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

We have studied the effects of magnesium sulfate (MgSO4) administration in chronically instrumented normotensive and hypertensive pregnant sheep. Animals of 90 to 144 days' gestation were divided in two groups; those with normotensive arterial pressure and those in which renovascular hypertension had been produced. Our results show that bolus injection of 2 or 4 Gm. of MgSO4 caused a transient decrease in systolic and diastolic pressure which returned to control values within 5 to 10 minutes. The continuous infusion of MgSO4 in doses of 2 or 4 Gm. per hour produced a slight increase in uteroplacental blood flow but did not alter the blood pressure. Heart rate showed a slight increase. Because MgSO4 produced no significant hemodynamic changes, we feel that: (1) its use in obstetrics must be based on its anticonvulsant action and (2) MgSO4 in either normotensive or hypertensive patients is not associated with impairment of uteroplacental blood flow.
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PMID:Circulatory effects of magnesium sulfate in normotensive and renal hypertensive pregnant sheep. 84 30

Deliberate hypotension is widely used during cerebral-artery aneurysm surgery to facilitate clipping and to prevent rupture. A large number of drugs are commonly employed to achieve hypotension, but all have their specific drawbacks. We investigated the effects of magnesium-sulphate-induced hypotension on haemodynamics, as well as on plasma catecholamine and renin concentrations in 11 patients undergoing cerebral-aneurysm surgery. Magnesium sulphate lowered blood pressure by reducing systemic vascular resistance. There was no reflex tachycardia or rebound hypertension, and cardiac output was not decreased. Plasma renin activity increased during hypotension but the inhibitory effects of magnesium on angiotensin converting enzyme prevented angiotensin-II-associated hypertension. Plasma catecholamine concentrations increased moderately during hypotension. Renal perfusion was not impaired since diuresis remained constant or even improved during and after hypotension. Magnesium sulphate in high doses has major drawbacks, however, among which are enhanced neuromuscular blockade and delayed return of consciousness. Although the haemodynamic effects of magnesium sulphate during hypotension appear to be beneficial, these side-effects might limits its usefulness, particularly in neurosurgery. More research must be conducted before magnesium sulphate can be considered a routine method.
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PMID:Haemodynamic and endocrine effects of deliberate hypotension with magnesium sulphate for cerebral-aneurysm surgery. 187 7

The effect of magnesium sulphate (MgSO4) infusion on blood pressure and circulating venous catecholamine levels in 8 patients with severe gestational proteinuric hypertension is described. A significant fall in blood pressure was noted after MgSO4 infusion; the maximal fall in diastolic blood pressure correlated with the greatest rise in serum magnesium levels (P less than 0.04). No significant change was observed in mean venous plasma adrenaline or noradrenaline levels after MgSO4 infusion, although the mean dopamine concentration declined significantly. It is concluded that the decrease in systemic vascular resistance after MgSO4 infusion in gestational proteinuric hypertension is mediated predominantly by mechanisms other than a change in circulating catecholamine levels.
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PMID:The effect of magnesium sulphate infusion on circulating catecholamine levels in severe gestational proteinuric hypertension. A report of 8 cases. 225 18

Recent in vitro studies have suggested that magnesium sulfate (MgSO4) infusions may increase prostacyclin production. We studied the effect of MgSO4 infusion on prostacyclin (PGI2) metabolite excretion in women with either pregnancy induced hypertension or preterm labor. Excretion of renal and systemic metabolites of PGI2 was measured prior to and following the start of MgSO4 infusion in the two groups. An increased in renal PGI2 metabolite preterm labor excretion was noted in the hypertension group but no change was noted in systemic PGI2 excretion in either group. These data fail to support a generalized, short term increase in endothelial cell PGI2 production as the basis for the beneficial effect of MgSO4.
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PMID:The effect of magnesium sulfate infusion on systemic and renal prostacyclin production. 225 68

