Role of endothelium in the response of the vein wall to magnesium withdrawal

Complete absence of magnesium has a two-fold effect on the arterial tone: direct smooth muscle contraction and relaxation via endothelium-derived relaxing factor (EDRF) release. In the present study performed on a systemic vein we investigated (1) which of these effects dominates following reduction of magnesium concentration from 1.2 mM to 0.8 and 0.4 mM and (2) whether the vessel segments asymmetrically respond when the magnesium concentration is reduced on either the intra- or extraluminal side. The effects of reducing magnesium concentration on both the isometric tension of isolated ring preparations and the diameter of isolated, perfused and superfused feline femoral veins were investigated. In noradrenaline-precontracted rings, rapid decreases in the extracellular magnesium concentration from 1.2 mM to 0.8 and 0.4 mM caused relaxation, whereas total omission of magnesium returned the tone to the level of the initial tone induced by noradrenaline. Both in the presence of haemoglobin (5 x 10(-6) M), and in vessels without endothelium, lowering the magnesium concentration caused a dose-dependent elevation of the noradrenaline-induced tone. In perfused and superfused noradrenaline-contracted vein segments, each reduction of extraluminal magnesium concentration caused contraction of the vessels, regardless of whether the endothelium was intact or not. A decrease in intraluminal magnesium concentration did not alter the diameter of the vessel when the endothelium was intact, but caused contraction when the endothelium was disrupted. The results of the present study demonstrate that both the reduction of magnesium concentration or its complete absence cause an EDRF-mediated relaxation and a directly mediated smooth muscle contraction in the femoral vein of the cat.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperpolarization contributes to endothelium-dependent relaxations to acetylcholine in femoral veins of rats

The contribution of membrane hyperpolarization to endothelium-dependent relaxations induced by acetylcholine was investigated in the femoral vein of the rat using a microelectrode technique and isometric tension recordings. Acetylcholine caused endothelium-dependent relaxations and hyperpolarization in tissues contracted with norepinephrine. The relaxation was sustained during a prolonged exposure to acetylcholine (less than or equal to 10 min). In contrast, the hyperpolarization declined with time. In the presence of nitro-L-arginine, a blocker of nitric oxide synthesis, the relaxation became smaller and transient, whereas the hyperpolarization was not affected. There was a temporal relationship between the relaxation and the hyperpolarization in the presence of nitro-L-arginine, when the two parameters were recorded simultaneously. In tissues contracted with 60 mM K+, in which hyperpolarization could not be observed, acetylcholine caused relaxations and these relaxations were abolished by nitro-L-arginine. The results suggest a contribution of both nitric oxide and membrane hyperpolarization to the endothelium-dependent relaxation induced by acetylcholine in the femoral vein of the rat.

Selective production of endothelium-derived nitric oxide in canine femoral veins

In arteries, analogues of L-arginine inhibit the synthesis of nitric oxide and thereby reduce endothelium-dependent relaxations. Experiments were designed to determine whether analogues of L-arginine affect endothelium-dependent responses in a systemic vein. Rings cut from canine femoral arteries and veins were suspended for the measurement of isometric force in organ chambers. In some rings, the endothelium was deliberately removed. All experiments were conducted in the presence of indomethacin (10(-5) M). NG-monomethyl-L-arginine (L-NMMA, 10(-4) M) reduced significantly endothelium-dependent relaxations to acetylcholine, ADP, and thrombin in arteries but not in veins. In the veins, the alpha 2-adrenergic agonist BHT-920 caused contractions which were reduced in rings with endothelium. L-NMMA eliminated the difference in contraction between rings with and without endothelium in the veins. This effect was reversed by L- but not D-arginine (3 x 10(-4) M). N omega-nitro-L-arginine (10(-4) M) reduced endothelium-dependent relaxations to acetylcholine, thrombin, and the calcium ionophore A23187 in venous rings. However, it did not alter the contractions to BHT-920 in rings with or without endothelium. L-Canavanine did not alter endothelium-dependent relaxations in the veins. These results suggest that synthesis of nitric oxide is associated with stimulation of alpha 2-adrenergic, muscarinic, and thrombin receptors on venous endothelial cells. Furthermore, the analogues of L-arginine affect endothelium-dependent relaxations in canine veins differentially.

