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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Clinical and experimental evidence demonstrates that hypertrophied cardiac tissue is more sensitive to ischemic injury than is normal myocardium. Recent studies indicate that cardiac ischemia-reperfusion injury involves the generation of toxic oxygen free radicals. We used the spontaneously hypertensive rat (SHR) model, with its otherwise genetically identical control (the Wistar-Kyoto [WKY] rat), to investigate the potential role of enzymes that generate and detoxify oxygen radicals in the sensitivity of hypertrophied heart to ischemia and reperfusion. Because hypertension develops progressively with age in SHRs, we assayed xanthine oxidase, superoxide dismutase, catalase, and glutathione peroxidase at three different time points and found significant fluctuations at different ages. At age 26 weeks, physiological measurements demonstrated hypertension and increased sensitivity to ischemia and reperfusion, measured as significantly decreased left ventricular recovery after injury. At this age, xanthine oxidase, which may generate oxygen radicals, was significantly increased in SHR compared with WKY rats (p = 0.003). Superoxide dismutase, which is a principal step in oxygen-radical detoxification, was significantly lower (p = 0.044). These data suggest that differences in the constitutive levels of oxygen-radical metabolic pathways are different in hypertrophied myocardium, and it is suggested that this finding may play a role in the response of these hearts to ischemia-reperfusion injury.
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PMID:Response to ischemia-reperfusion injury in hypertrophic heart. Role of free-radical metabolic pathways. 253 7

The validity of using EXP6803, a nonpeptide angiotensin II (AII) receptor antagonist, and KAA8, an AII monoclonal antibody, as specific tools for studying the physiology of AII has been established previously. In this study, we used these specific probes to examine the role of blocking AII formation in the antihypertensive effect of captopril in conscious renal artery-ligated rats (RALRs), a high renin, renal hypertensive model. Mean arterial pressure and plasma renin activity in a typical group of RALRs averaged 175 +/- 5 mm Hg and 28.2 +/- 6.2 ng of angiotensin 1 per ml/hr (n = 6), respectively. The antihypertensive effect of captopril (3 mg/kg i.v.) was determined in RALRs given either EXP6803 (30 mg/kg + 2 mg/kg/min i.v.) or KAA8 (10 mg + 1 mg/min i.v. per rat) with the corresponding vehicle-treated RALRs. These doses of EXP6803 and KAA8 were very effective in blocking the pressor response to AII but not to norepinephrine or vasopressin in RALRs. Captopril decreased mean arterial pressure by 44 +/- 2 and 53 +/- 8 mm Hg in the groups treated with the vehicles of EXP6803 (n = 5) and KAA8 (n = 5), respectively. In the presence of EXP6803 (n = 5) or KAA8 (n = 5), the antihypertensive effect of captopril was almost or totally abolished. Indomethacin did not alter the antihypertensive effect of captopril. These results suggest that the antihypertensive effect of captopril in conscious RALRs is due mainly to the blockade of AII formation. Furthermore, circulating AII rather than locally formed AII appears to play a major role in maintaining hypertension in hypertension in RALRs.
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PMID:Antihypertensive mechanism of captopril in renal hypertensive rats: studies with a nonpeptide angiotensin II receptor antagonist and an angiotensin II monoclonal antibody. 266 2

This paper reviews experimental findings which support the concept that vasopressin (VP) and the process of urine concentration may be involved in the progression of chronic renal failure (CRF). The influence of dietary protein intake on the progression of CRF may also involve VP and the operation of the concentrating process. VP receptors have been identified in glomeruli and VP is able to constrict mesangial cells as does angiotensin II. Acute VP infusion increases the glomerular transcapillary hydraulic pressure difference, and chronic VP infusion increases GFR. In rats with CRF (induced by 5/6 nephrectomy), VP levels were found elevated. In rats with 5/6 nephrectomy, we increased experimentally water intake in order to decrease circulating VP levels, urine concentration, and free water reabsorption. Several indices of progression of CRF, including proteinuria, hypertension and glomerulosclerosis, were significantly reduced, thus suggesting a contribution of VP in progression. Lowering protein intake in CRF could be beneficial because proteins, but not carbohydrates or lipids, produce metabolic end products (mainly urea, ammonia, protons, etc.) that are excreted by the kidney, and concentrated in the urine. In healthy subjects (man or rat), high protein (HP) intake favors urine concentration and causes changes in kidney function and morphology very similar to those induced by chronic VP infusion or water restriction. These changes involve an increase in transport activity of the thick ascending limb (where the initial active step of the concentrating process takes place) and may affect filtration rate and/or glomerular hemodynamics secondarily, by decreasing salt concentration at the macula densa and depressing tubuloglomerular feedback.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Possible involvement of vasopressin and urine concentrating process in the progression of chronic renal failure. 270

