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

The ability of human chorionic gonadotropin (HCG) to reduce the luteolytic effect of prostaglandin (PGF2 alpha) was demonstrated in cycling ewes. As expected, treatment with 10 mg of PGF2 alpha 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 PGF2 alpha 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 PGF2 alpha because plasma progesterone was reduced when the dose of PGF2 alpha was doubled. Whether CL regressed or continued to function after treatment with both HCG and PGF2 alpha appeared to depend upon a balance between the positive and negative effects of the two hormones.     

Assessment of possible luteolytic effect of intra-ovarian injection of prostaglandin F2α in the human

A group of five patients awaiting laparoscopic tubal diathermy were followed by daily assay of luteinising hormone (LH) and progesterone. Between five and eight days after the LH peak, prostaglandin F_2α (PGF_2α) was injected into either the corpus luteum or the ovarian stroma. Doses of 100 μg into the corpus luteum, 1000 μg into the adjacent stroma and 500 μg into an indeterminate ovarian structure had no effect on peripheral plasma progesterone levels or uterine bleeding.An injection of 500 μg or 1000 μg given unequivocally into the corpus luteum produced a rapid and profound fall in plasma progesterone levels, the nadir coinciding with the onset of uterine bleeding which commenced 24 hours after the injection and persisted for more than seven days. Injection of 100 μg in the same volume of saline had no such effect. Despite continued bleeding plasma progesterone levels returned to normal luteal levels for three days and then fell again.     

Reduction of testicular human chorionic gonadotropin receptors by human chorionic gonadotropin in vivo and in vitro

Changes in rat and human testicular human chorionic gonadotropin (hCG) binding sites induced by hCG were estimated in vivo and in vitro. After a single administration of hCG, the specific 125I-hCG bindings were significantly reduced for 7 and 5 days in rat and human testes, respectively. Thereafter, 125I-hCG bindings had recovered to pretreatment values by the 14th day after the administration. Occupied hCG bindings accounted for about half of the reduced bindings on the day after administration of hCG. After this time, however, the occupancy did not contribute so much to the reduction of the bindings. In experiments in vitro using the organ culture technique, an exposure to hCG for 24 h induced a dose-related significant loss of the specific 125I-hCG bindings for 7 and 5 days in rat and human testes, respectively. Thereafter, the loss was gradually recovered. These patterns of changes in 125I-hCG bindings in vitro were similar to those in vivo. These findings suggest that the reduction in hCG binding sites by hCG is due to not only occupancy but also downregulation of the binding sites and that the testicular organ culture method used in the present study is useful to study hormonal regulation of testicular function, especially in human testes.     

The enzymatic conversion of prostaglandin D2 to prostaglandin F2α

Prostaglandins E₂ and D₂ were both converted to prostaglandin F_2α (9α, 11α) by an enzyme present in sheep blood. Neither the 9β, 11α epimer nor the 9α, 11β epimer was produced from PGE₂ or PGD₂ respectively. The rate of reduction was measured using isotope dilution (D₄ PGF_2α) and multiple-ion detection gas chromatography-mass spectrometry.     

Localization of the prostaglandin F2 alpha receptor in rat tissues

The localization of the prostaglandin F_2α (FP) receptor was examined in rat tissues by immunohistochemistry and in situ hybridization. Immunohistochemistry on paraffin sections was performed with a rabbit polyclonal antiserum raised against a synthetic peptide derived from the rat FP receptor sequence. In situ hybridization on cryosections was done with ³⁵S-labelled rat FP receptor antisense and sense riboprobes. The most intense FP receptor-like immunoreactivity was observed in granulosa luteal cells, muscle and epithelial cells, e.g. cardiac, skeletal and smooth muscle, and hepatocytes. Weaker immunoreactivity was found in connective tissue fibroblasts. In the eye, intense immunostaining was associated with the corneal and conjunctival epithelium and moderate staining with the ciliary body, retina, iris and connective tissues. In situ hybridization generally confirmed the results. The riboprobe hybridized weakly with the heart, skeletal muscle, uterus, liver, lung and corpus luteum. Thus, the prostaglandin FP receptor was found to be widely distributed in rat tissues.     

