Stimulation of HCO3- transport in isolated proximal bullfrog duodenum by prostaglandins

An in vitro preparation of proximal duodenum from the bullfrog transported alkali into the luminal solution (approximately 1 mueq x h-1 x cm-2) and generated a transepithelial electrical potential difference (5-10 mV, lumen negative). Transport was inhibited by 2,4-dinitrophenol (10(-5) M), CN- (5 X 10(-3) M), indomethacin (5 X 10(-5) M), and acetazolamide (5 X 10(-3) M) indicating that metabolism is required. Both alkali transport and the electrical potential difference showed a dose-dependent increase on administration of the prostaglandins E2, 16,16-dimethyl E2, and F2 alpha. The minimal concentration stimulating transport was lower with the E-type prostaglandins (10(-8) M than with F2 alpha (10(-6) M), and the former also produced greater maximal responses. In addition to metabolic-dependent transport of alkali, there was passive transmucosal migration of HCO3-, amounting to approximately 40% of basal (unstimulated) transport and sensitive to variation of the transmucosal hydrostatic pressure. Morphological examination showed that the preparation is devoid of Brunner glands. Stimulation of duodenal epithelial HCO3- transport by prostaglandins may contribute to their previously demonstrated ability to prevent duodenal ulceration.

Smooth muscle physiology and effect of bladder and urethra muscle length/tension on response to stimulation. Part I. Review

With particular reference to the lower urinary tract, a review of basic anatomy and physiology of smooth muscle is presented. The relationship as altered by electrica and pharmacologic stimulation is discussed.

Pharmacological characterization of renal vascular dopamine receptors

We present an in vitro method for studying the renal effects of dopamine in the isolated rat kidney. The organ is perfused in an open circuit and can be maintained satisfactorily for up to 180 min. The responses to dopamine were studied in the presence of phenoxybenzamine (10(-5) M) and sotalol (10(-5) M) while stable renal vasoconstriction was maintained by perfusion with prostaglandine F2 alpha. Dopamine induced dose-dependent renal vasodilation with an ED50 of 2.53 X 10(-6) moles/liter, which was not modified by reserpine pretreatment. (+) Butaclamol but not (-) butaclamol shifted the dopamine dose-response curve to the right in a parallel fashion, indicating competitive antagonism. Haloperidol and sulpiride at concentrations without intrinsic effect on vascular resistance also acted as competitive inhibitors for dopamine. Calculation of empirical pA2 values yielded the following relative potencies for these antagonists: (+) butaclamol greater than haloperidol greater than sulpiride. The renal vascular dopamine receptors are tentatively classified as being of the D1 type.

Prostaglandins and the cardiotoxic effects of doxepin in rabbits and guinea-pigs

Intravenous administration of tricyclic antidepressants to rabbits leads to dysrhythmias largely attributable to their non-specific membrane effects. Further experiments with doxepin (Dx) were conducted to assess an eventual contribution by prostaglandins (PG) to these events. Dx infused intravenously to conscious or anaesthetized guinea-pigs proved as cardiotoxic as amitriptyline but more toxic than protriptyline, thus confirming our previous results in rabbits. PG F2 alpha given intravenously before or during the Dx infusion failed to antagonize cardiotoxicity. In conscious rabbits, pretreatment with drugs (aminophenazon, indomethacin, tolfenamic acid) known to inhibit PG synthesis failed to modify the Dx cardiotoxicity as also did PG F2 alpha which elevated blood pressure, however. PG F2 alpha also failed to counteract the ouabain cardiotoxicity in anaesthetized guinea-pigs and major Ba++-induced dysrhythmias in conscious rabbits. Our results suggest that a) at least Dx induced dysrhythmias are unresponsive to PGs, and that b) previous speculations about PGs as antiarrhythmic agents may be exaggerated.

Pregnancy blunts pulmonary vascular reactivity in dogs

Pregnancy decreases systemic vascular reactivity but comparatively little is known about the effects of pregnancy on the pulmonary circulation. Pulmonary vascular resistance (PVR) during acute hypoxia was lower (P < 0.01) in eight intact anesthetized pregnant dogs compared to the same animals postpartum. Mean pulmonary arterial pressure (Ppa) and PVR during infusion of prostaglandin (PG) F2 alpha were also reduced during pregnancy. Nonpregnant female dogs (n = 5) treated with estrogen (0.001 mg x kg-1 x da-1) for 2 wk had decreased Ppa (P < 0.01) during acute hypoxia compared to control measurements, but PVR was unchanged during hypoxia and PGF2 alpha infusion. Treatment with progesterone in four dogs had no effect on pulmonary vascular reactivity to hypoxia or PGF2 alpha. Inhibition of circulating PG with meclofenamate in four dogs during pregnancy did not appear to restore pulmonary vascular reactivity. Blunted pulmonary vascular reactivity is suggested by the limited data available for women, but is not seen in pregnant cows. We conclude that pregnancy decreases pulmonary as well as systemic vascular reactivity in the dog, but the mechanism is unclear.