In tissues rich in kallikrein, vasodilator kinins, acting as paracrine hormones, may play a role in the local regulation of blood flow. We studied the role of kinins in the regulation of blood flow in the rat submandibular gland using a kinin analogue with antagonistic properties, [DArg0]Hyp3-Thi5-8[DPhe7]bradykinin. When infused into the carotid artery (20 micrograms/min/rat), this antagonist blocked the effect of bradykinin (25-250 ng/kg, intracarotid injection) on glandular blood flow. In nephrectomized rats, the antagonist also blocked the increase in glandular blood flow caused by enalaprilat, a kininase II converting enzyme inhibitor. At a dose of 20 micrograms/min/rat, the antagonist produced no detectable change in basal glandular blood flow; however, at a higher dose (100 micrograms/min/rat), it caused a significant decrease (p less than 0.001). In eight of 10 rats, blood flow decreased by 75% or more; this effect was not blocked by the alpha-adrenergic receptor antagonist phentolamine. After antagonist infusion was stopped, blood flow returned toward normal. Sympathetic nerve stimulation of the gland induced vasoconstriction followed by poststimulatory vasodilatation. In rats displaying severe vasoconstriction after the antagonist, postsympathetic vasodilatation was abolished even when stimulation was performed after the antagonist infusion had been stopped and blood flow returned toward normal. Although a direct vasoconstrictor effect of the kinin antagonist cannot be completely ruled out, these data suggest that, in the rat submandibular gland, kinins may play a role in regulation of basal blood flow and vasodilatation after converting enzyme inhibitor or sympathetic stimulation.
Hypertension 1989 Jul
PMID:Role of kinin in regulation of rat submandibular gland blood flow. 273 39

In vitro the mineralocorticoid receptor is non-specific and does not distinguish between aldosterone and cortisol. In vivo certain tissues with this receptor are aldosterone selective (eg, kidney and parotid) whereas others with the same receptor are not (eg, hippocampus and heart). Experiments in rats showed that 11 beta-hydroxysteroid dehydrogenase (which converts cortisol to cortisone in man and corticosterone to 11-dehydrocorticosterone in the rat) was much more highly concentrated in aldosterone-selective tissues than in non-selective tissues. The localisation in the selective tissues was such that the enzyme could act as a paracrine or possibly an autocrine mechanism protecting the receptor from exposure to corticosterone. Autoradiographic studies showed that protection is lost when the enzyme is inhibited; 3H-corticosterone and 3H-aldosterone were bound to similar sites. These findings seem to explain why sodium retention, hypokalaemia, and hypertension develop in subjects with congenital deficiency of 11 beta-OHSD and those in whom the enzyme has been inhibited by liquorice.
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PMID:Localisation of 11 beta-hydroxysteroid dehydrogenase--tissue specific protector of the mineralocorticoid receptor. 290 93

Carbenoxolone Sodium (CS), a chemical derivative of liquorice is known to be associated with hypertension, increased sodium retention and hypokalemia. The present studies describe the effects of CS on the renal actions of the glucocorticoids Corticosterone (B) and Cortisol (F) on sodium and potassium in adrenalectomized male rats. B (50, 100 and 500 micrograms/rat) and F (1 mg/rat) were found to possess no intrinsic antinatriuretic activity which is represented by a decrease in the Na+ to creatinine ratio; while only B (500 micrograms/rat) demonstrated kaliuretic effects as indicated by an increase in K+ to creatinine ratios. B and F showed very significant antinatriuretic and kaliuretic properties following pretreatment with CS (2.5 mg/rat). CS alone was not found to be antinatriuretic at this dosage. Further experiments demonstrated that lower dosages of CS (500 and 1,000 micrograms/rat) also cause B to exhibit Na+ retaining and K+ excreting properties. Thus, we have demonstrated that pretreatment with CS can confer mineralocorticoid-like activity upon the glucocorticoids B and F.
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PMID:The antinatriuretic and kaliuretic effects of the glucocorticoids corticosterone and cortisol following pretreatment with carbenoxolone sodium (a liquorice derivative) in the adrenalectomized rat. 291 28

Alkaline phosphatase, sucrase, Na+,K+-ATPase and Mg2+-ATPase specific activities of crude membrane fractions, prepared from duodenal, jejunal, ileal and colonic mucosa, have been estimated in three types of hypertensive rats: the spontaneously hypertensive rat (SHR), the DOCA-saline treated rat and the renovascular rat (Goldblatt one-kidney, one-clip rat; 1K-1C). Alkaline phosphatase and sucrase specific activities have been measured in purified jejunal brush-border membranes. When compared with its normotensive age-matched control (WKY rat), the SHR has a lower activity of alkaline phosphatase in duodenal and jejunal crude membrane fractions, whereas a higher activity in colonic Na+,K+-ATPase is recorded. In purified jejunal brush-border membranes, lower alkaline phosphatase activity and higher sucrase activity were found. These differences occur in the young prehypertensive SHR as well as in the adult animal. In the DOCA-treated rat, the only significant alteration in crude membrane fractions is a decreased Mg2+-ATPase activity at all regions of intestinal mucosa. In purified jejunal brush-border membranes both alkaline phosphatase and sucrase activities are increased at 4 or 7 weeks but especially at 13 weeks of hypertension. In the 1K-1C rat, no significant modification appears in crude membrane fractions or in purified jejunal brush-border membranes, but a decrease in alkaline phosphatase and in sucrase activities is probable after 13 weeks of hypertension. Since alterations of the intestinal enzymes are different in the three types of hypertensive rats it is concluded that the changes are not secondary to the hypertension condition. In the SHR, these alterations are present in the young prehypertensive animal.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Alterations of intestinal membrane-bound enzymes in three types of hypertensive rats. 301 51