Urinary excretion of prostaglandin E2 and prostaglandin F2α in potassium-deficient rats

Potassium-deficiency was induced in rats by dietary deprivation of potassium. The animals became polyuric and urine osmolality decreased more then three-fold compared to controls. Urinary excretion of prostaglandin E₂ (PGE₂) and prostaglandin F_2α (PGF_2α) did not increase during 2 weeks of potassium depletion. Partial inhibition of renal prostaglandin synthesis by meclofenamate did not increase the urine osmolality after water deprivation. These results make unlikely the hypothesis that the polyuria of potassium-deficiency, is the result of enhanced renal synthesis of prostaglandins with subsequent antagonism of the hydro-osmotic effect of vasopressin. Male animals consistently excreted less PGE₂ than female animals.     

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.     

Dose and time dependent luteotropic and luteolytic action of prostaglandin F2α in the luteinized rabbit ovary

The mechanism of stimulatory and inhibitory action of PGF_2α on ovarian steroidogenesis both under and conditions has been studied in the pseudo-pregnant rabbits. Short term incubation of the ovaries with PGF_2α (2.82 × 10⁻⁵M) resulted in an increased synthesis of progesterone and 20α-OH P. The addition of PGF_2α in the medium and further incubation of the ovaries obtained from rabbits that had been constantly infused with PGF_2α (0.5 μg/min.) for two hours resulted in increased synthesis of these progestins. The ratio of progesterone to 20α -OH P was also enhanced under these conditions and thus supported the luteotropic action of small doses of PGF_2α under short term incubations. However, as the amount of PGF_2α infused was increased to 5 μg/min., the addition of PGF_2α under conditions strikingly decreased the production of these progestins. The ratio of progesterone to 20α -OH P was also decreased and thus was indicative of luteolytic action of higher doses of PGF_2α. High doses of PGF_2α (5.64 × 10⁻⁴M) failed to I cause any significant change in the progestin synthesis under short term incubation. These results thus suggest that the luteotropic and luteolytic action of PGF_2α in the luteinized rabbit ovary is dose and time dependent.     

The effect of prostaglandin F2β on expiratory flow rates

Prostaglandin F_2β (PGF_2β), a stereoisomer of F₂ was administered by ultrasonic nebulization to eight patients with bronchial asthma and four normal subjects in increasing doses up to a 200 μg maximum dose. Maximum expiratory flow (MEF) and forced vital capacity (FVC) were analyzed at 5, 15, 30, 60 and 120 minutes after administration of aerosol.

All expiratory flow rates were reduced after 5 minutes. Some increase in terminal flow rates was observed after 60 minutes. We conclude that PGF_2β is not an effective bronchodilator at this dose level.     

Biosynthesis of prostaglandin D2 1. Formation of prostaglandin D2 by human platelets

Formation of prostaglandin D₂ (PGD₂) during the aggregation of platelets was determined, employing a specific bioassay. PGD₂ was synthesized in human platelet rich plasma (PRP) in response to thrombin, collagen and epinephrine. Indomethacin pretreatment abolished the biosynthesis of PGD₂. When thrombin treated PRP was incubated for different periods of time and denatured in the presence of SnCl₂ to prevent the formation of PGD₂ from endoperoxides during the extraction procedure, PGD₂ formation was noted within the first minute of incubation and reached a peak level after 4 minutes. PGD₂ from thrombin stimulated PRP was conclusively identified by gas chromatography-mass spectrometry.The formation of PGD₂ during platelet aggregation could represent a mechanism of feedback inhibition of aggregation.     

Different responses to prostaglandin F2α and E2 in human extra- and intramyometrial arteries

Tubal segments of the ascending uterine arteries and of intramyometrial arteries were obtained from 18 women who underwent hysterectomy at various phases of the menstrual cycle. Ring preparations of the vessels were mounted in organ baths and isometric tension was recorded. In extramyometrial arteries (outer diameter 2–3 mm) prostaglandin (PG) F_2α most potently, but also PGE₂ caused concentration-related contractions. In contrast, the contractant effects of both PGs on intramyometrial arteries (outer diameter 0.5–0.6 mm) were negligible. Both extra- and intramyometrial vessels were relaxed to a moderate degree (10–25%) by low concentrations of PGF_2α and PGE₂. No significant differences between the responses to vasopressin and noradrenaline were found between the vessel preparations. Thus human uterine arteries seem to change their responses to PGF_2α and PGE₂ as they enter the myometrium and decrease in diameter, and the results raise doubt about the view that direct vasoconstrictor effects of these PGs contribute to the regulation of myometrial blood flow. Such effects of vasopressin and noradrenaline cannot be excluded.     

