Control of endometrial oxytocin receptor and uterine response to oxytocin by progesterone and oestradiol in the ewe

Abstract

The effects of administration of progesterone and oestradiol on ovine endometrial oxytocin receptor concentrations and plasma concentrations of 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM) after oxytocin treatment were determined in ovariectomized ewes. Ewes received progestagen pre-treatment, progesterone and/or oestradiol in 11 different treatment schedules. Progestagen pre-treatment decreased oxytocin receptor concentrations in endometrium from ewes treated subsequently with either progesterone for 5 days or progesterone for 5 days plus oestradiol on Days 4 and 5 of progesterone treatment. Oestradiol increased endometrial oxytocin receptor concentrations when administered on Days 4 and 5 of 5 days progesterone treatment. Progestagen pre-treatment followed by progesterone treatment for 12 days caused a large increase in oxytocin receptors and no further increase occurred when ewes were given oestradiol on Days 11 and 12, or when progesterone was withdrawn on Days 11 and 12, or these two treatments were combined. Oxytocin administration caused an increase in plasma PGFM concentrations in ewes which did not receive progestagen pre-treatment, and subsequently received progesterone treatment for 5 days and oestradiol treatment on Days 4 and 5 of progesterone treatment. Similarly treated ewes which received progestagen pre-treatment did not respond to oxytocin. Oxytocin administration also increased plasma PGFM concentrations in ewes which received progestagen pre-treatment followed by progesterone treatment for 12 days, progesterone treatment for 12 days plus oestradiol on Day 11 and 12 of progesterone treatment, progesterone withdrawal on Day 11 and 12, or progesterone withdrawal and oestradiol treatment combined. The results indicate that (1) progesterone pre-treatment affects oxytocin receptor concentrations in the endometrium and uterine responsiveness to oxytocin and (2) progesterone treatment alone for 12 days after a treatment which mimics a previous luteal phase and oestrus is sufficient to induce oxytocin receptors and increase oxytocin-induced PGF release. These results emphasize the importance of progesterone and provide information which can be used to form an hypothesis for control of luteolysis and oestrous cycle length in the ewe.

Role of the uterus in early regression of corpora lutea induced by the ram effect in seasonally anoestrous Barbarine ewes

“…Progesterone may act on the hypothalamic-pituitary pathway (Martin et al, 1983), or at the level of the ovary (Hunter et al, 1986;Brown et al, 1988) or uterus. This latter suggestion has been widely studied (Vallet et al, 1990).…”

“…However, this is unlikely as when one administers intramuscularly 20 mg progesterone to hysterectomized ewes, the elimination of the hormone is slower (4 days, fig 3c) than in intact ewes (1 day, Lassoued et al, 1995 (Hunter et al, 1989). Progestagen treatment inhibits the establishment of oxytocin receptors and the release of prostaglandins in response to oxytocin administration (Vallet et al, 1990 (Rubianes et al, 1996) and probably reduces the increase in E2 secretion observed by Mattner and Braden (1972).…”

“…Maximum concentrations occur during oestrus, and are lower, relatively, 4 to 5 days earlier or later (Roberts et al, 1976;Sheldrick and Flint, 1985). During oestrus, plasma concentrations of progesterone are minimal whereas oestradiol concentrations are maximal, suggesting that oxytocin receptor synthesis is inhibited by progesterone (Hunter et al, 1989;Vallet et al, 1990) and increased by oestradiol (Hixon and Flint, 1987).…”

Central oxytocin and reproductive behaviours

“…There may also be important variations within specific oxytocin synthesizing cells, with subpopulations of parvocellular and magnocellular neurones responding with different sensitivities. It is also likely that steroids influence post-receptor transduction events (Vallet et al, 1990). Certainly the results listed above provide compelling evidence that receptors in different brain areas respond differentially to gonadal steroids.…”

Influence du nombre de corps jaunes sur la libération d'ocytocine lutéale, le transfert du lait alvéolaire dans la citerne et la production laitière chez la brebis

“…En effet, ce nonapeptide peut aussi être synthétisé, stocké et libéré par le corps jaune (Wathes et Swann, 1982 ;Flint et Sheldrick, 1982 ;Watkins, 1983 ;Rodgers et al, 1983 ;Swann et al, 1984) et c'est ainsi que les augmentations de pression intramammaires observées dans cette espèce, après injection intrajugulaire de PGF2a (Labussière ef al, 1983), résul-tent probablement de l'action de cette hormone lutéale puisque les réponses sont abolies après castration (Labussière et al, 1986), lutectomie (Labussière et al, 1990) ou interruption de la circulation sanguine dans la vascularisation ovarienne (Labussière et Combaud, 1989 (Lakshmanan et al, 1958 ;Elliot, 1959 ;Linzell et Peaker, 1971 ;Labussière et al, 1978). (Nissenson et al, 1978 ;Soloff et al, 1983), il faut malgré tout signaler qu'un pré-traitement à l'acé-tate de fluorogestone suivi d'un traitement progestéronique peut conduire à des résul-tats inverses (Vallet et al, 1990) et il faut aussi savoir que les récepteurs à l'ocytocine de l'utérus et de la mamelle ne semblent pas être soumis au même type de régulation (Soloff et al, 1979 ;Soloff, 1982 Il apparaît donc souhaitable de poursuivre ces travaux sur l'effet galactopoïéti-que des corps jaunes multiples en cherchant à dissocier l'importance relative de l'ocytocinémie (qui facilite le transfert du lait alvéolaire dans la citerne) et de la progestéronémie qui pourrait intervenir non seulement sur le métabolisme des cellules sécrétrices mammaires mais aussi sur la réceptivité à l'ocytocine des cellules myoé-pithéliales.…”