Regional differences in the prostanoid receptors mediating prostaglandin F2 alpha-induced contractions of cat isolated arteries

Involvement of endothelial cyclo-oxygenase metabolites in noradrenaline-induced contraction of rat coronary artery

1. Noradrenaline (NA; 0.3 micromol/L) caused a contraction of the rat coronary artery that markedly increased in the presence of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME; 100 micromol/L) and arachidonic acid (1 micromol/L; P < 0.05). 2. The present experiments attempted to elucidate the endothelium dependency of the contraction and to pharmacologically characterize the factors involved in the contraction induced by NA (0.3 micromol/L) in the presence of L-NAME and arachidonic acid in ring preparations of the rat coronary artery. 3. The NA (0.3 micromol/L)-induced contraction was attenuated by a chemical remover of the endothelium (saponin at concentrations of 0.1 and 0.4 mg/mL) in a concentration-dependent manner (P < 0.05). 4. The cyclo-oxygenase (COX)-1 inhibitor flurbiprofen (0.01-1 micromol/L) and the COX-2 inhibitor nimesulide (0.01-1 micromol/L) attenuated the NA-induced contraction in a concentration-dependent manner and the inhibitory effect of flurbiprofen was significantly more potent than that of nimesulide (P < 0.05). The 5-lipoxigenase inhibitor ZM-230487 (1 micromol/L) did not affect the NA-induced contraction. 5. The thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (30 micromol/L) and the TXA2 antagonist S-1452 (0.1-10 micromol/L) did not attenuate the NA-induced contraction. 6. These results indicate that the contraction induced by NA in the rat coronary artery in the presence of L-NAME and arachidonic acid is endothelium dependent and is due to endothelial COX metabolites of arachidonic acid.

Indomethacin depresses prostaglandin F2 alpha-induced contraction in guinea-pig uterine artery with both intact and denuded endoth

The purpose of this study was to explore whether cyclooxygenase products derived from endothelium or vascular muscle participate in the response of guinea-pig uterine arterial rings to prostaglandin F2 alpha (PGF2 alpha). Contraction to PGF2 alpha (0.1-30 microM) occurred with and without endothelium at similar potency and efficacy (pEC50 (-log EC50) values respectively 5.87 +/- 0.06 and 5.97 +/- 0.07; maximal response respectively 78.1 +/- 1.3% and 76.9 +/- 1.5% of contraction induced by 126 mM KCl). Indomethacin (3-30 microM) suppressed the maximum response to PGF2 alpha and induced a rightward shift of concentration-response curves, regardless of the presence of endothelium. pIC50 values for indomethacin were 4.67 and 4.74 for vessels with and without endothelium, respectively. In contrast, the thromboxane synthesis inhibitor OKY-046 (10 and 100 microM) did not affect the response to PGF2 alpha. We conclude that the PGF2 alpha-induced contraction in guinea-pig uterine artery is mediated, at least in part, through constrictor non-thromboxane prostanoid(s) of vascular muscle origin.

Responses to mechanical stimuli of isolated basilar and femoral arteries of the Rhesus monkey are different

The present study aimed to determine regional differences in diameter response to mechanical stimuli such as flow (shear stress) and transmural pressure (myogenic response) of the isolated basilar artery and femoral artery from Rhesus monkeys. Whether or not spontaneous tone developed, a transmural pressure-diameter relation was determined after the equilibration period. Vessels were then constricted with a submaximal dose of prostaglandin-F(2 alpha) (PGF(2 alpha); 1.23-2 mu M) and a flow-diameter relation (0-2,000 mu l/min) and a pressure-diameter (15-125 cm H(2)O) relation were determined. Endothelium function was tested with the calcium ionophore A-23187 (1.0 mu M). The vessels were then maximally dilated (papaverine, 100 mu M) and a passive pressure-diameter relation was determined. The responses of the basilar and the femoral arteries were markedly different. The basilar artery developed spontaneous tone, while the femoral artery did not. The basilar artery showed flow-induced constriction (P = 0.024), while the femoral artery dilated when flow was increased (P = 0.0005). The myogenic index of the two arteries during treatment with PGF(2 alpha) was not different (P = 0.49) and the strength of the myogenic response was such that the diameter of both arteries stayed constant over the pressure range studied. We conclude that the responses to mechanical stimuli of the basilar artery and the femoral artery of the Rhesus monkey are markedly different.

