A human arterial preparation for studying the effects of vasoactive agents

Differing calcium sensitivities of human cerebral and digital arteries, human metatarsal veins, and rat aorta

1. The effects of the voltage dependent calcium channel blocking agent nifedipine, and of a calcium free bathing medium, on the responses of human blood vessels obtained postmortem to various agonists have been compared with those of the rat aorta. The human vessels studied were digital arteries, basilar arteries and metatarsal veins. 2. Responses to potassium chloride (5-80 mM), noradrenaline (10(-9)-10(-4) M), 5-hydroxytryptamine (10(-8)-10(-4) M) and U46619 (10(-11)-10(-6) M), in the presence and absence of nifedipine (1, 10, and 100 nM) or in a calcium-free bathing medium, were assessed using an area-under-curve analysis. 3. In general, the order of sensitivity of the vessels to inhibition of agonist induced contractures by nifedipine was basilar arteries greater than metatarsal veins = digital arteries = rat aorta. 4. For all the vessels, the order of sensitivity for antagonism of responses to the agonists by nifedipine was potassium chloride greater than 5-hydroxytryptamine = noradrenaline greater than U46619. 5. A calcium free bath inhibited responses of digital arteries to potassium chloride more than noradrenaline, 5-hydroxytryptamine or U46619, and responses of rat aorta to a greater extent than responses of the digital arteries. 6. In the rat aorta, a calcium-free bath inhibited responses to all agonists (except KCl) to a greater degree than did nifedipine. 7. We conclude that inhibition of extracellular calcium entry through voltage dependent calcium channels affects contractile responses of different blood vessels to different extents, and, within the same blood vessel, responses to different contractile agonists to different extents.

Lack of effect of granulocyte-macrophage colony stimulating factor on the rat aorta or human saphenous vein

1. In order to assess whether the observed hypotensive response in some patients given human granulocyte-macrophage colony stimulating factor (GM-CSF) is caused by a direct vascular effect of the GM-CSF, the effects of mouse and human GM-CSF were examined in rat aortic rings and human saphenous veins respectively. 2. No effects of GM-CSF were observed, either in the presence or absence of endothelium, on responses to the alpha-adrenoceptor agonist phenylephrine. 3. These data suggest that GM-CSF does not have direct effects on either vascular endothelium or smooth muscle, and that a direct vascular effect of GM-CSF is not the explanation for the observed clinical response.

Platelet serotonin in systemic sclerosis

Platelet serotonin concentrations were measured in 43 patients with systemic sclerosis, in 11 patients with primary Raynaud's phenomenon, and in 38 normal controls. Patients with the CREST variant (calcinosis, Raynaud's phenomenon, oesophageal dysmotility, sclerodactyly, telangiectasia) had significantly lower platelet serotonin concentrations than normal controls. Patients with diffuse systemic sclerosis had normal platelet serotonin concentrations. In patients with CREST treatment with ketanserin, a specific serotonin antagonist, normalised platelet serotonin concentrations. These data provide further evidence suggesting that in systemic sclerosis, particularly the CREST variant, there is widespread platelet activation.

Barium ions reduce contraction kinetics in rat tracheal smooth muscle

In isolated rat tracheal smooth muscle, contraction was induced by electrical field stimulation (= EL; frequency = 30 Hz; pulse duration = 0.17 ms), 10 mumol/l acetylcholine (= ACh), potassium depolarization (137 mmol/l K), or by 10 mmol/l barium (= BA). Contraction kinetics were studied by analyzing tension recovery after cessation of a 1.8 s length vibration (100 Hz sinusoidal; amplitude = 6% of the muscle length). The contraction speed was high during EL as can be seen from the short time constant of post-vibration tension recovery (tau = 5.90 +/- 0.14 s) found 30 s after onset of stimulation. The time constants of tension recovery during long-term (50 min) activation averaged 12.88 +/- 0.32 s (K) and 13.24 +/- 0.17 s (ACh) when the vibration was stopped 8-45 min after onset of activation. As both of these stimuli act mainly via cholinergic receptors, similar down-regulated contraction kinetics occur under steady-state conditions of tonic contraction. However, during barium activation steady-state conditions need a 45 min agonist incubation, and the time constant of post-vibration tension recovery was extended to 34.05 +/- 2.21 s. Thus, calcium may be replaced by barium in the force generation process but it produces slower cycling of cross-bridges.

