxytocin of the pituitary at different stages of the estrous cycle. Therefore activity of the neuropeptide in vivo might be modulated by steroids.