Stimulation of cAMP formation by prostaglandin D2 in primary cultures of bovine adrenal medullary cells: identification of the responsive population as fibroblasts

In primary cultures of bovine adrenal medulla, chromaffin cells responded to prostaglandin (PG) E2 by stimulating phosphoinositide metabolism (Yokohama et al. (1988) J. Biol. Chem. 263, 1119-1122). In contrast, nonchromaffin cells were found to respond to PGD2 by elevating their intracellular cAMP level. The formation of cAMP was detected at as low as 0.1 nM PGD2 and increased more than 100-fold over the basal level at 0.1 microM, and the response was specific for PGD2 (greater than PGE1 greater than PGE2 greater than PGF2 alpha = PGI2). The magnitude of cAMP formation and its specificity to PGD2 were retained throughout a 40-day culture period. Based on the inhibitory effect of cis-4-hydroxy-L-proline, an inhibitor of collagen synthesis, on cAMP formation, morphology, and immunoreactivity of cells to anti-collagen type I antiserum, the responsive cells were identified as fibroblasts. These results taken together demonstrate that the adrenal medulla is composed of chromaffin and nonchromaffin cells, which respond to PGE2 and PGD2, respectively, by two different signal transduction pathways. The cAMP formation by PGD2 was also observed in fibroblasts from bovine embryonic trachea among cell lines tested, suggesting that some populations of fibroblasts responsive to PGD2 exist in various tissues and may discriminate the signal from that of PGE1 or PGE2.     

On the multiplicity of platelet prostaglandin receptors. II. The use of N-0164 for distinguishing the loci of action for PGI2, PGD2, PGE2 and hydantoin analogs

The omega-chain variant analogs of prostacyclin (PGI2) and PGD2 in which n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI2, but converts PGD2 to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD2 by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD2, cyclohexyl-PGD2, and BW-245C; with essentially no effect on PGI2, cyclohexyl-PGI2 and PGE2 at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre, but supports the view that the anti-aggregatory effect of high doses of PGE2 (EC50=50 microM) is mediated by the PGI2 receptor. The hydantoin acts at the platelet PGD2 receptor.     

Characterization of prostaglandin (PG)-binding sites expressed on human basophils. Evidence for a prostaglandin E1, I2, and a D2 receptor.

Recent data suggest that prostaglandins (PGs) are involved in the regulation of basophil activation. The aim of this study was to characterize the basophil PG-binding sites by means of radioreceptor assays using 3H-labeled PGs. Scatchard analysis for pure (greater than 95%) chronic myeloid leukemia (CML) basophils revealed two classes of PGE1-binding sites differing in their affinity for the natural ligand (Bmax1 = 217 +/- 65 fmol/10(8) cells; Kd1 = 0.5 +/- 0.2 nM; Bmax2 = 2462 +/- 381 fmol/10(8) cells; Kd2 = 47 +/- 20 nM; IC50 = PGE1 less than PGI2 less than PGD2 less than PGE2 less than PGF2 alpha) as well as two classes of PGI2 (iloprost)-binding sites (Bmax1 = 324 +/- 145 fmol/10(8) cells; Kd1 = 0.5 +/- 0.3 nM; Bmax2 = 2541 +/- 381; Kd2 = 27 +/- 6 nM; IC50 = PGI2 less than PGE1 less than PGD2 less than PGE2 less than PGF2 alpha. In addition, CML basophils exhibited a single class of PGD2-binding sites (Bmax = 378 +/- 98 fmol/10(8) cells; Kd = 13 +/- 4 nM; IC50: PGD2 less than PGI2 less than PGE1 less than PGE2 less than PGF2 alpha). In contrast, we were unable to detect specific saturable PGE2-binding sites. Primary and immortalized (KU812) CML basophils revealed an identical pattern of PG receptor expression. Basophils (KU812) expressed significantly (p less than 0.001) lower number of PGE1 (PGI2)-binding sites (Bmax1: 9% (20%) of control; Bmax2: 36% (50%) of control) when cultured with recombinant interleukin 3 (rhIL-3), a basophil-activating cytokine, whereas rhIL-2 had no effect on PG receptor expression. Functional significance of binding of PGs to basophils was provided by the demonstration of a dose-dependent increase in cellular cAMP upon agonist activation, with PGE1 (ED50 = 1.7 +/- 1.1 nM) and PGI2 (ED50 = 2.8 +/- 2.3 nM) being the most potent compounds. These findings suggest that human basophils express specific receptors for PGE1, PGI2 as well as for PGD2.     

