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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mechanically and chemically sensitive receptors in the ventricle have been described histologically and electrophysiologically. Early experiments documented the hypotension and bradycardia that resulted from the intracoronary administration of one of the veratrum alkaloids (the Bezold-Jarisch reflex). Mechanical distension of the ventricles also results in a reflex decrease in heart rate and a reduction in peripheral resistance. Skeletal muscle and coronary vascular resistance appear to be most prominently affected by stimulation of ventricular receptors. Coronary ischemia has also been shown to evoke reflex effects which are attributable to stimulation of ventricular receptors. The resultant bradycardia can be especially ominous in acute myocardial infarction. Changes in myocardial inotropic state have been shown to alter ventricular receptor discharge in experimental animals. This stimulus may evoke reflex changes in peripheral hemodynamics. A variety of humoral substances can alter ventricular receptor discharge and evoke Bezold-Jarisch like responses. These include bradykinin and prostaglandins. PGI2, when given intracoronary in small doses or intravenously in larger doses will lower blood pressure while inhibiting the baroreflex induced tachycardia. It has also been shown in some experiments that PGI2 and arachidonic acid can evoke overt bradycardia and hypotension via a reflex mechanism. The role of prostaglandins in cardiovascular reflex control may be important in pathophysiologic states such as coronary ischemia and heart failure. Ventricular receptors can interact centrally with the arterial baroreceptors to attenuate the baroreflex control of both heart rate and peripheral resistance. Finally, the stimulation of ventricular receptors can alter a variety of humoral substances which are important regulators of cardiovascular and fluid volume homeostasis. These include vasopressin, renin and catecholamines. Those studies which have been done within the last 10 years or so, especially in unanesthetized animals, have demonstrated that the Bezold-Jarisch reflex is more important to cardiovascular control than previously thought. Future work will be necessary to determine the precise role ventricular receptors play in various pathological situations.
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PMID:Left ventricular receptors: physiological controllers or pathological curiosities? 354 77

Acute hemorrhagic ulceration of the gastric mucosa is seen frequently in patients with hypovolemic or cardiogenic shock. Although such lesions clearly are related to regional gastric ischemia, little attention has been directed at the underlying mechanism(s) mediating the ischemia itself. To this end, anesthetized pigs were subjected to sustained cardiogenic shock (mild hemorrhage and pericardial tamponade) such that cardiac output was reduced to 38 +/- 1% of the baseline level for 4 hours, followed by release of the tamponade, reinfusion of the shed blood, and resuscitation for 2 hours. During the period of shock, there was profound regional gastric ischemia, resulting from severe and disproportionate gastric vasoconstriction. "Blinded" gross and microscopic evaluation of the stomachs removed after the experiment revealed severe mucosal ischemic necrosis, hemorrhage, and ulceration, whereas sham-operated pigs showed no lesions. The characteristics of this model therefore mimic the essential features of the gastric "stress ulceration" syndrome. Prior confirmed total alpha-adrenergic blockade with phenoxybenzamine failed to alter these features significantly. In contrast, prior ablation of the renin-angiotensin axis, whether by angiotensin-converting enzyme inhibition with teprotide or by bilateral nephrectomy, significantly and substantially ameliorated the ischemia, vasospasm, and mucosal injury. In this model of cardiogenic shock, acute gastric mucosal "stress ulceration" is caused by a disproportionately severe regional gastric ischemia resulting from selective splanchnic vasospasm that is unaffected by sympathetic blockade but abolished by prior ablation of the renin-angiotensin axis. Like nonocclusive small bowel ischemia, ischemic colitis, and the "shock liver" syndrome, gastric "stress ulceration" is yet another component of the multiple splanchnic organ failure syndrome that appears to be mediated primarily by the remarkable sensitivity of the splanchnic vascular bed to the renin-angiotensin axis.
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PMID:The fundamental hemodynamic mechanism underlying gastric "stress ulceration" in cardiogenic shock. 359 3

