Relationship of cAMP and calcium messenger systems in prostaglandin-stimulated UMR-106 cells

The effect of prostaglandins (PG) on free cytosolic calcium concentrations [( Ca2+]i) and cAMP levels was studied in the osteosarcoma cell line UMR-106. PGF2 alpha and PGE2, but not 6-keto-PGF1 alpha, induced an increase in [Ca2+]i which was mainly due to Ca2+ release from intracellular stores. The EC50 for PGF2 alpha was approximately 7 nM, whereas that for PGE2 was approximately 1.8 microM. Maximal doses of PGF2 alpha increased [Ca2+]i to higher levels than PGE2. Both active PGs also stimulated phosphatidylinositol turnover in UMR-106 cells. The effects of the two PGs were independent of each other and appear to involve separate receptors for each PG. PGE2 was a very potent stimulator of cAMP production and increased cAMP by approximately 80-fold with an EC50 of 0.073 microM. PGF2 alpha was a very poor stimulator of cAMP production; 25 microM PGF2 alpha increased cAMP by 5-fold. The increase in cellular cAMP levels activated a plasma membrane Ca2+ channel which resulted in a secondary, slow increase in [Ca2+]i. High concentrations of both PGs (10-50 microM) inhibited this channel independent of their effect on cAMP levels. Pretreatment of the cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate inhibited the PG-mediated increase in phosphatidylinositol turnover and the increase in [Ca2+]i. However, pretreatment with 12-O-tetradecanoyl-13-acetate had no effect on the PGE2-mediated increase in cAMP. The latter finding, together with the dose responses for PGE2-mediated increases in [Ca2+]i and cAMP levels, suggests the presence of two subclasses of PGE2 receptors: one coupled to adenylate cyclase and the other to phospholipase C. With respect to osteoblast function, the cAMP signaling system is antiproliferative, whereas the Ca2+ messenger system, although having no proliferative effect by itself, tempers cAMP's antiproliferative effect.

Hepatocyte heterogeneity in response to icosanoids. The perivenous scavenger cell hypothesis

1. The metabolic and hemodynamic effects of prostaglandin F2 alpha, leukotriene C4 and the thromboxane A2 analogue U-46619 were studied during physiologically antegrade (portal to hepatic vein) and retrograde (hepatic to portal vein) perfusion and in a system of two rat livers perfused in sequence. 2. The stimulatory effects of prostaglandin F2 alpha (3 microM) on hepatic glucose release, perfusion pressure and net Ca2+ release were diminished by 77%, 95% and 64%, respectively, during retrograde perfusion when compared to the antegrade direction, whereas the stimulation of 14CO2 production from [1-14C]glutamate by prostaglandin F2 alpha (which largely reflects the metabolism of perivenous hepatocytes) was lowered by only 20%. Ca2+ mobilization and glucose release from the liver comparable to that seen during antegrade perfusion could also be observed in retrograde perfusions; however, higher concentrations of the prostaglandin were required. 3. The glucose, Ca2+ and pressure response to leukotriene C4 (20 nM) or the thromboxane A2 analogue U-46619 (200 nM) of livers perfused in the antegrade direction were diminished by about 90% during retrograde perfusion. Sodium nitroprusside (20 microM) decreased the pressure response to leukotriene C4 (20 nM) and U-46619 (200 nM) by about 40% and 20% in antegrade perfusions, respectively, but did not affect the maximal increase of glucose output. 4. When two livers were perfused antegradely in series, such that the perfusate leaving the first liver (liver I) entered a second liver (liver II), infusion of U-46619 at concentrations below 200 nM to the influent perfusate of liver I increased the portal pressure of liver I, but not of liver II. At higher concentrations of U-46619 there was also an increase of the portal pressure of liver II and with concentrations above 800 nM the pressure responses of both livers were near-maximal [19.6 +/- 0.8 (n = 7) cm H2O and 16.5 +/- 1.1 (n = 8) cm H2O for livers I and II, respectively]. There was a similar behaviour of glucose release from livers I and II in response to U-46619 infusion. When liver I was perfused in the retrograde direction, a significant pressure or glucose response of liver II (antegrade perfusion) could not be observed even with U-46619 concentrations up to 1000 nM. 5. Similarly, the perfusion pressure increase and glucose release induced by leukotriene C4 (10 nM) observed with liver II was only about 20% of that seen with liver I.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of the Cloudman melanoma cell cycle by prostaglandins E1 and E2 determined by using a 5-bromo-2'-deoxyuridine method of DNA analysis

