Increased prostacyclin and thromboxane A2 formation in human varicose veins

Increased urinary metabolites of the antiaggregatory vasodilator prostacyclin (PGI2) and the proaggregatory vasoconstrictor thromboxane A2 (TXA2) have been reported in deep vein thrombosis; however, the tissue(s) of origin is uncertain. Because little is known about the formation of PGI2 or TXA2 from its common precursor, prostaglandin (PG) endoperoxide H2 (PGH2), by varicose veins, we determined the formation of 6-keto-PGF1 alpha (the stable metabolite of PGI2), TXB2 (the stable metabolite of TXA2), and PGE2. Segments of normal saphenous vein and varicose vein (nine and six patients, respectively) were incubated with 10 microM [14C]PGH2 for 2 min at 37 degrees C; products were separated by thin-layer chromatography. Surface area and mass of normal and varicose vascular segments were 19.5 +/- 0.8 versus 18.8 +/- 0.6 mm2 and 11.6 +/- 1.4 versus 10.7 +/- 0.7 mg, respectively. Formation of 6-keto-PGF1 alpha and TXB2 by the segments of varicose vein was significantly increased over that of normal vein: 157 +/- 14 versus 243 +/- 17 pmole of 6-keto-PGF1 alpha (P less than 0.005) and 22 +/- 3 versus 35 +/- 5 pmole of TXB2 (P less than 0.01). The formation of PGE2 by segments of varicose vein was not significantly different from that of normal vein (201 +/- 9 vs 219 +/- 11, respectively). Deoxyribonucleic acid (DNA) content of normal and varicose vein was 1.69 +/- 0.12 and 1.51 +/- 0.13 mg per gram of tissue, respectively. The data suggest that the increased PGI2 formation may reflect increased activity or content of PGI2 synthase. The increase in TXA2 formation may reflect increased productivity or an increased presence of residual platelets or microemboli.

Concentration-activity profile of the modulation of cyclooxygenase product formation by reduced glutathione in microsomal fractions from the goat lung

Age-related changes in pulmonary formation of arachidonic acid (AA) metabolites are thought to play an important role in regulating cardiopulmonary function. This study addresses the potential role of reduced glutathione (GSH) in modulating cyclooxygenase product formation in the developing lung. Prostaglandin H2 (PGH2) metabolism was studied in microsomal fractions isolated from the lungs of unventilated fetal, neonatal and adult goats. GSH-dependent PGH2 to PGE2 isomerase activity in microsomal fractions from the perinatal (fetal and neonatal) goat lung was not saturable with respect to GSH and can respond to changes in GSH concentration over the range of 0.01 to 30 mM, which encompasses the full range the intracellular GSH levels reported in the literature. However, in fractions from the adult, a lower rate of PGE2 formation is observed at higher GSH concentrations. In addition, the tissue levels of GSH exhibited developmental stage-related differences with fetal being higher than neonatal or adult. The present observations may have physiologic relevance, in that decreases in pulmonary GSH levels after birth may contribute to decreases in plasma PGE2 levels by decreasing pulmonary PGE2 synthesis, thereby contributing to closure of the ductus arteriosus; conversely, increased GSH levels associated with hyperoxia may contribute to persistence of ductal patency. Formation of 6-keto-PGF1 alpha and of TXB2 (the stable metabolites of prostacyclin and TXA2) was decreased when PGE2 formation was increased by GSH activation of PGE2 isomerase in fractions isolated from all three developmental stages. A similar pattern of product formation was observed when AA was employed as substrate. These data suggest the possibility that changes in GSH concentration may modulate eicosanoid formation in cells that contain GSH-dependent PGE2 isomerase, as well as either or both prostacyclin or thromboxane synthase(s).

Analysis of cardiovascular and pulmonary responses to endothelin-1 and endothelin-3 in the anesthetized cat

Cardiovascular and pulmonary responses to endothelin (ET)-1, ET-3 and neuropeptide Y (NPY) were investigated in the anesthetized cat. ET-1, 0.1 to 1 nmol/kg i.v., decreased or elicited biphasic changes in arterial pressure (AP), whereas ET-3, in the same doses, decreased AP. Both ETs increased cardiac output (CO) and, at the highest doses, a secondary decrease in CO was observed. NPY, 0.3 to 3 nmol/kg i.v., increased AP and at the highest dose decreased CO. All three peptides had inconsistent effects on right ventricular contractile force and increased central venous pressure. ET-1 at lower doses increased heart rate (HR) and, at 1 nmol/kg, caused a biphasic change. ET-3 increased HR, whereas NPY decreased HR. Systemic vascular resistance (SVR) was increased by NPY and decreased by ET-3, whereas ET-1 elicited biphasic changes. ET-1 and ET-3 increased pulmonary arterial pressure, left atrial pressure and caused biphasic changes in pulmonary vascular resistance (PVR). NPY had no significant effect on PAP or PVR. When pulmonary blood flow was maintained constant, ET-1 and ET-3 had only pulmonary vasoconstrictor activity, whereas NPY and the ET analog had no significant effect. The increase in SVR in response to NPY, the decrease in response to ET-3 or the biphasic change in response to ET-1 were not modified by meclofenamate, hexamethonium or propranolol. Increases in HR in response to ET-1 and ET-3 were reduced by the beta receptor and ganglionic blocking agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiographic evidence for cocaine cardiotoxicity in cat

Recent case studies suggest that cocaine overdose may produce life-threatening cardiac arrhythmias. We therefore investigated its effects on the electrocardiogram (leads II and V1) and arterial blood pressure in cats anesthetized with pentobarbital. Cocaine was administered by intravenous infusion over a 2-min interval at 1 mg/kg in 10 cats. In 5 out of 10 cats an additional infusion of 3 mg/kg cocaine was also administered after hemodynamic and electrocardiographic parameters had returned to control values (i.e., within 10 min). During and following infusion of 1 mg/kg cocaine, no significant change in heart rate or systolic or diastolic blood pressure were found, however the QRS duration increased by 38% (from 46 +/- 5 to 64 +/- 12 ms) (p less than 0.01). Evidence for bundle branch block and (or) premature ventricular beats was observed in 9 out of 10 cats after 1 mg/kg cocaine. Infusion of a further 3 mg/kg cocaine in five cats significantly lowered diastolic blood pressure (from 98 +/- 18 to 64 +/- 28 mmHg; 1 mmHg = 133.3 Pa) (p less than 0.01), and further prolonged QRS to 79 +/- 14 ms, a 75% increase from the mean control value (p less than 0.01). In addition, 1st and 2nd degree atrioventricular block, ventricular extrasystoles, and ectopic rhythms (AV junctional or idioventricular) were observed in four out of five cats given 3 mg/kg cocaine. Mean plasma concentrations of cocaine were 1.37 +/- 0.39 micrograms/mL (4.28 +/- 1.22 microM) (n = 5) at the end of a 1 mg/kg infusion and 2.93 +/- 0.43 micrograms/mL (9.16 +/- 1.34 microM) after a 3 mg/kg infusion (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative responses to endothelin 2 and sarafotoxin 6b in systemic vascular bed of cats

Cardiovascular responses to endothelin 2 (ET-2) and sarafotoxin 6b (S6b) were investigated in the cat. ET-2 (0.1-1 nmol/kg iv) decreased or elicited biphasic changes in arterial pressure (AP), whereas S6b (0.1-1 nmol/kg iv) only decreased AP. Central venous pressure (CVP), cardiac output (CO), and pulmonary arterial pressure (PAP) were increased. ET-2 produced biphasic changes in systemic vascular resistance (SVR), whereas S6b decreased SVR at the two lower doses and caused a biphasic change at the 1 nmol/kg dose. The effects of ET-1 and ET-2 were similar, whereas the effects of S6b were similar to ET-3. ET-2 and S6b had small effects on right ventricular contractile force and caused transient increases in heart rate. Distal aortic blood flow was increased in response to all doses of both peptides, whereas increases in carotid blood flow were observed only in response to the higher doses of ET-2 and S6b. ET-2 produced dose-dependent decreases in superior mesenteric artery (SMA) blood flow, whereas decreases in SMA flow in response to S6b were observed only at the 1 nmol/kg dose. Renal blood flow was decreased significantly only at the higher doses of ET-2 and S6b. The present data show that ET-2 and S6b can produce both vasodilation and vasoconstriction in the systemic and regional vascular beds of the cat and demonstrate previously unrecognized vasodilator activity in response to S6b. It is concluded that ET-2 and S6b produce complex cardiovascular responses in the anesthetized cat.

