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Biomedical subjects

A F Lever

Publications and source records attributed to A F Lever.

At least 145 records · Page 8Linked to original sources
PubMed1982

Effect of standard oral glucose loading on aldosterone secretion in primary hyperaldosteronism.

The effects of mild acute decreases in plasma potassium induced by standard oral glucose loading (100 g) on plasma aldosterone and renin levels were assessed in 10 patients with primary hyperaldosteronism as compared with 10 normal subjects. Following overnight fast, mean plasma glucose was identical in both groups; plasma insulin, potassium and renin levels were lower and plasma aldosterone higher in patients than in controls. Glucose loading significantly increased plasma glucose and insulin concentrations and decreased plasma potassium and aldosterone levels in both groups. The increases in plasma insulin and the decreases in plasma potassium or aldosterone tended to be blunted in primary hyperaldosteronism. glucose-induced changes in plasma aldosterone correlated significantly (P less than 0.025) with those in plasma potassium in the patients and with variations in plasma renin activity in the normal subjects. These findings suggest that the metabolic changes induced by glucose ingestion are capable of modifying aldosterone secretion in primary hyperaldosteronism. However, the glucose-induced decreases in plasma aldosterone are blunted in this disorder; this could be related to the impaired insulin response to glucose loading.

Adult↗
PubMed1982

Effect of oral glucose loading on plasma insulin, potassium, renin and aldosterone in normal subjects and patients with primary hyperaldosteronism.

The effects of standard oral glucose loading (100 g) on plasma aldosterone and some regulatory factors were assessed in patients with primary hyperaldosteronism and normal subjects. Following overnight fast, mean plasma glucose was identical (10 patients and normal subjects approximately matched per age and sex); plasma insulin, potassium and renin levels were lower and plasma aldosterone higher in the patients. Glucose loading significantly increased plasma glucose and insulin concentrations and decreased plasma potassium and aldosterone levels in both groups; plasma renin activity was significantly increased only in normal subjects. The increases in plasma insulin and the decreases in plasma potassium or aldosterone tended to be blunted in primary hyperaldosteronism. Relationships among glucose-induced changes in plasma aldosterone and other factors were assessed by multiple regression analysis in these patients and normal subjects as well as an additional group of 21 normal subjects; in the latter, plasma cortisol was also measured and found to decrease significantly after glucose loading. Changes in plasma aldosterone correlated (P less than 0.025) more closely with those in plasma potassium in the patients and with variations in plasma renin activity in the normal subjects. These findings suggest that complex metabolic changes occur following glucose ingestion which are capable of modifying aldosterone secretion in normal subjects and primary hyperaldosteronism. The aldosterone-inhibitory effect of glucose tends to be blunted in the latter disorder. This could be related at least in part to an impaired insulin response in primary hyperaldosteronism.

Administration, Oral↗
PubMed1982

Prolonged infusion of norepinephrine in the conscious dog: effects on blood pressure, heart rate, renin, angiotensin II, and aldosterone.

Eight conscious beagle dogs were given continuous intravenous infusions for 4 weeks: 0.9% NaCl solution was given for the first week; norepinephrine for the following 2 weeks, (at 125 ng/kg/min or at 250 ng/kg/min each in four dogs), 0.9% NaCl for the final week. Norepinephrine at the lower dose did not raise blood pressure but did reduce heart rate significantly. The higher rate of norepinephrine infusion raised blood pressure, but for the first week of infusion only, and again heart rate was reduced significantly during both weeks. Blood pressure fell on stopping infusion whether or not it had been raised previously. Plasma concentrations of renin, angiotensin II, and aldosterone were reduced, but the changes were of borderline significance only. These changes occurred when plasma concentrations of norepinephrine were increased four-sevenfold. The acute response to high infusion rates of norepinephrine (500, 1,000, and 2,000 ng/kg/min each for 1 h) was tested at weekly intervals in each dog. At each of these high rates of infusion, blood pressure, renin and angiotensin II, and haematocrit increased while plasma potassium concentration and heart rate fell. These changes occurred with increases of plasma norepinephrine greater than 14-fold. Prolonged infusion of norepinephrine did not alter the relation between plasma norepinephrine and arterial pressure as assessed by these dose-response studies.

Aldosterone↗
PubMed1981

Sodium and potassium in essential hypertension.

