Prostaglandin F2a inhibition of epinephrine stimulated cyclic AMP and progesterone production by rat corpora lutea of various ages

Epinephrine can mimic the stimulatory effects of LH in vitro on cyclic AMP (cAMP) and progesterone production by isolated rat corpora lutea. The aim of the present study was to test whether the effects of epinephrine in vitro on the rat corpus luteum, as with LH, can be inhibited by prostaglandin F_2a (PGF_2a. The stimulatory effect of epinephrine on tissue levels of cAMP in 1-day-old corpora lutea was not inhibited by PGF₂. A dose-dependent inhibition by PGF_2a (0.5–50 μM) was seen for 3-day-old corpora lutea and this inhibition could not be overcome by higher concentrations of epinephrine (0.165–165 μM). The stimulation by epinephrine on progesterone production was inhibited by PGF_2a (5 μM) in 3- and 5-day-old, but not in 1-day-old corpora lutea. Thus, PGF_2a can inhibit the stimulatory effect of epinephrine in 3- and 5-day-old corpora lutea, but not in the newly formed corpora lutea (1-day-old) and PGF_2a shows in this respect the same agedependent inhibitory pattern as in relation to LH stimulation.     

The effect of PGF2a on in vivo cerebral arteriolar diameter in cats and rats

We compared the effect of tropical application of PGF_2a on cerebral arterioles in cats and rats equipped with an acutely implanted cranial window. Arterial diameter was measured using a microscope and image splitting device. PGF_2a in a concentration ranging from 10^?7 to 10^?5 M had no effect on large (≥ 100 μm) or small (< 100 μm) cat pial arterioles, but induced a dose dependent constriction of rat pial arterioles with a maximum constriction fo 76% of control diameter. Dilation of cat large cerebral arterioles by topically applied PGE₂ was not affected by simultaneous application of PGF_2a and PGE₂ induced dilation of small arterioles was decreased 3% by PGF_2a. While we and others have previosuly shown that both cat and rat brain can synthesize PGF_2a, it appears that PGF_2a is not likely to normally be a major modulator of cerebral arteriolar resistance in all species.     

Prostaglandin F2a, an ovulatory intermediate in the in vitro perfused rabbit ovary model

PGF_2a has been proposed as a mediator of mammalian ovulation. To elucidate further the role of PGF_2a in the process of ovulation, PGF and PGF_2a metabolite were measured by radioimmunoassay in the perfusate of an perfused rabbit ovary preparation.Perfusion medium samples were collected over a 10 to 12 hour period from ovaries perfused with tissue culture M199 (total volume 150 ml, sample volume 3 ml) to which varying amounts of hCG had been added. [The PGF_2a antisera a 40% cross reaction with PGF_1a, hence total PGF was measured with this antisera.] Both PGF and PGF_2a metabolite showed a linear increase with time and numbers of ovulations.PGF media accumulation was 575 pg/ovary/ovulation/hr and PGF_2a metabolite accumulation was 367 pg/ovary/ ovulation/hr. Medium prostaglandin content could be correlated with numbers of ovulations, ovulatory efficiency (number of ovulations/total follicles) but total follicles. These data best fit a model of independent ovulatory units producing PFG_2a without recruitment or interaction between them. We infer the PGF and PGF_2a metabolites in this system can be used as a direct index of the ovulation process.     

Induction of term labor with intravenous prostaglandin F2α (a comparison of two dosage schedules)

The efficacy of intravenous Prostaglandin F_2α (PGF_2α) infusion for induction of labor in two different dosage schedules was studied in 90 women between 36 and 43 weeks of gestation. The rate of PGF_2α infusion was increased at four-hour intervals in 36 women in the low dosage group and every hour in 54 women in the high dosage group, never exceeding an infusion rate of 20 μg/min. in either group. Labor was successfully induced in approximately 90% of the patients in each group. There was no statistically significant difference in the mean induction-delivery interval between the two groups at the 5 percent level. Intravenous PGF_2α was found to be effective and safe for both mother and infant in the dosage schedules used in this study for induction of labor.     

Prostaglandin modulation of the mechanism of ACTH action in the human adrenal.