Influence of SQ 29,548 on vasoconstrictor responses in the mesenteric vascular bed of the cat

The effects of SQ 29,548 on vasoconstrictor responses were investigated in the feline mesenteric vascular bed. Injections of the thromboxane (TX) A2 mimics, U46619 and U44069, caused dose-related increases in mesenteric arterial perfusion pressure. After administration of SQ 29,548, 0.5 mg/kg i.v, vasoconstrictor responses to U46619 and U44069 were reduced markedly whereas responses to prostaglandin (PG) F2 alpha, angiotensin II, vasopressin and BAY K 8644, an agent which enhances calcium entry, were not altered. The duration of the TXA2 receptor blockade was greater than 2 h and SQ 29,548 had no significant effect on mesenteric vasodilator responses to PGE2, isoproterenol, nitroglycerin, acetylcholine or bradykinin. SQ 29,548, at a dose of 0.5 mg/kg i.v., significantly reduced the response to TXB2, which had modest vasoconstrictor activity in the mesenteric vascular bed. However, when the dose of SQ 29,548 was reduced to 0.05 mg/kg i.v., responses to TXB2 were not altered, whereas responses to U46619 were significantly decreased. SQ 29,548 had no significant effect on vasoconstrictor responses to norepinephrine or to sympathetic nerve stimulation. The TXA2 receptor antagonist blocked the vasoconstrictor component of the biphasic response to the PG precursor, arachidonic acid, and the endoperoxide, PGH2. The results of these studies suggest that SQ 29,548 is a specific TX receptor antagonist in the mesenteric vascular bed, that the vasoconstrictor component of the biphasic response to arachidonic acid and PGH2 is due to formation of TXA2, and that endogenously formed TXA2 does not modulate adrenergic responses in the mesenteric circulation of the cat.

Prostaglandin E2 formation by rat gastroduodenal tissue following intragastric acid perfusion

Rat gastroduodenal mucosa forms prostaglandin (PG) E2. However, little is known about regional differences in PGE2 formation or the effect of gastric hydrochloric acid (HC1) perfusion on regional PGE2 formation. In this study, the rats were divided into 3 groups. Group 1 received intravenous (i.v.), 1 Ml/h, and intragastric (i.g.), 8 ml/h, perfusions of saline simultaneously for 3 h. Group 2 received saline i.v. and 0.15 N HC1 i.g., 8 ml/h. Group 3 was injected with a bolus of asprin (ASA), 60 mg/kg, followed by ASA, 40 mg/kg/h i.v., and 0.15 N HC1 i.g.. The gastric aspirates were analyzed for volume and pH. Segments of gastroduodenal tissue from the fundus, corpus, antrum, and duodenum were minced and then incubated in 1 ml of 5 mM Tris buffer, pH 8.4, for 30 sec with mixing; the incubate was assayed for PGE2 by radioimmunoassay. Intragastric HC1 decreased the pH of aspirate without producing gastric mucosal lesions. However, when combined with i.v. ASA, ulcer formation was present in all animals (p less than 0.05). PGE2 was formed by isolated tissue from four different gastroduodenal regions. The duodenum formed significantly greater amounts than the fundus, antrum, or corpus, which were similar. Intragastric HC1 produced a trend toward increased PGE2 formation (pmol PGE2/mg tissue) in the fundus, 143 +/- 36 to 237 +/- 57; corpus, 87 +/- 13 to 200 +/- 57; antrum, 157 +/- 28 to 224 +/- 65; and duodenum, 235 +/- 56 to 338 +/- 51. However, statistical significance was not reached.

Influence of tone on responses to acetylcholine in the rabbit pulmonary vascular bed

Pulmonary vascular responses to acetylcholine were compared under resting and high tone conditions of the intact-chest rabbit. Under resting tone conditions, intralobar injections of acetylcholine increased lobar arterial pressure in a dose-related manner. The pressor responses to acetylcholine under resting conditions were blocked by meclofenamate, indomethacin, atropine, and pirenzepine. When lobar vascular resistance was raised to a high steady level, low doses of acetylcholine decreased lobar arterial pressure, whereas higher doses elicited a biphasic response with the pressor component predominating at the highest dose studied. Under high tone conditions, only the pressor component of the response was blocked by meclofenamate or indomethacin, whereas pressor and depressor responses were blocked by atropine or the 600-micrograms/kg iv dose of pirenzepine. Pressor responses to acetylcholine under resting and high tone conditions were blocked by pirenzepine (50 micrograms/kg iv), whereas gallamine had no effect on responses to acetylcholine. The 50-micrograms/kg iv dose of pirenzepine had no effect on depressor responses or the depressor component of the response to acetylcholine. The present data support the concept that acetylcholine has significant cyclooxygenase-dependent pressor activity in the rabbit pulmonary vascular bed and suggest that this response is mediated by a muscarinic M1-type receptor. These data also show that, under high tone conditions, a vasodilator response or a vasodilator component of a biphasic response is unmasked. This response is not dependent on the release of cyclooxygenase products and is mediated by a muscarinic receptor that is neither of the M1- nor the M2-type.

Adenosine does not mediate the pulmonary vasodilator response of adenosine 5'-triphosphate in the feline pulmonary vascular bed

Adenosine and ATP produce dose- and tone-dependent responses in the feline pulmonary vascular bed. That is, at baseline (low) pulmonary vascular tone adenosine and ATP produce vasoconstrictor responses and at elevated pulmonary vascular tone adenosine and ATP produce vasodilator responses. The mechanism mediating the vasodilator responses to adenosine and ATP was investigated in the intact-chest cat under conditions of controlled pulmonary blood flow and left atrial pressure. When lobar vascular resistance was raised with U46619, intralobar injections of adenosine and ATP caused dose-related decreases in lobar arterial pressure. The pulmonary vasodilator responses to ATP and adenosine were not altered by atropine, propranolol, meclofenamate or cimetidine indicating that these responses were not mediated by the release of vasodilator prostaglandins or to activation of beta adrenergic, muscarinic or histamine (H2) receptors. The decreases in lobar arterial pressure in response to adenosine were reduced significantly by BWA1433U, an adenosine (P1) receptor antagonist. BWA1433U induced a parallel shift of the adenosine dose-response curve to the right; however, it had no significant inhibitory effect on the decrease in lobar arterial pressure in response to ATP. The P1 receptor antagonist in doses of 10 and 30 mg/kg i.v. had no significant effect on the vasodilator response to nitroglycerin. The present data suggest that vasodilator responses to adenosine in the feline pulmonary vascular bed are mediated by adenosine (P1) receptors, whereas responses to ATP are mediated by a different mechanism that does not involve release of a vasodilator prostaglandin.

Analysis of responses to sympathetic nerve stimulation in the feline pulmonary vascular bed

The adrenergic receptor subtypes mediating the response to sympathetic nerve stimulation in the pulmonary vascular bed of the cat were investigated under conditions of controlled blood flow and constant left atrial pressure. The increase in lobar vascular resistance in response to sympathetic nerve stimulation was reduced by prazosin and to a lesser extent by yohimbine, the respective alpha 1- and alpha 2-adrenoceptor antagonists. Moreover, in animals pretreated with a beta-adrenoceptor antagonist to prevent an interaction between alpha- and beta 2-adrenoceptors, responses to nerve stimulation were reduced by prazosin, but yohimbine had no significant effect. On the other hand, in animals pretreated with a beta-adrenoceptor antagonist, yohimbine had an inhibitory effect on responses to tyramine and to norepinephrine. Propranolol had no significant effect on the response to nerve stimulation, whereas ICI 118551, a selective beta 2-adrenoceptor antagonist, enhanced responses to nerve stimulation and injected norepinephrine. The present data suggest that neuronally released norepinephrine increases pulmonary vascular resistance in the cat by acting mainly on alpha 1-adrenoceptors and to a lesser extent on postjunctional alpha 2-adrenoceptors but that this effect is counteracted by an action on presynaptic alpha 2-receptors. The present studies also suggest that neuronally released norepinephrine acts on beta 2-adrenoceptors and that the response to sympathetic nerve stimulation represents the net effect of the adrenergic transmitter on alpha 1-, alpha 2-, and beta 2-adrenoceptors in the pulmonary vascular bed.

Analysis of bronchoconstrictor responses to platelet-activating factor in the cat

Bronchoconstrictor responses to platelet-activating factor (PAF) were investigated in paralyzed, anesthetized, mechanically ventilated cats. Intravenous injections of PAF caused dose-dependent increases in lung resistance (RL) and decreases in dynamic compliance (Cdyn) and systemic arterial (aortic) pressure (PAO). The increases in RL and decreases in Cdyn in response to PAF were markedly reduced by sodium meclofenamate, a cyclooxygenase inhibitor, whereas the decreases in PAO were unchanged. Increases in RL and decreases in Cdyn but not PAO in response to PAF were reduced by SQ 29,548, a thromboxane (Tx) receptor blocking agent. CV 3988, a PAF receptor antagonist, reduced bronchoconstrictor and aortic depressor responses to PAF but had no effect on responses to the Tx mimic, U 46619, or to the prostaglandin precursor, arachidonic acid. The present studies suggest that bronchoconstrictor responses but not the hypotensive response to PAF are mediated in large part by the release of arachidonic acid from cell membrane phospholipids and the formation of cyclooxygenase products including TxA2. These data indicate that although airway and vasodepressor responses to PAF in the cat are mediated by different mechanisms, a similar PAF-CV 3988-sensitive receptor is involved.

