Contractility of rat testicular seminiferous tubules : Prostaglandin F1α and indomethacin

The frequency of spontaneous contractions of seminiferous tubules of the rat appeared to be increased in a dose-dependent manner by prostaglandin F_1α. PGF_1α treatment increased the tonus of the smooth muscle cells in the wall of the tubules as indicated by a reduction in the diameter of the tubules. When the tubules were rinsed successively with fresh Tyrode's solution, the contractile frequency was diminished. Returning the original bathing medium to the tubules restored their contractile frequency, as did treatment of the rinsed tubules with PGF_1α (10^-7 M). Pre-injecting the rats with indomethacin tended to reduce the contractile frequency of the extirpated tubules. Treating the tubules with a solution of indomethacin for 90 min. was more effective than pretreatment in reducing contractile frequency, but a combination of these two procedures produced the greatest inhibition. PGF_1α restored the contractile frequency of the indomethacin-treated tubules. Our results indicate that PGs modulate the contractility of the tubules.     

The absence of direct effects of prostaglandin F2α on preimplantation mouse embryos in vitro

Preimplantation mouse embryos were cultured in vitro in concentrations of PGF_2α ranging from 5 nanograms/ml to 100 micrograms/ml. Embryos were cultured at the 2-cell stage, 4-cell stage, 8-cell stage and the morula stage and observed for normal development to the blastocyst stage. There was no significant difference (P < .1) between the number of blastocysts attained in the control group and those in the experimental groups. After reaching the blastocyst stage, the embryos were transferred to the uteri of pseudopregnant recipient females. Again, there was no significant difference (P < .3) between controls and PGF_2α treated embryos in the number developing to term. These data suggest that exposure to PGF_2α does not result in teratogenic effects or early death in preimplantation embryos.     

The antagonism by anti-inflammatory analgesics of prostaglandin F2α-induced contractions of human and rabbit myometrium in vitro

The anti-inflammatory analgesic drugs, aspirin, indomethacin, phenylbutazone, mefenamic acid, ibuprofen and flurbiprofen are shown to inhibit in a dose-dependent manner the force of contraction of isolated human pregnant myometrial strips which have been stimulated to contract by adding prostaglandin (PG) F_2α to the tissue bath. These drugs and also flufenamic acid and salicin show a similar antagonism of the action of PGF_2α with isolated rabbit non-pregnant myometrium. The ratio of the inhibitory concentration in vitro to the maximum plasma level after a normal dose in vivo suggests that phenylbutazone and possibly ibuprofen may be capable of inhibiting human uterine contractions in vivo. Patients who were treated with aspirin during induction of abortion using PGF_2α during the second trimester of pregnancy showed no significant change in the induction-abortion interval compared with patients not taking aspirin.     

Prostaglandin F2α (PGF2α) and prolactin secretion in rats

Plasma prolactin and F-prostaglandins (PGF) were measured in anesthetized male Sprague-Dawley rats before and at 15, 30, 45 and 60 minutes following i.v. injection of either PGF_2α (4 mg/kg), chlorpromazine, 1 mg/kg or chlorpromazine (1 mg/kg) after pretreatment with i.p. indomethacin (2 mg/kg). Following PGF_2α administration, plasma prolactin levels increased significantly only at 15 and 30 minutes in spite of extremely high PGF levels throughout 60 minutes. Besides the expected rise in plasma prolactin, chlorpromazine caused a transient but statistically significant increase in PGF. Indomethacin blocked the chlorpromazine-induced PGF rise but not prolactin increase. Animals stressed with ether anesthesia showed elevation of plasma prolactin, which was not blocked by indomethacin although PGF concentration fell. These results indicate that PGF_2α can stimulate prolactin release. This effect does not appear to be physiologic since very high PGF levels are required. Furthermore, blockade of prostaglandin synthesis by indomethacin does not prevent the release of prolactin in response to chlorpromazine or stress. Our findings do not support a possible role of PGFs as intermediaries in prolactin release. However, it is possible that PGFs may work through other mechanisms not investigated in our study.     