Prostaglandins (PGs) E1 and E2 stimulate tyrosinase activity and suppress the proliferation of Cloudman S91 melanoma cells by altering their progression through the cell cycle. Prostaglandin E1 and PGE2 have prolonged or residual effects on melanoma cells. Cells treated for 5 or 24 hours with 10 micrograms/ml PGE1 or cells treated for 8 or 24 hours with 10 micrograms/ml PGE2 demonstrated decreased proliferation and increased tyrosinase activity for 48 hours after removal of the PGs. The effects of PGs on the cell cycle were investigated by determining total DNA content in cells stained with propidium iodide (PI) and analyzed by a fluorescence activated cell sorter (FACS). Prostaglandin E1 blocked cells in G2 phase after 5 hours of treatment, corresponding to when inhibition of proliferation was first evident. Similarly, after 9 hours of treatment with PGE2, more cells were in late S, early G2 phase and less in G1 than their control counterparts. Also, melanoma cells were pulse-labeled with 5-bromo-2'-deoxyuridine (BrdUrd) prior to or at the end of PG treatment and then stained with a fluoresceinated monoclonal antibody to BrdUrd, and with PI. This allows one to observe how BrdUrd-labeled S-phase cells cycle with time. Both PGE1 and PGE2 inhibit proliferation by blocking cells in G2 phase of the cell cycle. The PG-induced block in G2 may be required by melanoma cells to synthesize mRNA and proteins that are essential for stimulation of tyrosinase activity. Ultrastructurally, only a subpopulation of the cells treated with PGE1 or PGE2 contained more mature melanosomes than control cells.

Effects of prostaglandin F2 alpha and a gonadotropin-releasing hormone agonist on inositol phospholipid metabolism in isolated rat corpora lutea of various ages

The sensitivity of rat corpora lutea to luteolytic agents increases with luteal age. We examined the effect of prostaglandin F2 alpha (PGF2 alpha) and [D-Ala6,Des-Gly10]GnRH ethylamide (GnRHa) on inositol phospholipid metabolism in day 2 and day 7 corpora lutea from PMSG-treated rats. Isolated corpora lutea were incubated with 32PO4 or [3H]inositol and were treated with LH, PGF2 alpha, or GnRHa. Phospholipids were purified by TLC, and the water-soluble products of phospholipase-C activity (inositol phosphates) were isolated by ion exchange chromatography. In day 2 corpora lutea, PGF2 alpha, (10 microM) and GnRHa (100 ng/ml) significantly increased 32PO4 incorporation into phosphatidic acid (PA) and phosphatidylinositol (PI), but not into other fractions. LH provoked slight increases in PA. Results were similar with 30 min of prelabeling or simultaneous addition of 32PO4 and stimulants. In other experiments, PGF2 alpha and GnRHa provoked rapid increases (1-5 min) in the accumulation of inositol mono-, bis-, and trisphosphates. LH did not significantly increase inositol phosphate accumulation, but stimulated cAMP accumulation in 2-day-old corpora lutea. Inositol phospholipid metabolism was increased in day 7 corpora lutea compared to that in day 2 corpora lutea. This increase was associated with increased incorporation of 32PO4 into PA and PI and increased accumulation of [3H]inositol phosphates. In day 7 corpora lutea, which are very sensitive to the luteolytic effect of PGF2 alpha, the PG-induced increase in PA labeling was small and inconsistent, whereas PI labeling was unaffected in 30-min incubations. GnRHa was without effect in such corpora lutea. LH, PGF2 alpha, or GnRHa did not increase inositol phosphate accumulation in 7-day-old corpora lutea. These studies demonstrate that the transformation of young (day 2) to mature (day 7) corpora lutea is associated with an increase in luteal inositol phospholipid metabolism. The results also show that PGF2 alpha and GnRHa stimulate phospholipase-C activity in young corpora lutea, but are ineffective in mature corpora lutea, and suggest that an increase in inositol phospholipid metabolism by itself is not sufficient to explain the acute luteolytic action of PGF2 alpha and GnRH in vitro. However, phospholipase-C-derived second messengers may be involved in the action of hormones that control luteal function.