Nisoldipine inhibits adrenergic responses in the hindquarters vascular bed of the cat

The effects of the calcium entry blocking agent nisoldipine on adrenergic vasoconstrictor responses were investigated in the hindquarters vascular bed of the cat under conditions of controlled blood flow. Nisoldipine dilated the hindquarters vascular bed and inhibited vasoconstrictor responses to Bay K 8644, a nifedipine analog which promotes calcium entry. During infusion of nisoldipine, vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine, and tyramine were inhibited in a reversible manner. In addition to blocking responses to nerve-released and exogenous norepinephrine, the calcium entry antagonist decreased responses to methoxamine and BHT 933, alpha 1- and alpha 2-adrenoceptor agonists. Responses to methoxamine were reduced by prazosin, an alpha 1-adrenoceptor antagonist, but not by yohimbine, an alpha 2-adrenoceptor blocking agent, whereas responses to BHT 933 were decreased by yohimbine but not by prazosin. The results of these studies suggest that vasoconstrictor responses to neuronally released and exogenous norepinephrine, as well as to selective alpha 1- and alpha 2-adrenoceptor agonists, are dependent in part on an extracellular source of calcium in resistance vessels of the feline hindquarters vascular bed. The inhibitory effect of nisoldipine on vasoconstrictor responses to neuronally released norepinephrine may be important in the antihypertensive actions of calcium entry blocking agents.

Differential effects of rat endothelin on regional blood flow in the cat

Regional vascular responses to rat endothelin were investigated in the anesthetized cat. Intravenous injection of the peptide in doses of 0.1-1 nmol/kg decreased arterial pressure and increased distal aortic blood flow with a small secondary reduction in flow at the high dose. Mesenteric blood flow was decreased, and the decreases in flow were proportionately greater than the decreases in pressure so that mesenteric resistance increased at all doses. The rat peptide increased blood flow or caused biphasic changes in flow in the renal vascular bed. At 0.1 and 0.3 nmol the peptide decreased renal resistance, whereas at 1 nmol a biphasic change occurred. The present data suggest that responses to rat endothelin are dependent on dose and the vascular bed studied and indicate that the peptide can cause both vasodilation and vasoconstriction.

Nisoldipine inhibits vasoconstrictor responses in the cat pulmonary vascular bed

The influence of nisoldipine, a dihydropyridine calcium entry antagonist, on vascular resistance and vasoconstrictor responses was investigated in the feline pulmonary vascular bed under conditions of controlled blood flow. The calcium channel blocking agent caused a small reduction in lobar vascular resistance and blocked pulmonary vasoconstrictor responses to BAY K 8644, an agent which promotes calcium entry. The calcium entry blocking agent also reduced pulmonary vasoconstrictor responses to methoxamine and to BHT 933, alpha 1- and alpha 2-adrenoceptor agonists, and to U 46619, an agent which mimics the actions of thromboxane A2. Although there was a marked difference in vasoconstrictor potency in the pulmonary vascular bed, responses to the thromboxane mimic and to the alpha 1- and alpha 2-adrenoceptor agonists were reduced by approximately the same extent. The increases in systemic arterial pressure in response to BAY K 8644, methoxamine, and BHT 933 were also reduced by nisoldipine, and the calcium entry antagonist reduced systemic arterial pressure and systemic vascular resistance. The results of the present study suggest that an extracellular source of calcium is required for the maintenance of vascular tone and for the expression of vasoconstrictor responses, resulting from activation of alpha 1- and postjunctional alpha 2-adrenoceptors and thromboxane receptors in the feline pulmonary vascular bed.

Effects of porcine and rat endothelin and an analog on blood pressure in the anesthetized cat

Arterial responses to a wide range of doses of porcine and rat endothelin and a monocyclic analog were compared in the anesthetized cat. Injections of the porcine peptide in doses of 0.01-0.1 nmol/kg i.v. decreased systemic arterial pressure in a dose-related manner, whereas doses of 0.3 and 1 nmol/kg i.v. elicited biphasic responses. The rat peptide, in doses of 0.03-1 nmol/kg i.v., also decreased arterial pressure in a dose-related fashion, whereas injection at 3 nmol/kg i.v. caused a biphasic response. With both peptides the biphasic response was characterized by an initial short-lived decrease followed by a secondary sustained increase in pressure. The monocyclic porcine analog in doses of 3-30 nmol/kg i.v. had no significant effect on arterial pressure. Both peptides increased cardiac output, and changes in peripheral vascular resistance in response to both peptides were not altered by sodium meclofenamate. These data suggest that arterial depressor responses to porcine and rat endothelin are similar and dose-dependent. However, the porcine peptide has 3-fold greater pressor activity in the cat. The lack of effect with the monocyclic porcine analog suggests that the two disulfide linkages are necessary for activity.

Differential effects of ibuprofen, indomethacin, and meclofenamate on prostaglandin endoperoxide H2 metabolism

Previous studies have suggested the possibility that the non-steroidal antiflammatory drug (NSAID), ibuprofen, may inhibit thromboxane (TX) A2 synthase activity in addition to inhibiting cyclooxygenase activity. Microsomal fractions isolated from the cat lung contain cyclooxygenase as well as prostacyclin (PGI2) synthase, TX synthase, and a GSH-dependent prostaglandin (PG) E2 isomerase activities. When [1-14C] PG endoperoxide H2 (PGH2) was used as substrate, ibuprofen, indomethacin, and meclofenamate exhibited differential effects on terminal enzyme activities. Ibuprofen, at concentrations up to 1 mM, had no effect on the activities of PGI2 synthase, TXA2 synthase of GSH-dependent PGE2 isomerase, whereas indomethacin selectively inhibited PGI2 synthase activity at 5 X 10(-4) M and 10(-3) M. Meclofenamate selectively inhibited TXA2 synthase activity at 5 X 10(-4) M and 10(-3) M. At concentrations of 5 X 10(-3) M, this selectivity was not observed, and indomethacin and meclofenamate decreased the formation of both 6-keto-PGF1 alpha and TXB2. These data indicate that the choice of NSAID and the concentration employed may specifically alter PGH2 metabolism. This action may affect the physiologic consequences of the exchange of PGH2 between cells. The data further indicate that indomethacin has the potential for use as a tool to specifically attenuate PGI2 synthase activity in vitro.

Influence of endothelin on systemic arterial pressure and regional blood flow in the cat

Regional vascular responses to endothelin were investigated in the anesthetized cat. I.v. injection of endothelin at 0.1 nmol/kg decreased arterial pressure and renal vascular resistance but increased vascular resistance in the small intestine. At 0.3 nmol/kg i.v. the peptide caused a greater decrease in arterial pressure and increased mesenteric resistance but had no significant effect on renal resistance. In contrast, at 1 nmol/kg i.v. endothelin caused a biphasic change in arterial pressure and marked increases in mesenteric and renal resistance. Injection of the peptide in doses of 0.1-1 nmol/kg i.v. caused only increases in carotid blood flow. These data suggest that responses to endothelin are dependent on dose and vascular bed studied.

Evidence for a bidirectional prostaglandin endoperoxide shunt between platelets and the bovine coronary artery

While platelets have been shown to be capable of supplying prostaglandin (PG) H2 to endothelial cells in culture for PGI2 synthesis, endothelial cells have been shown unable to supply PGH2 to platelets for thromboxane (TX) A2 synthesis. We incubated rings of the bovine coronary artery (BCAR) with human platelets treated with aspirin (to inhibit cyclooxygenase) or CGS 13080 (to inhibit TXA2 synthase) in the presence of 20 microM arachidonic acid. BCAR, with damaged endothelium, produced significantly less PGI2 than that with intact endothelium. However, co-incubation with CGS 13080-treated platelets resulted in an increase in PGI2 independent of endothelium, demonstrating a shunt of PGH2 from platelets to BCAR. Co-incubation of BCAR with aspirin-treated platelets resulted in a net increase in TXA2 demonstrating a shunt of PGH2 from BCAR to platelets. Employing [14C]PGH2 as substrate, BCAR with and without intact endothelium produced similar amounts of 6-keto-[14C]PGF1 alpha. Likewise, homogenates (50 micrograms protein) of intimal and subintimal regions of BCAR and BCAR converted similar amounts of PGH2 to 6-keto-PGF1 alpha. These data suggest that vascular production of PGH2 is more dependent on an intact endothelium than is the conversion of PGH2 to PGI2. These data also suggest a potential for a bidirectional exchange of PGH2 between platelets and vascular wall during platelet-vascular wall interactions.