Effect of the molsidomine metabolite SIN-1 on coronary arteries and peripheral vessels of sheep with special reference to tolerance and endothelium

In vitro experiments on rings from coronary arteries, femoral arteries, and femoral veins of sheep were performed, and cumulative concentration-relaxation responses were established for glyceryl trinitrate (GTN) and the molsidomine metabolite SIN-1. Paired preparations of control and deendothelialized coronary artery rings were used, and the vessels were precontracted with different agonists at a concentration that elicited 30% of maximal contractions (EC-30). In coronary arteries, the responses for GTN and SIN-1 on normal and deendothelialized preparations were not significantly different. In coronary arteries preincubated with 0.44 mM GTN or SIN-1 to study tolerance development, there was a significant loss of efficacy to the relaxant effect of GTN, whereas the effect SIN-1 was essentially maintained. Femoral arteries and veins were readily relaxed with GTN. and SIN-1. In veins relaxation in relation to resting tone was much more pronounced than in coronary or femoral arteries. In conclusion, the molsidomine metabolite SIN-1 is a potent coronary and venous vasodilator that does not induce tolerance.

[The participation of humoral factors released by the endothelium in the development of reactive hyperemia]

In anesthetized dogs and on test-preparations of isolated vascular rings of femoral artery used for detection of appearance of vasoactive substances in venous blood, the reactive hyperemia was accompanied by the appearance of vasodilation substances in blood, the concentration of which increased with the occlusion duration. Chemical injury of endothelium by saponin, inhibition of lipoxygenase by quercetin and guanylate cyclase by methylene blue decreased the reactive hyperemia and the relaxation of test-preparation. Cyclooxygenase inhibition by indomethacin did not affect the reactive hyperemia or release of vasoactive substances. The endothelium seems to play an important role in development of reactive hyperemia induced by endothelium-derived relaxing factor release.

Dissociation between endothelium-dependent relaxations and increases in cGMP in systemic veins

In canine systemic veins, in contrast to what is observed in mammalian systemic arteries, endothelium-dependent relaxations to the calcium ionophore A23187 are not diminished by the inhibitor of soluble guanylate cyclase, methylene blue. Therefore, experiments were designed to determine whether these relaxations in the veins are associated with the accumulation of guanosine 3',5'-cyclic monophosphate (cGMP). Rings of canine femoral arteries and veins with and without endothelium were suspended for the measurement of isometric force in organ chambers; cGMP was measured by radioimmunoassay. In arteries and veins contracted with norepinephrine, the tissue content of cGMP was greater in rings with than without endothelium. This difference was decreased by methylene blue (10(-5) M). A23187 (3 X 10(-7) M, for 1 min) increased the accumulation of cGMP, which was temporally related with the onset of relaxation in tissues with endothelium. Methylene blue inhibited the accumulation of cGMP in both blood vessels but inhibited the relaxations only in the arteries. In rings without endothelium, sodium nitroprusside (3 X 10(-7) and 10(-5) M) initiated increases in cGMP, which followed the onset of relaxation. Neither response to sodium nitroprusside was reduced by methylene blue. These results suggest that in canine femoral arteries and veins, relaxation of the smooth muscle to sodium nitroprusside are mediated by a mechanism distinct from changes in cGMP. Likewise, in canine systemic veins, endothelium-derived factor(s) released in response to A23187 also can initiate relaxation of the smooth muscle by a mechanism distinct from changes in cGMP.

Pertussis toxin reduces endothelium-dependent and independent responses to alpha-2- adrenergic stimulation in systemic canine arteries and veins

A pertussis toxin-sensitive guanine nucleotide regulatory protein (G-protein) is involved in the signal transduction of certain endothelium-dependent responses in mammalian arteries. To determine whether a similar mechanism mediates endothelium-dependent responses in mammalian veins, rings of canine femoral arteries and veins with and without endothelium were suspended for the measurement of isometric force in organ chambers. In femoral arteries, incubation of the rings with pertussis toxin (from Bordetella pertussis, 100 ng/ml for 2 hr) in the presence of indomethacin and propranolol did not reduce significantly endothelium-dependent relaxations to acetylcholine and adenosine diphosphate, thrombin or the calcium ionophore A23187. However, endothelium-dependent relaxations evoked by the alpha-2 adrenergic agonist UK 14,304 were blocked by the pertussis toxin. In venous rings, endothelium-dependent relaxations to acetylcholine were reduced by the toxin, whereas the endothelium-dependent relaxations evoked by adenosine diphosphate, thrombin and A23187 were not affected. UK 14,304 contracted the veins; these contractions were augmented by removal of the endothelium. Pertussis toxin inhibited contractions to UK 14,304 in venous rings without but not with endothelium. Relaxations of arterial and venous smooth muscle to nitric oxide were unaffected by the toxin. Contractions to phenylephrine were not altered by either removal of the endothelium or the toxin in the arteries or veins. These results suggest that the release of endothelium-derived relaxing factor in response to stimulation of purine and thrombin receptors probably does not involve a pertussis toxin-sensitive G-protein in canine femoral arteries or veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-toxic antiseptic irrigation with chlorhexidine in experimental revascularization in the rat