The influence of cyclosporine A on renal function was investigated in unilaterally nephrectomized rats subjected to 30 or 45 min of ischemia. Acute i.v. administration of high dose CyA equivalent to 1000 mg/kg/d, did not produce a decrease in glomerular filtration or renal blood flow within 2 hours and its influence on proximal tubular pressure could be attributed to the cremophor vehicle. Chronic oral administration of 20 mg/kg/d CyA after ischemia produced no alteration in renal function after 2 or 9 days, but 40 mg/kg/d CyA lowered renal function demonstrably by 9 days. When pair-fed to eliminate CyA-induced weight loss as a cause of depressed renal function, the loss of renal function after 9 days was smaller but still evident. At this time renal cortical prostaglandin E2 and thromboxane B2 production were also reduced, but plasma renin remained unaltered because of the exclusion of volume depletion through weight loss. These kidneys showed no signs of delayed regeneration from ischemic renal injury but did show signs of tubulotoxicity, which seemed to be more apparent after longer periods of ischemia.
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PMID:Effect of cyclosporine A on ischemic renal failure in the rat. 370 27

The nonocclusive component of ischemic colitis in anesthetized pigs was mimicked using cardiogenic shock produced by pericardial tamponade. Increases in pericardial pressure produced decreases in arterial pressure (PA) and cardiac output (CO), with corresponding rises in total peripheral resistance (i.e., cardiogenic shock). This was associated with marked reductions in blood flow through the inferior mesenteric artery (IMA), due primarily to disproportionate increases in IMA vascular resistance. Levels of plasma renin activity correlated closely with these changes in mesenteric hemodynamics. Confirmed, total alpha adrenergic blockade with phenoxybenzamine failed to block this selective mesenteric vasoconstriction, while ablation of the renin-angiotensin axis with captopril completely abolished it, thereby ameliorating the colonic ischemia. Central intravenous infusions of pathophysiologic levels of angiotensin II, without tamponade, mimicked the response to shock seen with tamponade alone. In an additional group of pigs, 4 hours of sustained shock (tamponade) followed by 2 hours of normotension (release of tamponade and resuscitation) produced lesions characteristic of ischemic colitis, including full-thickness mucosal ulceration. Such lesions were ameliorated significantly in pigs in which the renin-angiotensin system had been ablated by bilateral nephrectomy. Nonocclusive ischemic colitis appears to be mediated primarily by a remarkable sensitivity of the colonic vasculature to the renin-angiotensin axis.
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PMID:Pathogenesis of nonocclusive ischemic colitis. 371 27

In a pericardial tamponade model of cardiogenic shock in pigs, we had previously shown that acute reductions in cardiac output produce severe mesenteric ischemia due to disproportionate splanchnic vasoconstriction. In this study, we extended the period of cardiogenic shock in order to investigate the pathogenesis of ischemic injury to the small intestinal wall. Four hours of tamponade produced sustained changes in splanchnic hemodynamics, similar to those observed in the prior short-term experiments. The resultant mesenteric ischemia caused necrotic lesions of the small intestine which were characteristic of those seen in nonocclusive mesenteric ischemia in human subjects. Prior alpha-adrenergic blockade failed to prevent either sustained mesenteric vasospasm or ischemic injury. In contrast, prior blockade of the renin-angiotensin axis, whether by nephrectomy or angiotensin-converting enzyme inhibition, blocked the splanchnic vasoconstriction, and thereby protected the small intestine from ischemic injury. The primary hemodynamic and pathologic features of this model of nonocclusive mesenteric ischemia appear to be mediated by the renin-angiotensin axis.
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PMID:Protection of the small intestine from nonocclusive mesenteric ischemic injury due to cardiogenic shock. 379 86

That local splanchnic ischemia is associated with the acute gastric "stress" erosions seen in shock is well established. The hemodynamic mechanism mediating that ischemia is unknown. Pericardial tamponade was produced in anesthetized pigs while hemodynamic parameters were monitored in the systemic circulation as a whole and in the vascular beds of the celiac and left gastric arteries, respectively. Stepwise increases in pericardial pressure produced progressive decreases in arterial pressure and cardiac output (i.e., reproducible, quantitable, and rapidly reversible levels of cardiogenic shock). This produced a profound reduction in blood flow in the celiac and gastric beds that was significantly disproportionate to the reduction in cardiac output. This was due to significant increases in celiac and gastric vascular resistance that were more than twice as great as those seen in the systemic circulation as a whole (i.e., selective splanchnic vasoconstriction). This response was abolished by ablation of the renin-angiotensin axis, whether by bilateral nephrectomy, captopril, or saralasin, and mimicked, without tamponade, by the infusion of angiotensin II. Levels of celiac artery blood flow and resistance correlated significantly with endogenous levels of plasma renin activity. On the other hand, this response was not abolished by confirmed alpha-adrenergic blockade (phenoxybenzamine) or by sympathectomy. In this model, cardiogenic shock produces regional splanchnic ischemia in the celiac and gastric vascular beds by inducing a severe and disproportionate vasospasm that is mediated primarily by the renin-angiotensin axis.
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PMID:Control of gastric vascular resistance in cardiogenic shock. 389 36