Methylene blue selectively inhibits pulmonary vasodilator responses in cats

The effects of methylene blue on vascular tone and the responses to pressor and depressor substances were investigated in the constricted feline pulmonary vascular bed under conditions of controlled blood flow and constant left atrial pressure. When tone was elevated with U46619, intralobar injections of acetylcholine, bradykinin, nitroglycerin, isoproterenol, epinephrine, and 8-bromoguanosine-3',5'-cyclic monophosphate (8-bromo-cGMP) dilated the pulmonary vascular bed. Intralobar infusions of methylene blue elevated lobar arterial pressure without altering base-line left atrial or aortic pressure, heart rate, or cardiac output. When methylene blue was infused in concentrations that raised lobar arterial pressure to values similar to those attained during U46619 infusion, the pulmonary vasodilator responses to acetylcholine, bradykinin, and nitroglycerin were reduced significantly, whereas vasodilator responses to isoproterenol, epinephrine, and 8-bromo-cGMP were not altered. Moreover, the pressor responses to angiotensin II and BAY K 8644 during U46619 infusion and during methylene blue infusion were similar. The enhancing effects of methylene blue on vascular tone and inhibiting effects of this agent on responses to acetylcholine, bradykinin, and nitroglycerin were reversible. These responses returned to control value when tone was again increased with U46619, 30-45 min after the methylene blue infusion was terminated. The present data are consistent with the hypothesis that cGMP may play a role in the regulation of tone in the feline pulmonary vascular bed and in the mediation of vasodilator responses to the endothelium-dependent vasodilators, acetylcholine and bradykinin, and to nitrogen oxide-containing vasodilators such as nitroglycerin.

Analysis of regional responses to endothelin in hindquarters vascular bed of cats

Regional responses to endothelin, a peptide derived from endothelial cells in culture, were investigated in the hindquarters vascular bed of cats, when flow varied naturally and when flow was maintained constant with a pump. Intravenous injections of endothelin at doses of 0.03 and 0.1 nmol/kg caused dose-dependent decreases in systemic arterial pressure and increases in distal aortic blood flow. Injection of endothelin at a dose of 0.3 nmol/kg iv caused a biphasic response characterized by an initial decrease in arterial pressure and an increase in blood flow, which was followed by a secondary rise in pressure and a fall in blood flow. When blood flow to hindquarters was maintained constant with a pump, intra-arterial injection of 0.03 nmol endothelin caused a decrease in perfusion pressure, whereas 0.1-1 nmol doses elicited biphasic responses characterized by an initial decrease followed by a secondary increase in perfusion pressure. When compared with other vasoactive peptides, the pressor activity of endothelin was less than angiotensin II by an order of magnitude but was threefold greater than that of neuropeptide Y in the hindquarters vascular bed. The pressor component of the response to endothelin and the response to the calcium agonist BAY K 8644 were decreased in a reversible manner by nisoldipine, a dihydropyridine calcium entry blocking agent. The results of these studies indicate that porcine-human endothelin has both vasodilator and vasoconstrictor activity in the hindquarters vascular bed of cats. The predominant response at a low concentration is vasodilation, whereas at higher concentrations a vasoconstrictor response that was dependent in part on the influx of extracellular calcium could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of pulmonary thromboxane A2 synthase activity and airway responses by CGS 13080

The effects of CGS 13080, a thromboxane (TXA2) synthase inhibitor, on airway responses to arachidonic acid (AA) were investigated in the anesthetized cat. Feline and human lung microsomal fraction exhibited prostaglandin I2 (PGI2, prostacyclin), and TXA2 synthase activities, and human platelet microsomal fractions exhibited TXA2 synthase activity. Cat and human lung microsomal fractions, but not human platelets, exhibited the presence of GSH-dependent PGE2 isomerase activity. CGS 13080 inhibited TXA2 synthase activity in all three microsomal fractions in a concentration-dependent manner. The increases in transpulmonary pressure and lung resistance and decreases in dynamic compliance in response to AA were decreased significantly by CGS 13080. These data suggest that the bronchoconstrictor actions of AA are mediated in large part by the formation of TXA2. The data further indicate that cyclooxygenase products other than TXA2 are involved in the bronchoconstrictor response to AA since meclofenamate had greater inhibitory activity than did CGS 13080. Moreover, the effects of CGS 13080 were due to inhibition of TXA2 synthase rather than an effect on TXA2 receptors, since airway responses to the TXA2 mimic, U46619, were not altered. The present data show that CGS 13080 inhibits TXA2 synthase activity without altering cyclooxygenase, PGI2 synthase, or GSH-dependent PGE2 isomerase activities. The data further indicate that in vivo administration of CGS 13080 may selectively increase PGI2 synthase activity.

Prostacyclin and thromboxane A2 formation by atherosclerotic carotid artery: comparison with normal aorta, saphenous vein, and platelets

Prostacyclin (PGI2) and thromboxane A2 (TxA2) formation by whole-tissue segments of nine carotid endarterectomy specimens (CES), five normal aortic specimens (NAS), six saphenous vein specimens (SVS), and four platelet samples were determined by incubation with 10 mumol/L 1-14C-radiolabeled prostaglandin endoperoxide H2 (PGH2), and in other experiments with and without 10 mumol/L of CGS 13080, a TxA2 synthase inhibitor. PGI2 formation (expressed as picomoles 6-keto-PGF1 alpha/2-min incubation per sample) by nonatheromatous proximal intima of CES (307 +/- 23, mean +/- standard error) and distal intima of CES (260 +/- 22) was not statistically different; however, it was greater than atheromatous transitional plaque (159 +/- 13 pmol) (p less than 0.01) and ulceration regions (140 +/- 15 pmol) (p less than 0.01) of CES, NAS (204 +/- 16 pmol) (p less than 0.01), and SVS (165 +/- 9 pmol) (p less than 0.01). TxA2 formation (expressed as picomoles TxB2/2-min incubation per sample) by CES ulceration (51 +/- 2 pmol) was low but greater than proximal (17 +/- 2 pmol) (p less than 0.01), distal (19 +/- 3 pmol) (p less than 0.01), and transitional (23 +/- 3 pmol) (p less than 0.01) regions. TxA2 formation by NAS and SVS was not detected (less than 10 pmol). CGS 13080 inhibited TxA2 formation by CES below the limits of detection. Incubation of 1.9 x 10(5) intact platelets with 10 mumol/L of PGH2 formed a quantity of TxA2 equal to that of CES ulceration.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary vascular responses to forebrain stimulation in the cat

The effects of forebrain stimulation on the pulmonary vascular bed were investigated in the intact-chest cat under conditions of controlled blood flow and constant left atrial pressure. When pulmonary vascular tone was raised to a high steady level, direct electrical stimulation of the forebrain elicited a biphasic change in lobar arterial pressure. The response was characterized by an initial transient increase in lobar arterial pressure that was followed by a prolonged secondary decrease in pressure. When a delay coil was added to the extracorporeal perfusion circuit, the secondary vasodilator response was separated into initial brief and delayed prolonged components, suggesting that it was mediated in part by the release of a humoral factor. The entire response to forebrain stimulation was abolished by cervical cord section or freezing. The initial constrictor response and early brief dilator response were not blocked by classic pharmacological blocking agents. The delayed humorally mediated vasodilator response was blocked by propranolol or ICI 118551, indicating that it was mediated by a circulating factor with beta 2-stimulating properties. The delayed vasodilator response was associated with a large increase in arterial epinephrine levels, and this rise in plasma epinephrine was not altered by propranolol. The present data suggest that electrical stimulation of the forebrain causes a prolonged pulmonary vasodilator response that is mediated by way of a descending pathway, which results in a large rise in arterial epinephrine levels.

The pharmacological effects of allicin, a constituent of garlic oil

Garlic has been used in herbal medicine for thousands of years. While garlic oil contains many components and has been widely studied, the pharmacology of pure allicin, a constituent of garlic oil, is not well understood. We report that allicin inhibits human platelet aggregation in vitro without affecting cyclooxygenase or thromboxane synthase activity or cyclic adenosine monophosphate (AMP) levels. Allicin does not alter the activity of vascular prostacyclin synthase. However, it inhibits ionophore A23187-stimulated human neutrophil lysosomal enzyme release. In vivo allicin dilates the mesenteric circulation of the cat independent of prostaglandin release or a beta adrenergic mechanism.

