Modification of high saturated fat diet with n-3 polyunsaturated fat improves glucose intolerance and vascular dysfunction.

AIMS: The ability of dietary enrichment with monounsaturated fatty acid (MUFA), n-3 or n-6 polyunsaturated fatty acids (PUFAs) to reverse glucose intolerance and vascular dysfunction resulting from excessive dietary saturated fatty acids is not resolved. We hypothesized that partial replacement of dietary saturated fats with n-3 PUFA-enriched menhaden oil (MO) would provide greater improvement in glucose tolerance and vascular function compared to n-6 enriched safflower oil (SO) or MUFA-enriched olive oil (OO). METHODS: We fed mice a high saturated fat diet (HF) (60% kcal from lard) for 12 weeks before substituting half the lard with MO, SO or OO for an additional 4 weeks. At the end of 4 weeks, we assessed glucose tolerance, insulin signalling and reactivity of isolated pressurized gracilis arteries. RESULTS: After 12 weeks of saturated fat diet, body weights were elevated and glucose tolerance was abnormal compared to mice on control diet (13% kcal lard). Diet substituted with MO restored basal glucose levels, glucose tolerance and indices of insulin signalling (phosphorylated Akt) to normal, whereas restoration was limited for SO and OO substitutions. Although dilation to acetylcholine was reduced in arteries from mice on HF, OO and SO diets compared to normal diet, dilation to acetylcholine was fully restored and constriction to phenylephrine was reduced in MO-fed mice compared to normal. CONCLUSION: We conclude that short-term enrichment of an ongoing high fat diet with n-3 PUFA rich MO, but not MUFA rich OO or n-6 PUFA rich SO, reverses glucose tolerance, insulin signalling and vascular dysfunction.

Role of sex differences and effects of endothelial NO synthase deficiency in responses of carotid arteries to serotonin.

We examined the hypothesis that contraction of the carotid arteries to serotonin is normally inhibited by endothelial NO synthase (eNOS) and is enhanced in mice lacking the gene for eNOS. Because the influence of eNOS may vary with the sex of the mouse, we also tested whether responses to serotonin were dependent on sex. We studied carotid arteries in vitro from littermate control (eNOS(+/+)) mice, heterozygous (eNOS(+/-)) mice, and homozygous eNOS-deficient (eNOS(-/-)) mice (male and female). Contraction to serotonin was greater in male eNOS(+/+) mice than in female eNOS(+/+) mice. In male mice, contraction to serotonin increased by approximately 40% and 2.5-fold in male eNOS(+/-) and eNOS(-/-) mice, respectively. Contraction to serotonin was more than doubled in female eNOS(+/-) mice and increased >5-fold in arteries from eNOS(-/-) mice. In contrast, maximum vasoconstriction to U46619 was similar in male and female eNOS(+/+), eNOS(+/-), and eNOS(-/-) mice. Relaxation to acetylcholine was not different in male and female eNOS(+/+) or eNOS(+/-) mice but was absent in eNOS(-/-) mice. These findings suggest that the contraction of carotid arteries to serotonin is influenced by the sex of the animal. eNOS deficiency in gene-targeted mice is associated with enhanced contraction to serotonin, particularly in female mice, providing direct evidence that eNOS is a major determinant of vascular effects of serotonin. The results with eNOS(+/-) mice suggest a "gene-dosing" effect for vascular responses to serotonin.

Response of coronary microvascular collaterals to activation of ATP-sensitive K+ channels.