Stimulatory action of prostaglandin F2 alpha on androgen aromatization in the pig follicle

Previous in vitro studies with pig tissues have demonstrated that follicle-stimulating hormone (FSH) can stimulate follicular prostaglandin F2 alpha (PGF2 alpha) production, and both FSH and PGF2 alpha can stimulate follicular estradiol production. The present study was designed firstly to confirm that in the pig, as in the rat, FSH increases estradiol production by stimulation of the aromatase enzyme system, and secondly to investigate the possibility that PGF2 alpha may play a role in the FSH stimulation of androgen aromatization. FSH increased the incorporation of [3H]testosterone into estradiol during a 3-h incubation of halved pig follicles or isolated granulosa cells by 85% compared to controls. PGF2 alpha increased the incorporation by 107%, whilst the two substances together caused an increase of 124%. Indometacin, an inhibitor of PG synthesis, reduced the incorporation of 21% of the control value, and completely inhibited the FSH stimulation. These results show that FSH stimulates the aromatase enzyme system of pig granulosa cells, and suggest that PGF2 alpha may play an obligatory role in androgen aromatization.

Peripheral serum progesterone and luteinizing hormone concentrations of goats during synchronization of estrus and ovulation with prostaglandin F2 alpha

Prostaglandin F2 alpha (PGF2 alpha) (2 doses, 11 days apart) was given to 20 mixed-breed dairy does to synchronize estrus and ovulation. The dose of PGF2 alpha used was the free-acid equivalent of 8 mg which was divided between 2 injections at 0800 and 1200 hours. At the initiation of treatments, does were from day 0 (estrus) to day 18 of the estrous cycle. Seventeen of the doses exhibited estrus within a mean (+/- SE) interval of 53 +/- 2 hours after the first 0800-hour injection. Peripheral progesterone concentrations determined at daily intervals indicated that PGF2 alpha was luteolytic as early as day 4 of the cycle. Does were in the 8th to 12th days of the cycle at the time of the 2nd treatments with PGF2 alpha. Estrus was observed in all 20 does at 50 +/- 1 hour after the 0800-hour injections. Serum progesterone concentrations confirmed that luteolysis occurred in all of the does. In 19 does, concentrations of luteinizing hormone characteristic of a preovulatory peak were observed 55 +/- 2 hours after the 2nd 0800-hour injection. One doe did not demonstrate a luteinizing hormone peak within the 72-hour period. Laparotomies were performed 6 days after estrus, and ovaries were examined for corpora lutea. The mean number of corpora lutea was 2.0 +/- 1.0.

Bronchodilator effects of prostacyclin (PGI2) in dogs and guinea pigs

prostacyclin (PGI2), a recently discovered unstable product in the biosynthetic conversion of prostaglandin endoperoxides, was examined for bronchopulmonary actions. in anesthetized dogs, PGI2 given i.v. (0.3-30.0 microgram/kg) and by aerosol (0.002-0.2%) inhibited significantly PGF2 alpha-induced increases in pulmonary resistance and decreases in dynamic lung compliance in a dose-related fashion. Intrinsically, PGI2 affected resting bronchopulmonary and cardiac functions minimally, but decreased peripheral and pulmonary vascular pressures. PGI2 (0.1-10 mg/kg, i.p.) afforded protection against histamine-induced asphyxial collapse in normal guinea pigs and ovalbumin-induced anaphylaxis in sensitized animals. Cumulative concentrations of PGI2 (1.0 x 10(-9)--3.0 x 10(-4) M) relaxed contractions of the isolated guine pig trachea produced by carbachol. These bronchodilator and hemodynamic effects could not be ascribed to the stable metabolic product of PGI2, because 6-keto-PGF1 alpha was inactive or markedly less active than PGI2 in these test systems. The results of this investigation suggest that PGI2 possesses considerable bronchodilator and vasodilator activity in experimental animal systems.

A selective concentration-dependent dysrhythmogenic and antidysrhythmic action of prostaglandins E2, F2 alpha and I2 (prostacyclin) on isolated rat hearts

Prostaglandins (PGs) E2, F2 alpha and I2 were examined for their effects on the electrical and mechanical activities of isolated rat, rabbit and guinea-pig hearts. All PGs produced dysrhythmias in rat hearts at low concentrations only, while higher concentrations were antiarrhythmic. Guinea-pig hearts were less responsive while rabbit hearts were completely resistant.