Prostaglandin F2α and human prostatic affinity for testosterone

Earlier work had shown that the lactogen, LTH and HPL, foster testosterone binding by the prostate. This study was undertaken to see if prostaglandin F_2α would oppose the effect of the lactogen on the prostate as it does the luteotrophic action of the hormone on the corpus luteum. When it was found instead that the PGF increases steroid binding and that its interaction with lactogen was neither antagonistic nor additive, attention was directed to further characterization of the prostaglandin's effect. A dosage/response study of F_2α alone showed that concentrations of 4 ng/ml and 40 ng/ml increased binding but that 400 ng/ml did not. Glands with stromal hyperplasia and/or inflammation were more responsive than those with epithelial hyperplasia. Assays of water extracts of the tissue revealed concentrations of about 340 ng of F_2α per gram fresh weight and that the concentration varied inversely as the β-glucuronidase activity. If the enzyme level is considered an index of the epithelial cell density within the specimen, the inverse relationship suggests a non-epithelial (stromal) site of prostaglandin concentration.     

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.     

Prostaglandin F2α levels in the human ovarian follicle

Prostaglandin F_2α concentrations measured in ovarian follicular fluid from thirty-four patients rose significantly during the pre-ovulatory phase, reaching a peak at day 14 and falling after mid-cycle. These findings provide evidence in women to support a role for prostaglandins, acting at the follicular level, in the process of ovulation.     

Prostaglandin F2α increases responsiveness of pulmonary airways in dogs

We studied the effect of prostaglandin F_2α (PGF_2α) on the responsiveness of pulmonary airways in dogs. Airway responsiveness was assessed by determining the bronchoconstrictor response to increasing concentrations of acetylcholine aerosol delivered to the airways. In each of five dogs, we determined responsiveness during treatment with physiologic saline, histamine, or PGF_2α aerosols. The doses of histamine and PGF_2α were determined by establishing the largest dose of each which could be given to the dog without causing bronchoconstriction (subthreshold doses). We found that airway responsiveness was not significantly different during histamine treatment than after saline, however, responsiveness increased during treatment with PGF_2α. In addition, the hyperresponsiveness induced by PGF_2α was prevented by pretreatment with the ganglion blocking drug hexamethonium (5 mg/kg given intravenously). The results show that PGF_2α specifically increases the responsiveness of pulmonary airways in doses that do not cause bronchoncostriction, and suggest that the hyperresponsiveness involves a neural mechanism such as increased responsiveness of airway sensory nerves.     

Effects of indomethacin and prostaglandin F2α on parturition in the hamster

In the female hamster, temporary sterility for a period of 10 or 15 days was induced by an intraperitoneal Silastic-PVP-tube containing 0.5 or 1.0 mg of PGF_2α, respectively. All Silastic-PVP-PGF_2α tube bearing animals regained fertility and delivered normal litters at various times after the placement of the tube. The release rate of ³H-PGF_2α from the Silastic-PVP tube was described and their potential use as a drug delivery system discussed.     

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.     

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.     

Cardiovascular actions of prostaglandins F2α; 15-me-F2α; F1α; F2β and F1β in the cat

Prostaglandin F_2α (5μg/kg, i.v.) causes an increase in pulmonary arterial pressure, decrease in systemic arterial pressure, and reflex bradycardia in the anesthetized cat. The same dose of the 15-methyl analogue of PGF_2α produces the same triad of effects but of greater magnitude and duration. Although prostaglandins F_1α, F_2β and F_1β also cause the same cardiovascular effects as F_2α, there is a decrease in potency for all parameters measured, with PGF_2α>PGF_1α>PGF_2β>PGF_1β. When compared to the actions of PGF_2α in producing an increase in pulmonary arterial pressure, PGs F_1α, F_2β and F_1β were less potent by approximately 10, 100, and 1000 fold respectively.     

Contractility of rat testicular seminiferous tubules in vitro: prostaglandin f 1 alpha and indomethacin-1,2.

The frequency of spontaneous in vitro contractions of seminiferous tubules of the rat appeared to be increased in a dose-dependent manner by prostaglandin F1alpha. PGF1alpha treatment increased the tonus of the smooth muscle cells in the wall of the tubules as indicated by a reduction in the diameter of the tubules. When the tubules were rinsed successively with fresh Tyrode's solution, the contractile frequency was diminished. Returning the original bathing medium to the tubules restored their contractile frequency, as did treatment of the rinsed tubules with PGF1alpha (10(-7) M). Preinjecting ther rats with indomethacin tended to reduce the contractile frequency of the extirpated tubules. Treating the tubules with a solution of indomethacin for 90 min. in vitro was more effective than pretreatment in vivo in reducing contractile frequency, but a combination of these two procedures produced the greatest inhibition. PGF1alpha restored the contractile frequency of the indomethacin-treated tubules. Our results indicate that PGs modulate the in vitro contractility of the tubules.     

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.     