OBJECTIVE: Studies have suggested that collateral vessels of the coronary and hind-limb circulations are more sensitive to activation of ATP-sensitive K+ channels than are non-collateral vessels. The objective of the present study was to compare responses of microvascular non-collaterals, native collaterals and stimulated collaterals in the heart to three vasodilators which act through different mechanisms: activation of ATP-sensitive K+ channels with aprikalim, release of nitric oxide with acetylcholine, and endothelium-independent activation of soluble guanylate cyclase with nitroglycerin. METHODS: Collateral growth was stimulated by placing an Ameroid occluder on the proximal left circumflex artery in dogs. Non-collaterals, native collaterals and stimulated collaterals (100-220 microns in diameter) were isolated, cannulated on micropipettes and pressurized in vitro. Vessel diameters were measured using videomicroscopy. RESULTS: Dilation to aprikalim (10(-8)-10(-5) M), acetylcholine (10(-9)-10(-6) M) and nitroglycerin (10(-8)-3 x 10(-4) M) were similar in non-collateral, native collateral and stimulated collaterals. Dilation of native collaterals to aprikalim and acetylcholine was attenuated by glibenclamide (10 microM), an inhibitor of ATP-sensitive K+ channels, but not by tetraethylammonium (1 mM), a non-selective inhibitor of K+ channels. Dilation of native collaterals to acetylcholine but not aprikalim was also inhibited by nitro-L-arginine (10 microM), an inhibitor of nitric oxide synthase. CONCLUSION: These findings suggest that microvascular native and stimulated collaterals respond to activation of ATP-sensitive K+ channels and acetylcholine similar to non-collaterals of similar size. Thus, changes in reactivity of collaterals to activation of ATP-sensitive K+ channels are not related to changes in the ability of the vessels to respond to vasodilators but may primarily be determined by a change in the distribution of collateral vessel size.

Effect of acute hypertension in the coronary circulation: role of mechanical factors and oxygen radicals.

OBJECTIVE: In previous studies severe, acute hypertension damaged the endothelium in proximal coronary arteries and selectively potentiated constriction of the artery to serotonin. In the present study we investigated the role of several mechanical factors and of oxygen radicals in this response. DESIGN: To test the role of mechanical factors in the response to acute hypertension, the effect of different magnitudes of elevation of perfusion pressure and the rate of the rise in perfusion pressure were studied. Pharmacologically induced increases in blood pressure were produced by infusion of angiotensin II or phenylephrine. The role of oxygen radicals was tested by measuring responses to serotonin before and after increases in perfusion pressure in dogs treated with a combination of superoxide dismutase and catalase or with deferoxamine. METHODS: In open-chest anesthetized dogs the diameter of the left anterior descending coronary artery (LADCA) was measured using sonomicrometer crystals, and the LADCA was perfused at a constant pressure of 80 mmHg from a reservoir. Responses to serotonin were measured at this perfusion pressure before and after an abrupt increase in perfusion pressure. RESULTS: Intracoronary serotonin (5 or 50 micrograms/min) produced a dose-dependent constriction of the LADCA while increasing coronary flow. Abruptly increasing the coronary perfusion pressure from 80 to 120, 150 or 200 mmHg augmented the constriction to serotonin twofold, whereas increases in perfusion pressure to 100 mmHg had no effect. Increasing coronary pressure slowly (over a 4-min period) from 80 to 200 mmHg augmented constriction to serotonin. Inducing acute hypertension (coronary pressure 200 mmHg) pharmacologically with angiotensin II also augmented constriction to serotonin, whereas phenylephrine-induced hypertension did not. Superoxide dismutase, a scavenger of superoxide anions and catalase, a scavenger of hydrogen peroxide, prevented the augmented constriction to serotonin following a pressure increase. Deferoxamine, which prevents generation of hydroxyl radicals from superoxide anions and hydrogen peroxide, also prevented the enhanced constriction to serotonin following an acute pressure increase. CONCLUSIONS: Moderate physiological increases in pressure, induced either mechanically or pharmacologically, can augment the responses to serotonin. Oxygen-derived free radicals, particularly hydroxyl radicals, might be involved in the abnormal response to serotonin following an abrupt increase in coronary pressure.

Characterization of endothelium-dependent vasodilation and vasoconstriction in coronary arteries from spontaneously hypertensive rats.