Effect of gonadotrophin releasing hormone on levels of luteinising hormone in cattle synchronised with dinoprost

Synchronisation of oestrus was achieved in a group of three cows and two heifers with dinoprost. Sixty-six hours after the second injection of dinoprost, 0.125 mg synthetic gonadotrophin releasing hormone (GnRH) was given intramuscularly. Concentrations of luteinising hormone (LH) were monitored in peripheral blood and close grouping of preovulatory LH peaks was seen around 2.5 hours after injection of GnRH.

Studies on the modulation of immunoglobulin production by prostaglandins

The present study investigated the effect of prostaglandins (PG) on the in vitro production of polyclonal IgG and IgM by pokeweed mitogen- stimulated normal human peripheral mononuclear cells. Concentrations of PGE1 and PGA1 in excess of 10(-6)M were suppressive. PGE2 and PGs of the F series were less effective and significant suppression was seen in concentrations greater than 10(05)M. Indomethacin added to cell cultures did not enhance Ig production. This discrepancy between physiologic PG concentrations and the very large pharmacologic concentration necessary to suppress Ig synthesis in vitro makes the physiologic role of PG in the modulation of Ig synthesis questionable.

Facilitation of sympathetic neurotransmission in the rat anococcygeus muscle by prostaglandins D2 and F2 alpha

1 Investigations were made into the effects of prostaglandins D2 (PGD2) and F2 alpha (PGF2 alpha) on the responses of the rat anococcygeus muscle to field stimulation of intrinsic motor (sympathetic) and inhibitory nerves, and to exogenous noradrenaline. 2 PGD2 (2.8 X 10(-6) mol/1) substantially increased the motor responses to field stimulation at all frequencies tested (2 to 32 Hz), and caused a smaller increase in the responses to noradrenaline. 3 PGF2 alpha (2.8 X 10(-6) mol/1) strongly potentiated the motor responses to field stimulation (2 to 32 Hz) and also to noradrenaline. This prostaglandin had quantitatively similar effects on the responses to both types of stimulus. 4 PGD2 was without effect on the inhibitory responses evoked by field stimulation in the presence of guanethidine. PGF2 alpha seemed to reduce the inhibitory responses to low frequencies of stimulation (0.5 to 1.5 Hz), but this effect was marginal. 5 The results suggest that PGD2 facilitates sympathetic neurotransmission in this tissue by both pre- and post-junctional actions. The effect of PGF2 alpha seems likely to be mediated predominantly post-junctionally.

Metabolism of 3H-dopamine continuously perfused through push-pull cannulas in rats' brains: modification by amphetamine or prostaglandin F2 alpha

Using perfusion cannulas implanted in the lateral cerebroventricles, the metabolism of a trace concentration of 3H-dopamine, continuously presented, was investigated in rats performing an operant for food reinforcement. The subjects were mature, drug-naive, male Long-Evans rats. Perfusate contained measurable quantities of 3H-3,4-dihydroxyphenylacetic acid (3H-DOPAC), 3H-3-methoxy-4-hydroxyphenylacetic acid (3H-homovanillic acid, 3H-HVA), 3H-3-methoxytyramine (3H-3-MT) and the 3H-noradrenaline metabolite, 3H-3-methoxy-4-hydroxyphenylethyleneglycol (3H-MHPG). Systemic injection of d-(1.5 mg/kg) or 1-(3.0 mg/kg) amphetamine resulted in decreased quantities of 3H-DOPAC, 3H-HVA and 3H-MHPG in perfusate with a concurrent decrease in fixed-ratio 20 behavior. Addition of prostaglandin F2 alpha (10 ng/microliters perfused at a rate of 10 microliters/minute) had no effect on the rats' fixed-ratio 20 behavior or rectal temperature, but resulted in decreased quantities of 3H-DOPAC, 3H-HVA and 3H-MHPG in perfusate. It is concluded that this methodology allowed us to monitor drug-induced changes in CNS dopaminergic and noradrenergic function in conscious rats engaged in schedule-controlled operant behavior. Furthermore, a trace concentration of PGF2 alpha in perfusion medium caused changes in 3H-dopamine metabolism in a manner similar to that of systemically administered amphetamines.