Vasodilator activity of human alpha-calcitonin gene-related peptide in the feline mesenteric vascular bed

Human alpha-calcitonin gene-related peptide (CGRP) is a substance immunohistochemically present in a number of organ systems; however, the biologic significance of this peptide is uncertain. The present study was undertaken to investigate the effects of CGRP in the feline mesenteric vascular bed under conditions of controlled blood flow. Bolus injections of CGRP decreased mesenteric perfusion pressure in a dose-related fashion. When compared with nitroglycerin, CGRP possesses markedly greater vasodilator activity in the intestinal vascular bed of the cat. Because circulating levels of CGRP have been identified, the present data suggest CGRP may play a role in the regulation of systemic vasomotor tone and regional hemodynamics, as well as involve altered calcium metabolism seen with other calcium-regulating hormones in hypertensive states.

Tone-dependent responses to acetylcholine in the feline pulmonary vascular bed

The effects of an increase in base-line tone on pulmonary vascular responses to acetylcholine were investigated in the pulmonary vascular bed of the intact-chest cat. Under conditions of controlled blood flow and constant left atrial pressure, intralobar injections of acetylcholine under low-tone base-line conditions increased lobar arterial pressure in a dose-related manner. When tone was increased moderately by alveolar hypoxia, acetylcholine elicited dose-dependent decreases in lobar arterial pressure, and at the highest dose studied, acetylcholine produced a biphasic response. When tone was raised to a high steady level with the prostaglandin analogue, U46619, acetylcholine elicited marked dose-related decreases in lobar arterial pressure. Atropine blocked both vasoconstrictor responses at low tone and vasodilator responses at high tone, whereas meclofenamate and BW 755C had no effect on responses to acetylcholine at low or high tone. The vasoconstrictor response at low tone was blocked by pirenzepine (20 and 50 micrograms/kg iv) but not gallamine (10 mg/kg iv). The vasodilator response at high tone was not blocked by pirenzepine (50 micrograms/kg iv) or gallamine or pancuronium (10 mg/kg iv). The present data support the concept that pulmonary vascular responses to acetylcholine are tone dependent and suggest that the vasoconstrictor response under low-tone conditions is mediated by a high-affinity muscarinic (M1)-type receptor. These data also suggest that vasodilator responses under high-tone conditions are mediated by muscarinic receptors that are neither M1 nor M2 low-affinity muscarinic-type receptor and that responses to acetylcholine are not dependent on the release of cyclooxygenase or lipoxygenase products.

Influence of OKY-1581 on responses to arachidonic acid in the feline pulmonary vascular bed

The effects of OKY-1581, a thromboxane synthesis inhibitor, on pulmonary vascular responses to arachidonic acid (AA) were investigated under baseline and elevated tone conditions in the intact chest cat. Under conditions of controlled blood flow at baseline tone, intralobar injections of AA increased lobar arterial pressure in a dose-related manner. These pressor responses were reduced by OKY-1581, and a small vasodilator response was unmasked. The administration of indomethacin to these same animals abolished all responses to AA. When baseline tone in the pulmonary vascular bed was elevated by infusion of U46619, intralobar injections of AA caused a biphasic change in lobar arterial pressure characterized by an initial increase followed by a secondary fall in pressure. Treatment with OKY-1581 attenuated the pressor component of the response and enhanced the depressor component of the response. All responses to AA at elevated tone were also blocked by indomethacin. Pressor responses to intralobar injections of U46619 were not altered by OKY-1581 or indomethacin and were similar under baseline and high pulmonary vascular tone conditions. The results of this study suggest that the pulmonary pressor response to AA in the cat is dependent in large part on the formation of TXA2 and also suggest that TXA2, PGI2, and vasoconstrictor prostaglandins (PGF2 alpha, PGD2, PGE2) are formed from AA in the cat lung.

Inhibitory effects of diltiazem on vasoconstrictor responses in the cat

The effect of diltiazem on vasoconstrictor responses was investigated in the feline mesenteric vascular bed under conditions of controlled blood flow. Diltiazem inhibited vasoconstrictor responses to sympathetic nerve stimulation, tyramine and norepinephrine suggesting that responses to both nerve-released and exogenous norepinephrine are dependent in part on an extracellular source of calcium. The calcium entry antagonist inhibited vasoconstrictor responses to alpha 1 and to alpha 2 adrenoceptor agonists over a wide range of concentration. Diltiazem also inhibited mesenteric vasoconstrictor responses to angiotensin II, vasopressin, prostaglandin F2 alpha and KCl. The inhibitor effects of diltiazem on vasoconstrictor responses to nerve stimulation and the pressor agents were reversible, and all responses returned to control value 30 to 45 min after the infusion of the calcium entry antagonist. The present data suggest that the inhibitory effects of diltiazem on responses to sympathetic nerve stimulation are postjunctional in nature, as responses to nerve-released and exogenous norepinephrine and nonadrenergic pressor agents are reduced to a similar extent. The present results suggest that vasoconstrictor responses to neuronally released and exogenous norepinephrine, as well as agents which activate membrane receptors or depolarize vascular smooth muscle in the feline mesenteric vascular bed, are dependent in part on an extracellular source of calcium. The inhibitory effects of diltiazem on vasoconstrictor responses to sympathetic nerve stimulation and pressor hormones may be relevant to the antihypertensive actions of this calcium entry antagonist.

Prostacyclin, thromboxane A2, and prostaglandin E2 formation in atherosclerotic human carotid artery

Prostaglandin (PG) formation in 16 atherosclerotic human carotid endarterectomy specimens was compared systematically with that of normal carotid artery from seven white pigs and six rhesus monkeys. Prostacyclin (PGI2) formation (picomoles 6-keto-PGF1a/2 min/100 micrograms homogenate protein plus 2 mM glutathione [GSH]) of nonatheromatous intima adjacent proximal (276 +/- 32, mean +/- SEM) or distal (271 +/- 14) to carotid plaque was comparable to that of normal carotid artery from white pig (272 +/- 25, NS) and rhesus monkey (219 +/- 41, NS), and was greater than stenotic intima (156 +/- 17, p less than 0.01), subintimal plaque (168 +/- 14, p less than 0.01), and ulceration (65 +/- 16, p less than 0.01). GSH modulated PGI2 synthesis in all carotid specimens except areas of ulceration (p less than 0.05), but did not restore PGI2 formation in atheromatous fractions to basal level. No detectable arterial thromboxane A2 (TXA2) formation or GSH-dependent PGE2 isomerase activity was observed. The decrement in atherosclerotic carotid artery PGI2 formation was focal (confined to the plaque) and may have been related to loss of effective GSH modulation. These conditions could contribute to a localized imbalance between arterial PGI2 and platelet TXA2 with adverse vascular thromboregulatory consequences.

Influence of calcium-entry blockade on vasoconstrictor responses in feline mesenteric vascular bed

The subtypes of postjunctional alpha-adrenoceptors activated by neuronally released and exogenous norepinephrine and the source of calcium used for vasoconstrictor responses were investigated in the feline mesenteric vascular bed. Under constant flow conditions, intra-arterial injections of phenylephrine and UK14304, alpha 1- and alpha 2-adrenoceptor agonists, increased mesenteric arterial perfusion pressure in a dose-related manner. Prazosin, an alpha 1-antagonist, reduced vasoconstrictor responses to phenylephrine without altering responses to UK14304. Yohimbine, an alpha 2-antagonist, reduced responses to UK14304 without altering responses to phenylephrine. The same pattern of blockade was observed in animals pretreated with 6-hydroxydopamine to destroy the integrity of adrenergic terminals. Responses to phenylephrine and UK14304 were reduced by nitrendipine, a calcium-entry blocking agent, and this agent decreased vasoconstrictor responses to sympathetic nerve stimulation, tyramine, and norepinephrine. Responses to sympathetic nerve stimulation were selectively blocked by prazosin, but responses to norepinephrine were selectively blocked by yohimbine. Vasoconstrictor responses to tyramine were reduced by both prazosin and yohimbine. Nitrendipine also reduced responses to angiotensin II, U46619, a prostaglandin endoperoxide analogue, Bay K 8644, and potassium chloride. These data suggest the presence of alpha 1- and postjunctional alpha 2-adrenoceptors and support the hypothesis that norepinephrine released by nerve excitation acts mainly on alpha 1-receptors but that exogenous norepinephrine acts primarily on alpha 2-receptors. However, norepinephrine released by tyramine acts on both receptor subtypes. Nitrendipine inhibited responses to the alpha 1- and alpha 2-adrenoceptor agonists as well as those to nerve released and exogenous norepinephrine, the calcium agonist, Bay K 8644, and to other vasoconstrictor agents. These data suggest that in the feline mesenteric vascular bed, an extracellular source of calcium ions is required for vasoconstriction induced by a variety of mechanisms including activation of alpha 1- and postjunctional alpha 2-adrenoceptors.