Role of COX-1 and COX-2 on skin PGs biosynthesis by mechanical scratching in mice

We examined the involvement of cyclooxygenase (COX)-1 and COX-2 on mechanical scratching-induced prostaglandins (PGs) production in the skin of mice. The dorsal regions of mice were scratched using a stainless brush. COXs expressions in the skin were analyzed using real-time PCR and Western blotting. The effect of acetylsalicylic acid (ASA) on the ability of PGs production were determined based on skin PGs level induced by arachidonic acid (AA) application. Mechanical scratching increased PGD2, PGE2, PGI2 and PGF(2 alpha). COX-1 was constitutively expressed and COX-2 expression was enhanced by scratching. Intravenous administration of ASA inhibited PGs biosynthesis in the normal skin. PGs levels of the skin 6h after ASA administration (ASA 6 h) were almost equal to those of the skin 10 min after ASA administration (ASA 10 min). In the scratched skin, AA-induced PGE2 and PGI2 of ASA 6 h were significantly higher than those of ASA 10 min. The skin PGD2 and PGF(2 alpha) of ASA 10 min were almost same to those of ASA 6 h. In the normal skin of COX-1-deficient mice, skin PGD2 level was lower than that of wild-type mice, although PGE2, PGI2 and PGF(2 alpha) levels were almost equal to those of wild type. In the scratched skin of COX-1-deficient mice, PGD2, PGE2, PGI2 and PGF(2 alpha) levels were lower than those of wild-type mice. These results suggested that cutaneous PGD2 could be mainly produced by COX-1, and PGE2 and PGI2 could be produced by COX-1 and COX-2, respectively, in mice.     

Intraluteal infusions of prostaglandins of the E, D, I, and A series prevent PGF2 alpha-induced, but not spontaneous, luteal regression in rhesus monkeys

A luteotropic role for prostaglandins (PGs) during the luteal phase of the menstrual cycle of rhesus monkeys was suggested by the observation that intraluteal infusion of a PG synthesis inhibitor caused premature luteolysis. This study was designed to identify PGs that promote luteal function in primates. First, the effects of various PGs on progesterone (P) production by macaque luteal cells were examined in vitro. Collagenase-dispersed luteal cells from midluteal phase of the menstrual cycle (Day 6-7 after the estimated surge of LH, n = 3) were incubated with 0-5,000 ng/ml PGE2, PGD, 6 beta PGI1 (a stable analogue of PGI2), PGA2, or PGF2 alpha alone or with hCG (100 ng/ml). PGE2, PGD2, and 6 beta PGI1 alone stimulated (p less than 0.05) P production to a similar extent (2- to 3-fold over basal) as hCG alone, whereas PGA2 and PGF2 alpha alone had no effect on P production. Stimulation (p less than 0.05) of P synthesis by PGE2, PGD2, and 6 beta PGI1 in combination with hCG was similar to that of hCG alone. Whereas PGA2 inhibited gonadotropin-induced P production (p less than 0.05), that in the presence of PGF2 alpha plus hCG tended (p = 0.05) to remain elevated. Second, the effects of various PGs on P production during chronic infusion into the CL were studied in vivo. Saline with or without 0.1% BSA (n = 12), PGE2 (300 ng/h; n = 4), PGD2 (300 ng/h; n = 4), 6 beta PGI1 (500 ng/h; n = 3), PGA2 (300 ng/h; n = 4), or PGF2 alpha (10 ng/h; n = 8) was infused via osmotic minipump beginning at midluteal phase (Days 5-8 after the estimated LH surge) until menses. In addition, the same dose of PGE, PGD, PGI, or PGA was infused in combination with PGF2 alpha (n = 3-4/group) for 7 days. P levels over 5 days preceding treatment were not different among groups. In 5 of 8 monkeys receiving PGF2 alpha alone, P declined to less than 0.5 ng/ml within 72 h after initiation of infusion and was lower (p less than 0.05) than controls. The length of the luteal phase in PGF2 alpha-infused monkeys was shortened (12.3 +/- 0.9 days; mean +/- SEM, n = 8; p less than 0.05) compared to controls (15.8 +/- 0.5). Intraluteal infusion of PGE, PGD, PGI, or PGA alone did not affect patterns of circulating P or luteal phase length.(ABSTRACT TRUNCATED AT 400 WORDS)     