The possible mode of action of prostaglandins: X. Antagonism between prostaglandin F2a and prolactin or human chorionic gonadotropin : A comparative study

A comparative assessment of the efficacy of prolactin or HCG in reversing the luteolytic property of a single dose (2.0 mg/kg) of PGF₂a was conducted in pregnant (day 10) rats. It was found that prolactin maintained pregnancy in 90% of the test animals. HCG though found to maintain pregnancy in 70% of the PGF₂a-treated pregnants, the fetal survival rate was, however, recorded to be 62% against the control value of 98%. Conversely, prolactin replacement maintained the fetal survival rate as high as 93.4%. Moreover, the growth of the fetuses, placentae and corpus luteum in the pregnants having prolactin in conjunction with PGF₂a was also found to be greater compared to the animals which h ad a combined regimen of PGF₂a and HCG, but identical to controls. On the other hand, similar combined regimen when applied to hysterectomized pregnant rats, it was observed that though the vaginal diestrus was maintained by the prolactin or HCG in the presence of PGF₂a, the prolactin regimen was found to be superb compared to HCG in the maintenance of luteal weight and functional activity. It was concluded that the antifertility effect of PGF₂a in the rat is primarily the consequence of luteolysis and prolactin seems to be a much more appropriate hormonal replacement compared to HCG, a long-acting LH, in antagonizing the luteolytic property of PGF₂a.     

Cardiac arrhythmias induced by prostaglandin F2α in cats

Intravenous administration of prostaglandin F_2α results in transient episodes of sinus bradycardia in anesthetized cats. In addition, ventricular bigeminy was observed in approximately 40% of those cats anesthetized with pentobarbital (36 mg/kg) and 58% of those anesthetized with chloralose (70 mg/kg). This arrhythmogenic effect of PGF_2α is abolished following bilateral vagotomy, indicating that the arrhythmias are most likely due to a marked stimulation of vagal tone in this species.     

Stereospecificity of enzymatic reduction of prostaglandin E2 to F2α

Antibodies directed toward PGF_2β were prepared in rabbits. The serologic specificity of the immune reaction was determined by inhibition of sodium borohydride-reduced (³H) PGE₂ anti-PGF_2β binding by several prostaglandins. The antibodies to PGF_2β recognize the β-hydroxyl configuration in the cyclopentane ring of PGF_2β. With the use of both anti-PGF_2α and anti-PGF_2β, the product of PGE₂ reduction by 9-ketoreductase purified from chicken heart was identified as PGF_2α. Guinea pig liver and kidney homogenates were examined for PGE 9-ketoreductase activity. Although enzyme activity was present, no evidence of PGF_2β production was found.     

An intra-corpus luteum site for the luteolytic action of prostaglandin F2α in the rhesus monkey

It has not been possible to demonstrate prostaglandin F₂α (PGF₂α) participation in primate luteolysis under conditions of systemic administration or of acute intraluteal injection. These study designs were hampered by the short biological half-life in the first instance and brevity of administration in the latter. In this study, luteolysis has resulted from chronic, intraluteal delivery of PGF₂ α. Using the Alzet osmotic pump-cannula system, normally cycling rhesus monkeys were continuously infused, until menses occurred, with PGF₂ α (10 ng/1/hr) directly into the corpus luteum (CL, n=6), into the stroma of the ovary bot bearing the corpus luteum (NCL, n=3), or subcutaneously (SC, n=5). An additional 5 monkeys received vehicle (V) into the corpus luteum. All experiments commenced 5–7 days after the preovulatory estradiol surge. Luteal function was assessed by the daily measurements of plasma progesterone, estradiol, and LH. Intraluteal PGF₂α caused premature functional luteolysis in all monkeys, as reflected by a highly significant decline in circulating progesterone and estradiol and the early onset of menstruation, when compared to the other groups. V, NCL, and SC infusions had no effect on either circulating steroid levels or luteal phase lengths. None of the experimental groups showed any change in plasma LH concentrations. These are the first data to indicate that PGF₂α can induce functional luteolysis in the primate, and the site of action appears to be the corpus luteum.     