Blockade of thromboxane responses in the airway of the cat by SQ 29,548

The effects of SQ 29,548, a thromboxane receptor antagonist, on airway responses were investigated in paralyzed, anesthetized, mechanically ventilated cats. Intravenous injections of the thromboxane and prostaglandin precursor, arachidonic acid (AA), and the thromboxane mimic, U 46619, produced dose-related increases in transpulmonary pressure and lung resistance and decreases in dynamic compliance. After administration of SQ 29,548 (0.5 mg/kg iv), bronchoconstrictor responses to AA were reduced by approximately 50%, whereas responses to U 46619 were reduced by approximately 90%. The cyclooxygenase inhibitor, sodium meclofenamate (2.5 mg/kg iv), blocked the component of the airway response to AA remaining after treatment with SQ 29,548. The thromboxane receptor antagonist had no significant effect on bronchoconstrictor responses to prostaglandins F2 alpha, and D2, methacholine, 5-hydroxytryptamine, histamine, or BAY K 8644, an agent that promotes calcium entry. Reductions in systemic arterial pressure in response to AA were enhanced by the thromboxane receptor antagonist and abolished by meclofenamate. SQ 29,548 had no effect on terminal enzyme activity in microsomal fractions from cat lung. These data support the hypothesis that AA-induced bronchoconstriction in the cat is mediated in large part by the actions of thromboxane A2. These data also suggest that U 46619 and U 44069 stimulate the same airway receptor as thromboxane A2 and mimic the bronchomotor effects of this hormone, which has not yet been isolated as a pure substance. These data demonstrate that SQ 29,548 is a selective thromboxane receptor antagonist in the airways of the closed-chest cat and may be a useful probe for studying responses to thromboxane A2 in physiological and pathophysiological processes in the lung.

Effects of OKY 1581 on bronchoconstrictor responses to arachidonic acid and PGH2

The influence of OKY 1581, a thromboxane synthase inhibitor, on airway responses to arachidonic acid and endoperoxide, [prostaglandin (PG) H2], were investigated in anesthetized, paralyzed, mechanically ventilated cats. Intravenous injections of arachidonic acid and PGH2 caused dose-related increases in transpulmonary pressure and lung resistance and decreases in dynamic and static compliance. OKY 1581 significantly decreased airway responses to arachidonic acid but not to PGH2. Sodium meclofenamate, a cyclooxygenase inhibitor, abolished airway responses to arachidonic acid but had no effect on airway responses to PGH2. OKY 1581 or meclofenamate has no effect on airway responses to PGF2 alpha, PGD2, or U 46619, a thromboxane mimic. In microsomal fractions from the lung, OKY 1581 inhibited thromboxane formation without decreasing prostacyclin synthesis or cyclooxygenase activity. These studies show that OKY 1581 is a selective thromboxane synthesis inhibitor in the cat lung and suggest that a substantial part of the bronchoconstrictor response to arachidonic acid is due to thromboxane A2 formation. Moreover, the present data suggest that airway responses to endogenously released and exogenous PGH2 are mediated differently and that a significant part of the response to exogenous PGH2 may be due to activation of an endoperoxide/thromboxane receptor, since responses to PGH2 are blocked by the thromboxane receptor antagonist SQ 29548.

Characterization of the vasoconstrictor activity of indomethacin in the mesenteric vascular bed of the cat

The effects of indomethacin on vascular resistance were investigated in the feline mesenteric vascular bed under conditions of constant blood flow. Indomethacin produced mesenteric vasoconstriction that was dose-dependent but was less active than U46619, the thromboxane mimic, angiotensin II, PGF2 alpha and norepinephrine. The vasoconstrictor response to indomethacin was not altered by meclofenamate and phenoxybenzamine. Indomethacin, in a dose that blocked the systemic vasodepressor response to arachidonic acid, did not alter mesenteric vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine, angiotensin II, U46619, and U44069. The present data suggest that in the feline intestinal vascular bed indomethacin has marked vasoconstrictor activity that occurs independent of activation of alpha-adrenoceptors and formation of cyclooxygenase products possessing pressor activity. The present data suggest that cyclooxygenase products do not modulate vasoconstrictor responses as well as the sympathetic nervous system in the intestinal vascular bed of the cat.

Influence of nisoldipine on vascular resistance and vasoconstrictor responses in cats

The influence of nisoldipine, a calcium entry antagonist, on vascular resistance and vasoconstrictor responses was investigated in the anesthetized cat. Nisoldipine, a dihydropyridine calcium entry blocking agent, decreased total peripheral resistance and dilated the intestinal vascular bed. This calcium antagonist blocked intestinal vasoconstrictor responses to BAY K 8644, a nifedipine analogue, which promotes calcium entry. The calcium entry antagonist decreased intestinal vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine, and tyramine. Nisoldipine also reduced intestinal vasoconstrictor responses to potassium chloride and agonists that elicit vasoconstriction by specific receptor-mediated actions including stimulation of alpha 1- and alpha 2-adrenoceptors. The vasodilator and inhibitory effects of nisoldipine on vasoconstrictor responses were reversible, and responses returned to control value over a 60-min period. The present data suggest that an extracellular source of calcium is required for maintenance of tone and for vasoconstriction induced by neuronally released or exogenous norepinephrine as well as a diverse group of agents that act through specific receptor mechanisms or depolarize vascular smooth muscle. The present results suggest that similar sources of calcium are required for vasoconstriction elicited by alpha 1- and alpha 2-adrenoceptor agonists in the feline intestinal vascular bed.

Analysis of airway responses to A23187 in the cat

Airway responses to ionophore A23187 were investigated in anesthetized, paralyzed cats under conditions of controlled ventilation. Intravenous injections of A23187 caused dose-related increases in transpulmonary pressure and lung resistance and dose-related decreases in dynamic compliance and aortic pressure. Airway responses to A23187 were reduced by sodium meclofenamate, a cyclooxygenase inhibitor, in a dose that decreased bronchomotor responses to the prostaglandin precursor, arachidonic acid. The cyclooxygenase inhibitor had no significant effect on airway responses to U-46619, a prostaglandin endoperoxide analog whose actions mimic those of thromboxane A2. Bronchomotor responses to ionophore A23187 were also reduced by SQ 29,548, a thromboxane receptor antagonist. SQ 29,548 reduced airway responses to the thromboxane A2 mimic, U-46619, but had no significant effect on airway responses to prostaglandins D2 or F2 alpha. These data indicate that ionophore A23187 constricts smooth muscle in central airways and in peripheral portions of the lung. In addition, these results suggest that in the closed-chest cat, bronchoconstrictor responses to A23187 are mediated mainly by formation of cyclooxygenase products and that a substantial part of the response is due to thromboxane A2 formation.

Nature of alpha 1 and postjunctional alpha 2 adrenoceptors in the pulmonary vascular bed

The subtypes of postjunctional alpha adrenoceptors in the feline pulmonary vascular bed were studied by using selective alpha-adrenoceptor agonists and antagonists. Under conditions of controlled pulmonary blood flow and constant left atrial pressure, intralobar injections of the alpha 1 agonists phenylephrine and methoxamine, and the alpha 2 agonists UK 14,304 and B-HT 933, increased lobar arterial pressure in a dose-related manner. Prazosin, an alpha 1-adrenoceptor antagonist, reduced responses to phenylephrine and methoxamine to a greater extent than responses to UK 14,304 and B-HT 933. Yohimbine, an alpha 2 blocker, decreased responses to UK 14,304 and B-HT 933 without altering responses to phenylephrine or methoxamine. The same pattern of blockade was observed in animals pretreated with 6-hydroxydopamine, an adrenergic neuronal blocking agent. However, in propranolol-treated animals, prazosin antagonized responses to phenylephrine and methoxamine without altering responses to UK 14,304 or B-HT 933, and the selectivity of the blocking effects of yohimbine were preserved. Responses to intralobar injections of norepinephrine (NE) were markedly decreased by prazosin, whereas yohimbine had only a small effect. These data suggest the presence of both postjunctional alpha 1 and alpha 2 adrenoceptors mediating vasoconstriction in the pulmonary vascular bed. These results also indicate that the vasoconstrictor responses to injected NE in the cat pulmonary vascular bed result mainly from activation of alpha 1 adrenoceptors.