The combined use of isolated strips of guinea-pig lung parenchyma and ileum as a sensitive and selective bioassay for leukotriene B4

The biological effects of leukotriene (LT)B4 were compared, on a molar basis, with those of LTC4, LTD4, LTE4, 5-hydroxyeicosatetraenoic acid (5-HETE), PGD2, PGE1, PGE2, PGF2 alpha, PGI2, 6-oxo-PGF1 alpha, bradykinin (BK) and angiotensin II (Ang II) on isolated strips of guinea-pig lung parenchyma (GPP) and ileum smooth muscle (GPISM) superfused in series. LTB4 was similar to LTC4 and LTD4 on GPP, in relation to potency and contractions induced, but differed from LTE4 in being ten times more active and causing contractions of a much shorter duration of action on this tissue. However, unlike the other LTs, LTB4 produced contractions which were resistant to FPL 55712 (1.9 microM) and, when given repeatedly, caused tachyphylaxis in GPP. LTB4 was considerably more active on GPP than the other substances investigated. Further, PGD2, PGF2 alpha and PGI2 contracted GPP, the order of potency being PGD2 greater than PGF2 alpha approximately equal to PGI2, whereas PGE1 and PGE2 relaxed this tissue. In contrast to all other agonists tested which contracted GPISM, LTD4 displaying the highest activity, LTB4 was inactive on this tissue. 5-HETE and 6-oxo-PGF1 alpha were inactive on both GPP and GPISM. On the basis of differential effects of LTB4 on GPP and GPISM, this assay represents a simple and selective means to distinguish LTB4-like materials from other naturally-occurring substances likely to be generated in inflammatory fluids.     

On the multiplicity of platelet prostaglandin receptors. I. Evaluation of competitive antagonism by aggregometry

Methods for the evaluation of competitive interactions at receptors associated with platelet activation and inhibition using aggregometry of human PRP have been developed. The evidence supports the suggestion that PGE1 and PGI2 share a common receptor for inhibition of platelet reactivity, but only a portion (if any) of the aggregation stimulation associated with PGE2 is the result of PGE2 binding (without efficacy) to this receptor. PGE2 (at .3-20 microM) is an effective antagonist of PGE1, PGI2, and PGD2 producing a shift of about one order of magnitude in the IC50-values obtained from complete aggregation inhibition dose response curves. The antagonism of PGD2 inhibition is particularly notable, 80 nM PGE2 levels are detectable. This and other actions of PGE2 indicate another platelet receptor for PGE2. PGE1 acts at both the PGE2 and PGI2 receptor. Other substances showing PGI2-like actions only at high doses (1-30 microM), display additive responses with PGI2 indicative of decreased affinity for the I2/E1 receptor and the absence of PGE2-like aggregation stimulation activity. PGI2 methyl ester has intrinsic inhibitory action not associated with in situ ester hydrolysis. The methyl ester is dissaggregatory showing particular specificity for inhibition of release and second wave aggregation.     

Stimulatory and inhibitory effects of prostaglandins on the gonadotropin-sensitive adenylate cyclase in the monkey corpus luteum

Detailed analysis of the action of prostaglandins (PGs) on the corpus luteum in primate species is very limited. In this study we examined the response of the adenylate cyclase system to PGs in homogenates prepared from the corpus luteum of rhesus monkeys at midluteal phase of the menstrual cycle. The conversion of [alpha 32p] ATP to [32p] cyclic AMP (cAMP) was assessed in the absence (control activity; 50 microM GTP) and presence of various concentrations of seven PGs and arachidonic acid, either alone or in combination with 250 nM hCG. Cyclic AMP production increased up to three-fold in the presence of PGD2, PGE2, PGI2 or PGF2 alpha; however PGA2, PGB2, 13, 14-dihydro-15-keto PGE2 and arachidonic acid alone did not alter cAMP levels. In dose-response studies, adenylate cyclase was 10 and 100-fold more sensitive to PGD2 (Vmax at 1 X 10(-5) M) than to PGE2 or to PGI2 and PGF2 alpha, respectively. Activity in the presence of hCG plus either PGD2, PGE2, PGI2 or PGF2 alpha did not differ from that for hCG (or the PG) alone. In contrast, addition of PGA2 or arachidonate inhibited (p less than 0.05) hCG-stimulated cAMP production by 50 and 100 percent. We conclude that the gonadotropin-sensitive adenylate cyclase of the macaque corpus luteum is also modulated by several PGs. These factors may either mimic (e.g., PGD2, PGE2, PGI2) or suppress (PGA2) gonadotropin-stimulated cAMP production and possibly cAMP-mediated events in luteal cells.     