Coronary artery disease often occurs in patients with hypertension. The present study was designed to evaluate coronary vascular function in isolated coronary arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats and to determine the effect of antihypertensive treatment on coronary vascular responsiveness. Male SHR and WKY rats (12 to 14 weeks old) were divided into control and hydralazine-treated (120 mg/L drinking water for 10 days) groups. After 10 days, arterial pressure and heart rate were recorded while rats were conscious and unrestrained. Left ventricular coronary arteries (200 to 300 microns diameter) were isolated and intraluminal diameter was continuously recorded while vessels were maintained at a constant intraluminal pressure of 40 mm Hg. Relaxation of coronary arteries to both acetylcholine and nitroprusside was slightly, but significantly, enhanced in vessels from SHR compared to WKY rats. The enhanced relaxation was a specific effect, since isoproterenol induced similar relaxation in coronary arteries from SHR and WKY rats. Contraction to phenylephrine, but not endothelin-1, was augmented in coronary arteries from SHR compared to WKY rats. Treatment with hydralazine significantly lowered arterial pressure in SHR and WKY rats, but did not alter the enhanced contraction to phenylephrine or the enhanced relaxation to acetylcholine and nitroprusside in coronary arteris from SHR. These results indicate that coronary arteries of 12 to 14 week-old SHR do not have impaired endothelium-dependent relaxation, but to exhibit enhanced alpha-adrenoceptor-mediated contraction that is not reduced by lowering arterial pressure.

Hypertension and the coronary circulation. With special attention to endothelial regulation.

Calcium channel antagonists are commonly used to treat chronic hypertension. Several studies of intact vascular tissues suggest that these agents may impair the production of the endothelium-derived relaxing factor and alter endothelium-dependent vascular relaxation. These studies are difficult to interpret because the calcium channel antagonist may have direct effects on vascular smooth muscle. In our study, a chemiluminescence assay was used to measure the release of nitrogen oxides from bovine aortic endothelial cells (BAEC) grown in monolayer. Under basal conditions, the release of nitrogen oxides was 0.2 nmol/100 mg protein and was increased approximately two-fold by 0.1 micrograms, bradykinin. Incubations with diltiazem, verapamil, and nifedipine for 60 min did not influence the basal and bradykinin-stimulated release of nitrogen oxides by BAEC. These data illustrate that the production of the endothelium-derived relaxing factor is not altered by the calcium channel antagonist, and are compatible with an absence of L-type calcium channels in vascular endothelial cells. Chronic hypertension produces myriad adverse effects in the coronary circulation. After coronary occlusion, infarct size, expressed as a function of myocardial mass perfused, is increased by 33%, and the wavefront of infarction from subendocardium to subepicardium is hastened. Both chronic and acute hypertension produce numerous abnormalities of coronary flow regulation. These include impairments of autoregulation, changes in vascular responsiveness, and alterations of endothelial cell function. Many of these may worsen the clinical consequences of ischemic heart disease, either by producing structural alterations of the coronary vasculature, or equally importantly, by altering coronary vascular responsiveness to either mechanical or neurohumoral stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of native and stimulated collateral vessels to serotonin.

Previous studies suggest that collateral vessels constrict in response to serotonin. The objective of these studies was to directly measure responses of native and stimulated collateral vessels 30-400 microns in diameter to serotonin and to determine the mechanisms involved in responses to serotonin. Serotonin was suffused onto the left ventricle of dogs, and microvascular diameters were measured with computer-controlled stroboscopic illumination coupled to a microscope-video system. Stimulated collateral vessels and arterioles in collateral-dependent myocardium were measured after Ameroid constriction of the left circumflex artery. Noncollateral and native collateral vessels were examined in dogs without a constrictor. Serotonin produced dose-dependent dilation of noncollateral vessels that was decreased in native collateral vessels, stimulated collateral vessels, and vessels in collateral-dependent myocardium. Dilation in response to nitroprusside was similar in all groups. Dilation in response to serotonin was enhanced by inhibition of 5-hydroxytryptamine (5-HT)2 receptors with ketanserin and blocked by nonselective 5-HT1 and 5-HT2 receptors with methiothepin. Inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine decreased dilation in response to serotonin. Thus collaterals and arterioles in collateral-dependent myocardium are less sensitive to the dilating effect of serotonin. Responses to serotonin involve a balance between dilation mediated by 5-HT1 receptors and constriction mediated by 5-HT2 receptors.

Collateral response to activation of potassium channels in vivo.

