Citations

Experiments were performed to determine whether acetylcholine affects the sympathetic activation of the cutaneous veins of the dog. Changes in isometric tension of saphenous vein strips were recorded at 37°C in an organ bath. Addition of acetylcholine at 10 -11 to 10 -8 g/ml did not affect basal tension, but larger doses (5 x 10 -8 to 5 x 10 -7 g/ml) caused a contraction of the strips which varied from slight to marked. Acetylcholine at 10 -8 to 10 -7 g/ml caused a further increase in tension when it was added to strips already contracted by norepinephrine, tyramine, KCl, or BaCl 2 ; in contrast, similar doses of acetylcholine caused relaxation of strips contracted by liberation of norepinephrine from the nerve terminals by electrical stimulation (1-10 cps). This relaxation was not influenced by propranolol or hexamethonium but was abolished by atropine (10 -8 g/ml). In intact dogs, the lateral saphenous vein was perfused with autologous blood at constant flow. A sustained venoconstriction was induced either by electrical stimulation of the lumbar sympathetic chain or by a continuous infusion of norepinephrine. An infusion of acetylcholine (10 -7 to 10 -6 g/ml min -1 ) relaxed veins constricted by sympathetic stimulation but not those constricted by norepinephrine. Thus, acetylcholine, in doses smaller than those known to have a direct constrictor effect, causes relaxation of cutaneous veins, probably by inhibiting the release of norepinephrine from nerve terminals.

Experiments were designed and performed to determine whether endothelial function remained chronically impaired after coronary artery reperfusion. Canine left anterior descending coronary arteries were exposed to ischemia (60 minutes) followed by reperfusion (12 weeks). Rings (3-4 mm wide) of the reperfused artery and of normal left circumflex (control) coronary artery segments were suspended in organ chambers containing physiological saline solution (37 degrees C, gassed with 95% O2-5% CO2) for isometric force measurement. Endothelium-independent contractions to KCl or prostaglandin F2 alpha and endothelium-independent relaxations to nitric oxide or isoproterenol were comparable in control and chronically reperfused arteries. However, chronically reperfused coronary arteries exhibited impaired endothelium-dependent relaxations to aggregating platelets. In addition, the reperfused coronary arteries exhibited impaired endothelium-dependent relaxations to the platelet-derived compounds adenosine diphosphate, serotonin, and thrombin. However, the endothelium-dependent relaxations to acetylcholine were comparable between control and reperfused arteries. Thus, after 12 weeks of reperfusion, previously occluded coronary arteries exhibited a selective impairment of endothelium-dependent relaxation evoked by aggregating platelets. In vivo, this phenomenon could favor platelet adhesion, aggregation, and platelet-induced contraction of coronary smooth muscle and thus facilitate ischemic events such as vasospasm and coronary thrombosis.

The inhibitory effects of the endothelium against ergonovine-induced contraction were examined in isolated porcine coronary arteries under normal conditions and after endothelial regeneration. Endothelium-dependent responses were examined in vitro in normal Yorkshire pigs (n = 16) and in pigs that had undergone balloon endothelium removal of the left anterior descending coronary artery (LAD) 4 weeks before the study (n = 10). The presence of a complete endothelial lining was confirmed histologically. In rings from normal arteries contracted with prostaglandin F2 alpha in the presence of indomethacin and ketanserin (a 5-HT2-serotonergic blocker), ergonovine caused endothelium-dependent relaxations. They were attenuated by rauwolscine (an alpha 2-adrenergic blocker), inhibited by methiothepin (a combined 5-HT1- and 5-HT2-serotonergic blocker) or by pertussis toxin (an inhibitor of several G proteins) and abolished by oxyhemoglobin (a selective inactivator of endothelium-derived relaxing factor). In quiescent rings from normal arteries, ergonovine caused contractions that were inhibited by the presence of the endothelium; this endothelium-dependent inhibition was abolished by oxyhemoglobin. The direct contractions were not affected by prazosin (an alpha 1-adrenergic blocker), rauwolscine, 6-hydroxydopamine (an agent causing chemical sympathetectomy), or diphenhydramine (an H1-histaminergic blocker) but were inhibited by ketanserin. In rings with regenerated endothelium contracted with prostaglandin F2 alpha, the endothelium-dependent relaxations to ergonovine were reduced significantly and were not inhibited by pertussis toxin. In quiescent rings with regenerated endothelium, the endothelium-dependent inhibition of ergonovine-induced contraction was less.(ABSTRACT TRUNCATED AT 250 WORDS)