The effect of different wound irrigation fluids upon femoral arteries and veins was investigated in the rat, using microsurgical techniques. Toxicity was evaluated by microscopical observation after selective staining of histological slides. Povidone-iodine, 10%, proved to be a very irritant solution, provoking an attack on the vascular endothelium and secondary thrombosis. Chlorhexidine at 0.05%, 0.02% and 0.001% was found by contrast to have a very low toxicity which was comparable to physiological saline. Experimental investigation of antiseptic solutions should not only include the determination of the antibacterial effect, but also the potential for cell toxicity, using an irrigation technique.

Effects of vasodilators on venous tone in vivo in dogs

The authors investigated, in vivo, the effects of four vasodilators on venous tone in dogs. Baseline venous tone was determined from the pressure: diameter relationships in the inferior vena cava (VSIVC) and femoral vein (VSFV) as measured during several seconds of occlusion of the proximal inferior vena cava. All of the slopes were nearly linear. All vasodilators were administered in dosages sufficient to lower blood pressure by approximately 20%; these dosages also decreased systemic vascular resistance by 15% to 30%. Isosorbide dinitrate reduced VSIVC from 7.17 +/- 0.81 to 5.81 +/- 0.73 mmHg/mm and VSIVC from 59.4 +/- 13.5 to 37.2 +/- 6.6 mmHg/mm. Neither nifedipine nor nisoldipine altered VSIVC or VSFV. However, prazosin decreased VSIVC from 13.2 +/- 3.3 to 10.7 +/- 2.7 mmHg/mm and VSFV from 43.5 +/- 11.3 to 29.9 +/- 8.8 mmHg/mm. These results suggest that isosorbide dinitrate and prazosin decrease venous tone in vivo, whereas nifedipine and nisoldipine do not.

Increased vasoconstrictor response to noradrenaline in femoral vascular bed of diabetic dogs. Is thromboxane A2 involved?

STUDY OBJECTIVE

The aim was to determine the role of cyclo-oxygenase products in the vasoconstrictor response of femoral arterial bed to noradrenaline and to analyse the role of vascular adrenoceptors in the synthesis of cyclo-oxygenase products.

DESIGN

The influence of intra-arterially injected cyclo-oxygenase inhibitors indomethacin and acetylsalicylic acid on alterations in conductance of femoral arterial bed induced by noradrenaline was compared in metabolically healthy and alloxan diabetic dogs. PGI2 and TXA2 synthesising ability of isolated femoral arterial rings was measured with and without inhibition of alpha adrenoceptors by phentolamine.

SUBJECTS

18 metabolically healthy and 18 alloxan (560 mumol.kg-1) diabetic dogs of either sex, weight 16-28 kg, were studied.

MEASUREMENTS AND MAIN RESULTS

Noradrenaline produced greater (p less than 0.01) pressor effects in the femoral arterial bed of alloxan diabetic dogs than in the hind limb of control animals. Blockade of cyclo-oxygenase either by indomethacin 10 mumol.kg-1 or by acetylsalicylic acid 140 mumol.kg-1 markedly reduced the response to noradrenaline in alloxan treated animals, but not in controls, thereby eliminating the different responsiveness of the two groups. Femoral arterial rings from diabetic animals synthesised similar amounts of PGI2 as control rings but formed more TXA2 (p less than 0.05). Phentolamine pretreatment (5 mumol.litre-1) markedly reduced the production of TXA2, but not of PGI2, in diabetic vessels.

CONCLUSIONS

The results show an increased release of TXA2 by isolated diabetic femoral arteries. It is therefore suggested that an alpha adrenoceptor mediated increase in TXA2 biosynthesis may play a part in the vascular hyperreactivity of the diabetic femoral arterial bed.