Activation of ATP-sensitive K+ channels is involved in the coronary vascular response to decreases in perfusion pressure and ischemia. Since activation of ATP-sensitive K+ channels in collateral vessels may be important in determining flow to collateral-dependent myocardium, the ability of collaterals to respond to activation of the channel was tested. In the beating heart of dogs, we compared responses of non-collaterals less than 100 microns in diameter to collaterals of similar size using computer-controlled stroboscopic epi-illumination of the left ventricle coupled to a microscope-video system. Aprikalim, a selective activator of ATP-sensitive K+ channels (0.1-10 microM) produced similar dose-dependent dilation of non-collaterals and collaterals. Relaxation was decreased by inhibition of ATP-sensitive K+ channels with glibenclamide, but not by inhibition of nitric oxide synthase with nitro-L-arginine. Bradykinin (10-100 microM) produced similar dilation of non-collaterals and collaterals which was decreased by nitro-L-arginine but not glibenclamide. Thus, in microvascular collaterals, relaxation to both nitric oxide and activation of ATP-sensitive K+ channels is similar to non-collaterals.

Flow-mediated dilation attenuates constriction of large coronary arteries to serotonin.

We tested the hypothesis that flow-mediated endothelium-dependent dilation can attenuate humorally mediated constriction of large coronary arteries in vivo. Accordingly, we measured constriction of large coronary arteries to serotonin when flow was allowed to increase and when flow was constant in the presence and absence of endothelium. The left anterior descending coronary artery of anesthetized dogs was perfused at constant pressure (100 mmHg) and diameter measured with an ultrasonic dimension gauge. Coronary flow was measured with an in-line electromagnetic flow probe. Flow-mediated dilation was demonstrated by measuring diameter (D) after increased flow in response to adenosine (1 mg/min ic). Adenosine (n = 9) increased flow (341 +/- 69%) and resulted in large artery dilation [diameter change (delta D) = 101 +/- 54 microns], which was abolished by maintaining constant flow (distal snare) or by removing endothelium. Serotonin (n = 9, 50 micrograms/min ic) increased flow (298 +/- 45%) while simultaneously decreasing large artery diameter (delta D = -58 +/- 22 microns). When flow was kept constant, serotonin produced a greater constriction (delta D = -173 +/- 29 microns). After the removal of endothelium (n = 10), constrictor responses to serotonin were similar when flow increased (delta D = -84 +/- 13 microns) and when flow was kept constant (delta D = -79 +/- 23 microns). We conclude that flow-mediated dilation of large coronary arteries can attenuate constriction to serotonin and that this effect is dependent on endothelium.

Acute hypertension selectively potentiates constrictor responses of large coronary arteries to serotonin by altering endothelial function in vivo.

We tested the hypothesis that acute coronary artery hypertension may damage vascular endothelium and alter vasomotor responses to humoral agents. We examined effects of intracoronary infusion of the endothelium-dependent agent serotonin and two endothelium-independent agents, angiotensin II and methoxamine, on large coronary artery diameter in the blood perfused dog heart. Responses were examined before and 30 minutes after brief periods of coronary hypertension (200 mm Hg for 10 seconds to 15 minutes). In open-chest anesthetized dogs, the left anterior descending coronary artery was perfused at constant pressure. Coronary diameter (D) was measured with piezoelectric crystals. At a control perfusion pressure of 80 mm Hg, serotonin produced dose-dependent constriction of the large coronary artery (mean +/- SEM; delta D = -22 +/- 10 microns at 5 micrograms/min; -108 +/- 50 microns at 50 micrograms/min). Increasing perfusion pressure to 200 mm Hg increased flow 515 +/- 79% and coronary diameter 509 +/- 9 microns. After 15 minutes of hypertension, when coronary diameter had returned to baseline values, the constriction of the large artery to serotonin was potentiated (delta D = -89 +/- 33 microns at 5 micrograms/min; -207 +/- 45 microns at 50 micrograms/min; p less than 0.05). Hypertension for 1-5 minutes potentiated constrictor responses of large coronary arteries for at least 2 1/2 hours. Removal of endothelium prevented effects of hypertension on constrictor responses of large arteries to serotonin. Hypertension did not alter constrictor responses to angiotension II (1 and 2.5 micrograms/min) or methoxamine (50 and 100 micrograms/min) or the dilator response to acetylcholine (40 micrograms/min). Acute hypertension altered endothelial morphology. There were small endothelial craters following 10 seconds of hypertension, and disruption of endothelial junctions with leukocyte adherence following 1-15 minutes of hypertension. We conclude that acute hypertension alters constrictor responses of large coronary arteries to serotonin by impairing endothelial function and not by directly affecting vascular smooth muscle. These effects of acute hypertension on vascular reactivity are selective in that they do not involve non-endothelium-dependent agents or the endothelium-dependent agent, acetylcholine. The effect of hypertension also persists long after pressure is restored to normotensive levels.