Central and peripheral circulatory effects and metabolic effects of different prostaglandins given I.V. to man

Cardiac output, heart rate, stroke volume, pressures in the brachial artery, right ventricle and pulmonary artery, forearm blood flow, and arterial concentration of FFA, lactate and glucose were measured in healthy male volunteers during i-v infusion of PGE1, PGE2, PGF2 alpha or 15-methyl PGF2 alpha in increasing doses. In accordance with previous findings PGE1 and PGE2 increased cardiac output by a vasodilating effect in the systemic and pulmonary vascular bed, probably in combination with an inotropic effect on the heart. 15-methyl PGF2 alpha had essentially the same cardiovascular effects as PGF2 alpha. They induced a slight increase in cardiac output due to effects on heart rate, while systemic vascular resistance was unchanged. Forearm vascular resistance increased and pressures in the pulmonary circulation rose, indicating a vasoconstriction in these vascular beds. Glucose concentrations was not affected nor were lactate concentrations, except for a slight decrease of unclear significance in the group receiving 15-methyl PGF2 alpha. FFA increased slowly in the same manner as seen spontaneously in fasting individuals. These data do not indicate direct metabolic effects of the prostaglandins studied when given i-v.

Influence of analgesic antipyretics on the central cardiovascular effects of clonidine in rats

The centrally acting antihypertensive drug clonidine has been found to stimulate the synthesis of PGF2 alpha in the brain. Centrally administered PGF2 alpha, in turn, induces rises of blood pressure and heart rate. We therefore studied the influence of inhibitors of prostaglandin (PG) synthesis on the cardiovascular effects of clonidine in urethane-anaesthetised rats. Pretreatment with indomethacin or paracetamol (100 micrograms/rat into the fourth cerebral ventricle) antagonised the central hypotensive effect of clonidine (0.125-16.0 micrograms/rat into the fourth cerebral ventricle). The bradycardic effect of centrally administered clonidine was, however, enhanced by pretreatment with paracetamol but not influenced by indomethacin pretreatment. Sodium meclofenamate (100 micrograms/rat into the fourth cerebral ventricle) did not significantly affect the clonidine-induced changes in blood pressure and heart rate. These results suggest that the clonidine-induced hypotension on one hand and bradycardia on the other hand may be mediated by partly different mechanisms. An interference of the formation of PGF2 alpha with the cardiovascular effects of clonidine cannot be completely excluded since paracetamol pretreatment potentiated the bradycardic effect of clonidine. However, inhibitors of PG synthesis did not enhance but antagonised the hypotensive effect of clonidine. Therefore it is likely that the synthesis of PGF2 alpha does not interfere with the hypotensive effect of clonidine. Moreover, the antagonism of the hypotensive effect by inhibitors of PG synthesis suggests that some hypotensive metabolite of arachidonic acid in the brain could be involved in the central hypotensive effect of clonidine.

Evaluation of the role of the F prostaglandins in canine bile flow

Prostaglandin F2 alpha (PGF2 alpha) has been shown to be an effective stimulant of hepatic bile flow producing a specific chloride rich bile. Subsequent evaluation by radioimmunoassay has shown that prostaglandin F compounds are present in relatively large amounts in canine hepatic bile. This study evaluates the effect of PGF2 alpha administration and of prostaglandin synthetase inhibition by aspirin and indomethacin on bile flow and radioimmunoassayable prostaglandin F (iPGF) secretion. Chronic, canine bile fistula preparations were utilized and the enterohepatic circulation was maintained by intravenous bile salts. Bile volume and composition were evaluated by standard techniques as well as bile PGF concentration by radioimmunoassay during bile salt infusion and during bile salt and PGF2 alpha, aspirin and indomethacin infusion in varying doses. Both aspirin and PGF2 alpha were potent stimulants of hepatic bile flow with aspirin producing a chloride rich bile similar to that produced by PGF2 alpha. PGF2 alpha produced dose related increases in bile iPGF concentration and output indicating that as the systemic concentration increases during infusion of PGF2 alpha the lipid appears in bile. Aspirin in the highest dose administered, decreased iPGF concentration in bile while output was unchanged. Indomethacin was ineffectual in consistently altering bile flow or iPGF secretion. This study demonstrates that iPGF is present in canine bile, that its concentration can be altered by prostaglandin infusion while prostaglandin synthetase inhibition has minimal effects on bile iPGF secretion.

The effects of prostaglandins on aqueous humor dynamics

PGE2, applied topically to the cornea of enucleated, arterially perfused cat eyes, produced an increase in the rate of aqueous humor (AH) production but only minimal changes in eye pressure, as observed in vivo. In contrast, PGE1, E2 and F2 alpha, administered intrarterially, induced no change in AH productin or arterial perfusate flow rate. In eyes which the AH inflow rate had been accelerated by prior administration of acetylcholine plus eserine, PGE1, E2 and F2 alpha caused a lowering of the inflow rate as well as vascular dilatation.