Effect of epidural anesthesia for cesarean delivery on maternal femoral arterial and venous, uteroplacental, and umbilical blood flow velocities and waveforms

The effect of epidural anesthesia on the maternal femoral arterial and venous, uteroplacental, and umbilical circulations was studied by the pulsed Doppler technique in 13 women undergoing elective cesarean delivery. Resistance and pulsatility indices of umbilical arterial velocity waveforms did not change with the use of epidural anesthesia. In the uteroplacental circulation, these indices increased in 11 patients, suggesting an increase in resistance. Reduction of sympathetic tone in resistance and capacitance vessels was reflected in the femoral artery by an increase in systolic and end-diastolic velocities, a reversal of the post-systolic backward flow, and an increase in mean velocity. The latter also occurred in the femoral vein. The diameters of these large maternal vessels did not change. This study suggests an impairment in uteroplacental circulation associated with a drop in peripheral vascular resistance and an increase in leg blood flow after epidural anesthesia.

Is nitric oxide the only endothelium-derived relaxing factor in canine femoral veins?

Nitric oxide may be an endothelium-derived relaxing factor in systemic arteries and pulmonary veins. The endothelium-derived relaxing factor of systemic veins has not been characterized. Experiments were designed to determine whether the endothelium-derived relaxing factor of systemic veins shared chemical properties and mechanisms of action with nitric oxide. Rings of the canine femoral vein with and without endothelium were suspended in organ chambers for the measurement of isometric force. In rings without endothelium, relaxations to nitric oxide were augmented by superoxide dismutase plus catalase and were inhibited by hemoglobin, methylene blue, and LY 83583. The endothelium-dependent relaxations to acetylcholine and A23187 were not augmented by superoxide dismutase plus catalase but were inhibited by hemoglobin and only moderately reduced by either methylene blue or LY 83583. Relaxations to sodium nitroprusside were not inhibited by methylene blue and LY 83583. Relaxations to sodium nitroprusside were inhibited by ouabain and K+-free solution; those to nitric oxide were not. These results indicate that although the endothelium-derived relaxing factor released from canine systemic veins shares some chemical properties with nitric oxide, the mechanism by which relaxations are induced by the two differ. A factor dissimilar to nitric oxide but acting like sodium nitroprusside may be released by the endothelium of canine systemic veins.

Effect of heparinized irrigating solutions on patency of experimental microvascular anastomoses

The effect of five different irrigating solutions on patency of four different types of microvascular anastomoses was studied. The solutions used were lactated Ringer's without heparin and four lactated Ringer's solutions with varying concentrations of heparin ranging from 10,000 units/liter to 100,000 units/liter. These were tested on four different anastomotic models in the rat: 1) end-to-end femoral arterial anastomosis; 2) end-to-side arterial bypass graft; 3) end-to-end venous anastomosis; and 4) end-to-side venous bypass graft. There were statistically significant differences in patency rates among the solutions only in the end-to-end venous anastomosis group. In these, significantly higher patency was achieved with heparinized lactated Ringer's solution at 20,000 units/liter. The use of higher concentrations of heparin in these solutions resulted in decreasing patency rates and appears to be contraindicated.

Peptide-containing nerves in the rat femoral artery and vein. An immunocytochemical and vasomotor study

