In vivo inhibition of the human non-pregnant uterus by prostaglandin E2

In vitro characterization of prostanoid EP-receptors in the non-pregnant human myometrium

1. Prostaglandin receptors of the PGE type have been characterized in the non-pregnant human myometrium in vitro according to the scheme of Coleman et al. (1984) by use of the agonists PGE2, sulprostone, rioprostil, AY23626, butaprost, misoprostol, 16,16-dimethylprostaglandin E2, enprostil and iloprost, and, the antagonist AH6809. 2. All prostanoids tested were active in non-pregnant human myometrium either as stimulators and/or inhibitors of spontaneous activity or both. Biphasic responses to PGE2 indicate that at least two receptor types of the EP-receptor exist, one mediating relaxation and the other mediating contraction. 3. Further evidence for the EP-receptor mediating excitation and relaxation was provided by the action of the EP2-/EP3-receptor selective prostanoids rioprostil, AY23626 and misoprostol, and the EP1-/EP2-receptor selective agonist 16,16-dimethylprostaglandin E2. 4. Butaprost, an EP2-receptor selective agonist, produced potent inhibition of spontaneous activity in the tissue which was generally longer-lasting than that evoked by the natural prostanoid PGE2. 5. The EP1-/EP3-receptor selective agonist sulprostone and the EP3-receptor agonist enprostil produced potent contractile responses supporting the presence of contractile EP3-receptors in the non-pregnant human myometrium in vitro. 6. The EP1-/IP-receptor selective agonist, iloprost, produced mixed responses in non-pregnant human myometrium. The contractile response was inhibited by the EP1-receptor antagonist AH6809. However, responses to the EP1-/EP3-receptor selective agonist sulprostone were unaffected by AH6809 which may indicate that only a small population of EP1-receptors is present. 7. Therefore it would seem that a heterogeneous population of EP-receptors is present in the non-pregnant human myometrium.

Acute and chronic effects of oral enprostil, a synthetic dehydroprostaglandin E2, on uterine contractility

In acute experiments eleven nonpregnant women received a single oral dose of enprostil (prostaglandin E2 analogue) 35-140 mcg. Uterine activity was measured by a microtransducer-tipped Millar catheter. A single, oral dose of enprostil caused a long-lasting contracture response of the uterus. 3 h after enprostil, uterine resting pressure (RP) was still high. In chronic experiments, eleven women with regular menstrual cycles received 35 mcg or 70 mcg BID enprostil and placebo in a crossover, double-blind fashion from cycle day 10 +/- 3 for four weeks, then had a washout period of four weeks followed by another four-week treatment period. An increase of uterine RP after enprostil was dose-dependent. After two weeks of twice-daily administration of enprostil, the baseline RP was lower than after placebo (p less than 0.01) and the increase in RP after the morning enprostil less than that seen on the first day. In eight patients studied, the mean values of plasma progesterone were normal, both during placebo--and enprostil--treated cycles.

Reduced uterine response to PGF2alpha under oral contraceptives

The effect of prostaglandin F2alpha (PGF2alpha) on the nonpregnant human uterus was evaluated in 35 patients. The compound was administered both by intra-uterine and intravenous routes. Two groups of volunteers were studied;fifteen cases who were under oral contraceptives and twenty women with normal ovulatory cycles. The uterus under the influence of oral contraceptives showed a reduced response to local and systemic administration of PGF2alpha at all phases of the menstrual cycle. The implications of these findings in certain physiological and pathological conditions related to reproduction are discussed.

Aberrant uterine response to prostaglandin E2 as a possible etiologic factor in functional infertility

The clinical entity of functional infertility still remains unexplained and largely lacking a line of proper management. The uterine response to prostaglandin E2 (PGE2) and prostaglandin F2alpha (administered by intravenous and intrauterine routes) was evaluated during different phases of the menstrual cycle in five functionally infertile women. The results (quantitative and qualitative) were compared with those elicited among 20 fertile women. There were no apparent differences between the two groups with respect to either compound (systemic or local) when given during the proliferative or luteal phase of the cycle. However, at midcycle, about the time of ovulation (days 13 to 18), there was a salient deviation in the type of response following local instillation of PGE2; in the normal fertile group there was a definite inhibition of motility, while uteri in the functionally infertile group showed marked stimulation. The possible role of this aberrant uterine response in the etiology of functional infertility is discussed.

The effect of locally administered PGE2 on the contractility of the nonpregnant human uterus in vivo

The effect of locally administered prostaglandin E2 on the sensitivity and reactivity of the nonpregnant human uterus during the menstrual cycle was studied in seven women. An increase in uterine contractility in response to as little as 0.25 mug PGE2 could be observed during both the mid-proliferative and mid-secretory phases of the menstrual cycle, but around ovulation a marked decrease in sensitivity to PGE2 was noted. An inhibition of uterine motility was observed during menstruation in response to 30--40 mug PGE2. Endogenous E prostaglandin normally occurs in the secretory endometrium in levels comparable to the amount of exogenous PGE2 which elicited increased or decreased uterine activity in this study. These findings suggest that PGE2 may play an important role in the cyclical regulation of uterine motility during the menstrual cycle.

The relaxant property of local prostaglandin E-2 on the non-pregnant uterus - a cyclic triphasic response

The response of the non-pregnant human uterus to intravenous (i.v.) injections and intra-uterine instillation of various doses of prostaglandin E-2 (PGE-2) was evaluated at the different phases of the menstrual cycle in 13 fertile regularly menstruating women who were neither lactating nor using any hormonal therapy. Uterine contractility was recorded by the microballoon technique in at least three sessions(proliferative, mid-cycle and secretory) in a single cycle with endometrial biopsy performed immediately following the last session to ascertain that the particular cycle was an ovulatory one. Single i.v. injections of PGE-I had a consistent stimulatory effect on the contractility throughout the cycle with a tendency towards a decreased uterine response at mid-cycle and luteal phase as compared to the proliferative part of the cycle. Intra-uterine instillation of the compound induced a peculiar and interesting type of response. In the proliferative and secretory phases of the cycle the response was one of stimulation; being more pronounced in the former period. However, around ovulation time, the local administration induced an evident uterine relaxation in most cases without any instance of stimulation. The possible implication of this triphasic response behaviour on the non-pregnant uterus within certain physiological events and pathological conditions is discussed.