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

The renin-angiotensin system appears to play a major role in the regulation of sodium excretion and fluid intake in a wide variety of animal species from mammals to teleosts. In mammals the system has evolved further importance in terms of blood pressure homeostasis. This hormonal system in all species appears to involve a serum protein prohormone, angiotensinogen, a proteolytic enzyme, renin, and angiotensin I, the decapeptide product of the reaction between renin and angiotensinogen. The importance of this system to the organism appears to correlate directly with the necessity to conserve sodium while an abnormality of this process may underlie the development of hypertension in man. As the starting point of the system, angiotensinogen assumes special importance as a possible index of evolutionary development. In addition, it has been known for many years that human (viz. primate) angiotensinogen differs from that found in other mammals in its inability to be a substrate for animal renins while animal angiotensinogens readily react with human renin. Thus, the enzymatic specificity appears to reside with the prohormone. The biochemical basis for this difference is unresolved due primarily to the lack of purified human angiotensinogen. In this paper we describe methods for the purification of human angiotensinogen which have direct applicability to animal angiotensinogens. Our approach utilizes ammonium sulfate precipitation, Sephadex G-150 chromatography, multiple isoelectric focusing, and concanavalin A-Sepharose affinity chromatography. With the availability of highly purified human angiotensinogen we compared the molecular weights, heterogeneity, isoelectric points, and thermal lability of hog, rabbit, and human angiotensinogen in order to define the biochemical basis of the species variation in renin reactivity...
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PMID:Human angiotensinogen. Purification partial characterization, and a comparison with animal prohormones. 1 60

In dogs, anaesthetized with chloralose, fentanyl (5 mug/kg i.v.) augmented the bradycardia produced by electrical stimulation of the carotid sinus nerves. In contrast, the same dose of the drug did not change the bradycardic response to stimulation of the nucleus of the solitary tract (NTS) indicating that a central facilitation of baroreceptor impulses occurs within the NTS, probably at the first synapse of baroreceptor reflex fibres. Bilateral destruction of the NTS caused a fulminating hypertension and tachycardia similar to that after cutting the baroreceptor afferent fibres. After both procedures, fentanyl (20 mug/kg i.v.) produced marked hypotension and bradycardia. The bradycardic effect was abolished by cutting both vagal nerves when the dogs were pretreated with a beta-adrenoceptor blocking agent (S 2395, 50 mug/kg i.v.). The results provide evidence that the NTS is not the main site of action either for the hypotensive effect or for the vagally mediated bradycardia of fentanyl. Since the dorsal nucleus of the vagal nerve was destroyed together with the NTS, this nucleus does also not appear to be a major site of the action of fentanyl. Blockade of dopamine receptors by haloperidol or pimozide or of serotonin receptors by methysergide did not change the hypotensive, bradycardic and sympathoinhibitory effects of fentanyl.
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PMID:Central sites and mechanisms of the hypotensive and bradycardic effects of the narcotic analgesic agent fentanyl. 1 7

Under the voluntary reporting scheme 499 cases of adverse drug reaction or reactions were reported. Noteworthy items included immediate hypersensitivity-type reactions to anaesthetic agents, a number of life-threatening reactions to anti-inflammatory drugs, paradoxical increase in blood pressure with high-dose pindolol and rebound hypertension after cessation of clonidine. A further 904 reactions were reported during an intensive survey in general practice and 342 from the ongoing hospital monitoring studies in units at the Auckland and Hutt hospitals. Data from numerous sources are now being channelled through the Committee's administrative centre. During the 11th year of operations 499 reports were received under the spontaneous reporting scheme. Additionally 342 reactions derived from the established hospital monitoring programmes at the Auckland Hospital and School of Medicine and the Hutt Hospital were notified to the Committee, and a further 904 reactions were received as a result of the intensive monitoring survey of drug reactions in general practice carried out in October and November 1975. The significance of each of these sets of data is substantially different and they will be discussed separately.
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PMID:New Zealand Committee on Adverse Drug Reactions: eleventh annual report 1976. 1 21