Serotonin and the vascular wall

Serotonin possesses both vasoconstrictor and vasodilator properties. The constrictor action of the monoamine can be due to: (a) direct activation of vascular smooth muscle; in most blood vessels, this is mediated by S2-serotonergic receptors; (b) augmentation (amplification) of the action of other endogenous vasoconstrictors such as catecholamines, angiotensin II and the prostanoids; and (c) release of norepinephrine from adrenergic nerves. The dilator action of serotonin can be due to: (a) activation of endothelial cells which release endothelium-derived relaxing factor(s); this response appears to be mediated by S1-serotonergic receptors; (b) direct inhibition of vascular smooth muscle; (c) inhibition of adrenergic neurotransmission by an action on S1-serotonergic prejunctional receptors; and (d) release of other endogenous mediators. The net effect of serotonin on the blood vessel wall depends on: (a) the integrity of the endothelium; (b) the degree of activation of the vascular smooth muscle; (c) the level of sympathetic tone; and (d) local (e.g. PO2, temperature) and chronic (e.g. blood pressure) modulating factors. S2-serotonergic antagonists prevent the constrictor action of serotonin, and often unmask its dilator potential.

Vascular responsiveness of simian digital artery to various vasoactive substances

The stainless steel cannula inserting method was used to observe vascular effects of 7 vasoactive substances on the isolated and cold-stored digital artery of the monkey. The arterial preparation was suspended in a bath at 37 degrees C and perfused with Ringer's solution under constant flow rate. Drugs were administered in the endothelial side of the artery through a cannulated tubing, and the response was obtained as changes in perfusion pressure. All used agonists increased perfusion pressure in a dose-related manner. The order of potency for inducing vasoconstriction was norepinephrine greater than serotonin = phenylephrine = clonidine greater than xylazine greater than tyramine greater than potassium chloride. Inhibiting effect of prazosin (0.001-0.01 microgram) was greater on phenylephrine (0.03 microgram)-induced contractile responses than on clonidine (0.03 microgram)-induced responses, and the reverse was true in the case of yohimbine (0.01-1.0 microgram). Thus, it was suspected that the simian digital artery would be a good model for in vitro investigation of vascular responsiveness as a conduit artery which mainly supplies blood flow to the skin, and that this artery might be contracted not only via postjunctional alpha 1- but also alpha 2-adrenoceptors.

Interaction between platelet-released serotonin and thromboxane A2 on human digital arteries

Synergism between the contractile effects of platelet-derived serotonin (5HT) and thromboxane A2 (TXA2) on a human blood vessel has been investigated by incubating strips of digital arteries in subcontractile concentrations of either 5HT or the TXA2-mimetic agent U46619. Either agonist U46619 or 5HT, in subcontractile concentrations, significantly potentiated the contractile response to the other. The 5HT antagonist ketanserin (10 mumol/l), the Ca2+ antagonist drugs verapamil (3 mumol/l), or nifedipine (10 nmol/l), or a Ca2+-free bathing medium, reduced the contractile responses to 5HT, but had no effect on the potentiation mediated by U46619. The interaction between TXA2 and 5HT derived from platelets was studied by measuring responses to platelets 1 min after aggregation (in the absence or the presence of ketanserin 10 mumol/l), and 20 min after aggregation. The results indicated that the response to platelets mediated by TXA2 and 5HT was greater than the sum of those mediated by TXA2 or 5HT separately. It is concluded that synergism between the contractile effects of 5HT and U46619 occurs in human blood vessels; that this is mediated by enhanced utilization of intracellular, rather than extracellular calcium; and that synergism can also occur when 5HT and TXA2 are released from stimulated human platelets.

Neuronally released norepinephrine does not preferentially activate postjunctional alpha 1-adrenoceptors in human blood vessels in vitro

Human isolated digital arteries and metatarsal veins, obtained postmortem, have been used to compare the effects of alpha-adrenoceptor antagonists on contractile responses to nerve stimulation. The antagonists used were prazosin, rauwolscine, BE 2254, and yohimbine. Rauwolscine (alpha 2-antagonist), as well as prazosin and BE 2254 (alpha 1-antagonists), in concentrations of 10(-9), 10(-8), and 10(-7) mol/liter, potently antagonized the frequency-response curves to nerve stimulation. Yohimbine (alpha 2-antagonist) was slightly less potent, failing to antagonize responses to nerve stimulation in arteries at the concentration of 10(-9) mol/liter significantly, but producing potent antagonism of responses in both arteries and veins at higher concentrations (10(-8), 10(-7) mol/liter). All antagonists inhibited the contractile responses to nerve stimulation to a greater extent in veins than in arteries. Rauwolscine (10(-9), 10(-8), and 10(-7) mol/liter) and BE 2254 (10(-7) but not 10(-8) mol/liter) significantly enhanced stimulation-induced tritium efflux in arteries and veins. These results suggest that alpha 2-adrenoceptor antagonists, despite their prejunctional effects, are potent antagonists of contractile responses to nerve stimulation. Thus, in these human blood vessels, endogenously released norepinephrine does not preferentially activate postjunctional alpha 1-adrenoceptors, but activates receptors with the properties of both the alpha 1- and alpha 2-adrenoceptor subtypes.