Prostacyclin synthetase activity in human diabetic and nondiabetic vascular tissue

A decrease in the formation of prostacyclin (PGI2), a potent vasodilating and platelet antiaggregatory substance, has been implicated in the pathogenesis of diabetic vasculopathy. This defect, as well as others, may contribute to imbalances in the thrombo-regulatory system resulting in enhanced platelet aggregability, accelerated atherosclerosis, and subsequent vessel injury. Until recently the major thrust of relevant literature has been directed toward abnormalities in PGI2 quantity or function in vascular tissue from experimentally induced diabetic animal models. For the past 2 years our laboratory has studied prostaglandin metabolism in human diabetic and nondiabetic blood vessels. We determined prostacyclin synthetase (PGI2ase) activity in saphenous veins of diabetic and nondiabetic patients (HSV-D and HSV-ND) undergoing coronary artery bypass grafts and in tibial arteries and tibial veins of diabetic patients (HTA-D and HTV-D) and nondiabetic patients (HTA-ND and HTV-ND) undergoing limb amputation for arterial disease of the lower extremity. Carbon 14-labeled prostaglandin endoperoxide (PGH2) was incubated for 2 minutes with vascular microsomal protein. The products were separated via thin-layer chromatography and quantified by radiochromatographic scan. PGI2ase activity was determined by the formation of 6-keto-PGF1 alpha, the stable breakdown product of PGI2. Results of this study indicate that the microsomal fractions of all vascular tissues studied contain an active PGI2ase capable of forming PGI2; formation is enzymatic, as the amount of product increased with increasing microsomal protein concentration; there is no significant difference in PGI2ase activity between HSV-D and HSV-ND; PGI2ase activity in HTA-D and HTV-D is less than in HSV-D and HSV-ND.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of alpha- and beta-adrenoceptor responses by elevations in vascular tone in pulmonary circulation

The influence of increases in vascular tone on responses to selective alpha 1- and alpha 2-adrenoceptor agonists, norepinephrine, epinephrine, and isoproterenol was investigated in the feline pulmonary vascular bed. Under resting tone conditions with constant pulmonary blood flow and left atrial pressure, intralobar injections of the alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, and the alpha 2-adrenoceptor agonists, UK 14304 and B-HT 933, increased lobar arterial pressure. When pulmonary vascular resistance was raised to a high steady level, vasoconstrictor responses to the alpha 2-adrenoceptor agonists were markedly increased, responses to methoxamine were increased to a lesser extent, and pressor responses to phenylephrine and epinephrine were reversed. These vasodilator responses to phenylephrine and epinephrine at elevated vascular tone were blocked by propranolol. Moreover, after beta-adrenoceptor blockade, vasoconstrictor responses to phenylephrine, epinephrine, and norepinephrine were also greater at elevated tone than at resting tone. Vasodilator responses to the beta-adrenoceptor stimulant, isoproterenol, were enhanced at higher levels of vasoconstrictor tone and were blocked by propranolol and by albuterol, a selective beta 2-adrenoceptor antagonist. The enhanced vasoconstrictor responses to the alpha 2-adrenoceptor agonists were selectively blocked by yohimbine, whereas the enhanced responses to the alpha 1-adrenoceptor agonists and, for the most part, the vasoconstrictor responses to norepinephrine and epinephrine, were blocked by prazosin. The present data support the hypothesis that postjunctional alpha 1- and alpha 2-adrenoceptors mediating vasoconstriction and beta 2-adrenoceptors mediating vasodilation are present in the feline pulmonary vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prostaglandin H2 on perinatal pulmonary circulation

A pivotal intermediate in prostaglandin (PG) biosynthesis is the endoperoxide PGH2. This endoperoxide is capable of eliciting direct responses in biological systems without undergoing conversion to other PGs. Effects of PGH2 include stimulation of platelet aggregation and vascular smooth muscle contraction in vitro; injections of PGH2 in vivo cause increases in pulmonary arterial pressure. The response of the pulmonary vasculature of perinatal lambs to PGH2 was measured using an in situ pump-perfused left lower lung preparation. Intrapulmonary injections of PGH2 (0.24-0.61 microgram/kg) into six unventilated fetal lambs (0.93-0.97 gestation) produced decreases in pulmonary vascular resistance (PVR) of 10-21%. The fall in PVR was rapid in onset, reached a peak at 10 s after injection, and returned to baseline within 35 s. Following ventilation (FIO2 = 0.21) of fetal lambs, injections of PGH2 (0.24-0.61 microgram/kg) caused increases in PVR (ave increase = 50% over control PVR). The pulmonary pressor response to PGH2 in ventilated fetal lambs was depressed almost 50% by inhibition of thromboxane synthetase. Injections of a "heat-inactivated" PGH2 did not affect PVR in ventilated fetuses. We did not observe any effects on systemic blood pressure or heart rate of intrapulmonary arterial injections of PGH2. These findings suggest a metabolism of PGH2 to dilator PGs before ventilation and constrictor PGs and thromboxanes after ventilation, and/or direct effects of PGH2 on vascular smooth muscle that are dependent on existing vascular tone.

Activation of purified soluble guanylate cyclase by endothelium-derived relaxing factor from intrapulmonary artery and vein: stimulation by acetylcholine, bradykinin and arachidonic acid

The objective of this study was to ascertain whether "endothelium-derived relaxing factor" (EDRF) released from bovine intrapulmonary artery and vein is capable of directly activating soluble guanylate cyclase, thereby accounting for elevated vascular levels of cyclic GMP during EDRF release. Isolated arterial and venous rings, after equilibration and depolarization in bath chambers, were transferred to reaction tubes and incubated with soluble guanylate cyclase that had been purified to homogeneity from bovine lung. Addition of test agents to either bath chambers or enzyme reaction mixtures enabled the determination of their sites of action. Arterial and venous rings caused an endothelium-dependent 2- to 3-fold enzyme activation that was inhibited by methylene blue. Endothelium-dependent enzyme activation in artery but not vein was enhanced several-fold by acetylcholine in an atropine-sensitive manner. Bradykinin, which relaxes both artery and vein when endothelium is intact, activated guanylate cyclase upon addition of endothelium-intact rings to enzyme reaction mixtures. Vasoactive intestinal peptide, which causes endothelium-dependent relaxation of artery but not vein, also activated guanylate cyclase in the presence of endothelium-intact artery but not vein. Arachidonic acid activated the enzyme directly as well as through EDRF release from artery but not vein. Atrial peptides, prostacyclin, isoproterenol and nitroglycerin were inactive. Methylene blue was a powerful inhibitor of EDRF-elicited activation of guanylate cyclase but was without effect when rings were merely pretreated with methylene blue in bath chambers with no further addition to enzyme reaction mixtures. Thus, methylene blue did not interfere with the formation, release or chemical stability of EDRF, but rather inhibited its influence on guanylate cyclase. No agent was found to inhibit EDRF generation or release.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid and acetylcholine induced relaxation of bovine coronary artery: effect of indomethacin and methylene blue

Endothelial intact bovine coronary artery (BCA) rings precontracted with U46619 relax to acetylcholine (Ach) and arachidonic acid (AA). Relaxation to Ach is blocked by atropine. In an attempt to elucidate the mechanisms of these responses, we found that preincubation with methylene blue, an inhibitor of soluble guanylate cyclase activity, inhibited both Ach and AA induced relaxation. Preincubation with indomethacin had no effect on Ach induced relaxation, but partially inhibited the relaxation of endothelial intact BCA rings to AA.

Atriopeptin II relaxes and elevates cGMP in bovine pulmonary artery but not vein

Atriopeptin II, a 23-amino acid synthetic peptide fragment of atrial natriuretic factor, caused an endothelium-independent relaxation of isolated precontracted rings of bovine intrapulmonary artery that was accompanied by the concomitant accumulation of guanosine 3',5'-cyclic monophosphate (cGMP) but not adenosine 3',5'-cyclic monophosphate. In contrast, rings of intrapulmonary vein were unaffected by atriopeptin II whether or not endothelium was present. Whereas methylene blue, an inhibitor of soluble guanylate cyclase, abolishes endothelium-dependent and independent arterial relaxation and cGMP accumulation in response to acetylcholine and glyceryl trinitrate, respectively, methylene blue failed to alter these responses to atriopeptin II. Similarly, the effects of atriopeptin II were unaltered by propranolol, indomethacin, or atropine. These results indicate that relaxation elicited by atriopeptin II may be selective for arterial smooth muscle receptors, does not require endothelial cells, and does not involve the soluble form of guanylate cyclase, although cGMP accumulation is stimulated.