We investigated the distinct ability of various antihypertensive drugs to modulate the extent (%) of rapid (15 minutes) resetting of the baroreceptors of normotensive rats to hypotensive levels. In one protocol, hemorrhage produced a complete resetting to hypotension in rats chronically treated (6 days) with captopril. Also, hemorrhage produced only partial resetting in rats acutely treated (10-15 minutes before baroreceptor recording) with captopril and in control (untreated) rats (73 +/- 7% and 49 +/- 5%, respectively). In another protocol, all vasodilators produced hypotension in normotensive rats. Nifedipine produced complete (93 +/- 4%) resetting to hypotension, whereas prazosin produced near-maximal (83 +/- 3%) resetting. The remaining drugs studied (phenoxybenzamine, trimethaphan, and MgSO4) induced a partial resetting (63 +/- 7%, 63 +/- 9%, and 50 +/- 5%, respectively) that did not differ significantly from the extent observed with hemorrhage in control (untreated) rats. These results demonstrate that different antihypertensive drugs distinctly modulate rapid baroreceptor resetting to hypotensive levels and that nifedipine and long-term treatment with captopril associated with hemorrhage modulate rapid resetting to hypotension in a more efficient manner.
Hypertension 1990 Feb
PMID:Antihypertensive drugs distinctly modulate the rapid resetting of the baroreceptors. 240 63

Ten pregnant ewes were alternated in a study of the blocking effect of parenteral magnesium on the catecholamine response to cocaine. Indirect blood pressures were recorded at 1-minute intervals for 12 minutes before and after a bolus of 2 mg/kg of cocaine. Fetal heart rates were continuously recorded from skin electrodes. Platelet counts were performed before and 12 minutes after cocaine. Control ewes received lactated Ringer's solution, and test animals had 5 mg/kg of elemental magnesium in the form of MgSO4-7H2O in a rapid infusion. A semicrossover was also performed. Platelet counts fell precipitately in controls and rose after magnesium infusions. Fetal heart rates rose in controls at 5-minute intervals and were unchanged in magnesium-treated mothers. Because of disparity of the baseline mean arterial pressure, direct comparisons were not significant before and after cocaine. Alterations from the baseline were different in magnesium-treated versus control animals, with values in the latter rising by 28 +/- 10 mm Hg with lactated Ringer's solution plus cocaine and falling by 3 +/- 5 mm Hg with magnesium pretreatment. Values in test animals originally treated with magnesium rose 4 +/- 11 mm Hg for an overall significance of p less than 0.05. Low beginning serum magnesium levels were associated with ovine hypertension and reduced fetal weight and survival.
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PMID:Effect of magnesium on cocaine-induced, catecholamine-mediated platelet and vascular response in term pregnant ewes. 258 60

Recent interest has centred on the role of divalent cations in hypertension, particularly in relation to the renin-angiotensin system. This study was undertaken to determine the hypotensive effect of magnesium administration in relation to the state of activation of the renin-angiotensin system. The mean blood pressure (MBP) and heart rate (HR) response to either the acute intravenous administration of a pharmacological dose of MgSO4 or vehicle was determined in conscious mineralocorticoid-salt (DOCA-salt, low-renin) and two-kidney, one clip renovascular, high-renin hypertensive rats. Baseline MBP was higher in the renovascular than in the DOCA-salt rats, while there was no difference in HR or serum Mg concentration between the two. Following administration of MgSO4, serum Mg increased equally in both the DOCA-salt (1.4 +/- 0.8 to 4.9 +/- 0.16 mEq/l; P less than 0.001) and in the renovascular rats (1.8 +/- 0.14 to 4.4 +/- 0.27 mEq/l; P less than 0.001). Magnesium administration significantly lowered MBP over the 1-h infusion in the DOCA-salt (167 +/- 8 to 145 +/- 5 mmHg, P less than 0.001) but not the renovascular hypertensive rats (191 +/- 5 to 183 +/- 4, NS). We conclude that the blood pressure lowering effect of Mg is related, in part, to the state of activation of the renin-angiotensin system. The mechanism of this differential effect remains to be determined.
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PMID:Haemodynamic response to magnesium administration in mineralocorticoid-salt and two-kidney, one clip renovascular hypertension. 338 7

