Dose and time dependent luteotropic and luteolytic action of prostaglandin F2alpha in the luteinized rabbit ovary.

The mechanism of stimulatory and inhibitory action of PGF2alpha on ovarian steroidogenesis both under in vitro and in vivo conditions has been studied in the pseudopregnant rabbits. Short term incubation of the ovaries with PGF2alpha (2.82 times 10(-5)M) resulted in an increased synthesis of progesterone and 20alpha-OH P. The addition of PGF2alpha in the medium and further incubation of the ovaries obtained from rabbits that had been constantly infused with PGF2alpha (0.5 mug/min.) for two hours resulted in increased synthesis of these progestins. The ratio of progesterone to 20alpha -OH P was also enhanced under these conditions and thus supported the luteotropic action of small doses of PGF2 under short term incubations. However, as the amount of PGF2alpha infused was increased to 5 mug/min., the addition of PGF2alpha under in vitro conditions strikingly decreased the production of these progestins. The ratio decreased the production of these progestins. The ratio of progesterone to 20alpha -OH P was also decreased and thus was indicative of luteolytic action of higher doses of PGF2alpha. High doses of PGF2alpha (5.64 times 10(-4)M) failed to cause any significant change in the progestin synthesis under short term incubation. These results thus suggest that the luteotropic and luteolytic action of PGF2alpha in the luteinized rabbit ovary is dose and time dependent.     

Reduction by human chorionic gonadotropin of the luteolytic effect of prostaglandin F2 in ewes

The ability of human chorionic gonadotropin (HCG) to reduce the luteolytic effect of prostaglandin (PGF_2^α) was demonstrated in cycling ewes. As expected, treatment with 10 mg of PGF_2^α alone on Day 10 of the estrous cycle exerted a potent negative effect on the function and structure of corpus luteum (CL) as indicated by reduced plasma progesterone, CL progesterone, and CL weight. However, the identical PGF_2^α treatment failed to significantly reduce either luteal function or luteal weight when administered to ewes that were also treated with HCG on Days 9 and 10 of the estrous cycle. Treatment with HCG alone had a positive effect on CL as indicated by increased plasma progesterone, CL progesterone, and CL weight. Treatment with HCG did not render the CL totally insensitive to the negative effects of PGF_2^α because plasma progesterone was reduced when the dose of PGF_2^α was doubled. Whether CL regressed or continued to function after treatment with both HCG and PGF_2^α appeared to depend upon a balance between the positive and negative effects of the two hormones.     

PGF2α-induced loss of corpus luteum gonadotrophin receptors

In experiments and we have previously shown that PGF_2α directly antagonized the action of gonadotrophins on the corpus luteum. To determine if this action of PGF_2α may occur as a consequence of an induced loss of gonadotrophin receptors, binding of hCG to rat luteal tissue was measured following PGF_2α treatment . In immature rats which were treated with exogenous gonadotrophin to luteinize the gonads, PGF_2α produced a marked and highly significant decrease in circulating progesterone when administered 24 hours before sacrifice. Although the affinity constant (Ka; 1.2-2 × 10¹⁰ L/M) of the luteal receptor to hCG was not affected, PGF_2α treatment produced a marked fall in the binding capacity of the luteal tissue to hCG. This response was absent, however, when PGF_2α was incubated directly with luteal receptor or administered during early pseudopregnancy when corpora lutea are more resistant to luteolysis. Experiments are in progress to determine if the decrease in capacity of luteal receptors to bind hCG is the mechanism or a consequence of luteolysis produced by PGF_2α.     

Effect of prostaglandin F2α on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F_2α (PGF_2α) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated.Using experimental conditions under which spontaneous propulsive activity was negligible, PGF_2α (5×10⁻⁸×1×10⁻⁶M), added to the bathing medium, increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1×10⁻⁷g/ml).The contractions produced by PGF_2α(5×10⁻⁷ − 1×10⁻⁵M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1×10⁻⁷ g/ml).From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF_2α may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.     