Peptide-containing nerves have been examined in the rat femoral artery and vein using immunocytochemical and vasomotor techniques. The general neuronal marker PGP 9.5 revealed a moderate supply of nerve fibres and fascicles forming a loose network in the adventitia and the adventitial-medial border of the artery and vein. The majority of the nerve fibres in both the artery and vein displayed immunoreactivity for neuropeptide Y (NPY) and tyrosine hydroxylase (TH). The distribution pattern and number of these two types correlated well. The artery had a slightly richer PGP 9.5- immunoreactive nerve supply compared to the vein, but the nerve plexus in the vein displayed a more uniform arrangement. In contrast, relatively few nerve fibres displayed calcitonin gene-related peptide, substance P, or vasoactive intestinal peptide immunoreactivity in either the artery or vein. The calcitonin gene-related peptide immunoreactive fibres had a similar distribution to that of the substance P containing fibres. Using a sensitive in vitro method the vasomotor responses to perivascular peptides were characterized. In the femoral artery NPY potentiated alpha 1-adrenoceptor mediated contractions, and had very little effect by itself. In contrast, 10(-7) M NPY contracted femoral veins by up to 68% relative to 60 mM potassium induced contraction, and there was no potentiation of alpha-adrenoceptor mediated contractions. Acetylcholine, peptide histidine isoleucine, vasoactive intestinal peptide, substance P and calcitonin gene-related peptide, all relaxed the contracted femoral artery and vein. Regarding the putative parasympathetic neurotransmitters, acetylcholine caused stronger relaxation of veins as compared to arteries whereas for vasoactive intestinal peptide and peptide histidine isoleucine the relaxations were stronger in the arterial preparation. These three agonists were more potent in the femoral vein. Substance P was more potent on the femoral vein, having the same maximum response in both preparations. On the other hand, the response induced by CGRP was some three times greater in the venous than in the arterial preparation. These data reveal that although there appear to be only minor differences in the peptidergic innervation of the rat femoral artery and vein pronounced differences occur in the peptide effector responses. The data support the concept that perivascular peptides play different roles in regulating various parts of the circulation.

Effect of intravenous and intraperivenous injections of sclerosants (sodium tetradecyl sulfate and hydroxy polyethoxy dodecan) on the rat femoral vein

The sclerosant effect of injected tetradecyl sulfate of sodium (STS) and hydroxy polyethoxy dodecan (HPD) was studied in the rat femoral vein. Intravenous (i.v.) and intravenous plus perivenous (i.v. + p.v.) injections of both sclerosants and physiologic saline were compared as to vein lumen occlusion, fibrosis, phlogosis, and damage to the artery and surrounding nervous and muscular tissues. The study was carried out in 30 rats treated by STS, in 30 treated by HPD, and 15 animals were injected with saline. The neurovascular bundle and adjacent muscle were removed at 48 h, 7 and 30 days and examined histologically. I.v. injections of STS produced a solid occlusion of the vein in a significant number of cases, after 30 days (P less than 0.01). A statistically significant number of solid occlusions of the femoral vein resulted after i.v. + p.v. injection of STS and HPD, at 48 h, 7 and 30 days (P less than 0.05; P less than 0.01). There was no significant difference between STS and HPD after i.v. + p.v. injection. After i.v. + p.v. we recorded a marked inflammation of muscle with signs of focal necrosis, at 48 h and 7 days. Our study indicated that i.v. + p.v. injection of STS and HPD provided a high degree of efficacy as regards vein occlusion. On the other hand, i.v. + p.v. injection induced a severe inflammation and necrosis of the tissues surrounding the sclerosed vein. Extrapolating our results to the endoscopic sclerotherapy for esophageal variceal bleeding, we conclude that paravariceal injection of sclerosants is a dangerous procedure, even though efficacious to reduce variceal hemorrhage, owing to the high risk of iatrogenic ulcers and esophageal perforation caused by muscular and mucosal necrosis.

Effects of calcium channel blockers on the contractile response to dihydroergotamine in isolated human femoral veins

Contractions induced in spirally cut human postmortem femoral veins by dihydroergotamine, noradrenaline, or 5-hydroxytryptamine (5-HT) were measured isometrically. The influence of calcium channel blockers (verapamil, diltiazem and nifedipine), lanthanum chloride and withdrawal of external calcium on the contractile response of veins to dihydroergotamine was investigated. The agonists noradrenaline and 5-HT were studied in comparison. Verapamil and nifedipine up to a concentration of 1 mumol/l caused a shift to the right of the cumulative concentration-response curves for noradrenaline and 5-HT with a reduction of the maximum contraction. Diltiazem affected the contractile response to 5-HT slightly. The venocontractions induced by dihydroergotamine at a concentration of 0.03 mumol/l were inhibited by the calcium channel blockers in a concentration-dependent manner. Verapamil was most effective, followed by nifedipine and diltiazem. In dihydroergotamine-precontracted veins nifedipine produced a more pronounced relaxation than verapamil. Lanthanum chloride (5 mmol/l) inhibited the dihydroergotamine-induced contraction by about 90%. Exposure of veins to a calcium-free medium for 30 min resulted in an inhibition of the dihydroergotamine-induced venocontraction by more than 90%. The addition of calcium ions to the medium caused an increase in the contraction with a maximum which closely resembled that of the control. The present studies demonstrate that the contractile response of human femoral veins to dihydroergotamine depends to a great extent on extracellular calcium. However, the calcium channel blockers verapamil, diltiazem and nifedipine, inhibit the agonist-induced venocontractions in part only.