Effects of 17 beta-estradiol on coronary microvascular responses to endothelin-1.

The objective of this study was to examine the effects of 17 beta-estradiol on responses of coronary microvessels to endothelin-1 (ET-1). With the use of isolated pressurized coronary microvessels from the left ventricle of male or female dogs, constrictions to ET-1 were similar in vessels from male and female dogs. 17 beta-Estradiol (1 microM) attenuated constriction to ET-1 of small arteries from both male (percent constriction at 10 microM control: 39 +/- 9%, estradiol: 3 +/- 2%; P < 0.05) and female (percent constriction at 10 microM control: 39 +/- 8%, estradiol: 6 +/- 3%; P < 0.05) dogs similarly. In contrast, testosterone (1 microM) had no effect on constriction to ET-1. Constrictions to ET-1 were completely abolished by BQ-123 (1 microM), a selective ETA-receptor antagonist, and enhanced by BQ-788 (1 microM), a selective ETB-receptor antagonist. Constrictions to ET-1 alone were not altered by indomethacin (Indo, 10 microM) or NG-nitro-L-arginine (L-NNA, 100 microM). 17 beta-Estradiol produced dose-dependent relaxation of coronary microvessels preconstricted with ET-1 that was similar to the response to testosterone and progesterone. Indo or L-NNA alone had no effect on relaxation to 17 beta-estradiol. However, the combination of Indo and L-NNA attenuated Taxation to 17 beta-estradiol (percent dilation at 1 microM control: 64 +/- 13%; Indo plus L-NNA: 21 +/- 6%; P < 0.05) but did not affect relaxation to testosterone. Thus 17 beta-estradiol attenuated constrictions of coronary microvessels to ET-1 more than did similar concentrations of testosterone. The ability of 17 beta-estradiol to modulate responses to endothelin may involve release of vasodilator prostaglandins and/or nitric oxide by 17 beta-estradiol.

Comparison of coronary microvascular response to nipradilol and nitroglycerin.

Nitrovasodilators and beta-adrenoceptor antagonists are effective in the treatment of angina pectoris and hypertension, but each has side effects that may prevent their long-term use. In the present study responses of coronary arteries and arterioles to nipradilol, a beta-adrenoceptor antagonist with nitrovasodilator action, were compared to nitroglycerin in normal myocardium of the beating left ventricle in anesthetized dogs. Coronary arteries and arterioles were visualized using stroboscopic illumination of epicardial surface of the heart and intravital microscopy with fluorescence angiography. Diameters were measured under control conditions and during topical suffusion of nipradilol (10(-8)-10(-4) M) or nitroglycerin (10(-8)-10(-4) M). Nipradilol produced dose-dependent dilation of all size arteries and arterioles however, dilation was inversely related to vessel size. Arterioles less than 100 microns in diameter dilated more than arteries greater than 200 microns in diameter. In contrast, dilation to nitroglycerin was directly related to vessel size. Arteries larger than 200 microns dilated more than arterioles less than 100 microns. In conclusion, although nipradilol and nitroglycerin are both nitrovasodilators the microvascular response to these agents is different.

Role of endothelium-derived relaxing factor and prostaglandins in responses of coronary arteries to thromboxane in vivo.

