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Biomedical subjects

C R Edwards

Publications and source records attributed to C R Edwards.

At least 91 records · Page 5Linked to original sources
PubMed1991

Lessons from licorice.

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11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

Serotonin stimulates calcium influx in isolated rat adrenal zona glomerulosa cells.

To investigate the role of calcium as a second messenger in serotonin-stimulated aldosterone secretion, radiolabelled calcium influx studies were carried out in purified rat adrenal zona glomerulosa cells using 45CaCl2. The results show that serotonin caused calcium influx within 45 seconds of addition and this continued for up to 105 seconds. Angiotensin II also caused calcium influx; however, the effect was significantly smaller than that of serotonin. Serotonin-stimulated calcium influx could be inhibited by the calcium antagonist verapamil and by methysergide, a selective serotonin receptor type-1/2 antagonist. The data indicate that serotonin directly stimulates calcium uptake in zona glomerulosa cells via calcium channels which are coupled to specific serotonin receptors.

Angiotensin II↗
PubMed1991

Liquorice.

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11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

Cutaneous vasoconstrictor response to glucocorticoids in asthma.

The aim of the study was to find out whether asthma patients whose airways obstruction is sensitive (CS) or resistant (CR) to corticosteroid treatment also differ in their cutaneous vasoconstrictor response to a potent topical glucocorticoid. Corticosteroid resistance was defined by failure of forced expiratory volume in 1 s (FEV1) and peak expiratory flow rate to improve by at least 15% after a 2-week trial of corticosteroids (prednisolone 20 mg daily for 1 week, then 40 mg daily for 1 week) despite more than 15% improvement with inhaled beta agonists. Beclomethasone dipropionate in concentrations of 3 micrograms/ml, 10 micrograms/ml, 30 micrograms/ml, and 100 micrograms/ml was applied to forearm skin; the site was occluded under plastic and the degree of blanching assessed after 18 h. CS asthmatic subjects (n = 31), asthma patients with mild airways obstruction (n = 26), asthma patients taking long-term prednisolone (n = 13), and healthy volunteers showed similar vasoconstrictor responses. In CR asthmatic subjects (n = 15), the response (expressed in terms of either blanching intensity or the proportion of patients showing a positive response) was significantly lower than that in the CS group at concentrations of 3 micrograms/ml (p less than 0.01), 10 micrograms/ml (p less than 0.01), and 30 micrograms/ml (p less than 0.05), but not at 100 micrograms/ml. This resistance to glucocorticoids in the skin, together with reported evidence of glucocorticoid resistance in peripheral blood leucocytes, suggests a general defect in the ability of tissues to respond to glucocorticoids in CR asthma.

Administration, Oral↗
PubMed1991

A lack of effect of captopril on platelet aggregation in patients with congestive heart failure.

We have studied the acute and chronic effects of an ACE inhibitor (captopril) on platelet function and the renin-angiotensin system in patients with congestive heart failure. Plasma concentrations of angiotensin II fell significantly after a single dose of captopril (25 mg) and during long-term treatment with captopril (2 weeks, 75 mg/day). Plasma renin activity increased significantly after both the single and repeated doses. Captopril did not affect ADP-induced platelet aggregation or concentrations. It seems unlikely that circulating angiotensin II affects ADP-induced platelet aggregation in patients with congestive heart failure.

Angiotensin II↗
PubMed1991

Posture determines the nature of the interaction between angiotensin converting enzyme inhibitors and loop diuretics in patients with chronic cardiac failure.

The effects of inhibition of the renin angiotensin aldosterone system on the natriuretic and diuretic actions of an intravenous dose of frusemide 40 mg in patients with chronic cardiac failure maintained on oral diuretics were studied in the supine and erect positions. In the patients studied in the supine position the total 4 hour diuresis was decreased from 995 (92) ml to 668 (66) ml and the total 4 hour natriuresis fell from 105 (14) mmol to 67 (14) mmol following the administration of captopril. Creatinine clearance fell from 87 (8) ml/minute to 52 (15) ml/minute. In the patients studied in the erect position the total 4 hour diuresis was 596 (87) ml without captopril and 562 (83) ml with captopril. Total 4 hour natriuresis was 71 (13) mmol without captopril and 65 (9) mmol with captopril. Creatinine clearance was reduced by captopril from 82 (7) ml/minute to 47 (12) ml/minute. The reduction in the diuretic and natriuretic response to frusemide caused by captopril in the supine position is mediated through a fall in glomerular filtration rate. However, in the erect position, which is associated with even further increases in activity of the renin angiotensin aldosterone system, the reduction in diuresis and natriuresis that a fall in glomerular filtration rate would cause is offset by abolition of the rise in sodium retaining hormones, angiotensin II and aldosterone that mediate the antinatriuretic effect of the erect position.