The use of urokinase in ischemic replanted extremities in rats

We compared the efficacy of intra-arterial infusion of urokinase, a fibrinolytic agent, with that of intra-arterial infusion of nitrendipine, a peripheral calcium-channel blocking agent, in preventing the no-reflow phenomenon in rats after prolonged ischemia at room temperature. Urokinase increased the survival of the limbs after both four and five hours of ischemia at room temperature to 100 per cent compared with 50 and 20 per cent, respectively, in untreated controls. Nitrendipine significantly increased the blood flow but failed to significantly increase the survival of the limb. Scanning electron microscopy was used to assist in the evaluation of the endothelium of the vessels. The etiological mechanism of the no-reflow phenomenon appears to be that ischemia damages the endothelial cells, causing impairment of the fibrinolytic system, retraction of the endothelial membrane, exposure of the subintimal collagen, and fibrin-platelet deposition. Thrombosis of the vessels ensues, resulting in the no-reflow phenomenon.

CLINICAL RELEVANCE

Experimentally, intra-arterial infusion of urokinase increased the survival of the limb in replanted extremities that were subjected to ischemia. This effectively lengthened the safe limit of ischemia at room temperature before microsurgical replantation or elective free-tissue transfer. Clinical trials of the use of intra-arterial fibrinolytic agents for the treatment of revascularized tissue are indicated.

Interactions of dihydroergotamine with etilefrine in human leg veins in vitro and in situ

The aim of the present study was to provide evidence for an interaction of dihydroergotamine (DHE) and etilefrine (Et) with regard to their constrictor effect on human leg veins both in vitro and in situ. In isolated strips of the femoral vein, DHE exerted a concentration-dependent sustained contraction which also continued after washing out the preparation. Et induced a reversible contraction of the strip at considerably higher concentrations as compared to DHE and noradrenaline. When DHE (0.01 mumol/l) and Et (6 mumol/l) were simultaneously applied, there was only an additive venoconstrictor effect. The influence of DHE and Et on the compliance of dorsal foot veins was studied in 14 male volunteers by means of a variable differential transformer. In the short-term experiment, an oral dose of 10 mg DHE was ineffective, whereas after the subcutaneous injection of 1 mg DHE a significant venoconstrictor effect was observed. Et, orally given in a dose of 10 mg, was also ineffective, while 20 mg Et caused a short-lasting effect which could not be augmented by the concurrent intake of 10 mg DHE. When 10 mg Et were administered 30 or 60 min after a single oral dose of 10 mg DHE, a distinct venoconstrictor effect occurred. These findings suggest that no pharmacodynamic synergism of the two drugs can be expected when DHE and Et directly act on the veins. The augmentation of the venoconstrictor in situ effect of Et after pretreating the volunteers with DHE could result from an amelioration of the oral bioavailability of Et by DHE, i.e., from a pharmacokinetic interaction of the two drugs.

Effects of nitro compounds, isosorbide dinitrate, 5-isosorbide mononitrate and glyceryl trinitrate on Ca-uptake into Ca-stores and Ca-release from Ca-stores in rabbit isolated femoral veins and femoral arteries

In organ bath studies, effects of isosorbide dinitrate (ISDN), 5-isosorbide mononitrate (ISMN), a major metabolite of ISDN, and glyceryl trinitrate (GTN) on Ca-uptake into Ca-stores and Ca-release from Ca-stores were tested in the rabbit isolated femoral veins and femoral arteries. ISDN (10(-4) M) and GTN (10(-4) M) inhibited Ca-uptake in the femoral veins but not in the femoral arteries. The selectivity to the femoral veins was not observed in ISMN (10(-3) M) and GTN (3 X 10(-6) M). All the nitro compounds inhibited Ca-release from Ca-stores more effectively in the femoral veins than in the femoral arteries. The present results may explain the selectivity of the nitro compounds to the femoral veins.

