Effects of a luteolytic dose of oestradiol benzoate on uterine oxytocin receptor concentrations, phosphoinositide turnover and prostaglandin F-2  secretion in sheep

Abstract

Administration of oestradiol-17 beta benzoate on Days 9 and 10 of the oestrous cycle resulted in episodic secretion of PGF-2 alpha (as indicated by elevated circulating concentrations of 13,14-dihydro-15-ketoprostaglandin F-2 alpha) and a decline in circulating progesterone. Release of PGF-2 alpha began 35 +/- 3 h after first injection of oestrogen and progesterone concentrations declined from 42 +/- 3 h. Secretion of oxytocin, which was first observed 26 +/- 3 h after oestrogen treatment, preceded secretion of PGF-2 alpha; 69% of pulses of oxytocin coincided with episodes of PGF-2 alpha secretion. Uterine oxytocin receptor concentrations were raised in ewes treated with oestrogen, increases occurring in caruncular endometrium and myometrium by 12 h after treatment and in intercaruncular endometrium by 24 h. Raised receptor concentrations were followed at 24 h by increases in the incorporation of [3H]inositol into phosphatidylinositol and in the hydrolysis of labelled tissue phosphoinositides in response to oxytocin in slices of caruncular endometrium incubated in vitro. The following sequence of events is therefore suggested to occur at oestrogen-induced luteolysis: induction of the oxytocin receptor; increased turnover of phosphoinositides; onset of episodic secretion of PGF-2 alpha; and functional luteolysis.

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

“…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).…”

Cigarette smoke extract enhances oxytocin-induced rhythmic contractions of rat and human preterm myometrium

“…However, it remains unclear whether the inhalation of cigarette smoke directly enhances the expression of OTR mRNA in the myometrium. Since OTR levels are known to be upregulated through progesterone regression, which occurs during luteolysis in the ewe (Hixon & Flint 1987, Zhang et al 1992, the increased expression of OTR mRNA in the pregnant rat myometrium, in the smoking group, may be caused indirectly through progesterone regression via luteolysis. Thus, inhalation of cigarette smoke may damage the function of the corpus luteum in the pregnant rat.…”

“…This uncertainty is based upon the findings that progesterone decreases the levels of uterine OTR mRNA and protein in pregnant rats (Soloff et al 1983), and estrogen increases the levels of OTR in the rat uterus and in human-cultured myometrial cells (Soloff 1975, Adachi & Oku 1995. Additionally, it has been reported that OTR levels are upregulated through progesterone regression, which occurs during luteolysis in the ewe (Hixon & Flint 1987, Zhang et al 1992. Therefore, the increased expression of OTR mRNA in the pregnant rat myometrium in the smoking group may be caused indirectly through progesterone regression via luteolysis.…”

Regulation of Interferon-.TAU. Gene Expression and the Maternal Recognition of Pregnancy.

“…Oxytocin then up-regulates an enzyme, cyclooxygenase-2 (COX-2), which converts arachidonic acid to PGG2 and PGH2, precursors for PGE2 and PGF2α, respectively [41][42][43], and subsequently induces pulsatile PGF2α production during luteolysis [44,45]. Estrogen affects the oxytocin-induced PGF 2α production presumably through the up-regulation of the OTR receptor [46,47]. Estrogen receptor (ER) is up-regulated before luteolysis, which coincides with an increase in OTR [39,48,49].…”