Hormone receptor control of prostaglandin F2 alpha secretion by the ovine uterus.

The interaction of the ovarian steroid hormones (estrogen and progesterone) and the polypeptide hormone of posterior pituitary origin (oxytocin) appear to regulate the ovine estrous cycle by controlling production of the uterine luteolytic hormone PGF2 alpha. From our results, it appears that these steroid hormones may control PGF2 alpha release by regulating the availability of receptors for oxytocin in the endometrium, the primary site of PGF2 alpha production. Secondarily the ovarian steroid hormones may also regulate basal endogenous levels of oxytocin in the blood stream which may reinforce the luteolytic release of PGF2 alpha. Similar mechanisms may also be operative during the initiation of parturition in which steroid hormones, OT, and PGF2 alpha appear to play major roles (26). In addition to the known interdependence of steroid hormones and the gonadotropins (FSH, LH, and prolactin) required to initiate follicular growth, ovulation, and CL function, there appears to be a second interdependence required to terminate the ovarian cycle via the uterine luteolytic hormone PGF2 alpha, namely by the interaction between ovarian steroids and the posterior pituitary hormone, OT. Thus for both the initiation and termination of the ovarian cycle, there is evidence of a close interaction between the ovary and brain.