Dissimilarities between methylene blue and cyanide on relaxation and cyclic GMP formation in endothelium-intact intrapulmonary artery caused by nitrogen oxide-containing vasodilators and acetylcholine

The objective of the present study was to ascertain whether cyanide shares the properties of methylene blue as a selective inhibitor of vascular smooth muscle relaxation elicited by agents that stimulate the formation of cyclic GMP. Experiments were performed with endothelium-intact rings prepared from bovine intrapulmonary artery. Methylene blue, a good inhibitor of soluble guanylate cyclase, antagonized both arterial relaxation and cyclic GMP accumulation in response to sodium nitroprusside, glyceryl trinitrate, S-nitroso-N-acetylpenicillamine and acetylcholine. In contrast, cyanide inhibited only the responses to sodium nitroprusside. Increasing concentrations of methylene blue depressed resting arterial levels of cyclic GMP and caused slowly developing but marked contractions whereas cyanide was without effect. Contractile responses to phenylephrine, potassium and U46619 were potentiated by methylene blue but not by cyanide. Preincubation of dilute solutions of cyanide containing sodium nitroprusside in oxygenated Krebs' buffer at 37 degrees C for 15 min before addition to bath chambers depressed relaxation and cyclic GMP accumulation caused by sodium nitroprusside markedly. Similar treatment of glyceryl trinitrate, however, failed to alter its effects in arterial rings. A chemical inactivation of sodium nitroprusside by cyanide appears to account for the specific inhibitory action of cyanide on arterial responses to sodium nitroprusside. This study indicates clearly that cyanide does not share the properties of methylene blue as an inhibitor of arterial relaxation elicited by vasodilators that stimulate cyclic GMP formation.

Cyclooxygenase mediated airway response to leukotriene D4 in the cat

The effects of leukotriene D4 (LTD4) on pulmonary mechanics were investigated in anesthetized, paralyzed cats under conditions of controlled ventilation. Intravenous injections of LTD4 in doses of 3, 10, and 30 micrograms caused significant increases in transpulmonary pressure (PTP) and lung resistance (RL) while decreasing dynamic compliance (Cdyn). LTD4 also increased systemic arterial pressure (PAo). The changes in PTP, RL, and Cdyn in response to LTD4 were blocked by sodium meclofenamate, a cyclooxygenase inhibitor. However, there was no significant change in the increase in PAo following cyclooxygenase blockade. U 46619, a thromboxane mimic, was 30 to 100 times more potent than LTD4 in increasing PTP, RL and decreasing Cdyn in the cat. These data show that LTD4 has significant smooth muscle constrictor activity in central airways as well as peripheral portions of the feline lung. In addition, these data suggest that in the cat the actions of intravenously administered LTD4 on lung mechanics are mediated by release of cyclooxygenase products while the systemic pressor effects are not dependent upon the integrity of the cyclooxygenase pathway.

Evidence for existence of postjunctional alpha 1- and alpha 2-adrenoceptors in cat pulmonary vascular bed

The subtypes of postjunctional alpha-adrenoceptors in the feline pulmonary vascular bed were studied using selective alpha-adrenoceptor agonists and antagonists. Under conditions of controlled pulmonary blood flow and constant left atrial pressure, intralobar injections of the alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, and the alpha 2-adrenoceptor agonists, UK 14,304 and BHT 933, increased lobar arterial pressure in a dose-related manner. Prazosin, an alpha 1-adrenoceptor antagonist, reduced responses to phenylephrine and methoxamine to a greater extent than responses to UK 14,304 and BHT 933. Yohimbine, an alpha 2-adrenoceptor blocker, decreased responses to UK 14,304 and BHT 933 without altering responses to phenylephrine or methoxamine. The same pattern of blockade was observed in animals pretreated with 6-hydroxydopamine, an agent that destroys the integrity of adrenergic nerve terminals. However, in propranolol-treated animals, prazosin antagonized responses to phenylephrine and methoxamine without altering responses to UK 14,304 or BHT 933, and the selectivity of the blocking effects of yohimbine were preserved. Responses to intralobar injections of norepinephrine were markedly decreased by prazosin, whereas yohimbine had only a small effect. These data suggest the presence of both postjunctional alpha 1- and alpha 2-adrenoceptors mediating vasoconstriction in the pulmonary vascular bed. These results also indicate that the vasoconstrictor responses to injected norepinephrine in the cat pulmonary vascular bed are due mainly to activation of alpha 1-adrenoceptors.

Influence of mediators of anaphylaxis on collateral ventilation and the lung periphery of the dog

The relative activities of three bronchoconstrictive mediators of anaphylaxis, prostaglandin (PG) D2, PGF2 alpha and histamine, were investigated in anesthetized dogs using two different measures of peripheral lung reactivity: resistance to flow through collateral airways (Rcoll) and dynamic lung compliance (Cdyn). In the collateral system, the three agonists exhibited approximately 3-fold differences in their relative activities when administered by rapid injection into the superior vena cava, with PGD2 greater than PGF2 alpha greater than histamine. PGD2 was approximately three times more active than PGF2 alpha in reducing Cdyn, whereas responses to PGF2 alpha and histamine were equivalent. These relationships were unchanged in vagotomized animals. Pretreatment with atropine (1 mg/kg) significantly attenuated changes in Rcoll, but had only small and inconsistent effects on changes in Cdyn. Although the time to initial response in both measures of peripheral airways reactivity was similar, the time to maximal response in Rcoll was approximately twice that of Cdyn. In lung parenchymal strips, the rank order of contractile activity of the three mediators was opposite that observed in the peripheral airways in vivo. These data demonstrate that airflow through the collateral system can be modulated by mediators of anaphylaxis in the pulmonary circulation and suggest that such mediators may influence ventilation/perfusion relationships in the lung periphery through their differential effects on peripheral airways and other parenchymal contractile elements. The present study also indicates that the determinants of flow through the collateral system exhibit certain basic pharmacologic and physiologic differences from those of Cdyn and suggests that these two measures of peripheral airways reactivity are not equivalent.

Differences in responsiveness of intrapulmonary artery and vein to arachidonic acid: mechanism of arterial relaxation involves cyclic guanosine 3':5'-monophosphate and cyclic adenosine 3':5'-monophosphate

The objective of this study was to examine the relationship between responses of bovine intrapulmonary artery and vein to arachidonic acid and cyclic nucleotide levels in order to better understand the mechanism of relaxation elicited by arachidonic acid and acetylcholine. Arachidonic acid relaxed phenylephrine-precontracted arterial rings and elevated both cyclic GMP and cyclic AMP levels in arteries with intact endothelium. In contrast, endothelium-damaged arterial rings contracted to arachidonic acid without demonstrating significant changes in cyclic nucleotide levels. Indomethacin partially inhibited endothelium-dependent relaxation and abolished cyclic AMP accumulation whereas methylene blue, a guanylate cyclase inhibitor, partially inhibited relaxation and abolished cyclic GMP accumulation in response to arachidonic acid. All vessel responses were blocked by a combination of the two inhibitors. Prostaglandin (PG) I2 relaxed arterial rings and elevated cyclic AMP levels whereas PGE2 and PGF2 alpha caused contraction, suggesting that the indomethacin-sensitive component of arachidonic acid-elicited relaxation is due to PGI2 formation and cyclic AMP accumulation. The methylene blue-sensitive component is attributed to an endothelium-dependent but cyclooxygenase-independent generation of a substance causing cyclic GMP accumulation. Intrapulmonary veins contracted to arachidonic acid with no changes in cyclic nucleotide levels and PGI2 was without effect. Homogenates of intrapulmonary artery and vein formed 6-keto-PGF1 alpha, PGF2 alpha and PGE2 from [14C]arachidonic acid, which was inhibited by indomethacin. Thus, bovine intrapulmonary vein may not possess receptors for PGI2. The failure of endothelium-intact vein to relax to acetylcholine may be related to the lack of a relaxant effect by arachidonic acid, perhaps attributed to the absence of generation of an endothelium-derived relaxing factor.

Pulmonary vasodilator responses to vasoactive intestinal peptide in the cat

We investigated the effects of vasoactive intestinal peptide (VIP) in the feline pulmonary vascular bed under conditions of controlled pulmonary blood flow when pulmonary vascular tone was at base-line levels and when vascular resistance was elevated. Under base-line conditions, VIP caused small but significant reductions in lobar arterial pressure without affecting left atrial pressure. Decreases in lobar arterial pressure in response to VIP were greater and were dose related when lobar vascular resistance was increased by intralobar infusion of U 46619, a stable prostaglandin endoperoxide analogue. Acetylcholine and isoproterenol also caused significant decreases in lobar arterial pressure under base-line conditions, and responses to these agents were enhanced when lobar vascular tone was elevated. Moreover, when doses of these agents are expressed in nanomoles, acetylcholine and isoproterenol were more potent than VIP in decreasing lobar arterial pressure. Responses to VIP were longer in duration with a slower onset than were responses to acetylcholine or isoproterenol. Pulmonary vasodilator responses to VIP were unchanged by indomethacin, atropine, or propranolol. The present data demonstrate that VIP has vasodilator activity in the pulmonary vascular bed and that responses are dependent on the existing level of vasoconstrictor tone. These studies indicate that this peptide is less potent than acetylcholine or isoproterenol in dilating the feline pulmonary vascular bed and that responses to VIP are not dependent on a muscarinic or beta-adrenergic mechanism or release of a dilator prostaglandin.