Effects of dibuturyl cAMP, LHRH, and aromatase inhibitor on simultaneous outputs of prostaglandin F2α, and 13,14-dihydro-15-keto-prostaglandin F2α by term placental explants

Explants from term human placentas were maintained in culture with daily changes of medium. Daily output of PGF_2α and PGFM¹ decreased during the course of the incubation. Addition of 4 μg/ml DHEAS or 67 μg/ml LDL cholesterol had no effect on output of PGF_2α or PGFM. Addition of 1.6, 3.2, or 6.4 μg/ml of LHRH to the culture plates had no effect on output of PGFM or PGF_2α, but LHRH increased hCG output. Dibutyryl cAMP (1mM, 2mM, and 4mM) increased output of PGF_2α, PGFM, and hCG. Aromatase inhibitor decreased hCG output, but it was without effect on output of PGF_2α, or PGFM. Significant correlations were demonstrated between progesterone, PGFM, PGF_2α, and hCG, suggesting that PGF_2α originates in the syncytiotrophoblast cell. The ability of LHRH to stimulate output of hCG but not PGF_2α while dbcAMP stimulated both suggests that either PGF_2α and hCG arise in different cells or that LHRH does not act through cAMP.     

Luteolytic potencin in a novel prostaglandin analogue

Estrus induction in cycling sows with exogenous prostaglandin is hindered by the extended refractory period and resistance of swine to the luteolytic action of PG's. The luteolytic potency of a novel PGF_2α analogue, Schering ZK 71677, was assessed at four different dosages in chronically cannulated cycling swine. Dosages totalling 1, 1.5, 3 and 10 mg of ZK 71677 were split into two injections given intramuscularly on day 13 of the estrous cycle. Onset of behavioural estrus and serum levels of progesterone and PGF metabolite were monitored. The three lowest doses did not advance estrus but did cause a transitory decline in serum progesterone concentration on day 13. The 10 mg level advanced estrus in three of four sows although the overall mean cycle length did not differ from pretreatment cycles (18.5 ± 1.3 vs 21.3 ± 0.6 days). Progesterone values droppd steadily in all four sows in the 10 mg treatment group. No level of ZK 71677 affected serum levels of PGF metabolite. The highest level tested of PGF_2α analogue ZK 71677 elicited an uninterrupted decline in serum progesterone concentrations but was inconsistent in its ability to promote early onset of behavioural estrus in swine.     

Effects of prostaglandins, dibutyryl camp, LHRH, estrogens, progesterone, and potassium on output of prostaglandin F2α, 13, 14-dihydro-15-keto-prostaglandin F2α, HCG, estradiol, and progesterone by placental minces

In order to compare the endocrine response of placental minces to luteinizing hormone releasing hormone (LHRH) and dibutyryl cAMP (dbcAMP) and to screen for effects of potential stimulatory and inhibitory substances, the simultaneous outputs of PGF_2α, 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM), progesterone, 17β-estradiol, and hCG were evaluated during a 4 hour incubation in 5 placentas. The output of hCG was highest for 12-week placentas, intermediate for a 16 week placenta, and lowest for term placentas. The output of 17β-estradiol by 12 and 16 week placentas in the presence of 30 μM dehydroepiandrosterone sulfate (DHEAS) was greater than that by term placentas. Progesterone output was apparently independent of gestational age although some variation between 12-week placentas was demonstrated. Output of PGF_2α was lower in 12 and 16-week placentas than in term placentas and that of PGFM was lower in 12-week placentas than in term placentas. LHRH (100 nM) produced stimulation of PGF_2α output (P<.005) and a trend toward inhibition of progesterone output (which failed to achieve statistical significance) but no stimulation of hCG under these conditions. Stimulation of the outputs of hCG (P<.005) and PGF_2α (P<.001) and inhibition of that of progesterone (P<.005) was produced by 20 mM dbcAMP. DHEAS inhibited output of progesterone (P<.01) and PGF_2α (P<.01). There were no effects of potassium, estrogens, progesterone, or prostaglandins on output of any measured substance.     

Prostaglandin E1 and F2α specific binding in bovine corpora lutea: Comparison with luteolytic effects

Preliminary characterization indicated the presence of separate prostaglandin (PG)E₁ and (PG)F_2α binding sites in membrane fractions prepared from bovine corpora lutea. These differ in the rate and temperature dependence of the specific binding. Equilibrium binding data indicate the apparent dissociation constants as 1.32 × 10⁻⁹M and 2.1 × 10⁻⁸M for PGE₁ and PGF_2α, respectively. Competition of several natural prostaglandins for the PGE₁ and PGF_2α bovine luteal specific binding sites indicates specificity for the 9-keto or 9α-hydroxyl moiety, respectively. Differences in relative ability to inhibit ³H-PG binding were found due to sensitivity to the absence or presence of the 5,6-cis-double bond as well.Bovine luteal function was affected following treatment of heifers with 25 mg PGF_2α as measured by reduced estrous cycle length, decreased corpus luteum size and significantly decreased plasma progesterone levels. In contrast, treatment with 25 mg PGE₁ resulted in cycle lengths comparable to those of non-treated herdmates with no apparent modification in corpus luteum size. However, plasma progesterone levels were increased significantly following PGE₁ treatment compared to pretreatment values. In so far as data obtained on PGF_2α relative binding affinity to the bovine CL can be compared to data obtained independently on PGF_2α induced luteolysis in the bovine, PGF_2α relative binding to the CL and luteolysis appeared to be associated. By similar reasoning, there was no apparent relationship between PGE₁ relative binding affinity in the luteal fractions and luteolysis in estrous cyclic cattle.     