Effect of prostaglandin F2α on the hCG-stimulated progesterone production by human corpora lutea

The effect of prostaglandin PGF_2α on the hCG stimulated and basal progesterone production by human corpora lutea was examined . hCG (40 i.u./ml) stimulated progesterone formation in corpora lutea of early (days 16–19 of a normal 28 day cycle), mid (days 20–22) and late (days 23–27) luteal phases. This stimulation was inhibited by PGF_2α (10 μg/ml) in corpora lutea of mid and late luteal phases. PGF_2α alone did not show a consistent effect on basal progesterone production. The inhibition of hCG stimulated progesterone production by PGF_2α at times corresponding to luteolysis indicates a role for that prostaglandin in the process of luteolysis in the human corpus luteum.     

Effects of indomethacin, prostaglandin E2, prostaglandin F2α and 6-keto-prostaglandin F1α on hatching of mouse blastocysts

The present study has been performed to investigate how PGs would participate the hatching process. Effects of indomethacin, an antagonist to PGs biosynthesis, on the hatching of mouse blastocysts were examined in vitro. Furthermore, it was studied that prostaglandin E₂ (PGE₂), prostaglandin F_2α (PGF_2α) or 6-keto-prostaglandin F_1α (6-keto-PGF_1α) were added to the culture media with indomethacin. (1) The hatching was inhibited by indomethacin yet the inhibition was reversible. (2) In the groups with indomethacin and PGE₂, no improvement was seen in the inhibition of hatching and the inhibition was irreversible. (3) In the groups with indomethacin and PGF_2α, inhibition of hatching was improved in comparison with the group with indomethacin. (4) In the groups with indomethacin and 6-keto-PGF_1α, no improvement was seen. The above results indicated that PGF_2α possibly had an accelerating effect on hatching and a high concentration of PGE₂ would exert cytotoxic effect on blastocysts.     

Effect of prostaglandin F3α on gastric mucosal injury by ethanol in rats: Comparison with prostaglandin F2α

In humans eicosapentaenoic acid can be converted to 3-series prostaglandins (PGF_3α, PGI₃, and PGE₃). Whether 3-series prostaglandins can protect the gastric mucosa from injury as effectively as their 2-series analogs is unknown. Therefore, we compared the protective effects of PGF_3α and PGF_2α against gross and microscopic gastric mucosal injury in rats. Animals received a subcutaneous injection of either PGF_3α or PGF_2α in doses raning from 0 (vehicle) to 16.8 μmol/kg and 30 min later they received intragastric administration of 1 ml of absolute ethanol. Whether mucosal injury was assessed 60 min or 5 min after ethanol, PGF_3α was significantly less protective against ethanol-induced damage than PGF_2α. These findings indicate that the presence of a third double bond in the prostaglandin F molecule between carbons 17 and 18 markedly reduces the protective effects of this prostaglandin on the gastric mucosa.     

Determination of prostaglandin F2α, E2, D2 and 6-keto-F1α in human cerebrospinal fluid

Prostaglandin (PG)F_2α, E₂, D₂ and 6-keto-F_1α were determined in human cerebrospinal fluid by a mass spectrometric technique. The samples were obtained from 12 patients with suspected intracranial disease. A 64 fold variation in PG levels was observed. The major PG was 6-keto-F_1α (0.12–15 ng/ml). PGF_2α and PGE₂ were present in lower concentrations PGD₂ was below the level of detection (0.05 ng/ml) except in one patient with extremely high total levels of PGs.     

Histophysiological studies of prostaglandin F2a on isolated organs: I. Effect of prostaglandin F2a on the heart

The physiological and histochemical effects of PGF_2a on isolated rabbit hearts were examined. The results showed a positive inotropic effect. The coronary flow increased. From the histochemical studies, adenosine triphosphatase (ATP-ase) and succinic dehydrogenase activities were increased while that of alkaline phosphatase was decreased. Glycogen granules were depleted. These findings were discussed on a histophysiological basis.