In vitro calcium dependence of arterial smooth muscle in human hypertension

Digital arteries, removed at autopsy from 12 hypertensives and 11 normotensives, have been compared in vitro for the calcium dependence of contractures produced by potassium chloride and noradrenaline, and the potency of verapamil to antagonize contractures to noradrenaline. No significant differences were found between the vessels from the hypertensives and normotensives for the pD2 values or the maximum response to either potassium chloride or noradrenaline in bathing solutions containing 2.5, 1.0, 0.5 or 0 mmol/l calcium chloride. There were also no significant differences between the vessels, from the hypertensive or normotensives, in the pD2 values for the addition of calcium chloride to arteries exposed to potassium chloride or noradrenaline in a calcium free bathing medium, in the ability of verapamil to shift the pD2 values for noradrenaline, nor in the ability of verapamil to reduce the maximum responses to noradrenaline (except at the two highest concentrations of verapamil tested). It is concluded that it is unlikely to be a primary abnormality of the mechanisms regulating calcium ion entry and release in vascular smooth muscle in human hypertension.

Responses of human arterial muscle to stable vasoactive substances released from human platelets by collagen and heat aggregated IgG

The supernatant solutions obtained after aggregation or sonication of washed human platelets were superfused over preparations of human isolated digital arteries using a small volume bioassay method. The agents released from the platelets caused strong contractions of the artery strips. Platelet aggregation induced by 10 micrograms/ml collagen or by 100 micrograms/ml heat aggregated IgG, released 31.5% and 38.5% respectively, of the contractile activity produced by sonication of the platelets. The quantitative contractile effect of supernatants from platelets aggregated by 50 micrograms/ml IgG was significantly less than that for 100 micrograms/ml HA IgG. Similarly, the maximum contractile effect of supernatants from platelets aggregated by 300 ng/ml collagen was significantly less than that for 1 microgram/ml collagen. This suggests that the concentration of contractile agents released from platelets depends on the concentration of aggregating stimulus. Comparison with concentration-effect curves for exogenous serotonin suggests that if the contractility of the platelet supernatant occurring after sonication of platelets is solely due to serotonin, then it is present in a concentration of approximately 3.3 X 10(-6) mol/l (6.6 nmol per 10(9) platelets). It is suggested from this study that in certain clinical situations characterized by hypertension, and in which circulating immune complexes have been found, in vivo platelet activation by immune complexes may be releasing sufficient concentrations of serotonin to constrict peripheral blood vessels and contribute to the hypertension.

Vascular effects of ergot alkaloids: a study on human basilar arteries

Postmortem examinations on human basilar arteries were performed in vitro by recording isometric tension from spiral strips in tissue baths at 37 degrees C. Antagonism of 5-HT by ergotamine, dihydroergotamine and methysergide was of the non-competitive type, that of noradrenaline was either absent (i.e. ergotamine) or considerably weaker. In addition each ergot alkaloid acted as a partial agonist in the following order of efficacy: ergotamine greater than dihydroergotamine greater than methysergide, producing pD2 values of 9.30, 9.60 and 7.10 respectively. Evidence is provided that the stimulant activity of ergotamine is mediated through 5-HT receptors. The present results are compared to those obtained on isolated human vein strips as well as to those on canine blood vessels.