Potential role for prostaglandin F2 alpha, D2, E2 and thromboxane A2 in mediating the metabolic and hemodynamic actions of sympathetic nerves in perfused rat liver

In isolated rat liver perfused at constant pressure perivascular nerve stimulation caused an increase of glucose and lactate output and a reduction of perfusion flow. The metabolic and hemodynamic nerve effects could be inhibited by inhibitors of prostanoid synthesis, which led to the suggestion that the effects of nerve stimulation were, at least partially, mediated by prostanoids [Iwai, M. & Jungermann, K. (1987) FEBS Lett. 221, 155-160]. This suggestion is corroborated by the present study. 1. Prostaglandin D2, E2 and F2 alpha as well as the thromboxane A2 analogue U46619 enhanced glucose and lactate release and lowered perfusion flow similar to nerve stimulation. 2. The extents, the kinetics and the concentration dependencies of the metabolic and hemodynamic actions of the various prostanoids were different. Prostaglandin F2 alpha and D2 caused relatively stronger changes of metabolism, while prostaglandin E2 and U46619 had stronger effects on hemodynamics. Prostaglandin F2 alpha elicited greater maximal alterations than D2 with similar half-maximally effective concentrations. Prostaglandin F2 alpha mimicked the nerve actions on both metabolism and hemodynamics best with respect to the relative extents and the kinetics of the alterations. 3. The hemodynamic effects of prostaglandin F2 alpha could be prevented completely by the calcium antagonist nifedipine without impairing the metabolic actions of the prostanoid. Apparently, prostaglandin F2 alpha influenced metabolism directly rather than indirectly via hemodynamic changes. The present results, together with the previously described effects of prostanoid synthesis inhibitors, suggest that prostanoids, probably prostaglandin F2 alpha and/or D2, could be involved in the actions of sympathetic hepatic nerves on liver carbohydrate metabolism. Since prostanoids are synthesized only in non-parenchymal cells, nervous control of metabolism appears to depend on complex intra-organ cell-cell interactions between the nerve, non-parenchymal and parenchymal cells.

Fertility of postpartum dairy cows after administration of gonadotropin-releasing hormone and prostaglandin F2 alpha: a field trial

Our objective was to examine further the potential profertility effects of gonadotropin-releasing hormone and prostaglandin F2 alpha in postpartum Holstein cows. Reproductive performance was monitored in 843 cows milked thrice daily. One group of cows (n = 218) was untreated, while three groups received either 100 micrograms gonadotropin-releasing hormone administered once between d 11 and 25 (n = 211); 25 mg prostaglandin F2 alpha given once between d 11 and 25 (n = 215); or 25 mg prostaglandin F2 alpha given once between d 25 and 40 postpartum (n = 190). No profertility effects were detected in cows, regardless of their health status during the periparturient period, except cows given gonadotropin-releasing hormone between d 11 and 18 had shorter intervals to first estrus and to first service than controls. Cows with reproductive disorders (abnormal health status) in the concurrent lactation had longer intervals from calving to conception after receiving gonadotropin-releasing hormone between d 18 and 25 or prostaglandin F2 alpha between d 33 and 40. Abnormal health status adversely affected every reproductive trait measured. Early postpartum treatments with either hormone failed to improve reproductive performance of dairy cows, in contrast to several reports of profertility effects for gonadotropin-releasing hormone, and a few reports for prostaglandin F2 alpha.

Prostaglandin production and contractile response of umbilical arteries in preeclamptic pregnancies with and without intrauterine growth retardation

Biochemical and biophysical properties of umbilical arteries from normotensive and preeclamptic pregnancies were examined. The production of prostaglandins E and F, 6-keto-PGF1 alpha, and thromboxane B2 by umbilical arteries from normotensive, mildly preeclamptic, and severely preeclamptic pregnancies were measured in incubation media at baseline and after addition of arachidonic acid. The initial baseline values of 6-keto-PGF1 alpha were decreased in the severely preeclamptic patients with intrauterine growth retardation (IUGR) but not in any of the other groups. Addition of arachidonic acid resulted in a significant increase in 6-keto-PGF1 alpha production over initial baseline in all groups except in the severely preeclamptic pregnancies without IUGR. These results suggest a differential defect in the 6-keto-PGF1 alpha metabolic pathway in severely preeclamptic patients with IUGR compared with those without IUGR. The stretch response curve to serotonin was decreased in the severely preeclamptic group with IUGR compared with the control group. The contractile response to individual vasoactive agents (serotonin, prostaglandin F2, norepinephrine, angiotensin II, and arachidonic acid) showed no significant difference between the normotensive and preeclamptic groups.