Aged↗
PubMed1991

The cortisol-cortisone shuttle and the apparent specificity of glucocorticoid and mineralocorticoid receptors.

In vitro studies on both the purified cytosolic mineralocorticoid receptor (MR) and the recombinant expressed human MR have shown that it is non-specific and does not distinguish between cortisol and aldosterone. These contrast with the apparent in vivo selectivity of the MR in tissues such as the kidney for aldosterone in preference to cortisol despite the 100-fold molar excess of cortisol. This review gives the evidence that indicates that 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD), the enzyme responsible for the interconversion of cortisol and inactive cortisone, acts as a protective mechanism for the MR. In aldosterone-selective tissues it shuttles cortisol to cortisone and thus prevents glucocorticoid access. Aldosterone itself is not a substrate for the enzyme. The current data suggest that this is an autocrine system with both the enzyme and the MR present within the same cell. In certain tissues such as the kidney there may also be additional upstream steroid metabolism indicating a paracrine system. Lack of this protective system results in cortisol acting as a potent mineralocorticoid. This may be congenital as in the apparent mineralocorticoid excess syndrome or acquired secondary to liquorice-induced inhibition of 11 beta-OHSD. In addition to its role in MR protection 11 beta-OHSD may also be important in modulating steroid access to glucocorticoid receptors. The ontogeny of the enzyme in the testis and the brain suggests that its tissue-specific control may be crucial in allowing normal development.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

The cortisol-cortisone shuttle and hypertension.

11 beta-OHSD is an enzyme complex consisting of 11 beta-DH, converting cortisol to cortisone in man and an 11-keto-reductase performing the reverse reaction. Congenital deficiency of 11 beta-DH should be considered in any child presenting with mineralocorticoid hypertension and suppression of the renin-angiotensin-aldosterone axis. The keystone to diagnosis is the demonstration of a reduced daily production rate of cortisol and an increase in its plasma half-life. In the majority of cases diagnosis can be made from a urinary steroid metabolite profile indicating a high excretion of cortisol relative to cortisone metabolites. Cortisol is the responsible mineralocorticoid, and as such treatment with the pure glucocorticoid dexamethasone will prevent life-threatening hypokalemia, although additional anti-hypertensive drugs are usually required to control blood pressure. Liquorice and carbenoxolone, for years thought to be direct "agonists" of the mineralocorticoid receptor, in fact cause sodium retention through inhibition of 11 beta-DH. The demonstration of 11 beta-DH activity in the vasculature raises the possibility that it locally modules access of glucocorticoids to mineralocorticoid and possibly glucocorticoid receptors in the vessel wall. It remains possible that subtle alterations of this cortisol-cortisone shuttle are responsible for other forms of hypertension which are currently classified under the umbrella diagnosis of essential hypertension.

Animals↗
PubMed1991

Acute administration of captopril lowers the natriuretic and diuretic response to a loop diuretic in patients with chronic cardiac failure.