We examined the relative contribution of endothelial and vascular smooth muscle-derived prostaglandins and endothelium-derived relaxing factor in modulating both the large coronary artery and resistance vessel responses to thromboxane in vivo. Vascular responses to the thromboxane analogue U46619 were measured in four separate experimental protocols: 1) The vascular responses were measured in the presence and absence of intact endothelium to examine the role of endothelium-derived vasodilators. 2) Responses were measured in the presence of intact endothelium before and after inhibition of cyclooxygenase with indomethacin to examine the role of endothelial and vascular smooth muscle-derived prostaglandins. 3) Responses were measured after endothelial removal before and after indomethacin to examine the role of vascular smooth muscle-derived prostaglandins. 4) Responses were measured after indomethacin and before and after removal of endothelium to examine the role of endothelium-derived relaxing factor. In anesthetized dogs (n = 41) that underwent constant pressure perfusion of the left anterior descending coronary artery (LAD), LAD diameter was measured with sonomicrometer crystals, and coronary flow was measured with an electromagnetic flow probe. Intracoronary infusion of U46619 (0.01-1.0 microgram/min) produced a dose-dependent constriction of LAD. Constriction of the LAD was augmented after endothelial removal, after indomethacin treatment in both the presence and absence of endothelium, and after removal of the endothelium in the presence of indomethacin. Inhibition of prostaglandin synthesis had the greatest effect of augmenting constriction of LAD to thromboxane. Coronary flow was decreased by U46619 only in the presence of indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of a role for compounds derived from arginine in coronary response to serotonin in vivo.

Recent studies have demonstrated that a nitroso compound derived from L-arginine (Arg) may be the endothelium-derived relaxing factor (EDRF) released from vascular endothelium. Synthesis of EDRF from L-Arg is inhibited by analogues of Arg such as NG-monomethyl-L-arginine (L-NMMA) and N omega-nitro-L-arginine (L-NNA). We tested the role of compounds derived from Arg in the constriction of the proximal left anterior descending coronary artery (LAD) to serotonin in vivo by measuring responses before and during infusion of L-NMMA or L-NNA. In open-chest anesthetized dogs the LAD was perfused at constant pressure (80 mmHg) from a reservoir. Large-artery diameter was measured with piezoelectric crystals, and coronary flow was measured with an in-line electromagnetic flow probe. Intracoronary serotonin (5 and 50 micrograms/min) caused a dose-dependent constriction of the proximal LAD and increase in coronary flow. Intracoronary L-NMMA (2 mg/min) or L-NNA (2 mg/min) augmented the constriction to serotonin, whereas the increase in coronary flow was blunted only by L-NNA. L-Arg (10 mg/min, intracoronary) alone did not alter either the large-artery constriction or the increase in flow to serotonin; however, it prevented the enhanced constriction to serotonin following L-NMMA. Constriction to the endothelium-independent agent prostaglandin F2 alpha was not affected by L-NMMA. We conclude that a metabolite of L-Arg modulates the large coronary artery response to serotonin in vivo.

Removal of the endothelium potentiates canine large coronary artery constrictor responses to 5-hydroxytryptamine in vivo.

Recent studies in isolated epicardial coronary artery rings have shown that the endothelium modulates vasomotor responses to certain endogenous neurohumoral agents. It is not known whether the endothelium plays a role in large coronary vasoregulation in the intact coronary circulation. Accordingly, we examined effects of endothelial removal on vasoconstrictor responses of the proximal coronary artery in anesthetized adult mongrel dogs. The left anterior descending artery was perfused at 100 mm Hg with arterial blood from a pressurized reservoir. Coronary diameter was measured continuously with 7-MHz sonomicrometer crystals attached to the adventitia of the artery. Fifteen minutes after mechanical disruption of the endothelium with a balloon-tipped catheter, baseline diameter was unchanged from a control value of 2.60 +/- 0.13 mm (mean +/- SE, n = 17). Endothelial denudation resulted in a dose-dependent potentiation of the constrictor response to intracoronary 5-hydroxytryptamine (1-50 micrograms/min, n = 8). With the endothelium intact, a 5 micrograms/min infusion of 5-hydroxytryptamine reduced diameter by 24 +/- 14 micron, while a 50 micrograms/min dose reduced diameter by 54 +/- 25 micron. After endothelial removal, the decrease in diameter averaged 74 +/- 18 microns at 5 micrograms/min and 132 +/- 29 micron at 50 micrograms/min, indicating a 10-fold increase in the sensitivity to 5-hydroxytryptamine. The constrictor responses to angiotensin II (1 and 5 micrograms/min, n = 7) and phenylephrine (1-5 micrograms/min, n = 7) were not altered by endothelial removal. Thus, endothelial removal selectively potentiates the constrictor responses to 5-hydroxytryptamine in the intact coronary circulation of the dog.