PGE₁ and PGE₂ significantly increased human adrenal cAMP levels $\text{in}$$\text{vitro}$; cortisol output was also increased in a dose related fashion. In contrast, PGF_1a and PGF_2a depressed adrenal cAMP (except PGF_2a at 100 μg/ml). PGF_1a and PGF_2a depressed cortisol levels at all doses. Indomethacin or 7-oxa-13-prostynoic acid did not affect these parameters. However, when applied in conjunction with ACTH they inhibited or enhanced hormonal action depending upon the temporal sequence of application. The findings indicate that prostaglandins modulate ACTH-adrenocortical cell interaction bidirectionally, initially potentiating and subsequently depressing ACTH stimulated events.     

Effects of cerebral ventricular, systemic, and local administration of prostaglandin F2a on canine cerebral hemodynamics

The effects of Prostaglandin F_2a (PGF_2a) on cerebral blood flow, cerebral vascular resistance, and cerebrospinal and systemic arterial pressures were determined in anesthetized dogs. Flow was measured from the cannulated sinus confluens after occlusion of the transverse canals. Infusion of 1 to 100 ug/ml of PGF_2a into the cerebral ventricular system did not affect cerebral venous outflow but increased cerebral vascular resistance, arterial blood pressure, and cerebrospinal fluid pressure at the higher concentrations. Systemic, intra-aortic arch infusion of PGF_2a from 50 to 200 ug/min decreased cerebral venous outflow and increased cerebral vascular resistance slightly. Bilateral, intra-carotid artery infusion of PGF_2a at 20 to 80 ug/min produced effects similar in magnitude and direction to systemic, intra-aortic infusion. PGF_2a appears to increase cerebral vascular resistance by active vasomotion, dependent upon the route of administration. However, the magnitude of this constriction is not great considering the dose used. Also, PGF_2a can increase systemic arterial blood pressure via a central effect.     

The influence of PGF2a on experimental arrhythmias

The antiarrhythmic effect of PGF_2a was investigated on various models of experimental arrhythmias (CaCl₂- and aconitine-induced arrhythmias on rats, BaCl₂-induced arrhythmias on rabbits and ouabain-induced arrhythmias on cats). PGF_2a was i.v. infused or injected soon after injection of the arrhythmogenic substances. As standard drug we used ajmaline. PGF_2a protected maximal 84 % of the animals for 10 min from letal ventricular fibrillations due to CaCl₂, while ajmaline acted only in 50 %. The difference of equieffective doses in CaCl₂- and aconitine-induced arrhythmias was about one thousand fold. Arrhythmias due to BaCl₂ were temporary normalised in 60 % and improved in 40 % of the animals. Ouabain-induced arrhythmias showed normalisation in 40 % and improvement in 30 % of the cats. The difference of equieffective doses of PGF_2a and ajmaline in BaCl₂- and ouabain-induced arrhythmias was about one hundred fold. The mechanism of action of PGF_2a is discussed.     

Effect of intrauterine iodine infusion on luteal function and blood PGF2a concentration in cycling goats

Studies were conducted to determine the effect of iodine infusion on the luteal function of goats, as evident by blood progesterone concentration, and on plasma PGF_2a levels. Ten cycling mixed breed goats were synchronized for estrus by PGF_2a (5 mg) and given a single intrauterine iodine infusion on day 5 and on day 15 of the estrous cycle.Iodine infusion on day 5 (group II) resulted in shorter estrous length (8.2 days) and a 7-fold increase in plasma PGF_2a concentration as compared to control animals (group I) given distilled water infusion. Similar infusion on day 15 (group III), on the other hand, failed to alter the estrcus cycle length but induced a moderate increase in PGF_2a concentration which lasted only for a brief period. The progesterone levels declined concomitantly as PGF_2a levels rose after iodine infusion in group II animals but failed to decline until after 24 hours in group III animals.The studies indicate that the endometrium reacts to the chemical stimuli and releases PGF_2a which, in turn, alters the luteal function.     

Relation between prostaglandin E2, F2α, and cyclic nucleotides levels in rat brain and induction of convilsions

Fully convulsant doses of pentamethylenetetrazole cause marked increase in rat brain cortical PGF_2α, PGE₂, cGMP and cAMP during seizures, whereas subconvulsant doses cause an increase of rat brain cortical PGF_2α without affecting the other biochemical parameters considered. Rat cerebellar prostaglandins were not modified by the convulsant agent at either dosage.     