Potentiation of norepinephrine-induced contraction by primary prostaglandin receptor activation in rat aorta

This study investigates the role of primary prostaglandin receptor activation in the modulation of agonist-induced vascular smooth muscle contraction. Prostaglandin F2 alpha induced a concentration-dependent contraction of the rat aorta that was nearly abolished by the thromboxane A2 receptor antagonist, SQ29548. Prostaglandin F2 alpha in the presence of SQ29548 induced leftward shifts of the norepinephrine and KCl concentration-response curves. Nifedipine abolished the leftward shift of the norepinephrine concentration-response curve observed in the presence of prostaglandin F2 alpha and SQ29548. These results suggest that a function of primary prostaglandin receptor activation may be to potentiate agonist-induced contraction. The potentiation is dependent upon the opening of dihydropyridine-sensitive Ca2+ channels.

Vasoconstrictor reaction to prostaglandins E1 and E2 in the isolated rat hindlimb mediated through serotonin release

The vasoconstrictor effects of prostaglandins E (PGEs) were studied in the isolated perfused hindlimbs of the rat. Doses of PGE1 in the range of 0.01-10 micrograms caused dose-dependent increases in perfusion pressure with rapid development of tachyphylaxis. The pressure increases were inversely temperature-dependent, being 4.8 +/- 1.2 mm Hg at 37 degrees C and 22.2 +/- 1.8 mm Hg at 27 degrees C. The vasoconstriction was limited to PGE1 and PGE2. Other prostaglandins tested, PGF2 alpha, PGD2, PGA1, 7-oxo-PGI2 and arachidonic acid, were without any effect at 27 degrees C. Increased serotonin concentrations were found in the effluent after the administration of 1 microgram of PGE1. The pressor response to PGE1 was blocked by 5-HT2 antagonists, ketanserin (2 micrograms) and naftidrofuryl (100 micrograms), while the alpha-adrenoceptor antagonist phentolamine (6.7 micrograms) was without effect. Rapid tachyphylaxis of the development of vasoconstriction was observed after the repeated administration of PGE1 and PGE2. PGE1 (1 microgram) induced desensitization with more than 60 min duration. All the findings suggest that serotonin was liberated in the rat hindlimbs by PGEs.

Regional vascular responses to thromboxane A2 analogue and their blockade with vapiprost, a selective thromboxane receptor blocking drug, in anesthetized dogs

Regional vascular responses to the thromboxane A2 analogue U46619 and effects of the selective thromboxane receptor blocking drug vapiprost on these responses were examined in anesthetized dogs. Hemodynamic responses to U46619 (0.5 micrograms/kg into the left atrium), norepinephrine (NE, 0.3 microgram/kg, i.v.) and angiotensin II (AII, 30 or 60 ng/kg, i.v.) were periodically tested before and after administration of vapiprost (10, 30 or 100 micrograms/kg, i.v.) or its vehicle. In the absence of vapiprost, U46619 increased total peripheral (TPR), vertebral (VR), coronary (CR) and renal (RR) vascular resistance by 60.1 +/- 4.7%, 33.6 +/- 4.9%, 15.3 +/- 1.3% and 120.8 +/- 17.4%, respectively, indicating that vasoconstrictor responses to U46619 were most prominent in the renal vascular bed as compared to those in the vertebral or coronary vasculatures. Vapiprost as well as the vehicle did not affect the base-line hemodynamics. However, vapiprost apparently inhibited the U46619-induced vasoconstriction in all measured vascular beds in a dose-related manner without attenuating vasoconstrictor responses to NE compared to the inhibitions of VR and CR. These results demonstrate that there was a regional difference both in the vasoconstrictor responses to U46619 and in the blocking effects of vapiprost, and indicate that vapiprost is a potent and selective antagonist for thromboxane receptors in vivo.