Regulation of native collateral vessel dilation after coronary occlusion in the dog.

The purpose of this study was to examine mechanisms involved in the response of native collaterals to coronary occlusion. In anesthetized dogs native collaterals were identified as vessels coursing between the left anterior descending and left circumflex arteries using fluorescence angiography. After a left anterior descending occlusion in 12 dogs, collaterals < 100 microns in diameter progressively dilated by 21 +/- 4% (n = 12) 1 min after occlusion and by 39 +/- 6% 15 min after occlusion. Collaterals > 100 microns in diameter did not dilate after coronary occlusion. NG-nitro-L-arginine (1 mg/min intracoronary) caused constriction under basal conditions in collaterals < 100 microns but did not prevent the dilation of collaterals after occlusion. In contrast, glibenclamide (10(-5) M), an inhibitor of ATP-sensitive potassium channels, had no effect on baseline diameter of collaterals < 100 microns diameter but completely prevented dilation of collaterals after occlusion. We conclude that collaterals are not maximally dilated immediately after a coronary occlusion but rather progressively dilate for at least 15 min after an occlusion. This dilation of native collaterals after an occlusion is not mediated by release of an endothelium-derived relaxing factor derived from L-arginine but is mediated by activation of ATP-sensitive K+ channels.

Role of adenosine in vasodilation of epimyocardial coronary microvessels during reduction in perfusion pressure.

Previous studies in which an isolated heart or in situ constant pressure preparation was used suggested a minimal role for adenosine in autoregulatory control of coronary circulation. These results, however, are controversial, and the role of adenosine in autoregulation of flow in heart is uncertain. To test the hypothesis that adenosine mediates microvascular dilation in response to reduction in perfusion pressure (PP), we performed experiments in 41 open-chest chloralose-anesthetized dogs. Internal diameters (ID) of epicardial small arterioles < 100 mumol were measured with an intravital microscope and stroboscopic epiillumination synchronized to cardiac cycle. PP was reduced by graded stenoses of the left anterior descending coronary artery (LAD, mild stenosis PP = 60 mm Hg; critical stenosis PP = 40 mm Hg) and complete occlusion. 8-Phenyltheophylline (8-PT 10 microM) or adenosine deaminase (ADA 10 U/min) was topically superfused onto the heart. Arteriolar dilation induced by topically applied adenosine < or = 10 microM was completely blocked by 8-PT. Without 8-PT (vehicle group), mild critical stenosis and complete occlusion caused arteriolar dilation (percentage of change in diameter 8.6 +/- 2.6, 16.0 +/- 2.7, and 13.6 +/- 4.8%). 8-PT did not inhibit this dilation (8.5 +/- 2.8, 16.1 +/- 4.6, 15.1 +/- 5.7%, NS vs. vehicle group). Topically applied ADA significantly inhibited intravenously (i.v.) administered adenosine-induced arteriolar dilation. Without ADA, arteriolar dilation occurred (16.6 +/- 3.0, 28.2 +/- 4.3, 15.4 +/- 6.2%, at each PP). However, ADA did not inhibit dilation induced by gradual stenoses (10.6 +/- 1.4, 24.2 +/- 4.3, 17.5 +/- 6.9%, at each PP, NS vs. vehicle group).(ABSTRACT TRUNCATED AT 250 WORDS)

Atherosclerosis, vascular remodeling, and impairment of endothelium-dependent relaxation in genetically altered hyperlipidemic mice.