Only recently approved for use in the treatment of hypertension in the US, the beta-adrenergic receptor blocking compound propranolol has been used elsewhere for this purpose since 1964. The exact mechanisms to explain why and how "beta-blocking drugs" reduce arterial pressure are not known with certainty, but possible explanations include: (1) "resetting" of the baroreceptors, (2) reduction of cardiac output, (3) adaptation of circulation ("autoregulation"), (4) inhibition of renin release, (5) central nervous system effects, (6) possible antihypertensive metabolites, and (7) other unknown mechanisms or a combination of known mechanisms. Propranolol alone has been demonstrated to be extremely effective in reducing arterial pressure. In addition, the combination of propranolol and vasodilator and diuretic drugs would be expected to reduce vascular resistance without reflexive cardiac stimulation and with prevention of sodium and fluid retention.
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PMID:Pathophysiology of propranolol in hypertension. 1 2

Patients with essential hypertension can be subdivided into groups with low (19%), normal (59%) or high (23%) renin sodium index. The proportion with low renin hypertension increases with age. Patients with high renin fall in two categories: younger patients with fairly mild hypertension and older patients with more severe hypertension and signs of renal disease. The antihypertensive efficacy of betablocker monotherapy is best in high renin forms, good but less consistent in normal renin patients and uniformly bad in low renin hypertensives. In relation to age, betablockers normalized blood pressure (less than or equal to 95 mm Hg diastolic) in three-quarters of the younger-than-40-year-olds, in about half of those 40-60 years of age but in only 20% of those over 60 years. On this basis, it is postulated that the older patients with a low renin exhibit a relatively hypoadrenergic state whereas those with a normal or high renin--for a given age and elevated pressure--have a relatively increased adrenergic nervous activity. Because the betablockers have a potent suppressive action on the renin-angiotensin system--and, as a consequence, on angiotensin vasoconstriction, aldosterone volume expansion and central stimulatory feedback mechanisms--their antihypertensive mode of action may be linked to an important extent, although not exclusively, to renin suppression.
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PMID:Renin and age as determinants of a predominantly betablocker-based antihypertensive drug program. 1 85

Postoperative coronary bypass flow was evaluated in two groups of randomly selected patients with grafts to the left anterior descending artery (LAD). Saphenous vein bypass grafts were placed in 27 patients and internal mammary artery grafts in 25 patients. Postoperative flow studies were performed in both groups with roentgendensitometric methods based on the transit time of radiopaque media along the graft plus the mean graft diameter. There was no significant difference between the two groups of patients for age, duration of symptoms, or the frequency of hypertension, diabetes mellitus, prior myocardial infarction, or cardiomegaly. Intraoperative bypass flows were 75+/-27 and 77+/-24 ml. per minute for the saphenous vein group (SVG) and internal mammary artery group (IMAG), respectively. There was no significant difference in the heart rate or mean aortic pressure at the time of the roentgendensitometric flow study. The mean graft diameters were 3.0+/-0.5 and 1.9+/-0.3 mm. for the SVG and IMAG, respectively (p less than 0.001). The ratios of graft diameter to LAD diameter were 1.9+/-0.3 and 1.2+/-0.2 for the SVG and IMAG, respectively (p less than 0.001). The roentgendensitometric postoperative flows were 68+/-27 ml. per minute in the SVG and 46+/-16 ml. per minute in the IMAG (p less than 0.01). The present study indicates that flow in significantly higher in saphenous vein than in internal mammary artery bypasses and that the difference in flow may in part be explained on the basis of the graft diameter.
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PMID:Comparative study of the postoperative flow in the saphenous vein and internal mammary artery bypass grafts. 1 96

The unique action of propranolol and other beta blockers in lowering raised arterial pressure is discussed. Although the onset of the antihypertensive effect is not immediate, many trials have confirmed the efficacy of these drugs. Animal experiments have thrown little light on the mechanism of action of beta blockers in hypertension: this may be because in animals, especially the rat, peripheral beta adrenoceptor vasodilatation is relatively more important than in man. Five principal theories have been advanced to explain the antihypertensive effect. None of these, the renin, central nervous system, cardiac, baroceptor or metabolite theory, is totally satisfactory. A new theory is proposed suggesting that the essential action is to diminish sympathetic nerve output by damping sensory input to the central nervous system from a heart whose capacity to respond to exercise and stress is blunted by beta adrenoceptor blockade.
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PMID:The essential action of propranolol in hypertension. 1 98

