Determination of Secretion Rates of Estradiol, Progesterone, Oxytocin, and Angiotensin II from Tertiary Follicles and Freshly Formed Corpora Lutea in Freely Moving Sows*

Abstract

Two days before ovulation ovarian follicles of sows were implanted with microdialysis systems (MDS) which function like artificial capillaries with exteriorized inlets and outlets. Steroid hormones and paracrine acting factors such as oxytocin (OXT) and angiotensin II (AII) diffuse from ovarian tissue into the fluid, which is pumped through the MDS and collected in fractions. This allows determination of dynamic changes of estradiol (E2), progesterone (P), OXT, and AII secretion during the pre-, peri-, and postovulatory periods in freely moving sows. More than 80% of such implanted follicles ovulate and form competent corpora lutea (CL) allowing continuation of experimentation during the early luteal phase. Follicular E2 release increases before ovulation and decreases with increasing blood LH concentrations. Twenty to 30 h after beginning of the preovulatory LH surge P secretion increases gradually. Both peptides OXT and AII are released episodically by the preovulatory follicle. During the time of decreased E2 and not yet increased P secretion, i.e. during the periovulatory period, mean AII secretion was highest in comparison to the late follicular and early luteal phase. E2 remains measurable during the early luteal phase. OXT and AII were also topically applied into the follicular wall and after ovulation into the CL. AII had no effect on steroidogenesis of both structures. Although OXT was ineffective in the follicle, in young CL it stimulated P secretion. These results indicate that the MDS can be used to study late follicular and early luteal steroid and peptide secretion. The function of OXT and AII in the follicle remains obscure, whereas OXT has a luteotropic effect in young porcine CL.

In Vivo Evidence that Local Cortisol Production Increases in the Preovulatory Follicle of the Cow

“…The MDS for bovine mature follicles was based on the method developed for porcine follicles in vivo [14], and the same system was applied to bovine preovulatory follicles in vivo as previously described [15]. The MDS capillary membranes were implanted in the theca layer of follicles in the ovary contralateral to the regressing CL.…”

Luteinising hormone receptor kinetic and LH-induced prostaglandin production throughout the oestrous cycle in porcine endometrium

“…Since the concentration of oxytocin in porcine corpora lutea is many times lower than in ovine and bovine corpus luteum, and its level is maximal during the early luteal phase [6,29] it is thought that oxytocin may play a role as an intraovarian mediator necessary for the control of steroidogenesis [9,14,30] or corpora lutea development [6,29]. Einspannier et al [10] [12]. The presence of the blastocyst probably also acts to alter the final product such that the primary prostaglandin released is PGE 2 rather than PGF Za [1,28].…”

Effects of prolactin on estrogen, cAMP and oxytocin secretion by porcine granulosa cells in vitro

“…It has been shown (Ledwitz-Rigby, 1987;Einspanier et al, 1991) that, as in other mammals (Guraya, 1985), the luteinization of porcine follicles in vivo and in vitro is associated with a decrease in estradiol release and with the subsequent stimulation of progesterone output. Murphy and Rajkumar, 1985;Dusza and Tilton, 1990) that during corpus luteum development and lactation a high blood PRL level can inhibit follicular development, steroidogenesis and ovulation and maintain corpus luteum function.…”