Oestradiol administration raises luteal LH receptor levels in intact and hysterectomized pigs

Conceptus signals for establishment and maintenance of pregnancy

“…PGF from the uterus is taken up by the mesometrium and transferred to the ovary in arterial blood by a countercurrent system that exists in the broad ligament of the uterus [112]. Estrogen also changes the ratio of PGE:PGF [113][114][115] as well as maintains LH receptor levels in both CL and uterus [116,117]. PGE 2 may protect the CL from the luteolytic effects of PGF.…”

Direct luteotrophic effect of oestradiol-17 on pig corpora lutea

“…Bazer et al (1986) reviewed data that indicate that oestrogen decreases the release of prostaglandin (PG) F-2a into the uterine vein, thereby reducing the luteolytic signal, but oestrogen may also have a direct effect on corpora lutea (CL) in the pig. It has been reported that oestrogen prevented PGF-2a-induced luteolysis in hysterectomized gilts (Kraeling et al, 1975) and increased luteal LH receptor numbers in pregnant and hysterectomized animals (Garverick et al, 1982). Neither these nor other exper¬ iments performed so far, however, have been able to exclude the possibility of oestrogen-induced changes in pituitary luteotrophic support (Chakraborty et ai, 1972) (P > 0-5) at any amount of oestradiol, indicating that release was constant over the 7-day incu¬ bation period.…”

“…Because compensatory ovarian hypertrophy in the pig is accompanied by increases in follicular size and ovarian venous oestrogen concentrations (Redmer et al, 1984), it is tempting to speculate that a similar local exposure of CL to these increases in oestrogen may result in an increase in luteal weight. Although no changes in systemic LH concen¬ trations occur after unilateral ovariectomy (Redmer et al, 1984) or during oestradiol benzoateinduced pseudopregnancy (Flowers et ai, 1987), Garverick et al (1982) reported that oestradiol increased LH receptor levels in CL of pregnant and hysterectomized gilts. Therefore, it is possible that the increase in luteal weight observed in the present study may be due in part to increased LH sensitivity and response, perhaps through increased luteal LH receptor populations.…”

Effect of pregnancy, injection of oestradiol benzoate or hCG on steroid concentration and release by pig luteal cells

“…Nevertheless, a direct effect of oestradiol on (6) (10) testosterone (Grazul et al, 1986a) and progesterone (Watson & Walker, 1978;Grazul et al, 1986b) synthesis in vitro or in vivo (Anderson et al, 1967) by pig luteal cells has not been observed, but oestrogen in high concentrations has been shown to inhibit LH-stimulated follicular androgen production in the rat in vivo (Leung & Armstrong, 1980), and in pig granulosa and theca cells in vitro (Veldhuis, 1985;Hunter & Armstrong, 1987). Furthermore, Garverick et al (1982) concluded that oestrogens may have a direct effect on the corpus luteum in the pig, since oestradiol-17ß raised luteal LH receptor levels. However, Ziecik et al (1986) suggested that the reduction in progesterone secretion during pseudopregnancy in the oestradiol-treated pig seemed to be caused by a partial blockade of the synthesis of this hormone, probably due to lower adenylate cyclase activity.…”