Techniques for testing isolated blood vessels

There are many different techniques described for studying isolated blood vessels, either human or animal. 1. For postsynaptic responses, spiral strip preparations using isometric tension monitoring probably allow the greatest flexibility for drug concentration-effect relationships. Isotonic tension may be monitored if extreme sensitivity is necessary and ring preparations probably better mimic the situation in vivo, but are harder to use. 2. Minor differences in salt solutions, pH, temperature and degree of oxygenation are probably not important except in special situations such as pH alterations when studying cerebral vessels and pO2 alterations when studying pulmonary or umbilical vessels. It is most important that the calcium concentrations remain constant as altered contractile effect may occur with small alterations in the calcium concentration of the physiological salt solution. 3. Electrical stimulation is necessary for studying presynaptic mechanisms. Most commonly, vessels are canulated and perfused through their lumen and superfused to remove the transmitter which has overflowed from the perivascular nerve stimulation. Neurotransmitter is then measured after preloading with tritiated noradrenaline. Electrical stimulation can also be performed on spiral strips which are immersed in small volume tissue baths allowing rapid changes in the bathing fluid, and although this method allows better monitoring of the postsynaptic responses associated with the electrical stimulation, it is more difficult to perform than perfusion and superfusion.

Comparison of the effects of endrallazine, hydrallazine and verapamil on human isolated arteries and veins

1. The antagonist effects of endrallazine (BQ 22-708), hydrallazine and verapamil have been studied on the contractile responses produced by various agonists on human digital arteries and metacarpal veins obtained post mortem. 2. Endrallazine and hydrallazine antagonized the contractile responses to noradrenaline and serotonin in arteries by shifting the concentration-effect curves to the right and by reducing the maximum responses to both agonists. Neither drug had any effect on responses to BaCl2 in either tissue. 3. The same concentrations of endrallazine and hydrallazine which antagonized responses to noradrenaline and serotonin in arteries, had no effect on concentration-effect curves to those agonists in veins. 4. Hydrallazine was significantly more potent than endrallazine in reducing the maximum response to noradrenaline in arteries, and was less potent than endrallazine in reducing the maximum response to serotonin. 5. Verapamil antagonized the vasoconstrictor effect of all agonists tested in both arteries and veins. 6. It is concluded that in a similar manner to hydrallazine, endrallazine has a direct effect on human vascular smooth muscle at concentrations which are probably similar to those occurring in vivo. Both hydrallazine and endrallazine may produce selective arterio-dilatation by preventing the release of bound calcium from intracellular storage sites, an effect which is different to that of verapamil.

Prostacyclin and cerebral vessel relaxation

The authors have studied the ability of prostacyclin to reverse contractions of human basilar arteries in vitro that were induced by a wide range of substances implicated in the etiology of cerebral arterial spasm. Prostacyclin (10(-10) to 10(-6)M) caused a dose-related reversal of contractions induced by 5-hydroxytryptamine, noradrenaline, angiotensin II, prostaglandin (PG)F2 alpha, and U-46619 (a thromboxane-A2 mimetic). These agents were tested at concentrations or volumes that produced almost maximum or maximum responses and those that produced approximately 50% of the maximum response. Contractions induced by maximum concentrations of angiotensin II and U-46619 were least affected by prostacyclin. In addition, contractions induced by thromboxane-A2 generated from guinea-pig lung were reversed in a dose-dependent fashion by prostacyclin. This ability of prostacyclin to physiologically antagonize contractions of the human basilar artery in vitro induced by high concentrations of various spasmogenic agents suggests that such a potent vasodilator agent or more stable analogue may be of value in the treatment of such disorders as cerebral arterial spasm following subarachnoid hemorrhage.

Immune complexes and vasoactivity generated from platelets in pre-eclampsia

In vivo platelet activation by circulating immune complexes has been suggested as one of the underlying mechanisms in preeclampsia. Using a modification of the polyethylene glycol protein-A immune complex assay, immune complexes were found in excess of the equivalent of 20 micrograms/ml heat aggregated IgG in fourteen out of twenty patients diagnosed as having pre-eclampsia. Only six out of nineteen normal controls were found to have similar levels of immune complexes. Furthermore, using a small volume bio-assay method, concentrations of heat aggregated IgG in excess of 20 micrograms/ml were found to activate platelets to release sufficient concentrations of vasoactive agents to constrict a human blood vessel in vitro. These results support the hypothesis that in vivo platelet activation by immune complexes can release sufficient concentrations of vasoactive agents to contribute to the hypertension characteristic of pre-eclampsia.