Blood LH after PGF2α in diestrous and ovariectomized cattle

Two experiments were conducted to determine whether the increased serum LH which occurs within 12 hr after a luteolytic dose of PGF_2α is dependent upon changes in progesterone or estradiol secretion. In the first experiment, exogenous progesterone abolished the increase in serum LH caused by a subcutaneous injection of 25 mg PGF_2α in diestrous heifers, but not in ovariectomized heifers. In the second experiment, progesterone pessaries were removed at 6 hr after a subcutaneous injection of 25 mg PGF_2α. LH remained at pre-PGF_2α values while the pessaries were in place, but began to increase within 1 hr after they were removed. Blood estradiol also remained at pre-PGF_2α values until the pessaries were removed, and began to increase at 2 hr after pessary removal. We conclude that the increase in serum LH within 12 hr after PGF_2α treatment in diestrous cattle is dependent upon withdrawal of progesterone; it is not due to increased serum estradiol.     

Effects of PGF2α-induced luteolysis and progesterone on follicular growth in pregnant mice

The effects of a luteolytic dose of prostaglandin F_2α on follicular development within the ovary of pregnant mice were studied and vitro. The results showed that 1) PGF_2α reduced the number of growing primary follicles both and , 2) , progesterone and LH/FSH override this effect of PGF_2α and 3) progesterone suppresses the rate at which primary and preantral follicles grow. It is concluded that in the ovary of the pregnant mouse, progesterone regulates the number of primary follicles which start to grow; while gonadotropins and intraovarian progesterone levels control the rate at which primary and preantral follicles develop.     

Prostaglandin E1 and F2α specific binding in bovine corpora lutea: Comparison with luteolytic effects

Preliminary characterization indicated the presence of separate prostaglandin (PG)E₁ and (PG)F_2α binding sites in membrane fractions prepared from bovine corpora lutea. These differ in the rate and temperature dependence of the specific binding. Equilibrium binding data indicate the apparent dissociation constants as 1.32 × 10⁻⁹M and 2.1 × 10⁻⁸M for PGE₁ and PGF_2α, respectively. Competition of several natural prostaglandins for the PGE₁ and PGF_2α bovine luteal specific binding sites indicates specificity for the 9-keto or 9α-hydroxyl moiety, respectively. Differences in relative ability to inhibit ³H-PG binding were found due to sensitivity to the absence or presence of the 5,6-cis-double bond as well.Bovine luteal function was affected following treatment of heifers with 25 mg PGF_2α as measured by reduced estrous cycle length, decreased corpus luteum size and significantly decreased plasma progesterone levels. In contrast, treatment with 25 mg PGE₁ resulted in cycle lengths comparable to those of non-treated herdmates with no apparent modification in corpus luteum size. However, plasma progesterone levels were increased significantly following PGE₁ treatment compared to pretreatment values. In so far as data obtained in vitro on PGF_2α relative binding affinity to the bovine CL can be compared to data obtained independently in vitro on PGF_2α induced luteolysis in the bovine, PGF_2α relative binding to the CL and luteolysis appeared to be associated. By similar reasoning, there was no apparent relationship between PGE₁ relative binding affinity in the luteal fractions and luteolysis in estrous cyclic cattle.     

Effect of prostaglandin F2α on ovarian and pituitary function in the mid-luteal phase

The effects of PGF_2α infusion in a dose of 25 μg/min for 5 hours on serum levels of estradiol-17β, progesterone, LH, FSH, TSH and prolactin, and on the pituitary hormone responsiveness to LRH and TRH were studied in 10 apparently healthy cycling women in the mid-luteal phase. No systematic alteration was seen in the pituitary and ovarian hormone levels during PGF_2α infusion, and the pituitary hormone responses to releasing hormones were unaffected. Ovarian steroid production increased in response to increased gonadotropin levels after LRH injection during PGF_2α administration. These results confirm that PGF_2α is not luteolytic in humans and no apparent relationship between PGF_2α and pituitary hormone secretion exists.     