The unique architecture and organization of medullary vasculature permit regional regulation of medullary hemodynamics by vasoactive hormones and are conducive to the operation of the countercurrent multiplication system. Recent studies suggest that an increase in inner medullary blood flow causes medullary solute washout, which in turn decreases passive sodium transport in the thin ascending limb of Henle's loop. In canine models of chronic sodium retention accompanied by activation of the renin-angiotensin system, glomerular filtration rate (GFR), renal blood flow (RBF), and intracortical blood flow distribution were similar to those in normal dogs; however, papillary plasma flow (PPF) was markedly reduced and papillary tissue solute content was increased significantly both during hydropenia and after saline loading. During euvolemic diuresis with loop diuretics, there was an increased renin release associated with a marked reduction in PPF, despite an increase in total RBF. Direct intrarenal infusion of angiotensin II (AngII) (at a dose not affecting GFR and RBF) induced ipsilateral sodium retention, conservation of urinary concentration, and papillary ischemia. These studies provide evidence for regional regulation of medullary hemodynamics by AngII, possibly contributing to sodium retention in chronic salt-retaining states.
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PMID:Contribution of angiotensin to the control of medullary hemodynamics. 395 61

The renal transplant vascularity of 72 patients was investigated by intravenous digital subtraction angiography (IV DSA). The procedure was combined with selective venous renin sampling of the transplant and native kidneys to identify the source of hypertension in these patients. Abnormalities were found on IV DSA examination in 26 patients, of whom 7 had graft artery stenosis, 7 had diffuse intrarenal narrowing, 9 had lower pole ischemia, and 3 had aneurysmal dilatation. The combined outpatient procedure was well tolerated by all patients with no complications nor incidence of proteinuria.
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PMID:Digital subtraction angiography in renal transplant recipients. 636 Mar 60

The juxtaglomerular (JG) complex was studied at different times after 90 min of warm kidney ischemia: 2 h, 24 h, 3 days, 10 and 30 days following the ischemia. The ischemic injury was performed on the left kidney, under two experimental conditions: with and without previous nephrectomy of the contralateral nonischemic kidney. The activity of the JG complex was evaluated by assessing the JG index and by determination of plasma renin activity. Results show that, under given experimental conditions, fate of the particular JG complex depends on the fate of its own nephron. In the presence of the contralateral intact kidney most nephrons of the ischemic kidney underwent gradual degeneration and their JG complexes degenerated too. When ischemic kidney was the sole kidney, the majority of nephron units regenerated and their JG complexes recovered both morphologically and functionally.
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PMID:Fate of the juxtaglomerular complex after ischemic injury. 638 Jan 89

A unique case of renovascular hypertension in an asymptomatic, microhematuric 61/2-year-old girl is presented. Abdominal ultrasonographic (UT) and computed tomographic (CT) studies, splenic and renal radionuclide evaluations revealed that a 'boomerang'-shaped spleen, anterior and medial to the left kidney, compressed and flattened its upper pole. Arteriography excluded stenosis of the renal arterial vessels. Renal vein renin ratio of 1.78 and contralateral/caval ratio of 1.13 eventually demonstrated that hypertension was caused by a lateralized renin hypersecretion from the compressed upper pole through left superior and central renal veins. Overactivity of the renin/angiotensin system was presumably due to ischemia of the renal parenchyma extrinsically compressed by the spleen.
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PMID:Hypertension from ipsilateral renin hypersecretion following kidney upper pole compression by the spleen. 638 43


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