We examined the vascular structure and endothelium-dependent relaxation in two genetic models of hypercholesterolemia: apolipoprotein E (apoE)-knockout mice and combined apoE/LDL receptor-double-knockout mice. Intimal area was increased markedly in proximal segments of thoracic aortas from apoE/LDL receptor-knockout mice [0.13 +/- 0.03 (mean +/- SE) mm2] compared with normal (C57BL/6J) mice (0.002 +/- 0.002 mm2, P < .05). Despite intimal thickening, the vascular lumen was not smaller in the aortas of apoE/LDL receptor-knockout mice (0.52 +/- 0.03 mm2) than in normal mice (0.50 +/- 0.03 mm2). In apoE-deficient mice, intimal thickening was minimal or absent, even though the concentration of plasma cholesterol was only modestly less than that in the double-knockout mouse (14.9 +/- 1.1 vs 18.0 +/- 1.2 mmol/L, respectively, P < .05). Relaxation of the aorta was examined in vitro in vascular rings precontracted with U46619. In normal mice, acetylcholine produced relaxation, which was markedly attenuated by the nitric oxide synthase inhibitor NG-nitro-L-arginine (100 microM). Relaxation to acetylcholine and the calcium ionophore A23187 was normal in apoE-deficient mice (in which lesions were minimal) but greatly impaired in the proximal segments of thoracic aortas of apoE/LDL receptor-deficient mice, which contained atherosclerotic lesions. Vasorelaxation to nitroprusside was similar in normal and apoE-knockout mice, with modest but statistically significant impairment in atherosclerotic segments of apoE/LDL receptor-knockout mice. In distal segments of the thoracic aorta of apoE/LDL receptor-deficient mice, atherosclerotic lesions were minimal or absent, and the endothelium-dependent relaxation to acetylcholine and calcium ionophore was normal. Thus, in apoE/LDL receptor-knockout mice (a genetic model of hyperlipidemia), there is vascular remodeling with preservation of the aortic lumen despite marked intimal thickening, with impairment of endothelium-dependent relaxation to receptor- and nonreceptor-mediated agonists. Atherosclerosis may be accelerated in the apoE/LDL receptor-double-knockout mouse compared with the apoE-knockout strain alone. We speculate that other factors, such as the absence of LDL receptors, may contribute to the differences in the extent of atherosclerosis in these two models of hyperlipidemia.

Effects of three bradycardiac drugs on regional myocardial blood flow and function in areas distal to a total or partial coronary occlusion in dogs.

The effectiveness of three bradycardiac drugs for increasing distal coronary perfusion pressure and decreasing stenosis resistance (SR) in partially occluded vessels, and thereby for increasing collateral blood flow and segmental function (%SS) in an occluded area dependent on the stenotic vessel, was studied in anesthetized dogs. Initially, the distal portion of the left anterior descending (LAD) coronary artery was occluded followed by subsequent stenosis of the left circumflex (LC) coronary artery that supplies collateral flow to the ischemic LAD area. A decrease in LC flow (35 +/- 3 to 24 +/- 3 ml/min) and distal coronary pressure (109 +/- 4 to 47 +/- 4 mm Hg) resulted in an increase in SR (0.03 +/- 0.02 to 2.97 +/- 0.53 U), and decreases in LC %SS (9.3 +/- 1.1% to 1.9 +/- 2.0%), subendocardial blood flow (1.11 +/- 0.06 to 0.43 +/- 0.05 ml/min/g), and LAD collateral flow (0.36 +/- 0.11 to 0.22 +/- 0.05 ml/min/g). Upon intravenous administration on the beta-receptor-blocking drug sotalol (0.3 mg/kg) or metoprolol (0.1 mg/kg) and the non-beta-blocking bradycardiac drug N-dimethyl-propranolol (5.0 mg/kg) in doses that produced similar decreases in heart rate (30 to 40 beats/min), distal coronary pressure, subendocardial blood flow, and %SS in the LC area were markedly improved. SR was significantly reduced (2.97 +/- 0.53 to 1.66 +/- 0.37 U). The improvement in %SS of the LC area was highly correlated (r = .93, p less than .001) with the increase in subendocardial blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)