Angiotensin-converting enzyme inhibitors suppress plasma concentrations of the sodium retaining hormones angiotensin II and aldosterone. This action should potentiate the natriuretic and diuretic effects of loop diuretics. Some studies indicate, however, that the introduction of angiotensin-converting enzyme inhibitors for the treatment of cardiac failure is associated with transient weight gain and the development of oedema. We have compared the natriuretic and diuretic response to intravenous frusemide 40 mg alone with the natriuretic and diuretic response to intravenous frusemide 40 mg following the administration of a single dose of captopril in 12 supine male patients with stable chronic cardiac failure. Captopril lowered the 4 h diuretic response to frusemide from 1160 (60) to 685 (77) ml (P less than 0.05) and the natriuretic response from 120 (9.6) to 68 (11.7) mmol (P less than 0.05). Creatinine clearance fell after captopril from 91 (7.2) to 57 (7.7) ml min-1 (P less than 0.05). Systolic and diastolic blood pressures were lower after the administration of captopril but these changes were not significant. Plasma renin activity rose from 3.8 (1.04) to 12.34 (2.94) ng ml h-1 (P less than 0.05) and plasma angiotensin II was reduced from 24.9 (5.05) to 8.14 (1.8) pg ml-1 (P less than 0.05). Plasma aldosterone concentrations were not significantly lower following captopril. Angiotensin-converting enzyme inhibitors cause an acute fall in creatinine clearance which may reduce the effects of loop diuretics and attention must be paid to diuretic dosage when initiating angiotensin-converting enzyme inhibitors for the treatment of cardiac failure.

Aged↗
PubMed1991

Osmotic and non-osmotic regulation of thirst and vasopressin secretion in patients with compulsive water drinking.

OBJECTIVE: To examine the osmotic and non-osmotic regulation of thirst and AVP release in patients with compulsive water drinking. DESIGN: A 2-hour intravenous infusion of hypertonic (855 mmol/l) sodium chloride solution, followed by a 2-hour drinking period. PATIENTS: Seven patients with compulsive water drinking, seven patients with diabetes insipidus and seven healthy controls. MEASUREMENTS: Plasma AVP, osmolality, sodium and haematocrit, thirst ratings on a visual analogue scale and the volume of water drunk in 2 hours following infusion. RESULTS: Plasma AVP responses to osmotic stimulation, and non-osmotic inhibition by drinking, were normal in patients with compulsive water drinking. Basal thirst ratings were higher in compulsive water drinking than in either diabetes (P less than 0.001) or controls (P less than 0.001), despite lower basal plasma osmolalities. There was a significant rise in thirst ratings during saline infusion, which correlated closely with plasma osmolality, in all three groups, but the final thirst ratings were higher in compulsive water drinkers, who subsequently drank more water than in either diabetes insipidus (P less than 0.01) or controls (P less than 0.001). Drinking rapidly lowered thirst ratings in controls and diabetes insipidus before changes occurred in plasma osmolality, but remained elevated in patients with compulsive water drinking. Linear regression analysis defined a lower osmotic threshold for thirst in compulsive water drinking compared with controls or diabetes insipidus. CONCLUSIONS: There are abnormalities of the osmotic stimulation and non-osmotic inhibition of thirst in compulsive water drinking, suggesting that the underlying defect is one of interpretation of osmotic and non-osmotic inputs. Measurement of thirst responses during hypertonic saline infusion and subsequent water drinking may provide useful diagnostic information in the differentiation of polyuric states.

Adult↗
PubMed1991

11 beta-Hydroxysteroid dehydrogenase mRNA expression in rat kidney.

11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) protects nonspecific renal mineralocorticoid receptors from exposure to circulating glucocorticoid in vivo by catalyzing the conversion of corticosterone to inactive 11-dehydrocorticosterone. Although 11 beta-OHSD bioactivity and aldosterone binding sites are found in distal tubular cells, mineralocorticoid receptor and 11 beta-OHSD immunoreactivities are not colocalized. However, there are several kidney isoforms of 11 beta-OHSD, not all of which may be immunoreactive, whereas only a single mRNA species has been described. Using in situ hybridization we found 11 beta-OHSD mRNA is highly expressed in all renal tubular epithelia in the rat. It is therefore likely that 11 beta-OHSD is colocalized with mineralocorticoid receptors in distal tubular cells.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

Cerebrospinal fluid angiotensin converting enzyme levels in the diagnosis of neurosarcoidosis.

Cerebrospinal fluid angiotensin converting enzyme (CSF-ACE) level was measured in two patients considered to have neurosarcoidosis, three patients with possible neurosarcoidosis and in 38 control patients suffering from prolapsed intervertebral discs. Both neurosarcoidosis patients had elevated levels (1.8 and 5.4 mumol/l/min) while the possible neurosarcoidosis patients had values similar to the control patients (mean 0.59 +/- 0.42 mumol/l/min). We suggest that CSF-ACE values may be of use in some patients as a diagnostic test for neurosarcoidosis and provide a reference range of normal controls.