Disappearance of prostaglandins F2α and 15-methyl F2α from amniotic fluid as measured by radioimmunoassay

A sensitive and relatively specific radioimmunoassay for 15 (S) 15 methyl prostaglandin F_2α was used to determine the levels of the drug in amniotic fluid after it had been injected intra-amniotically for termination of second trimester pregnancy. The disappearance of the free acid (tham salt) and methyl ester of the prostaglandin analogue were similar. The results of this preliminary study suggest that the drug rapidly equilibrates in the fluid and this is followed by a slow removal from the amniotic sac. A comparison with a similar study with PGF_2α, revealed that the analogue had a longer half-life in the amniotic fluid.     

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.     

Prostaglandin F2α, oxytocin and progesterone secretion by bovine luteal cells at several stages of luteal development: Effects of oxytocin, luteinizing hormone, prostaglandin F2α and estradiol-17β

Bovine luteal cells from Days 4, 8, 14 and 18 of the estrous cycle were incubated for 2 h (1 × 10⁵ cells/ml) in serum-free media with one or a combination of treatments [control (no hormone), prostaglandin F₂α (PGF), oxytocin (OT), estradiol-17β (E) or luteinizing hormone (LH)]. Luteal cell conditioned media were then assayed by RIA for progesterone (P), PGF, and OT. Basal secretion of PGF on Days 4, 8, 14 and 18 was 173.8 ± 66.2, 111.1 ± 37.8, 57.7 ± 15.4 and 124.3 ± 29.9 pg/ml, respectively. Basal release of OT and P was greater on Day 4 (P<0.01) than on Day 8, 14 and 18 (rmOT: 17.5 ± 2.6 versus 5.6 ± 0.7, 6.0 ± 1.4 and 3.1 ± 0.4 pg/ml; P: 138.9 ± 19.5 versus 23.2 ± 7.5, 35.4 ± 6.5 and 43.6 ± 8.1 ng/ml, respectively). Oxytocin increased (P<0.01) PGF release by luteal cells compared with control cultures irrespective of day of estrous cycle. Estradiol-17β stimulated (P<0.05) PGF secretion on Days 8, 14 and LH increased (P<0.01) PGF production only on Day 14. Prostaglandin F₂α, E and LH had no effect on OT release by luteal cells from any day. Luteinizing hormone alone or in combination with PGF, OT or E increased (P<0.01) P secretion by cells from Days 8, 14 and 18. However on Day 8, a combination of PGF + OT and PGF + E decreased (P<0.05) LH-stimulated P secretion. These data demonstrate that OT stimulates PGF secretion by bovine luteal cells in vitro. In addition, LH and E also stimulate PGF release but effects may vary with stage of estrous cycle.     

Release of prostaglandin F1α and F2α from superfused platelets: Quantitative evaluation of the inhibitory effects of some aspirin-like drugs

The release of PGF_1α and PGF_2α from superfused blood platelets was studied by the combined use of two radioimmunoassay systems with different specificities. PGF_1α only accounted for approximately 30% of the total immunoreactivity. A substantially similar pattern of release was obtained with platelets of rat and human origin, although the latter released considerably lower amounts of both compounds. Indomethacin, Fenoprofen, Ditazole and Aspirin all inhibited PGF_2α release from rat platelets in descending order of potency. Hydrocortisone was practically inactive. The release of PGF_1α and PGF_2α was inhibited to the same extent by both Indomethacin and Fenoprofen. Moreover, a quite similar inhibitory effect by the same drug on rat and human platelets was found in preliminary experiments. In agreement with a previous similar finding, Aspirin displayed a higher inhibitory activity than that reported in other tissues. The use of superfused platelets seems to provide a simple and reproducible model for studying pharmacologic influences upon PG formation.     

Effects of intracerebroventricular administration of prostaglandins I2, E2, F2α and indomethacin on blood pressure in the rat

The effects of intraventricularly administered prostaglandins I₂ (PGI2), E₂ (PGE2), F_2α (PGF2α) and indomethacin on systemic blood pressure were investigated in conscious rats. PGI2 (1.25 – 10 g/kg) decreased blood pressure in a dose-related manner, whereas PGE2 (100 – 1000 ng/kg) dose-dependently increased blood pressure. Both PGF2α (0.31 – 20 μg/kg) and indomethacin (0.625 – 40 μg/kg) had no effects on blood pressure. These results indicate that intraventricular injection of PGI2 or PGE2 can induce significant changes in blood pressure, while endogenous prostaglandins synthesized in the brain seem to play a minor role in direct regulation of systemic blood pressure in the rat.