Drugs in obstetric anaesthesia

From the anaesthetist's viewpoint, pharmacokinetics of pregnancy, drugs affecting uterine muscle tension and foetal effects of anaesthetic drugs are reviewed.

PGF2 alpha on drug-induced contractile responses of frog rectus abdominis muscle

In the present study, augmentation of contractile responses to acetylcholine, potassium chloride and caffeine by prostaglandin F2 alpha on frog rectus abdominis muscle is documented. The PG-induced responses to ACh was restricted to brief exposure of the tissue to PG. Prolonged exposure resulted in disappearance of the enhancing effect and depression of ACh responses. The augmentation of ACh response was unaltered in presence of physostigmine and the pA2-value of d-tubocurarine was not changed by PGF2 alpha ruling out the involvement of a cholinergic mechanism. In potassium depolarized muscle, PGF2 alpha abolished the contractile response to caffeine, indicating an action at the trigger calcium site. PGF2 alpha also permitted reactivation contracture during repolarization.

Correlation of prostaglandin-induced mitochondrial calcium release with contraction in bovine intrapulmonary vein

The effects of prostaglandins A2, A1, F2 alpha, E2, E2, F1 beta and an analog of PGH2 upon calcium release from mitochondria isolated from bovine intrapulmonary vein and contraction of helical strips of the same tissue were determined. The order of activity of the prostaglandins for calcium release was similar to that for contraction with the exception of the PGH2 analog. It is suggested that prostaglandin A2, F2 alpha, E2 and A1 induced release of mitochondrial calcium may influence the contractile state of bovine intrapulmonary vein. However, the PGH2 analog has a subcellular mechanism other than or in addition to mitochondrial calcium release and is different from the other prostaglandins.

Pharmacologic induction of luteolysis in cynomolgus monkeys (Macaca fascicularis)

Earlier studies reported from this laboratory demonstrated the luteolytic effect of a 5-day sequential regimen of 3 days of estrogen overlapped with 3 days of PGF2 alpha administered during the midluteal phase to cynomolgus monkeys. In this study, a different regimen, containing estrogen, lower doses of PGF2 alpha, and methylergonovine maleate (MEM), was used. Individual components of this modified sequential regimen were not effective as luteolytic agents. When 3 days of estrogen (40 micrograms of depoestradiol cypionate [DEC] on the first day and 40 micrograms of estradiol benzoate [EB] on second and third day) was followed by 3 days of MEM (400 micrograms, twice daily) overlapping 1 day of estrogen treatment, there was a significant shortening of the length of the menstrual cycle (less than 26 days) in eight of 10 animals, with a concomitant decline in plasma levels of progesterone. When a low dose of MEM (100 micrograms, twice daily), which was completely ineffective in shortening cycle lengths with the same estrogen treatment, was administered alternately with PGF2 alpha (5 mg twice daily, 11 of 14 animals had shortened cycles, with an associated decline in levels of progesterone. PGF2 alpha and MEM without the estrogen pretreatment did not have a significant effect on cycle lengths or blood levels of progesterone, thus demonstrating a synergism between estrogen and the other compounds in inducing luteolysis. Since the agents used in these sequential regimens have potent effects on the uterus, the treatments were repeated in hysterectomized monkeys to determine whether the uterus was involved in the mediation of luteolysis. These treatments caused a significant drop in plasma levels of progesterone by the tenth day after the preovulatory estrogen peak, thus demonstrating that the uterus is not essential to the luteolytic action.

In vivo effect of cimetidine on canine pulmonary responsiveness to aerosol histamine

A series of experiments were designed to discover whether pulmonary histamine H2 receptors might be of physiologic importance in vivo in the dog. Dose-response curves were performed to aerosol histamine in 11 dogs both before and 1 hr after H2 receptor blockade with cimetidine (1 mg/kg as a rapid intravenous infusion). Cimetidine had no significant effect on control values of dynamic compliance or resistance of the lung. In the 11 dogs tested H2 receptor antagonism significantly potentiated (p less than 0.05) the animals' pulmonary responsiveness to aerosol histamine. The potentiation of histamine constrictor e-fects produced by cimetidine were more marked on those dogs initially least responsive to aerosol histamine (p less than 0.01). We have found evidence for the presence of inhibitory H2 receptors in canine airways and for the distribution of these receptors among dogs, explaining in part the previously described differences among dogs in the pulmonary responsiveness to aerosol histamine.