A study was carried out of arterial pressure and body content of electrolytes in 91 patients with essential hypertension and 121 normal controls. Exchangeable sodium was found to be positively correlated with arterial pressure in the patients, the correlation being closest in older patients; values of exchangeable sodium were subnormal in young patients; and plasma, exchangeable, and total body potassium correlated inversely with arterial pressure in the patients, the correlations being closest in young patients. Three hypotheses were proposed to explain the mechanisms relating electrolytes and arterial pressure in essential hypertension--namely, a cell-salt hypothesis, a dietary salt hypothesis, and a kidney-salt hypothesis. It was concluded that two mechanisms probably operate in essential hypertension. In the early stages of the disease blood pressure is raised by an abnormal process related more closely to potassium than to sodium. A renal lesion develops later, possibly as a consequence of the hypertension. This lesion is characterised by resetting of pressure natriuresis and is manifest by an abnormal relation between body sodium and arterial pressure and by susceptibility to increased dietary sodium intake.

Adult↗
PubMed1981

Blood pressure in acute and chronic vasopressin excess: studies of malignant hypertension and the syndrome of inappropriate antidiuretic hormone secretion.

We studied 29 patients with malignant hypertension and 28 patients with the syndrome of inappropriate antidiuretic hormone secretion to assess the relation of plasma vasopressin to blood pressure in states of acute and chronic vasopressin excess. In the patients with malignant hypertension, vasopressin levels were elevated (13 +/- 2 pg per milliliter. [+/- S.E.M.]) but did not correlate with arterial pressure; however, in normal volunteers, blood pressure did not rise when vasopressin was increased beyond these levels through infusion of the peptide. In the patients with inappropriate antidiuretic hormone secretion, blood pressure was not elevated, but vasopressin was raised (39 +/- 7 pg per milliliter) and did not correlate with systolic or diastolic pressure. These data do not support the concept that an acute or chronic excess of vasopressin makes an important contribution to the regulation of blood pressure.

Adult↗
PubMed1981

Combined captopril and spironolactone treatment in Conn's syndrome with renal impairment and refractory hypertension.

Spironolactone alone in full dosage failed to correct hypertension in a patient with Conn's syndrome and renal impairment, although the previously increased total exchangeable sodium fell to normal and the previously suppressed plasma angiotensin II did not rise above the normal range. Addition of the converting enzyme inhibitor captopril reduced plasma angiotensin II to very low levels, with a slight further fall in exchangeable sodium. Blood pressure was well controlled. Because hypertension in Conn's syndrome resistant to spironolactone usually also responds poorly to removal of the adenoma, and is difficult to treat with conventional hypotensive agents, the combination of a converting enzyme inhibitor with a potassium conserving diuretic is worthy of trial in such cases.

Adult↗
PubMed1981

Pre-operative localization of aldosterone-secreting adrenal adenomas.

Techniques for pro-operative localization of aldosterone-secreting adrenal adenomas were studied in thirty-seven patients, each with hypertension and biochemical evidence of primary hyperaldosteronism and each later having adrenal surgery (thirty-two adenomas, five bilateral hyperplasia). Bilateral adrenal vein catheterization was attempted in all cases; it was successful on the left side in all patients and in 92% of cases on the right. Adrenal vein plasma samples were obtained from the left side in 92% and from the right in 73% of cases. Adrenal vein plasma aldosterone measurements correctly indicated the presence of tumour in twenty-eight cases but falsely predicted unilateral adenoma in two cases of bilateral adrenal hyperplasia. Adrenal venography also correctly predicted unilateral adrenal adenomas in twenty-six cases but falsely suggested the presence of tumour in three cases of bilateral adrenal hyperplasia. Computed tomography (CT) was used in the last eight cases. In seven instances the predictions (six adenomas, one bilateral adrenal hyperplasia) were confirmed at surgery. However, the remaining patient harboured an adenoma 20 mm in diameter which was not detected by CT although diagnosed both by adrenal venography and adrenal vein aldosterone measurements. Ultrasound detected adenoma in only three of twenty-two cases examined. Although further comparative studies of the type described here are required, the results of computed tomography are promising and suggest that this non-invasive technique might well become the first choice procedure in localizing aldosterone-secreting adenomas.

Adenoma↗
PubMed1981

Low blood pressure in psychiatric inpatients.