Nitric oxide, ACh, and electrical and mechanical properties of canine arterial smooth muscle

The effects of nitric oxide and acetylcholine (ACh) were investigated on the electrical and mechanical properties of vascular smooth muscle cells of the canine mesenteric artery. Isolated tissues with or without the endothelium were contracted with prostaglandin F2 alpha. Nitric oxide caused comparable concentration-dependent relaxations in rings with and without endothelium. ACh induced concentration-dependent relaxations only in arteries with endothelium. The relaxations to both nitric oxide and ACh were inhibited by methylene blue or oxyhemoglobin. Either in the presence or absence of prostaglandin F2 alpha, ACh caused transient hyperpolarization of the cell membrane of the vascular smooth muscle. The ACh-induced transient hyperpolarization was not observed after mechanical removal of the endothelial cells or after treatment with atropine. Nitric oxide (less than or equal to 8 X 10(-6) M) did not alter membrane potential, in either the presence or absence of the endothelium. The excitatory junction potentials generated by perivascular nerve stimulation were inhibited by ACh but not by nitric oxide. These results suggest that in the canine mesenteric artery 1) the endothelium-derived hyperpolarizing factor generated by ACh is not nitric oxide; 2) nitric oxide relaxes vascular smooth muscle by a direct effect; and 3) nitric oxide does not modify adrenergic neurotransmission.

Effect of PGE2 and alpha-adrenergic agonists on AVP-dependent cAMP levels in rabbit and rat CCT

The effect of prostaglandins and alpha-adrenergic agonists on arginine vasopressin-induced adenosine 3',5'-cyclic monophosphate (cAMP) production was investigated in microdissected rat and rabbit cortical collecting tubules (CCT) incubated in vitro. In rabbit CCT, addition to all media of a prostaglandin synthesis inhibitor increased this production; exogenous prostaglandin E2 (PGE2) induced a reproducible dose-dependent inhibition of cAMP accumulation. Maximal inhibition (mean: 57.5%) was observed with 0.3 microM PGE2, and threshold inhibition was observed with concentrations ranging from 3 to 10 nM PGE2. Inhibition of cAMP levels in rabbit CCT was also obtained with 0.3 microM PGF2 alpha (mean inhibition: 44.3%) but not with alpha-adrenergic agonists studied under the same conditions. The opposite was observed in rat CCT studied in parallel: the alpha-agonists inhibited cAMP production by up to 80%, but PGE2 had no effect.

Stereoselective effect of diltiazem on endothelium-dependent relaxations in canine femoral arteries

Experiments were designed to analyze potential interactions between voltage-dependent calcium channel blockers and endothelium-dependent vascular responses. Rings of canine femoral artery were suspended for isometric force recording in organ chambers and contracted with prostaglandin F2 alpha. Removal of the endothelium had no effect on relaxations induced by d-cis-diltiazem (active stereoisomer), verapamil or nimodipine. When rings with endothelium were first partially relaxed with acetylcholine or the calcium ionophore A23187 the concentration-relaxation curve to d-cis-diltiazem (but not to verapamil or nimodipine) was significantly shifted to the right. Partial relaxation of femoral arterial rings without endothelium by sodium nitroprusside had no effect on relaxations evoked by diltiazem. Pretreatment with diltiazem (10(-6) M) had no effect on endothelium-dependent relaxations to acetylcholine in femoral artery rings. D-cis-Diltiazem partially reversed the relaxation induced by acetylcholine in a bioassay system, in which a ring of canine coronary artery without endothelium was superfused by solution passing through a segment of femoral artery with endothelium. D-cis-Diltiazem relaxed the bioassay ring when infused downstream of the perfused femoral artery with, or upstream of a femoral artery without endothelium. The effect of diltiazem was stereoselective (the less active l-cis-diltiazem had no effect). Verapamil did not reverse the relaxation induced by acetylcholine and did not affect the reversal induced by diltiazem. These findings indicate that diltiazem specifically antagonizes the production and/or the release of endothelium-derived relaxing factor(s) stimulated by acetylcholine or A23187 in canine femoral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cyclooxygenase inhibition on the pulmonary vasodilator response to furosemide

Furosemide is a potent vasodilator of the systemic arterial and venous systems. The mechanism of vasodilatation, however, remains unclear. We investigated the vasodilatory effect of furosemide and its relation to endogenous prostaglandins (PGs). In the isolated canine lung lobe, furosemide significantly decreased mean pulmonary artery pressure. This effect was inhibited by indomethacin. Furosemide also attenuated the pulmonary vasoconstrictor response to the endoperoxide analog U46619 and PGF2 alpha. The pulmonary pressor response to a submaximal constrictor dose of arachidonic acid was significantly enhanced by furosemide, however, the pressor response to a maximal constrictor dose of arachidonic acid was attenuated, although not significantly. In animals pretreated with indomethacin, furosemide had no effect on the vascular response to PGF2 alpha, but the response to U46619 was significantly increased. Prostacyclin reduced pulmonary perfusion pressure and inhibited the pressor response to PGF2 alpha and U46619. Furosemide failed to alter inactivation of PGE2 on pulmonary lobe transit. We conclude that: 1) the vasodilatory activity of furosemide is mediated by increased production and not decreased metabolism of an endogenous cyclooxygenase product; 2) the effect of prostacyclin on vascular reactivity is similar to that of furosemide; and 3) local formation of prostacyclin by vascular tissue most likely mediates the vascular activity of furosemide.