Prostaglandin endoperoxides IV. Effects on smooth muscle

The effect on smooth muscle of the endoperoxides PGG₂ and PGH₂, which are intermediates in prostaglandin biosynthesis, was studied in different systems $\text{in vitro}$ and $\text{in vivo}$. On gastrointestinal smooth muscle (gerbil colon, rat stomach) PGG₂ and PGH₂ produced contractions comparable to those of PGE₂ and PGF_2a whereas contractions elicited on vascular (rabbit aorta) and airway (guinea-pig trachea) smooth muscle were considerably greater than those of PGE₂ and PGF_2a respectively. On intravenous injection into guinea-pigs PGG₂ and PGH₂ caused a triphasic change in blood pressure and were 8–10 times more effective than PGF_2a in producing an increase in tracheal insufflation pressure. When given as aerosols the unstable endoperoxides were less effective than PGF_2a. It is concluded that the endoperoxides are potent smooth muscle stimulants and that they are more effective than their degradation products (PGD₂, PGE₂, PGF_2a) in some systems.     

Serum prostaglandin F2α concentration in the carcinoid syndrome

Using specific radioimmunoassay procedures we measured prostaglandin F₂α (PGF₂α) and 13, 14-dihydro-15-keto prostaglandin F₂α (PGF₂α metabolite) in 12 patients with carcinoid tumors. Although PGF₂α and PGF₂α metabolite were each modestly elevated in 17% of the patients the magnitude of the elevation did not correlate with the symptoms of the carcinoid syndrome. The 24 hour urinary 5-hydroxyindoleacetic acid excretion showed a good correlation with carcinoid symptoms while the serum serotonin concentration showed a fair correlation with carcinoid symptoms. We conclude that serum elevation of PGF₂α is not a frequent occurrence in patients with the carcinoid syndrome.     

Antiabortifacient action of dibenzyloxyindanpropionic acid in mice

DIPA [5,6-bis(dibenzyloxy)-1-oxo-2-propyl-2-indanpropionic acid] was evaluated for its antiabortifacient action in mice. PGF_2α administered intramuscularly twice daily at 525 μg/kg per dose starting on day-17 of gestation resulted in premature delivery (prior to day-19 of gestation) in 55% of the animals. This constituted an ED₅₀ abortifacient dosage schedule of PGF_2α. Intramuscular administration of DIPA at a dose of 50 mg/kg twice daily, starting on day-15 of gestation, protected the mice against the premature delivery induced by the ED₅₀ dosage schedule of PGF_2α in that only 20% of the animals delivered prematurely. In saline-treated controls, none of the animals delivered prior to day-19 of gestation. Thus, DIPA appears to be an effective antiabortifacient agent.     

The effects of prostaglandins on the beating activity of cultured heart cells

The effects on the beating behavior of cultured rat heart cells of fourteen prostaglandins of the A, B, D, E, and F series were investigated, together with adrenaline and ouabain, at dose levels of 10⁻⁷ and 10⁻⁵M. Single heart cell beating activity was monitored photo-electrically and five parameters of beating behavior measured. Only PGF_2a markedly increased rate while PGF_2B reduced it. Maintenance of a stable rate (rate range) was minimally affected by prostaglandins with PGF_2β possibly reducing, and PGF_1α and 2-decarboxy E₁ possibly increasing, rate range. PGF_1α and F_2α both statistically reduced the percentage of cells beating while the other prostaglandins had no effect. Most of the prostaglandins either produced no change, or reduced, indices of contractile force (optical density changes with contractions and its first derivative (dOD/dt)). Only the negative chronotropic agent PGF_2β positive density effect. In conclusion, except for PGF_2α, prostaglandins generally have limited actions on the beating activity of cultured heart cells.     

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.     