Corpus luteum function in the ewe: Effect of PGF2α and prostaglandin synthetase inhibitors

A series of experiments were conducted to evaluate the effects of mode and frequency of administration and estrous cycle stage on the response of the cycling ewe to PGF_2α. The effects of dexamethasone, arachadonic acid and prostaglandin synthetase inhibitors on estrous cycle length and plasma progesterone levels were also determined.Intramuscular administration of 5 or 10 mg of PGF_2α, on days 8 and 9 after estrus (5 ewes/group), significantly (p<.01) shortened the mean length of the estrous cycle and the interval from the end of treatment to estrus. Mean plasma progesterone levels, 24 hours after initial injection, were significantly (p<.01) lowered. When administered on day 8 only, these doses were considerably less effective in shortening estrous cycle length or lowering plasma progesterone levels. Intravaginal administration of PGF_2α, by polyurethane tampon, was also largely ineffective.Treatment of ewes with 10 mg of PGF_2α i.m., on days 3 and 4 of the estrous cycle, resulted in a return to estrus in 2 days in 25% of the treated animals. Plasma progesterone levels of PGF_2α-treated ewes were significantly lower than controls on the second, third and fourth days after the start of dosing. It would appear that PGF_2α exerts a retarding effect on developing CL functionality.The prostaglandin synthetase inhibitors, aspirin, flufenamic acid and 1-p-chlorobenzylidene-2-methyl-5-methoxy-3-indenylacetic acid, were administered orally or parenterally for 16 days beginning on day 8 of the estrous cycle. These compounds failed to prolong estrous cycle length. Parenteral administration of dexamethasone did not result in PGF_2α release in the cycling ewe, at least not in quantities sufficient to induce luteolysis. The prostaglandin precursor, arachadonic acid, also was not luteolytic when given parenterally to cycling ewes.     

Interactions of prostaglandins with subpopulations of ovine luteal cells. II. Inhibitory effects of PGF2α and protection by PGE2

Purified preparations of ovine large luteal cells were utilized in a series of experiments to test the effects of prostaglandins (PG) E₂ abd F₂α on cell morphology, viability and secretion of progesterone. Luteal cells were allowed to attach to culture dishes overnight before experiments. In the first series of experiments incubation of large steroidogenic cells with PGF₂α for 6 hr resulted in morphological changes including a retraction of the cell cytoplasm and apparent extrusion of cytoplasmic components which became more pronounced after 12 hr. In a second series of experiments, PGF₂α decreased and PGE₂ increased progesterone accumulation in media after 6 hr when media were not replaced during the incubation period, while progesterone accumulation was not different than that observed in control dishes when both prostaglandins were present. Hourly replacement of the media negated the inhibitory effects of PGF₂α but had no effect on the stimulated secretion of progesterone induced by PGE₂. Finally, in incubations without media replacement, PGF₂α induced a dose-dependent decrease in progesterone accumulation while PGE₂ elicited a biphasic response with progesterone secretion increasing from 0.1 ng/ml to maximal levels at 10 ng/ml followed by a dose-dependent decrease at 100 and 1000 ng/ml. These data are compatible with the hypotheses that: 1) luteolysis is initiated, at least in part, by an action of PGF₂α on large luteal cells; and 2) the embryonic signal from the pregnant uterus which rescues the ovine corpus luteum may be PGE₂.     

Effect of prostaglandin F2α on endocrine-ovarian function in the domestic cat

The effect of prostaglandin F_2α(PGF_2α) on endocrine and ovarian function during the early luteal phase of the domestic cat was investigated. Queens were induced to ovulate and then injected subcutaneously with 0.5–5.0 mg PGF_2α/kg body weight. The greatest dose was found to approach toxicity. Concentrations of progesterone were similar in cats following treatment with PGF_2α compared to values of controls. Development and regression of corpora lutea as determined by serial laparoscopy were similar in all groups. These data indicate that PGF_2α at the tested dosages, given during the early luteal phase is not luteolytic in this species and suggest that these regimens would be ineffective for the premature termination of pseudopregnancy.     

The effects of prostaglandins PGE1, PGE2, PGF1a, and PGF2a on canine synovial perfusion

In these experiments we have examined the effects of PGE₁, PGE₂, PGF_1α and PGF_2α on synovial perfusion in the normal canine synovial microcirculation. The effects of the drugs on synovial perfusion were determined indirectly from the changes produced in the rate of clearance of ¹³³Xenon from the joint by their intra-articular injection. Prostaglandins PGE₁ and PGE₂ were found to be strongly vasodilator with PGE₁ being the more active. PGF_1α appeared to have little or no vasoactive properties in doses up to 1 ugm. (2.8 × 10^−5M) in our I preparation while PGF_2α was vasodilator at this high dosage only. Neither SC19920 nor diphloretin phosphate antagonised the effects of PGE₁ in these experiments.     