The vasoconstrictor actions of arginine vasopressin (AVP) have been shown to occur in concentrations much lower than previously thought. Pressor responses to AVP are a poor index of vasoconstrictor activity since, in contrast to other vasoconstrictor agents, the expected rise of pressure is offset by dose-dependent decreases of cardiac output. The mechanisms for this appear to be, in large part, modulation of the autonomic nervous system whereby AVP enhances vagal nerve activity and reduces peripheral sympathetic nerve activity. AVP enhancement of baroreceptor reflex gain is in part responsible for these changes in some species (dog and rabbit), but not in others (rat). The release of AVP appears to contribute significantly to the normalization of arterial pressure in volume-depleted and hypotensive states. The link between plasma AVP and hypertension remains unclear, but it appears likely that it has an important permissive action in the development of sodium-dependent forms of hypertension.
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PMID:Vasopressin and blood pressure regulation. 306 Feb 96

The effects of i.v. injection of intact digoxin antibody (0.3 mg/rat) and of its Fab fragment (40 mg/rat) on blood pressure, cardiac output and total peripheral resistance were measured in conscious spontaneously hypertensive and deoxycorticosterone hypertensive rats. In vitro findings showed that Fab fragment bound radio-labelled digoxin, digitoxin and ouabain more efficiently than did intact antibody. In vivo, Fab fragment prevented the increase of total peripheral resistance induced by i.v. injection digoxin. However, Fab fragment of digoxin antibody did not alter blood pressure, cardiac output or total peripheral resistance in normal and salt-loaded spontaneously hypertensive rats (SHR) in uraemic SHR and in deoxycorticosterone hypertensive rats. We confirmed that intact digoxin antibody--bearing Fc domains with complement activating properties--lowered blood pressure in SHR and in deoxycorticosterone hypertension. This was due to a decrease in total peripheral resistance. Our data suggest that a circulating endogenous digitalis-like factor is unlikely to be important in blood pressure regulation in salt-loaded hypertension in the rat.
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PMID:Haemodynamic effects of intact digoxin antibody and its Fab fragments in experimental hypertension. 342 60

Male stroke prone spontaneously hypertensive rats (SHRSP) were fed 4% NaCl diet containing either 0.75% normal potassium or 2.11% high-potassium, starting at 6 weeks of age. After 8 months on these diets, 40 out of 58 SHRSP on 0.75% potassium had died (69% mortality) versus two dead out of 95 on 2.11% potassium (2% mortality), a 97% reduction in mortality, P less than 0.000 01. After 20 weeks on the diet, the daytime and night-time blood pressures (BPs) of each rat were measured intra-arterially under light ether. Using these accurate BPs, we selected two groups precisely matched for BP. One matched SHRSP group (BP 182) ate the 0.75% potassium diet and 30 out of 47 rats died (64% mortality). The other matched SHRSP group (BP 182) ate the 2.11% potassium diet and two out of 35 died (6% mortality) a 91% reduction of mortality, P less than 0.0001. Seemingly, the striking reduction in mortality rate with the 2.11% high-potassium diet does not depend on a lowering of BP. High-potassium diets do not change muscle, aorta or body sodium or potassium. Dry weight of mesenteric arterioles was reduced 29% on the 2.11% potassium diet versus the 0.75% potassium diet [5.43 mg versus 7.66 mg] (P less than 0.0001) indicating a greatly reduced hypertensive hypertrophy, even though BP was equal in the two groups being compared. Aortic wall wet weight was reduced 25.5% in 36 rats on a 2.11% potassium diet versus 26 rats on a 0.75% potassium diet (36.7 mg versus 49.2 mg) P less than 0.001, even though BP was equal in the two groups being compared. In nine surviving SHRSP rats on 0.75% potassium, 13 of 36 brain hemisphere slides (four slides per rat) showed infarcts (36%). In 11 surviving SHRSP rats on 2.11% potassium, one of 44 brain slides showed infarcts (2%, a 95% reduction) P less than 0.0001. In other SHRSP rats on a 0.75% diet for 8 weeks, 18 of 25 rats (72%) had spots of brain haemorrhages whereas only two of 36 rats (5.5%) on 2.11% potassium had similar haemorrhages - a 92% reduction (P less than 0.000 01). High-potassium diets allow cerebral arteries to carry very high BPs without sustaining damage to the artery wall, thereby drastically reducing brain haemorrhages and infarcts and lowering the death rate. Moreover, hypertension does not invariably lead to artery hypertrophy, since a high-potassium diet can prevent most of it.
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PMID:High-potassium diets markedly protect against stroke deaths and kidney disease in hypertensive rats, an echo from prehistoric days. 346 6


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