Hypotensive response to prostacyclin and 6-keto-PGE1 following hepatectomy in the rat

Prostacyclin (PGI2) is metabolized to 6-keto-prostaglandin E1 (6-keto-PGE1) which is more stable yet equipotent to PGI2 in lowering systemic arterial blood pressure in the dog. In this study, partial hepatectomy was performed to determine the role of the liver in the vasodepressor response to both intravenously administered PGI2 and 6-keto-PGE1. The magnitude and the duration of systemic hypotensive responses were measured in hepatectomized and sham-operated male Wistar rats following less than maximal, equidepressor doses of PGI2 (0.3 microgram/kg), 6-keto-PGE1 (1.0 microgram/kg), and also PGE1 (3.0 micrograms/kg) and PGE2 (3.0 micrograms/kg). Hepatectomy did not significantly alter the magnitude of the systemic hypotensive response to any of the prostaglandins tested. This indicates that the liver and hepatic circulation do not contribute significantly to the hypotensive effect of these prostaglandins by alterations of systemic vascular resistance, venous pooling of blood, or the generation of additional vasoactive metabolites as may be expected following administration of these prostaglandins. However, hepatectomy did significantly increase the duration of the hypotensive response to PGI2 and 6-keto-PGE1 but not PGE1 or PGE2. We conclude that in vivo, the liver has a more significant role in PGI2 and 6-keto-PGE1 inactivation than in the inactivation of PGE1 and PGE2 when administered intravenously. These results also support the relatively greater significance of the lung in the inactivation of PGE1 and PGE2 in vivo.     

Cardiovascular effects of prostaglandin I2 and prostaglandin F2 alpha in the unanesthetized bullfrog, Rana catesbeiana

The cardiovascular effects of prostaglandin (PG)I2 and PGF2 alpha were compared in the unanesthetized American bullfrog (Rana catesbeiana). Control mean arterial pressure (MAP) and heart rate (HR) were 25.7 +/- 1.1 mm Hg and 35.1 +/- 1.1 beats/min, respectively. Intravenous injections of PGI2 decreased MAP and increased HR in a dose-dependent fashion over the range of concentrations tested (0.03, 0.3, 3, and 10 micrograms/kg-body weight [bw]. Neither atropine (1 mg/kg-bw) nor verapamil (1 mg/kg-bw) treatment altered the MAP or HR responses to PGI2 (3 micrograms/kg-bw). However, propranolol (5 mg/kg-bw) significantly blunted the hypotensive effects without affecting the increase in HR. Prostaglandin F2 alpha (tested at 0.3, 3, 30, and 100 micrograms/kg-bw) increased both MAP and HR. Mean arterial pressure increased with concentrations greater than 0.3 microgram/kg-bw and reached peak effects at 30 micrograms/kg-bw. Prostaglandin F2 alpha increased HR at doses greater than 0.3 microgram/kg-bw. Neither the pressor nor positive chronotropic effects of PGF2 alpha (30 micrograms/kg-bw) were affected by atropine or propranolol. However, verapamil significantly attenuated the pressor effects without affecting the increase in HR. These results demonstrate that both prostaglandins have qualitatively similar effects on HR, but opposite effects on MAP. Prostaglandin I2 is a hypotensive prostaglandin, while PGF2 alpha is hypertensive. The pressor effects of PGF2 alpha are partially dependent on calcium influx. The positive chronotropic effects of both prostaglandins are independent of the autonomic nervous system, suggesting a different mechanism of action.     

Comparison of the effects of prostacyclin (PGI2), prostaglandin E1 and D2 on platelet aggregation in different species.