Blood pressure recordings in 116 female psychiatric inpatients were analysed. Sixty-nine women had schizophrenia, the remainder a variety of psychiatric conditions. All had been in hospital continuously for more than one year, the average for 19 years continuously. An average of seven recordings of blood pressure per patient had been made during that time. The latest of these compared well with measurements made independently using a sphygmomanometer free from observer bias. On admission to hospital the blood pressure of these patients was close to that of two normal populations. Thereafter it failed to rise at the normal rate and after an average of 19 years, in the women having measurements made by special sphygmomanometer, systolic pressure was 28 mmHg lower than controls of the same age while diastolic pressure was 12.8 mmHg lower. Lower than control blood pressure was apparent in schizophrenic and non-schizophrenic women and in women taking no drugs, phenothiazines, and other drugs. Weight loss is an unlikely explanation: the mean weight of these women was 61.5 kg compared with 64.1 kg in a local control population of the same age. Some factor related to prolonged isolation in hospital seems more important.

Adult↗
PubMed1981

Comparison of fast and slow pressor effects of angiotensin II in the conscious rat.

Female Wistar rats were infused intravenously with 5% dextrose for 3 days, then with angiotensin II (ANG II) in 5% dextrose at 20 ng . kg-1 . min-1 for 7 days, and finally with dextrose for 2.5 days. ANG II raised mean arterial pressure (MAP) gradually; by the 7th day it was 49.7 mmHg higher than during the dextrose control period in the same rats. Control rats were infused with dextrose for 12.5 days; MAP did not change. Plasma ANG II concentration was measured during infusion. In hypertensive rats on the 7th day of ANG II infusion, it was six times higher than in control rats infused with dextrose. Changes of blood pressure and plasma ANG II concentration were compared in further rats infused with much larger doses of ANG II. Rats receiving 270 ng . kg-1 . min-1 for 1 h had an almost maximal direct pressor response, MAP rising 45.3 mmHg and plasma ANG II rising 32-fold compared with controls. Thus, infusion of ANG II at low dose without direct pressor effect gradually raises blood pressure to a level similar to the maximum direct pressor effect produced by larger doses of ANG II. Sodium balance and food and water intakes were also measured and did not change during prolonged infusion of ANG II at 20 ng . kg-1 . min-1. Thus, the slow pressure effect of ANG II develops at a lower and more nearly physiological plasma concentration of the peptide than do the direct pressor effect and the effects on drinking, eating, and urinary sodium excretion.

Angiotensin II↗
PubMed1981

The renin-angiotensin system and aldosterone in hypertension: a brief review of some aspects.

The biochemistry of the renin-angiotensin system has been outlined. The relationship between plasma angiotension II levels, basal or raised as a result of infusion, and blood pressure and aldosterone has been explored in normal human subjects and animals, showing how these relationships can be modified by changes in sodium status and duration of exposure to high circulating levels of the octapeptide. Finally, the relationship has been examined in different categories of hypertensive disease, such as essential hypertension.

Aldosterone↗
PubMed1980

Reconstructive surgery versus nephrectomy in renal artery stenosis: comparison of effects on total and divided renal function and on blood pressure.

Twenty-six hypertensive patients with unilateral renal artery disease and normal overall renal function were treated surgically: eleven underwent arterial reconstruction and 15 unilateral nephrectomy. One year after operation there was similar reduction in blood pressure in each group (delta mean BP 45:3 mm Hg (p < 0.001) and 36.8 mm Hg (p < 0.001) respectively. contrary to previous reports, however, a small but significant improvement in overall renal function was observed in patients who underwent reconstructive surgery (delta mean serum creatinine--13.3 mumol/1 (p < 0.01); this was associated with a significant rise in para-aminohippurate (PAH) clearance in the operated kidney, while PAH clearance fell on the contralateral side. Overall renal function deteriorated in the patients who underwent unilateral nephrectomy (delta mean serum creatinine +22.7 mumol/1 (p < 0.01)). The latter was due partly to diminished clearance in the remaining kidney and partly to the loss of the excised kidney. The findings emphasise the superiority of renal artery reconstruction over nephrectomy in patients with renovascular hypertension.

Adolescent↗
PubMed1980

Combined treatment of severe intractable hypertension with captopril and diuretic.

The converting-enzyme inhibitor, captopril, in a dose of 450 mg daily, was given together with a diuretic to eleven patients with severe hypertension unresponsive to previous therapy. Sustained control of blood pressure was achieved. Plasma angiotensin II and aldosterone fell significantly, whereas plasma active and total renin, and blood-angiotensin-I concentrations increased. Adverse effects included temporary taste disturbance, tachycardia, nephrotic syndrome, and possible drug-induced Guillain-Barré neuropathy. The combination of captopril and diuretic is thus very effective in controlling refractory hypertension. However, because of the frequency and severity of side-effects it should probably be used only in patients whose blood pressure has previously been uncontrolled by other means.

Blood Pressure↗