Effects of gonadotrophin-releasing hormone and prostaglandin F-2 alpha on corpus luteum function and timing of the subsequent ovulation in the mare

Standard bred mares that were cycling normally were treated beginning on Days 9 or 10 of the oestrous cycle with repeated pulses of GnRH (20 micrograms/h) and/or a single injection of prostaglandin (PG)F-2 alpha (alfaprostol, 3 mg), and were subsequently bled and palpated daily until the next ovulation. GnRH treatment increased serum concentrations of LH and progesterone at 4 days after the start of treatment compared to controls. The combination of PGF-2 alpha + GnRH treatment resulted in an immediate decline in serum progesterone values, and subsequently decreased the interval to next ovulation by 4.5 days compared to controls. Mean serum concentrations of FSH were not different among treatment groups 4 days after the start of treatment, and there was a consistent trend among all treatment groups for decreasing concentrations of FSH within the 6 days before ovulation. We conclude that, under our experimental conditions, pulsatile administration of GnRH provides a short-term luteotrophic stimulus, probably by the elevation in serum LH, but that this stimulus cannot indefinitely prevent the luteolytic effects of exogenously administered PGF-2 alpha. Although GnRH treatment combined with PGF-2 alpha injection hastened the impending ovulation, this regimen was no more effective than PGF-2 alpha treatment alone.

[Changes in the activity of the oxidative and hydrolytic enzymes of the animal cerebral cortex in the early periods after gamma irradiation and the use of meksamine and the synthetic analog of prostaglandin F2 alpha-estrofan]

In experiments with (CBA x C57B1/6)F1 mice it was shown that LDH activity moderately increased 5 min after exposure of the head to 200 Gy gamma radiation. After 60 min, there was a 24.4 per cent decrease in alkaline phosphatase activity and a 24.3 per cent increase in SDG activity. Injected prior to irradiation meksamine precluded the postirradiation increase in SDH and alleviated the postirradiation decrease in alkaline phosphatase.

Role of pressor prostanoids in rats with angiotensin II-salt-induced hypertension

This study was designed to assess the contribution of thromboxane A2 to high blood pressure in rats with angiotensin II (Ang II)-salt hypertension. Hypertension was induced in rats drinking 0.15 M NaCl by infusion of Ang II (125 ng/min i.p.) for 12 days. Relative to values in water-drinking rats without Ang II infusion, Ang II-salt hypertensive rats exhibited augmentation (p less than 0.05) of blood pressure (from 129 +/- 3 to 217 +/- 12 mm Hg), urinary thromboxane B2 excretion (from 5.4 +/- 0.9 to 25.4 +/- 2.1 ng/day), and thromboxane B2 release from renal cortex slices (from 71.3 +/- 6.7 to 121.1 +/- 14.4 pg/mg) and aortic rings (from 28.8 +/- 2.9 to 115.8 +/- 12.8 pg/mg). Treatment with an inhibitor of thromboxane A2 synthetase, UK 38485, had no effect on blood pressure in normotensive and Ang II-salt hypertensive rats. Treatment with a thromboxane A2 receptor blocker, SQ 29548, decreased blood pressure in Ang II-salt hypertensive rats from 191 +/- 9 to 152 +/- 9 mm Hg after 3 hours, but it had no effect on blood pressure in normotensive rats. Since SQ 29548 interfered with the pressor effects of the prostaglandin endoperoxide analogue U-46619, prostaglandin F2 alpha, and 9 alpha,11 beta-prostaglandin F2, we suggest that the SQ 29548-induced blood pressure reduction in Ang II-salt hypertensive rats is the manifestation of blockade of the vascular actions of one or more endogenous prostanoids including thromboxane A2 and prostaglandin endoperoxides. If so, pressor prostanoids may be contributory factors in the pathogenesis of severe Ang II-salt hypertension in rats.