Adult↗
PubMed1991

11 beta-hydroxysteroid dehydrogenase in vascular smooth muscle and heart: implications for cardiovascular responses to glucocorticoids.

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) converts the active glucocorticoid corticosterone to inactive 11-dehydrocorticosterone in the rat (or cortisol to cortisone in man), thereby protecting renal mineralocorticoid receptors from corticosterone or cortisol and allowing preferential access for aldosterone. We have previously demonstrated that cortisol-induced cutaneous vasoconstriction in man is potentiated by the 11 beta-OHSD inhibitor glycyrrhetinic acid, suggesting that 11 beta-OHSD may protect vascular corticosteroid receptors. In this study we report quantitation of 11 beta-OHSD bioactivity in homogenates of rat aorta, mesenteric artery, caudal artery, and heart, expressed as the percent in vitro conversion of 3H-corticosterone to 3H-11-dehydrocorticosterone. Nicotinamide adenine dinucleotide phosphate (NADP+)-dependent 11 beta-OHSD activity was found in all of these tissues and was significantly higher in resistance vessels than aorta (P less than 0.05) [without NADP+: caudal artery (4.2 +/- 0.2%) greater than mesenteric artery (2.5 +/- 0.7%) = heart (1.67 +/- 0.2%) greater than aorta (0.79 +/- 0.2%); with 200 microM NADP+: caudal artery (43.9 +/- 2.1%) greater than heart (20.6 +/- 1.0%) = mesenteric artery (17.7 +/- 3.1%) = aorta (11.4 +/- 0.4%); heart greater than aorta]. All of these were lower than renal cortex (29.4 +/- 1.8% without NADP+; 82.4 +/- 0.4% with NADP+; P less than 0.001). 3H-11-dehydrocorticosterone was the major metabolite of 3H-corticosterone (greater than 97% of 3H-corticosterone metabolized). Reduction of 3H-11-dehydrocorticosterone to 3H-corticosterone was not detected in these experiments. We also report localization of 11 beta-OHSD-like immunoreactivity by immunohistochemistry using antisera raised against rat liver 11 beta-OHSD, and of 11 beta-OHSD messenger RNA expression by in situ hybridization using complementary RNA probes transcribed from complementary DNA encoding rat liver 11 beta-OHSD. We found 11 beta-OHSD immunoreactivity and messenger RNA expression in vascular and cardiac smooth muscle cytoplasm but not in endothelium. Thus, 11 beta-OHSD is appropriately sited to modulate access of corticosterone to vascular receptors and could influence vascular resistance, cardiac output and thereby blood pressure.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

Serotoninergic stimulation of aldosterone secretion in the rat in vivo: role of the renin-angiotensin system.

Serotoninergic control of aldosterone secretion in vivo was investigated in conscious rats with indwelling arterial cannulae. Serial blood samples were taken from the animals before and after i.p. administration of 1 ml (4 g/l) 5-hydroxytryptophan (5-HTP), the precursor of serotonin, or saline and they were analysed for 5-HTP, serotonin, 5-hydroxyindoleacetic acid, plasma renin activity (PRA), corticosterone, aldosterone, sodium and potassium concentrations. The role of the renin-angiotensin system was investigated in animals pretreated for 1 week with the angiotensin-converting enzyme inhibitor captopril (25 mg/day). 5-HTP caused a significant increase in all parameters within 45 min except for sodium and potassium. Saline administration showed no significant effect. Captopril pretreatment did not impair the increase in any parameter by 5-HTP, with the exception of the aldosterone response which was significantly attenuated, though not completely. The results show that administration of 5-HTP, which increases serum serotonin levels, stimulates PRA, aldosterone and corticosterone secretion. Captopril pretreatment inhibits the aldosterone response, suggesting that the aldosterone stimulatory properties of 5-HTP require the presence of angiotensin II, although it is unclear whether it acts in a mediatory or permissive capacity. The failure of captopril to inhibit the aldosterone response completely suggests the involvement of other mechanisms such as the hypothalamo-pituitary adrenal axis or a direct action of serotonin on the adrenal.

5-Hydroxytryptophan↗