There is good evidence from many sources that beta-adrenoreceptor blockade is an effective form of therapy in mild, moderate and severe hypertension either alone or in combination with other antihypertensive agents. Although a number os such beta blocking compounds are now available, they appear to have a hypotensive effect of approximately equal magnitude. This hypotensive effect is obtained in both the supine and standing positions thus avoiding postural hypotension. The maximum hypotensive effect may take some time to become apparent. Despite considerable work the mode of action remains uncertain, reduction in cardiac output, resetting of baroreceptors, reduction in plasma renin and a central nervous system effect have been suggested but remain unproved. There is evidence to suggest that these compounds can control, to some degree, the surges in blood pressure resulting from either mental or physical stress. A low incidence of serious side effects has been reported by many workers. Only the long-term use of these compounds in comparison with other antihypertensive agents will determine their place in the management of hypertension.
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PMID:Beta-adrenoreceptor blockade in hypertension. 1 2

The treatment response to beta-adrenoceptor blocking drugs was compared in two groups of patients with primary (essential) hypertension and different renin levels. Each group consisted of 25 patients and was equally distributed regarding age, severity and stage of hypertension. In the first group (group 1), the mean upright plasma renin activity was 0.8 ng ml-1h-1 (range 0.3 to 1.5) and the patients were considered to have low renin hypertension. In the other group (group 2) the patients had a mean plasma renin activity of 2.1 ng ml-1h-1 (range 1.1 to 5.1) and were considered to have normal to high renin hypertension. In both groups the patients were initially treated with beta-blocking drugs; in group 1 with a beta-blocker corresponding to an average dose of 311 mg propranolol a day for at least eight weeks and in group 2 with propranolol 320 mg a day in a fixed dose for eight weeks. The hypotensive response differed significantly between the two groups (p less than 0.001). In group 1 the pretreatment blood pressure was 197/117 mm Hg supine and 198/120 mm Hg standing. During treatment blood pressure decreased only 5/3 mm Hg supine and 9/5 mm Hg standing. The pretreatment blood pressure in group 2 was 187/114 mm Hg supine and 186/117 mm Hg standing. Beta-blocking therapy reduced blood pressure 36/23 and 34/18 mm Hg, respectively (both p less than 0.001). Pulse rates fell significantly in the two groups, both in the lying and standing positions. In 17 patients with low renin hypertension (group 1), a volume-depleting drug was added (spironolactone, 14 patients; thiazides, 3 patients) and this achieved a marked fall in blood pressure levels of 38/16 mm Hg supine and 37/19 mm Hg standing (both p less than 0.001). These results suggest the following: (1) Most patients with normal to high plasma renin activity respond well to moderate doses of propranolol. (2) Propranolol given in the same doses is almost without antihypertensive effect in patients with low renin hypertension. (3) A volume factor may be operating in patients with low renin hypertension since a hypotensive effect is demonstrated after the addition of volume-depleting drugs. (4) Determination of plasma renin activity with adequate methods can predict the treatment response to hypotensive agents.
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PMID:Different antihypertensive effect of beta-blocking drugs in low and normal-high renin hypertension. 1 4

Ganglioplegic drugs, including trimetaphan, have been imperfect agents of arterial hypotension, liable to produce tachyphylaxis, and not blocking intercurrent attacks of adrenergic hypertension the dose is inconstant and reversibility sometimes doubtful. The association of neuroleptics, in particulier promazines, permits an appreciable economy in dosage, stabilises the curves of hypotension, with the disadvantage of blocking normalisation of blood pressure. Sodium nitroprusside does not have the disadvantage of ganglioplegic drugs. Although usable alone, the blood pressure graphs sometimes have a certain instability mainly due to the difficulty of regulating the ideal perfusion flow rate. The authors show that the association of neuroleptic drugs has here also an effect of economy of dosage and facilitates the rise in blood pressure. Verification of reinforcement of the effect of sodium nitroprusside by chlorpromazine, acepromazine and levomepromazine was carried out in the dog. The authors show significant graphs.
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PMID:[Controlled arterial hypotension produced by nitroprusside combined with neuroleptics]. 1 64


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