Prostaglandin D2, a cerebral sleep-inducing substance in monkeys

The sleep-inducing effect of prostaglandin D2 (PGD2) was studied in five conscious male rhesus monkeys (Macaca mulatta) maintained in a 12-hr light/dark cycle. PGD2 was infused into the lateral or the third ventricle of the cerebrum slowly and continuously for 6 hr in the light period. Infusion of PGD2 into the lateral ventricle at 15-2250 pmol/min induced natural sleep as identified by electroencephalogram, electromyogram, electrooculogram, body temperature, heart rate, and animal behavior. Although sensitivity to PGD2 was slightly different among individual animals, the amount of total sleep time increased maximally up to 3- to 4-fold over the control level. PGD2 infused into the third ventricle induced effects similar to those observed for the lateral ventricular route, but infusion into the third ventricle was about 1000 times more effective than infusion into the lateral ventricle. In three monkeys, PGD2 increased the amount of sleep in a dose-dependent manner. Bell-shaped dose-response curves were observed for the other two monkeys. Infusion of prostaglandin E2 or F2 alpha into the lateral ventricle caused sedation but slightly reduced the amount of slow-wave sleep and produced increases in heart rate and body temperature. These findings suggest that endogenous PGD2 may be involved in the regulation of sleep by acting on the brain structures surrounding the third ventricle in the rhesus monkey.

Regional differences in the mechanical properties of rabbit airway smooth muscle

1. In studies of rabbit airway smooth muscle, differences in mechanical responses to acetylcholine, histamine and high K+ in intact muscles, and in Ca2+ sensitivity in skinned muscles, have been examined in tissue taken from 5 different regions of the airway. Interactions between prostaglandin F2 alpha and epithio-thromboxane A2 and the above spasmogenic agencies were also studied. 2. Mechanical responses to histamine (10 microM) and to 128 mM K+ were smallest in trachea and were largest in 3rd and 4th order bronchi. In all regions, spasm evoked by 10 microM acetylcholine was greater than that evoked by 10 microM histamine or 128 mM K+. 3. In the third and fourth branches of the rabbit right middle bronchus, contractions evoked by 10 microM acetylcholine, 10 microM histamine and 128 mM K+ showed similar amplitudes of phasic response. In Ca2+-free solution containing 2 mM EGTA, the phasic components of the acetylcholine- or histamine-induced contraction remained unchanged in comparison with that observed in Krebs solution, but the phasic and tonic components of the K+-induced contraction and the tonic changes induced by acetylcholine and histamine were abolished. 4. Two subtypes of the histamine receptor, excitatory H1- and inhibitory H2- receptors were detected on the bronchial smooth muscle. The H1-induced contraction was mediated by release of stored Ca2+ together with activation of Ca2+ influx relatively insensitive to Ca2+ antagonists. 5. The -log(EC50) values for acetylcholine and histamine (in the presence of cimetidine and atropine) were 6.11 +/- 0.11 and 5.33 +/- 0.08, respectively, in the third branch of right middle bronchus. These values were similar to those observed for trachea. 6. Prostaglandin F2. (10 microM) and 9,11-epithio-11,12-methano-thromboxane A2 (0.1 microM) neither provoked nor enhanced the contractions evoked by any stimulants. 7. No difference was observed between the Ca2+ sensitivity of chemically skinned muscle from the trachea and that of muscle from the third branch of the right middle bronchus. 8. Regional differences in the response to histamine and acetylcholine observed in airway smooth muscles are discussed and it is concluded that these may be due to differences in receptor numbers.

Potassium-induced release of endothelium-derived relaxing factor from canine femoral arteries

Experiments were designed in a bioassay system to analyze the effect of elevated (from 5.9 mM to 7.5-45.9 mM) extracellular K+ concentration on the release of endothelium-derived relaxing factor. Segments of canine femoral artery with endothelium (donor segment) were mounted in an organ bath and perfused with modified Krebs-Ringer bicarbonate solution; the effluent from the donor segment was used to superfuse a canine coronary artery ring without endothelium (bioassay tissue). Elevation of perfusate K+ concentration by 1.6-15 mM by intraluminal infusion of potassium chloride upstream of the donor segment evoked further contractions of bioassay rings contracted with prostaglandin F2 alpha. In contrast, the bioassay rings progressively relaxed when increasing concentrations of potassium chloride (10-40 mM) were added extraluminally to the organ bath where the perfused segment was mounted. Extraluminal application of phenylephrine or prostaglandin F2 alpha did not evoke relaxations in the bioassay ring. Removal of the endothelium from the donor segment or selective exposure of the segment (but not the bioassay ring) to Ca2+-deficient solution prevented the K+-induced relaxations. Treatment of the donor segment and the bioassay ring with inhibitors of known endogenous vasoactive substances (acetylcholine, norepinephrine, adenine nucleotides, and prostanoids) had no significant effect on the relaxation of the bioassay ring evoked by extraluminal application of potassium chloride. Simultaneous measurements of changes in isometric force in the donor segment and bioassay ring revealed that extraluminal elevation of K+ concentration relaxed the segments as well and that the relaxations could not be prevented by simultaneous intraluminal infusion of potassium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma luteinizing hormone and progesterone concentrations in goats with estrous cycles of normal or short duration after prostaglandin F2 alpha administration during diestrus or pregnancy