Some in-vitro comparisons of synovial cells dispersed by trypsin from rheumatoid and nonrheumatoid synovium

Life spans, growth rate, glucose utilisation, response to hydrocortisone, and intracellular activity of lysosomal N-acetyl-beta-glucosaminidase of rheumatoid synovial cells in culture were compared with these properties in nonrheumatoid synovial cells. Except for a small group of RA cells derived from tissue explants, the cells were all isolated by trypsinisation of synovial tissue, either within intact joints or after synovectomy. Cell lines were established by passaging with trypsin. In a study of 56 nonrheumatoid and 24 rheumatoid synovial lines isolated during a 7-year period the latter were found to have a shortened mean life expectancy in culture, though there was wide variation between individual lines. This is in agreement with reported findings from untrypsinised explant-derived synovial lines. However, in the present study mean multiplication rates were identical for nonrheumatoid and rheumatoid synovial cells, and on clear differences could be demonstrated for the other properties studied. No correlation could be found between the life spans of synovial cell lines and the age of the cell donors, whether from rheumatoid or nonrheumatoid sources. Rheumatoid synovial cells isolated from intact joints were notable for especially high proportions of macrophage-like cells and suppression of fibroblasts. In most cases cell lines could not be established from these rheumatoid primary cultures, and in others the lines were short-lived. Early association with relatively high proportions of macrophage-like cells in rheumatoid cultures might thus be important in influencing the establishment and behaviour of synovial cell lines.

A comparison of the effects of hydrallazine, diazoxide, sodium nitrite and sodium nitroprusside on human isolated arteries and veins

1 Human common palmar digital arteries and dorsal metacarpal veins have been studied in vitro to investigate the responses of arterial and venous muscle to hydrallazine, diazoxide, nitroprusside and sodium nitrite. 2 Tissues were removed at autopsy, cut into helical strips and suspended in organ baths under identical conditions. The contractile response to noradrenaline was tested in the presence of the same concentrations of the vasodilator drugs in arteries and veins. 3 Hydrallazine antagonised contraction of arteries, but not veins to noradrenaline. Diazoxide, nitroprusside or sodium nitrite antagonised responses in both arteries and veins. Diazoxide and nitrite were more effective on arteries and nitroprusside was more effective on veins. 4 These results are in accord with clinical observations and confirm that there are differences in the susceptibility of human arterial and venous smooth muscle to vasorelaxant drugs.

Reduced responses to noradrenaline of isolated digital arteries from hypertensives

1. Strips of digital arteries obtained post-mortem from thirteen hypertensives have been compared with those from thirteen normotensives. 2. The strips from hypertensives and from males had a significantly greater response to 80 mmol/l KCl, but this was due to the increased cross-sectional areas of the strips from hypertensives and from males. 3. The maximum responses to noradrenaline and serotonin, but not the pED50 values, were significantly smaller in the strips from the hypertensives than in those from the normotensives, but there were no differences between the strips from hypertensives and normotensives in either the maximum response or pED50 values to angiotensin or barium chloride. 4. it is concluded that these results suggest a decreased number of alpha-receptors are present in human hypertensive vascular smooth muscle and this is a sequel either of the increased pressure itself, or of increased exposure in vivo of the blood vessels from hypertensives to noradrenaline.

Are neuronal uptake mechanisms responsible for the difference in sensitivity to noradrenaline between human arteries and veins?

1. The sensitivity of human metacarpal veins and digital arteries obtained post-mortem to noradrenaline and phenylephrine has been tested. 2. pED50 values for noradrenaline were significantly higher in the veins (6.99, s.e.m. = 0.08) than in the arteries (6.56, s.e.m. = 0.09), whereas pED50 values for phenylephrine in the two tissues were not significantly different (arteries: 6.24, s.e.m. = 0.09; veins: 6.26, s.e.m. = 0.05). 3. The addition of propranolol (4 x 10(-6) mol/l) alone, or in combination with hydrocortisone (4 x 10(-5) mol/l), did not affect the responses to either noradrenaline or phenylephrine. The further addition of cocaine (3 x 10(-5) mol/l) slightly shifted the noradrenaline and phenylephrine concentration-effect curves to the left in both arteries and veins, but veins were still found to be more sensitive than arteries to noradrenaline whilst there was still no difference in the sensitivity of veins and arteries to phenylephrine. 4. Cocaine also slightly potentiated responses to barium chloride, potassium chloride and serotonin. 5. It is concluded that the difference in sensitivity to noradrenaline between arteries and veins cannot be explained by differences in neuronal uptake and it is possible that there may be differences in the properties of the postsynaptic alpha-adrenoreceptors of the two tissues. It is also concluded that the potentiation of the contractile effect of noradrenaline produced by cocaine is not solely due to inhibition of neuronal uptake of amines.