Effects of protein kinase C activation on prostaglandin production and cyclooxygenase mRNA levels in ovine astroglia

We examined effects of protein kinase C (PKC) activation by phorbol dibutyrate (PDB) on prostaglandin production in astroglia. Astroglia were cultured from sheep fetal cortex and grown in Eagle's basal media supplemented with 10% fetal calf serum (BME-C). Prostaglandin F_2a (PGF_2α) levels in media were determined at 2–24 hours after exposure to PDB. PDB increased production of PGF_2α at 10⁻⁸M and 10⁻⁶M. In addition, PDB increased the ratio of membrane to cytosolic PKC. Coapplication of H7 [1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine] (10⁻⁴M) with PDB (10⁻⁶M) inhibited PDB-induced PGF_2a production. To investigate the role of protein synthesis in increased prostaglandin production by PDB, astroglia were coincubated with actinomycin D (1 mg/ml) or cycloheximide (10 mg/ml). At 4 hrs, both actinomycin D and cycloheximide inhibited increases in PGF_2a in response to PDB application. In addition, COX-2 mRNA levels and COX activity levels were examined. PDB increased COX-2 mRNA levels by 2 hours, and COX activity tripled after 12 hr exposure to PDB. In addition, the increase in COX activity was blocked by cycloheximide. In summary, PKC activation promotes enhanced prostaglandin production via an increase in COX synthesis.     

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.     

Radioimmunoassays of prostaglandin F2α and prostaglandin F2α-main urinary metabolite with prostaglandin-I-tyrosine methylester amide

Radioimmunoassays for measuring prostaglandin F_2α (PGF_2α) and 5α, 7α-dihydroxy-11-keto tetranorprosta-1,16-dioic acid, PGF_2α-main urinary metabolite (PGF_2α-MUM), with ¹²⁵I-tyrosine methylester amide (TMA) of PGF_2α and PGF_2α-MUM were developed.Antibody to PGF_2α was produced in rabbits immunized with conjugates of PGF_2α coupled to bovine serum albumine. Antibody to PGF_2α-MUM was also produced in rabbits immunized with conjugates of PGF_2α-MUM coupled to bovine serum albumin.PGF_2α-¹²⁵I-TMA had an affinity to antiserum to PGF_2α. PGF_2α-MUM-¹²⁵I-TMA also responded to antiserum to PGF_2α-MUM.     

PGE2 attenuates PGF2α-induced increases in free intracellular calcium in ovine large luteal cells

When ovine large luteal cells are placed in culture and exposed to PGF_2α, there is a rapid and sustained increase in the concentration of free intracellular calcium which is believed to play a major role in the luteolytic and cytotoxic effects of PGF_2α. Since administration of exogenous PGE₂ can prevent spontaneous and PGF_2α-induced luteolysis in vivo, and the cytotoxic effects of PGF_2α on large luteal cells in vitro, the objective of this study was to determine if one mechanism by which PGE₂ acts is to attenuate increases in free intracellular calcium induced by PGF_2α. At concentrations of 10 nM or greater, PGF_2α caused a significant and sustained increase in free intracellular calcium in large luteal cells. Similarly, PGE₂ also induced increases in free intracellular calcium but required doses 20-fold greater than PGF_2α. When PGE₂ (1, 10 or 100 nM) was incubated with PGF_2α (100 nM) increases in free intracellular calcium induced by PGF_2α were attenuated (P<0.05) when measured 5 min, but not at 30 min, after initiation of treatment. The observed decrease in the concentration of free intracellular calcium at 5 min in response to PGF_2α was the result of fewer cells responding to PGF_2α. In addition, the concentrations of free intracellular calcium attained in the cells that did respond was reduced 25% compared to cells treated with PGF_2α alone. Thus, part of the luteal protective actions of PGE₂ appears to involve an inhibition of the early (5 min) increase in free intracellular calcium induced by PGF_2α.     

Induction of second trimester abortion: Comparison between vaginal 15-methyl-PGF2α methyl ester and intra-amniotic PGF2α

The efficiency and acceptability of a single-dose, long-acting vaginal suppository containing 3.0 mg of 15-methyl PGF_2α methyl ester was compared with intra-amniotic administration of 50 mg of PGF_2α in 100 patients with a second trimester pregnancy termination. Within 24 hours, 78 per cent of the patients in the vaginal group and 92 per cent in the intra-amniotic group had aborted. The mean induction-abortion interval was 17.9 hours in the vaginal group and 15.8 hours in the intra-amniotic group.Gastrointestinal side-effects were more frequent, but the procedure was less painful, with vaginal 15-methyl PGF_2α methyl ester than with intra-amniotic PGF_2α.The vaginal route is technically simple for adaptation to large-scale use, but the high frequency of gastrointestinal side-effects still limits the acceptability of 15-methyl PGF_2α methyl ester in vaginal administration.     

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.