Plasma luteinizing hormone (LH) and progesterone concentrations were compared in does experiencing short-duration estrous cycles and in does with estrous cycles of normal duration. The short-duration estrous cycles were observed immediately after induction of abortion in pregnant does by use of prostaglandin (PG) F2 alpha. Intramuscular administration of 5 mg of PGF2 alpha was accomplished in 8 does that were 52 to 63 days into gestation and in 9 cycling does at 7 to 10 days after estrus. In both groups, the mean plasma concentration of progesterone decreased from a luteal phase concentration immediately before to less than 1 ng/ml by 24 hours after PGF2 alpha administration. Of the 8 does that aborted, 6 experienced short-duration estrous cycles, and 4 of these 6 had an LH surge during the time of blood sample collection. The mean time from PGF2 alpha administration to the LH surge was significantly (P less than 0.05) longer in does with short-duration estrous cycles (71 hours) than that in does with estrous cycles of normal duration (58 hours). The mean area under the LH concentration curve was significantly (P less than 0.005) less for does with short-duration estrous cycles. Short-duration estrous cycles were associated with delayed preovulatory LH surges of reduced magnitude.

Prostaglandin D2 reduces intraocular pressure

When PGD2 was topically applied to the rabbit eye a reduction of intraocular pressure (IOP) was observed within 30 min. The IOP reduction lasted throughout the observation period of 7 hours. No increase of IOP was observed during the period. The effect of PGD2 was dose-dependent (0.4 microgram to 250 micrograms), and the minimum effective dose was estimated to be 2.0 micrograms. The application of PGD2 did not affect the pupil diameter. No sign of inflammatory response was observed by PGD2 application, that is, no hyperaemia, no flare, no irritation, and no increase of protein content in the aqueous humour. These results suggest that PGD2 or its analogues may be useful for treating glaucoma.

Heterogeneous vasomotor responses of anatomically distinct feline cerebral arteries

1. The vasomotor reactivity to a number of neurotransmitters and blood-borne substances was evaluated in several anatomically distinct arteries of the cat cerebral circulation. Few regional differences were observed in their vasoconstrictor responses to noradrenaline, dopamine, 5-hydroxytryptamine and prostaglandin F2 alpha. Only the anterior cerebral artery reacted strongly to all vasoconstrictor agents. 2. Adenosine, acetylcholine and histamine induced pronounced relaxation in the vast majority of the major cerebral arteries. The relaxation elicited by adenosine showed a slight degree of heterogeneity between the arteries and the overall response accounted for 81 +/- 6% of the pharmacologically-induced tone. On the other hand, the dilatation induced by acetylcholine and histamine varied as a function of the anatomical localization of the cerebral arteries. The acetylcholine-induced vasodilatation was significantly more pronounced in the middle cerebral, anterior communicating and anterior cerebellar arteries, with respective responses of 72, 66 and 83% of the induced tone as compared to 43% in the other vessels. However, all arteries were equally sensitive to acetylcholine with an overall mean pD2 value of 7.47 +/- 0.06. The most heterogeneous results were obtained with histamine and applied both to the magnitude of the maximal response and the sensitivity of the various arteries to this amine. The intensity of the relaxation varied from 20% (anterior communicating artery) to 118% (posterior cerebellar artery). 3. Among the neuropeptides studied, substance P and bradykinin were considerably less potent than vasoactive intestinal peptide on all the cerebral arteries. The least responsive vessel to bradykinin was the anterior cerebral artery with a maximal response of 22 +/- 5% of the induced-tone and a pD2 value of 7.56 +/- 0.24. All vessels responded weakly to substance P and those from the vertebrobasilar circulation were significantly less sensitive to this neuropeptide with pD2 values around 8.07 as compared to 9.82 in the more rostral arteries. Although all vessels were equally sensitive to vasoactive intestinal peptide, the dilator responses were significantly less pronounced in the middle cerebral and basilar arteries (maximal response of 86 +/- 5% and 69 +/- 6% of the induced-tone, respectively, as compared to 110 +/- 9% in the other vessels). 4. The vertebrobasilar arteries were as reactive, if not more reactive, to vasoconstrictors than the vessels originating from the carotid circulation. In contrast, the dilator responses were less marked in most caudal arteries. Such dichotomies may be important in the regulation of local cerebral blood flow. 5. The results emphasize the considerable heterogeneity in the vasomotor responses to a given substance among the various cerebral arteries. Further, they suggest the presence of multiple receptor populations which mediate opposite effects and which are distributed in different proportions among the cephalic arteries.