The activity of prostacyclin (PGI2), PGE1 or PGD2 as inhibitors of platelet aggregation in plasma from human, dog, rabbit, rat, sheep and horse was investigated. Prostacyclin was the most potent inhibitor in all species. PGD2 was a weak inhibitor in dog, rabbit and rat plasma whereas PGE1 and prostacyclin were highly active. Theophylline or dipyridamole potentiated the inhibition of human platelet aggregation by prostacyclin, PGE1 or PGD2. Compound N-0164 abolished the inhibition by PGD2 of human platelet aggregation but did not inhibit the effects of PGE1 or prostacyclin. The results suggest that prostacyclin and PGE1 act on similar sites on platelets which are distinct from those for PGD2.     

Efficacy of intravenous infusion of prostacyclin (PGI2) or prostaglandin E1 (PGE1) in augmentation of skin flap blood flow and viability in the pig

The dose-response effects of 6-h intravenous infusion of PGI2 (0, 5, 10, 25 or 75 ng/kg/min) or PGE1 (0, 25, 50, 100 or 300 ng/kg/min) on skin hemodynamics and viability were studied in 4 x 10 cm random pattern skin flaps (n = 24) raised on both flanks of the pig. Infusion of PGI2 or PGE1 was started immediately after intravenous injection of a loading dose 30 min before skin flap surgery. PGI2 infusion significantly (P less than 0.05) increased the total skin flap capillary blood flow at the dose of 10 ng/kg/min, compared with the control. However, the distance of blood flow along the skin flap from the pedicle to the distal end, i.e. perfusion distance, was not increased. Consequently, the length and area of skin flap viability was also not significantly increased. The effect of PGI2 infusion on skin blood flow was biphasic. Specifically, higher doses (greater than or equal to 25 ng/kg/min) of intravenous PGI2 infusion produced no beneficial effect on the skin flap capillary blood flow. PGI2 infusion at the dose of 10 or 75 ng/kg/min did not significantly increase plasma renin activities or plasma levels of norepinephrine compared with the control, therefore the biphasic effect of PGI2 on skin flap blood flow was not related to circulating levels of norepinephrine or angiotensin. Intravenous infusion of PGE1 did not produce any therapeutic effect on the skin capillary blood flow in the random pattern skin flaps at all doses tested. At the dose of 300 ng/kg/min, the mean arterial blood pressure was 17% lower (P less than 0.05) than the control, but the skin capillary flow still remained similar to the control. It was concluded that intravenous infusion of PGI2 or PGE1 was not effective in augmentation of distal perfusion or length of skin viability in the porcine random pattern skin flaps. Drug treatment modalities for prevention or treatment of skin flap ischemia is discussed.     

Beta-adrenergic agonist- and prostaglandin-mediated regulation of cAMP levels in Ewing's sarcoma cells in culture

This is the first report demonstrating hormonal control of cAMP levels in Ewing's sarcoma cells. Two classes of hormones, beta-adrenergic agonists and prostaglandins stimulate cAMP production in cultured Ewing's sarcoma cells. The efficacy order for beta-adrenergic agonists is (-)-isoprenaline greater than or equal to (-)-noradrenaline greater than or equal to (-)-adrenaline much greater than (-)-phenylephrine. The stimulatory effect of (-)-noradrenaline is antagonized by beta 1-selective metoprolol and also by beta 2-selective ICI 118,551. The efficacy order for prostaglandins (PG) is PGE1 greater than PGI2 greater than PGE2 much greater than PGF2 alpha; 6-keto PGF1 alpha and PGD2 do not influence cAMP levels in Ewing's sarcoma cells. Cultures pretreated with PGE2 are less responsive to a second challenge with PGE2 but their response to (-)-isoprenaline is unimpaired. Similarly, pretreatment with (-)-isoprenaline induces homologous desensitization to (-)-isoprenaline and has no effect on the PGE2-stimulated increase in cAMP. We conclude that these cells provide an ideal model for the study of the initial steps of beta-adrenergic and prostaglandin action in Ewing's sarcoma.     