Vascular responses of isolated canine and simian femoral arteries and veins to alpha-adrenoceptor agonists

Using isolated, perfused canine and simian femoral veins and arteries, vasoconstrictor responses to 6 alpha-adrenoceptor agonists and to potassium chloride were compared. The order of potencies of alpha-adrenoceptor agonists for inducing constriction was in canine arteries: epinephrine greater than norepinephrine = phenylephrine much greater than clonidine much greater than tyramine much greater than xylazine, in simian arteries: epinephrine greater than norepinephrine greater than phenylephrine greater than clonidine much greater than tyramine greater than or equal to xylazine, in canine veins: epinephrine greater than norepinephrine greater than phenylephrine greater than clonidine greater than or equal to xylazine much greater than tyramine, and in simian veins: norepinephrine = epinephrine greater than phenylephrine greater than clonidine greater than xylazine much greater than tyramine. A selective alpha 2-agonist, xylazine, did not induce any significant constrictor response in canine arteries, indicating a lack of alpha 2-adrenoceptors, but it induced significant constriction in 3 other vessels. In simian femoral arteries and veins dose-response curves to each agonist were steeper than in canine vessels and potassium chloride induced much greater vasoconstriction than in canine vessels, indicating high sensitivity to extracellular calcium concentrations in simian vessels. The cannula inserting method would be useful for investigating pharmacological responses of isolated arteries and veins.

Difference in mode of action of alpha 1-adrenoceptor antagonists on some vascular smooth muscles and efficacy

Effect of YM-12617, a selective and potent alpha 1-adrenoceptor antagonist on dose-response curves of alpha 1-adrenoceptor agonists, norepinephrine, phenylephrine and naphazoline, was tested in isolated rabbit vascular smooth muscles such as the femoral vein, portal vein and aorta. YM-12617 shifted the dose-response curves for norepinephrine and phenylephrine to the right and also declined the maximum response in the femoral vein, where norepinephrine and phenylephrine behaved as low efficacy agonists. Similar results were obtained on the curve of naphazoline in the portal vein, where the efficacy of naphazoline was low. However, the efficacies of norepinephrine, phenylephrine and naphazoline were high in the aorta. The dose-response curves for three alpha 1-agonists were shifted by YM-12617 in a parallel manner in the aorta. The curves of norepinephrine and phenylephrine were also shifted by YM-12617 in the portal vein, where the efficacies of both the alpha 1-agonists were high. The present results suggest that the mode of antagonism between the alpha 1-agonist and alpha 1-antagonist is dependent on the efficacy of the alpha 1-agonist which depends upon the receptor-density in the organ used.

Influence of dihydrolysergic acid amide on serotonergic and alpha-adrenergic receptors in human blood platelets and femoral veins in vitro

The effect of dihydrolysergic acid amide (DLSA) on responses of human blood platelets and isolated postmortem femoral veins to serotonin and catecholamines was studied in vitro in comparison to dihydroergotamine (DHE). DLSA inhibited the 5-HT-potentiated, ADP-induced platelet aggregation in approximately the same concentration range as DHE. It was three orders of magnitude less potent in inhibiting the adrenaline-induced aggregation and specific binding of 3H-yohimbine to intact platelets than DHE. In femoral vein strips, DLSA caused an increase in tone in the same concentration range (0.01-1.0 mumol/l) as DHE; however, its efficacy was somewhat lower. At concentrations of 0.1 to 1.0 mumol/l it antagonized the 5-HT-induced contractile response in a noncompetitive manner, the antagonist potency being one order of magnitude lower than that of DHE. DLSA (1 mumol/l) did not inhibit the noradrenaline-induced venoconstriction. The results show that DLSA possesses agonist activity in femoral veins and 5-HT-antagonist activity in platelets and veins.

Effects of intraportal prostacyclin on hepatic bile flow in the rat

Prostaglandins including prostacyclin (PGI2) have been demonstrated to have choleretic properties in dogs and in this study the effect of PGI2 on bile flow in rats has been investigated. PGI2 at a dose of 250 ng kg-1 min-1 was infused into the mesenteric vein of biliary cannulated rats and bile samples were collected every 10 min. Administration of PGI2 did not produce any significant changes in bile flow and in the output of bile acids or sodium, potassium and bicarbonate as compared to controls infused with buffer alone. Similarly no differences in pancreatic juice flow or bicarbonate output were observed between PGI2 treated rats and controls. No hypotension was observed at this dose of PGI2 given intraportally indicating inactivation by the liver. Thus in the rat, unlike the dog, no effects of PGI2 on bile flow were observed but this could be related to the route of administration.