Intracellular mechanisms of contraction in the hypertensive and normotensive rat aortas

The roles of intracellular mechanisms of contraction were compared in aortas from genetically hypertensive and normotensive rats by investigating the contractile activities of prostaglandin F2 alpha (PGF2 alpha) and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in the absence of extracellular calcium. PGF2 alpha induced a greater amount of tension in aortic strips from hypertensive than normotensive rats. Furthermore, in hypertensive but not normotensive rat aortas, PGF2 alpha- and TPA-induced contractions were additive and were capable of sustaining a near maximum degree of muscle activation. Therefore, the intracellular contractile mechanisms in hypertensive vascular tissue may differ from those in normotensive tissue.

Responsiveness of bovine corpora lutea to prostaglandin F2 alpha: comparison of corpora lutea anticipated to have short or normal lifespans

The objective of this study was to determine if corpora lutea anticipated to have short lifespans were more responsive to the luteolytic action of prostaglandin F2 alpha (PGF2 alpha) than corpora lutea anticipated to have normal lifespans. Sixteen cows were allotted randomly to a hysterectomized-control (HC) or hysterectomized-progestogen (norgestomet) implant (HN) group. To verify that progestogen treatment of postpartum cows prior to induction of ovulation with gonadotropin-releasing hormone (GnRH) results in an increased number of cows exhibiting normal-length luteal phases, 21 additional cows were allotted randomly to a uterine intact-control (IC) or a uterine intact-progestogen implant (IN) group. Cows allotted to the HN and IN groups received norgestomet ear implants for 9 d beginning 17 to 21 d postcalving. All cows were injected (i.m.) with 100 micrograms GnRH 28 to 32 d postcalving (48 h after implant removal in the HN and IN groups) to induce ovulation. Two or 3 d after GnRH injection (d 0), cows in the HC (n = 8) and HN (n = 8) groups were hysterectomized to remove the major endogenous source of PGF2 alpha, and on d 7 cows were injected (i.m.) with 10 mg PGF2 alpha to assess luteal sensitivity. The proportion of corpora lutea having normal lifespans was greater (P less than .1) for the IN than for the IC group. In HC and HN groups, concentration of progesterone (P) increased similarly from d 0 to 6. Injection of PGF2 alpha in HC and HN groups on d 7 decreased (P less than .01) concentration of P approximately 50% by 6 h after injection (similar for both groups). Complete luteolysis was induced by PGF2 alpha in none of eight and two of eight cows in the HC and HN groups, respectively. In remaining cows (HC and HN groups) concentration of P increased (P less than .01; similar for HC and HN groups) beginning 24 h after PGF2 alpha and remained elevated through d 30 to 34 (end of experimental-period). In summary, corpora lutea anticipated to be short-lived were not more responsive to PGF2 alpha than corpora lutea anticipated to have normal lifespans.

Gestational changes in the utilization of intracellularly stored calcium in the myometrium of guinea-pigs

1. The ability of oxytocin and prostaglandin F2 alpha (PGF) to induce contraction in guinea-pig myometrium in calcium-free solution was studied in an attempt to assess the extent to which intracellular calcium stores could be released by these two agonists. Both longitudinal and circular muscle layers were studied separately and the effects of gestational age were also examined. 2. In longitudinal strips, the responses to oxytocin and PGF in the absence of external calcium decreased progressively throughout gestation. Responses of circular strips to both agonists were unchanged throughout pregnancy, until day 64, when no response to PGF could be elicited. 3. Pre-treatment with high potassium (and normal calcium) increased the responses to the agonists in calcium-free medium while pre-treatment with beta-adrenoceptor agonists had no effect on responses to oxytocin or PGF. 4. Responses to both agonists decreased with time in calcium-free solution suggesting a loss of calcium from stores with a half-time of 3 min. The rate of the decline in the responses was the same in both muscle layers and did not change with gestational age. 5. In the presence of lanthanum contractions evoked by oxytocin, but not PGF, were augmented 2-3-fold. This potentiation of the response to oxytocin occurred in both muscle layers and throughout gestation. 6. Each agonist evoked only one response in calcium-free solution containing EGTA. The response to PGF in longitudinal strips following a challenge with oxytocin was reduced, compared with the response to PGF when applied first while the response to oxytocin in these strips was unchanged following exposure to PGF. In circular strips neither oxytocin- nor PGF-induced contractions were altered following prior exposure to the other agonist. 7. It is concluded that oxytocin and PGF operate via two distinct mechanisms to release intracellularly stored calcium in both longitudinal and circular components of the guinea-pig myometrium and a hypothesis to explain the results is presented.