Modulation of autonomic neurotransmission by PGD2: comparison with effects of other prostaglandins in anesthetized cats

Experiments with anesthetized cats were done to study possible roles of different prostaglandins (PGs) in modulating sympathetic neuroeffector transmission. We recorded contractions of the nictitating membrane (n.m.), blood flow in the carotid artery, heart rate and blood pressure, both under control conditions and while stimulating the cut cervical sympathetic nerve. Intra-carotid arterial injection (i.a.) of PGD2 depressed sympathetic transmission to the n.m. without depressing the effects of exogenous norepinephrine (NE). In contrast, PGE2 enhanced the effects of nerve transmission or exogenous NE on the stimulated n.m. PGI2 had similar but shorter effects to PGE2. PGF2 alpha or a stable PGH2 analog, contracted the n.m. smooth muscle with no detected effect on nerve transmission. Carotid blood flow was increased by PGD2, PGE2 and PGI2. PGD2 and PGI2 caused bradycardia that could be blocked by atropine. This ability of PGD2 to modulate autonomic nerve activity is of particular interest because of recent reports that nerve tissue synthesizes PGD2.     

The hyperalgesic effects of prostacyclin and prostaglandin E2.

Hyperalgesia induced in rat paws or dog knee joints by prostacyclin (PGI2) and prostaglandin E2 was measured by a modification of the Randall-Selitto method (1) or by the degree of incapacitation (2). In both species PGI2 induced an immediate hyperalgesic effect but the effect of PGE2 had a longer latency. Low doses of PGI2 caused a short lasting effect but PGE2, large doses of PGI2 or successive administration of small doses of PGI2 caused a long lasting effect. It is suggested that prostacyclin mediates rat paw hyperalgesia induced by carrageenin. The long lasting hyperalgesic effect of PGE2 and high doses of PGI2 is possibly an indirect effect caused by stimulation of a sensory nerve sensitising mechanism.     

Prostacyclin production by rat aorta "in vitro" is increased by the combined action of dipyridamole plus pentoxifylline

The present study evaluates the effect of dipyridamole and pentoxifylline, individually and in combination, on PGI2-like production and arachidonic acid metabolism of rat aorta "in vitro". Pentoxifylline 100 microM and dipyridamole 92 and 184 microM increased PGI2-like activity, as measured by the platelet aggregation inhibitory capacity of the aortic ring incubates, by 71%, 46% and 60% respectively; a greater increase in PGI2-like activity was observed with the combination of the drugs than when they were used separately. This effect was observed even at the lowest doses assayed. In fact, dipyridamole 9.2 microM plus pentoxifylline 1 microM increased the PGI2-like activity by 30% while the individual increase was 4.5% and 10.6% respectively. To obtain more information on the effect of the dipyridamole-pentoxifylline combination on arachidonic acid metabolism, arteries were incubated with (1-14C) arachidonic acid, and the 6-keto-PGF1 alpha and PGE2 quantified. Dipyridamole 92 microM plus pentoxifylline 1 and 10 microM increased 6-keto-PGF1 alpha and PGE2 production by about 30% and 48% respectively while the combination with pentoxifylline 100 microM increased the 6-keto-PGF1 alpha 76.5% and the PGE2 50%. The possible biological effect and therapeutic implications of increased PGI2 production by the arteries due to the dipyridamole-pentoxifylline combination remains to be ascertained.     

Pharmacological and cardiovascular properties of a hydantoin derivative, BW 245 C, with high affinity and selectivity for PGD2 receptors

Initial experiments demonstrated that the hydantoin prostaglandin derivative, BW 245 C, has potent anti-aggregatory activity on human platelets which may result from its structural similarity with one of the natural prostaglandins. The aim of the present study was to extend this preliminary pharmacological characterization and to determine which, if any, prostaglandin receptor-type is responsible for mediating the biological activity of BW 245 C. A marked species variation was observed in the anti-aggregatory potency of BW 245 C such that in the human (0.36 X PGE1) it was about one hundred times more effective than in the rat (0.003 X PGE1). The relative potencies of PGI2 (ca. 10 X PGE1) and PGE1 were, however, similar in both species. An intravenous bolus injection of 250 micrograms/kg BW 245 C lowered systolic (-23%) and diastolic (-34%) blood pressure in spontaneously hypertensive rats. In radioligand binding studies it showed a high affinity and selectivity for PGD2 platelet receptors, binding to PGI2 or PGE2 receptors was not detectable. Therefore it is concluded that the platelet and cardiovascular actions of BW 245 C are mediated by PGD2 receptors and this accounts for the observed species variation which is a characteristic of this prostaglandin.     