Preeclampsia is a disorder of pregnancy characterized clinically by hypertension, proteinuria, and edema and characterized pathologically in its late stages by widespread microvascular thrombi. There is evidence from a number of studies that production of prostacyclin (prostaglandin I2, PGI2), a potent vasodilator and inhibitor of platelet aggregation, is deficient in preeclamptic compared to normal pregnancy. Traditional therapy utilizes infusions of large amounts of MgSO4, but the physiologic basis for this is not clear. We studied the effect of MgSO4 on PGI2 release by cultured human umbilical vein endothelial cells (HUVEC) by several methods. By platelet aggregometry, the known antiaggregatory effect of intact HUVEC was enhanced by MgSO4. By radioimmunoassay for 6-keto-PGF1 alpha, the stable metabolite of PGI2, it was shown that MgSO4 amplifies release of PGI2 by HUVEC in a dose-dependent manner, with a peak occurring between 2 and 3 mM. In separate experiments, MgSO4 overcame the enhanced adherence of platelets to HUVEC exhausted by repeated exposure to thrombin. Finally, PGI2 production was 2- to 5-fold greater by HUVEC incubated with plasma obtained from preeclamptic patients undergoing MgSO4 therapy than by HUVEC incubated with pretherapy plasma. We conclude that MgSO4 mediates enhanced production of PGI2 by vascular endothelium, thereby potentially enhancing its thromboresistant properties.
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PMID:Magnesium sulfate: rationale for its use in preeclampsia. 351 61

Systolic and mean blood pressures were shown to increase from means of 159 +/- 7 and 111 +/- 7 mm Hg to 174 +/- 8 and 122 +/- 6 mm Hg, respectively (p less than 0.05 in each case), after a 2-hour intravenous infusion of CaCl2 during which serum magnesium levels were found to decrease from 1.8 +/- 0.06 to 1.4 +/- 0.05 mg/dl (p less than 0.0005). A significant increase in blood pressure was not seen when MgSO4 was given intravenously concomitantly with the CaCl2 so that serum magnesium levels did not decline. We conclude that hypercalcemic hypertension is due in part to altered serum magnesium and is prevented if serum magnesium is sustained.
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PMID:Magnesium prevents acute hypercalcemic hypertension. 369 13

Three patients with primary aldosteronism were treated surgically between February and September 1984. All patients had suffered from hypertension with U waves in ECG and laboratory examinations revealed hypokalemia, hyperaldosteronemia and suppressed plasma renin activity. The localization of the adrenal tumor was diagnosed accurately in all 3 patients by adrenal vein sampling and in 2 of the patients by PRP, CT scan, adrenal scanning with 131I-iodo cholesterol and adrenal venography. Adrenal tumors were surgically removed by unilateral adrenalectomy through the flank approach in all cases. Histological examinations of removed specimens showed adrenocortical adenoma. Removal of the adenoma caused a prompt reversal of the laboratory serum abnormalities and hypertension was normalized within 2 weeks postoperatively in all cases. Severe ventricular tachycardia (Torsades de Pointes) was observed suddenly in one of the patients after about 5 hours postoperatively. Therapy including conventional antiarrhythmic drugs, such as lidocaine or procainamide, and potassium administration failed to prevent the arrhythmia. Ventricular tachycardia was successfully treated and disappeared with the use of magnesium sulfate (MgSO4) intravenously. The serum potassium concentration was normal during the episode and the serum magnesium concentration, which was not detected before or just after the operation, was under the limit of normal range (1.4 mEq/l) after the use of magnesium sulfate. Hypomagnesemia which is retrospectively thought to be the result of primary aldosteronism may be responsible for the episode of postoperative ventricular tachycardia.
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PMID:[Three cases of primary aldosteronism including one case with postoperative ventricular tachycardia]. 396 10


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