The present study examined the protective role of the venous endothelium against aggregating platelets and its modulation by diet. Yorkshire pigs were fed a regular chow (control pigs), 2% high-cholesterol diet (for 10 weeks, cholesterol-fed pigs), and regular chow plus cod-liver oil (30 ml/day for 4 weeks, oil-fed pigs). Endothelium-dependent responses were examined in vitro in rings of femoral veins in the presence of the inhibitor of cyclooxygenase indomethacin. In control pigs, aggregating platelets, serotonin, and ADP caused endothelium-dependent relaxations. The platelet-induced relaxations were attenuated by methiothepin (a combined 5-HT1 and 5-HT2 serotonergic blocker) or apyrase (an ADPase and ATPase) and were abolished by the combination of the two agents. In quiescent rings, platelets caused contractions, which were reduced in the presence of endothelium; the contractions were prevented by ketanserin (a 5-HT2 serotonergic blocker) or methiothepin but not by R 68 070 (a thromboxane A2 receptor blocker) or dazoxiben (a thromboxane-synthetase blocker). In cholesterol-fed pigs, the platelet-induced relaxations were not altered, whereas in oil-fed pigs, the endothelium-dependent relaxations to platelets, serotonin, and ADP were augmented. Platelet-induced contractions were significantly reduced in rings with endothelium from oil-fed pigs, whereas the contractions were comparable in rings without endothelium among the three groups. Endothelium-dependent relaxations in response to the calcium ionophore A23187, direct relaxations in response to sodium nitroprusside, and direct contractions in response to potassium chloride were comparable among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The endothelium releases the powerful vasodilator and antiaggregatory substance, EDRF, both under basal conditions and upon stimulation by a wide variety of agents. Endothelial injury or dysfunction may play an important role in the spasmogenicity of the coronary artery, although other possible alterations related to atherosclerosis should also be considered. Among the possible stimuli, aggregating platelets are important as a source of vasoconstrictor substances. The endothelium may also produce the vasoactive substances EDHF and EDCF(s). Their pathophysiologic significance remains to be determined.

This study examined the effects of dietary supplementation with cod-liver oil on impaired endothelium-dependent relaxations in hypercholesterolemia and in atherosclerosis in porcine coronary arteries. Sixteen male Yorkshire pigs underwent balloon endothelium removal of the left coronary arteries and were fed a 2% high-cholesterol diet for 10 weeks, with or without dietary supplementation of cod-liver oil (30 ml/day) (oil-fed and cholesterol-fed groups, respectively). This model allowed the simultaneous examination of the effects of dietary cod-liver oil on vascular reactivity in hypercholesterolemia alone (right coronary artery) and in atherosclerosis (left coronary artery). After 10 weeks of feeding, the dietary treatment with cod-liver oil caused an increase in plasma levels of eicosapentaenoic acid and a decrease in the plasma levels of arachidonic acid, whereas the treatment had no significant effect on the increases in plasma lipid levels induced by the high-cholesterol feeding. Morphometric analysis showed significant inhibition of coronary atherosclerosis by the treatment. Endothelium-dependent responses were examined in vitro in ring preparations and in bioassay experiments. Endothelium-dependent relaxations to bradykinin, serotonin, and adenosine 5'-diphosphate were larger in both right and left coronary arteries from oil-fed than from cholesterol-fed animals. Aggregating platelets from cholesterol-fed and oil-fed pigs induced comparable, larger endothelium-dependent relaxations in rings from oil-fed than from cholesterol-fed pigs. The contractions induced by serotonin or aggregating platelets were significantly inhibited in rings with endothelium from oil-fed pigs, whereas they were comparable in rings without endothelium in both groups. Relaxations to sodium nitroprusside and contractions to potassium chloride or serotonin were comparable in rings without endothelium in both groups. The bioassay experiments revealed that the release of endothelium-derived relaxing factor in response to bradykinin and the relaxations of vascular smooth muscle to the endothelial factor were greater after the fish-oil diet. These results indicate that dietary supplementation of cod-liver oil delays the impairment of endothelium-dependent relaxations in hypercholesterolemia and in atherosclerosis, partly because of an improved release of endothelium-derived relaxing factor and partly because of an improved relaxation of coronary smooth muscle to the factor.