Arginine vasotocin-induced prostaglandin synthesis in vitro by the reproductive tract of the viviparous lizard Sceloporus jarrovi

Two experiments were performed to determine whether arginine vasotocin (AVT) stimulates synthesis of prostaglandins (PGs) in reptilian oviducts. Homogenized oviducal tissue from female Sceloporus jarrovi in early and late pregnancy were cultured with radiolabeled (14C) prostaglandin precursor, arachidonic acid (AA). In late pregnancy, oviducts exposed to AVT exhibited a greater conversion of AA to PGF2 alpha than did controls, whereas in early pregnancy there was no difference. The conversion of AA to other prostaglandins (PGA2, PGD2, PGE2, PGI2) was not influenced by AVT. The second experiment examined whether endogenous in vitro synthesis of PGF and PGE2 from intact, pregnant oviducts was stimulated by AVT (50 ng/ml; 100 ng/ml). Both doses of AVT induced a similar, significant rise in PGF concentrations within 30 min whereas no significant increase was noted in PGE2 concentrations until 90 min after treatment. Indomethacin pretreatment blocked synthesis of both PGF and PGE2 for 30 min following AVT treatment. These data indicate that AVT induces a highly specific rise in the synthesis of PGF from the oviduct of female S. jarrovi in late pregnancy. Furthermore, the prostaglandin-stimulating effect of AVT in reptiles appears homologous with the effect of oxytocin in mammals and AVT in birds. We hypothesize that this interaction is an evolutionarily conserved relationship found in all amniote vertebrates.     

Interrelationships among prostaglandins, vasopressin and cAMP in renal papillary collecting tubule cells in culture

To determine the influence of prostaglandins on cAMP metabolism in renal papillary collecting tubule (RPCT) cells, intracellular cAMP levels were measured after incubating cells with prostaglandins (PGs) alone or in combination with arginine vasopressin (AVP). PGE1, PGE2 and PGI2, but not PGD2 or PGF2 alpha, increased intracellular cAMP concentrations. At maximal concentrations (10(-5) M) the effects of PGE2 plus PGI2 (or PGE1), but not of PGI2 plus PGE1, were additive suggesting that at least two different PG receptors may be present in RPCT cell populations. Bradykinin treatment of RPCT cells caused an accumulation of intracellular cAMP which was blocked by aspirin and was quantitatively similar to that observed with 10(-5) M PGE2. PGs, when tested at concentrations (e.g. 10(-9) M) which had no independent effect on intracellular cAMP levels, did not inhibit the AVP-induced accumulation of intracellular cAMP in RPCT cells. These results indicate that PGs do not block AVP-induced accumulation of intracellular cAMP in RPCT cells at concentrations of PGs which have been shown to inhibit the hydroosmotic effect of AVP on perfused collecting tubule segments. However, at higher concentrations of PGs (e.g. 10(-5) M), the effects of AVP plus PGE1, PGE2, PGI2 or bradykinin on intracellular cAMP levels were not additive. Thus, under certain conditions, there is an interaction between PGs and AVP at the level of cAMP metabolism in RPCT cells.     

Prostaglandin D2 diminishes transmucosal potential difference in rat colonic mucosa in vitro in contrast to the increasing effect of prostaglandin E1

The effect of Prostaglandin D2 (PGD2) on ion transport was investigated in the rat colon in vitro. Ion transport across the intestinal mucosa was estimated by transmucosal potential difference (PD) and short circuit current (Isc) in the Ussing chamber. PGD2 added to the serosal reservoir induced a sustained reduction in PD and Isc at the concentration of higher than 10(-7)M, producing the maximal decrease at 10(-5)M. PGD2 at 10(-5)M completely blocked the increase in PD elicited by prostaglandin E1 (PGE1), theophylline, dibutyryl cAMP or serotonin. Adenylate cyclase activity was determined in the colonic mucosal homogenates after addition of PGD2 and PGE1. Treatment with PGD2 or PGE1 caused a significant increase in the enzyme activity. Combined treatment with both prostaglandins induced no more increase than that elicited by PGE1 alone. These results suggest that PGD2 has an anti-secretory effect on the rat colon and it may regulate the ion transport process through other mechanism than the modification of cyclic AMP concentration in mucosal cells.