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Biomedical subjects

J G Ledingham

Publications and source records attributed to J G Ledingham.

At least 127 records · Page 7Linked to original sources
PubMed1976

Reduced plasma renin activity in essential hypertension: effects of blood pressure, age and sodium.

1. Supine plasma renin activity and its responsiveness to erect posture and frusemide were reduced in fifty-one patients with essential hypertension, compared with fifty-one age- and sex-matched control subjects. 2. Twenty-four hour urinary sodium excretion was similar in hypertensive patients nad control subjects. 2. Twenty-four hour urinary sodium excretion was similar in hypertensive patients and control subjects, but after intravenous frusemide hypertensive patients excreted significantly less sodium. 3. A significant inverse relationship between plasma renin activity and diastolic blood pressure was demonstrated in hypertensive patients and in normotensive control subjects. 4. A significant inverse relationship between plasma renin activity and age, independent of blood pressure, was shown in hypertensive patients and control subjects. 5. It is concluded that the reduced renin values found in essential hypertension are, in part, the result of the elevated blood pressure acting on the kidney.

Adult↗
PubMed1976

Renin unresponsiveness and the effects of oxprenolol, methyldopa and spironolactone in pateints with essential hypertension.

Plasma renin activity (PRA), supine, erect and post-frusemide (1 mg/kg IV) was studied in 51 patients with previously untreated essential hypertension and their age- and sex-matched normotensive controls. Supine PRA, and the rise in PRA in response to the erect posture and frusemide, were significantly less in hypertensives compared to controls. When the hypertensives were arbitrarily divided into lower, mid, and upper subgroups according to supine PRA, the renin responsiveness was similar in each subgroup but significantly less in hypertensives compared to controls, subdivided in the same way. This does not support the existence of a separate "low renin" subgroup. The low supine PRA and reduced response to stimulation appears to be a feature of patients with essential hypertension. Thirty-nine of these hypertensives entered a double-blind cross-over drug trial of oxprenolol, methyldopa and spironolactone. All three drugs were equally effective in lowering the systolic and diastolic blood pressures in all three renin subgroups. Spironolactone caused a greater fall in systolic pressure in the lower renin group than in the other groups. Oxprenolol was the best tolerated drug, with only 5% of patients withdrawing due to side-effects compared to 13% on spironolacone and 29% on methyldopa.

Adult↗
PubMed1975

Measurement of intrarenal blood-flow distribution in the rabbit using radioactive microspheres.

1. Total renal blood flow and its distribution within the renal cortex of the conscious rabbit were studied with radioactive microspheres of 15 and 25 mum diameter. 2. The reliability of the microsphere technique was influenced by microsphere diameter and number (dose). The optimum microsphere diameter for determination of flow distribution in the rabbit kidney was 15 mum and dose 100-150 000 spheres. 3. Spheres of 15 mum nominal diameter were randomly distributed within the renal cortex of adult rabbits. The larger spheres in batches nominally 15 mum in diameter in young rabbits and 25 mum diameter in adult rabbits were preferentially distributed to the superficial cortex. 4. In adult rabbits 15 mum diameter spheres lodged in glomerular capillaries. Larger spheres occasionally lodged in interlobular arteries causing intrarenal haemorrhage. 5. Microspheres of 15 mum caused a decrease in renal clearance of creatinine and of p-amino-hippurate when the total injection dose was about 200 000 spheres. These effects were greater when the injection dose was increased to 500 000 spheres. 6. The reduction in total renal blood flow observed with large doses of spheres largely reflected decreased outer cortical flow, as measured by a second injection of spheres, and confirmed by a decrease in p-aminohippurate extraction. 7. The reproducibility of multiple injection studies was limited by these intrarenal effects of microspheres. 8. Total renal blood flow measured in six rabbits in acute experiments by the microsphere technique was 107 plus or minus 12 (mean plus or minus SD) ml/min and by p-amino-hippurate clearance was 100 plus or minus 10 ml/min. 9. Total renal blood flow in twelve conscious, chronically instrumented rabbits was 125 plus or minus 11 ml/min, of which 92 plus or minus 6 ml/min was distributed to the superficial cortex and 33 plus or minus 4 ml/min to the deep cortex.

Animals↗
PubMed1975

Renal circulatory responses to general anaesthesia in the rabbit: studies using radioactive microspheres.

1. Total renal blood flow and its cortical distribution were measured by the radioactive microsphere technique in conscious rabbits and after anaethesia with pentobarbitone, chloralose-urethane or ether. 2. Pentobarbitone anaesthesia caused a fall of 26% in total renal blood flow, of 26% in superficial cortical flow, and of 24% in deep cortical flow. Sodium excretion rate fell by 33%. 3. Chloralose-urethane anaesthesia caused no change in total or regional renal blood flow, or in sodium excretion. 4. Ether anaesthesia caused an insignificant fall in total renal blood flow, but superficial cortical flow fell by 13% and deep cortical flow rose by 21%. Urinary sodium excretion fell by 65%. 5. Possible mechanisms for these changes in response to anaesthesia are discussed. 6. The effects of anaesthetic agents may influence the interpretation of published work on control mechanisms in the renal circulation.

Anesthesia, General↗
PubMed1975

Effects of beta-adrenergic receptor blockade on the renal vascular response to a low sodium diet in the rabbit.

1. The effect of propranolol on total and regional renal blood flow was measured in conscious rabbits after 6 days on normal or low sodium diets. 2. Propranolol inhibited the fall in total superficial cortical renal blood flow which occurred in response to the low sodium diet but did not influence renal blood flow in rabbits on a normal sodium diet. 3. Reduction and redistribution of renal blood flow in response to a low sodium diet appears to be mediated by a beta-receptor mechanism and may be a consequence of intrarenal release of renin.

Animals↗
PubMed1975

Urinary tract in schoolgirls with covert bacteriuria.

During screening of 16,800 primary schoolgirls, aged 4-12 years, in Cardiff and Oxford, significant bacteriuria was found in 294 (1-7%). Intravenous urography and micturating cystography were performed in 246 of these girls. The urinary tract was abnormal in 47%. Pyelonephritis with or without vesicoureteric reflux was present in 26% and reflux without renal abnormality in a further 16%. The prevalence of pyelonephritis and reflux was independent of age. With few exeptions kidneys without pyelonephritic scars appeared to be normal in size, even when ureteric reflux was present.

Bacteriuria↗