To study the effect of dietary supplementation with fish oil on endothelium-dependent responses, Yorkshire pigs were maintained on a normal diet or on a low (0.6 ml/kg/day) or a high (1.0 ml/kg/day) dose of cod-liver oil for 4 weeks. Endothelium-dependent responses were examined in vitro in rings of proximal left anterior descending coronary arteries taken from control and treated animals studied in parallel. Endothelium-dependent relaxations in response to bradykinin, serotonin, adenosine diphosphate, and thrombin were facilitated in arteries from treated but not in those from control animals, whereas the relaxations in response to A23187 were unaltered. The facilitated relaxations were not altered by indomethacin but significantly inhibited by methylene blue. Aggregating platelets from control and treated pigs induced comparable, facilitated endothelium-dependent relaxations in rings taken from treated pigs. The platelet-induced contractions were significantly reduced in rings with endothelium taken from treated pigs, and they were comparable in rings without endothelium in both groups. Aggregating platelets from control and treated pigs released comparable amounts of serotonin and thromboxane A2. Endothelium-dependent relaxations induced by arachidonic acid and eicosapentaenoic acid were unaltered, whereas transient endothelium-dependent contractions induced by arachidonic acid were significantly reduced by the treatment with cod-liver oil. Relaxations to sodium nitroprusside or isoproterenol,and contractions to potassium chloride or serotonin were not different in rings without endothelium from control or treated pigs. These results indicate that dietary supplementation with cod-liver oil facilitates endothelium-dependent relaxations and inhibits endothelium-dependent contractions in porcine coronary arteries.

We sought to determine the effect of dietary omega-3 polyunsaturated fatty acids on cerebrovascular endothelium-dependent responses in studies performed on isolated porcine basilar arteries. Male Yorkshire pigs (6-8 weeks old) were kept for 4 weeks on a standard diet (control group, n = 12) or on chow supplemented with polyunsaturated fatty acids (eicosapentaenoic acid, 3.5 g/day, or docosahexaenoic acid, 1.5 g/day; treated group, n = 12). Isometric tension recording of the basilar artery was carried out and responses were compared between the two groups. The regimen resulted in a decrease in the plasma arachidonic acid level and an increase in eicosapentaenoic acid. Endothelium-dependent relaxations induced by bradykinin and adenosine diphosphate were augmented in the basilar arteries of the treated group. Incubation with indomethacin (10(-5) M) prevented the augmentation of the relaxations induced by bradykinin, but not those caused by adenosine diphosphate. The indomethacin-sensitive, endothelium-dependent contractions to arachidonic acid remained comparable in the two groups, indicating that the activity of cyclooxygenase was not affected by the diet. Dietary supplementation with omega-3 polyunsaturated fatty acids enhances endothelium-dependent relaxations in the basilar artery by two mechanisms: 1) replacement of endogenous arachidonic acid and suppression of the concomitant release of vasoconstrictor prostaglandins from the endothelium, and 2) enhancement of the release of endothelium-derived relaxing factor.

The effects of the calcium ionophore A23187, arachidonic acid, and acetylcholine were studied in isolated canine basilar arteries. Rings with and without endothelium were suspended for isometric tension recording in physiological saline. In unstimulated rings, A23187, arachidonic acid, and acetylcholine caused endothelium-dependent contractions. The contractions of rings caused by uridine 5'-triphosphate were not affected by removal of the endothelium. An inhibitor of cyclooxygenase, indomethacin (10(-5) M), prevented excitatory responses to A23187, arachidonic acid, and acetylcholine but did not alter contractions caused by KCl. An inhibitor of thromboxane synthetase, dazoxiben (10(-4) M), significantly reduced endothelium-dependent contractions to A23187 and arachidonic acid but did not significantly affect contractions caused by acetylcholine. These results demonstrate that A23187, arachidonic acid, and acetylcholine cause excitatory endothelium-dependent responses in canine cerebral blood vessels by increasing the release of product(s) of cyclooxygenase from endothelial cells; in the case of A23187 and arachidonic acid, thromboxane A2 contributes to the endothelium-dependent contractions.