The effect of intra-uterine prostaglandin F2α on corpus luteum function in the human

Prostaglandin F_2α (PGF_2α) was administered via a Foley catheter over a 12 hour period to 8 healthy volunteers awaiting laparoscopic sterilisation. The amount of PGF_2α infused varied between 500 μg and 2000 μg every 2 hours for 6 doses. Plasma progestins and oestradiol 17β, and urinary estrogens and pregnanediol were assayed throughout the study period.There was no evidence of luteolysis in any patient although vaginal bleeding of varying duration occurred in all women within 36 hours of administration of PGF_2α.     

Action of 7-oxa-13-prostynoic acid on rat uterine contractility and sensitivity to PGF2α and angiotensin II

The action of 7-oxa-13-prostynoïc acid on spontaneous contractions and on PGF_2α and angiotensin II elicited contractions has been studied on rat uteri excised during pro and metaoestrus At the concentration of 5 × 10⁻⁶M, the compound does not alter the spontaneous contractions of proestrus uteri and suppresses the phasic component of PGF_2α-elicited contractions. At the concentration of 5 × 10⁻⁵M, 7-oxa-13-prostynoïc acid inhibits spontaneous contractions and inhibits PGF_2α-elicited contractions. In metaoestrus uteri, the inhibitory effect is not competitive. 7-oxa-13-prostynoïc acid is also able to inhibit non competitively the contractor effect of angiotensin II in proestrus uteri. This result, together with those of previous investigations performed using other prostaglandin inhibitors, suggest that the contractor effect of angiotensin II on the uterus is partially mediated by endogenous prostaglandins.     

Effect of in vivo prostaglandin treatment on H-PGF2α uptake in hamster corpora lutea

Pregnant hamsters were administered (SC) prostaglandin or vehicle on the morning of the 4th day of pregnancy. Serum progesterone was significantly depressed (p<.01) at 0.5, 2, and 6 hours after treatment with 100 μg PGF_2α. Serum progesterone levels were unchanged 2 hours and 6 hours after treatment with 100 μg PGF_2β and 2 hours after treatment with 1 mg PGF_2β. Progesterone levels were depressed to less than 1 ng/ml 6 hours after treatment with 1 mg PGF_2β. The specific uptake of ³H-PGF_2α in whole hamster corpora lutea was significantly depressed 2 hours and 6 hours following 100 μg PGF_2α treatment. A 15% depression in specific uptake occurred 0.5 hour post-treatment. Treatment with 100 μg PGF_2β resulted in no change. Administration of 1 mg PGF_2β resulted in depressed ³H-PGF_2α uptake at both 2 and 6 hours post-treatment.Prostacyclin (PGI₂) treatment resulted in no change in either ³H-PGF_2α specific uptake or serum progesterone 2 hours after 100 μg treatment SC. These parameters were both reduced approximately 30% 6 hours post-treatment. Treatment with 6-keto-PGF_1α resulted in a complete lack of measurable ³H-PGF_2α uptake and serum progesterone levels less than 1 ng/ml at both 2 and 6 hours after treatment with 1 mg SC.     

Estradiol-17β and 2-hydroxyestradiol-17β-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition

Prostaglandin (PGE, 6-keto PGF_1α) output by cells dispersed from human amnion and decidua in the presence of increasing levels (0–5000 ng/ml) of estradiol-17β (E₂) or 2-hydroxyestradiol-17β (2-OH E₂) was studied in relation to parturition. Tissues were obtained from women at term either before (CS) or after (SL) spontaneous labor and vaginal delivery. In the absence of estrogens, the output of both PGs from amnion increased significantly with labor. No significant increase in decidua PG output occurred with labor. Neither estrogen influenced CS amnion PG output. However, both E₂ and 2-OH E₂ stimulated SL amnion PGE output (2-OH E₂>E₂) while having no affect on 6-keto PGF_1α output. Only the highest dose of 2-OH E₂ stimulated PGE output in CS decidua, but both estrogens significantly inhibited 6-keto PGF_1α output in this tissue. In SL decidua only 2-OH E₂ significantly stimulated PGE, and neither estrogen affected 6-keto PGF_1α output. These results might suggest that estrogens modulate PG biosynthesis at the level of endoperoxide to primary PG conversion.