PubMed Health⌕ Search

Biomedical subjects

M H Maxwell

Publications and source records attributed to M H Maxwell.

At least 127 records · Page 7Linked to original sources
PubMed1977

Renin stimulation by isoproterenol and theophylline in the isolated perfused kidney.

The intrarenal mechanisms of renin release were studied in the isolated perfused rabbit kidney during stimulation by isoproterenol, 0.01 mug/kg per min, and by theophylline, 0.87 mg/kg per min. In the absence of urinary flow during the early stages of perfusion, isoproterenol caused a 17% increase of renal vein serum renin concentration (RVSRC) (P less than 0.001) without changing renal blood flow, renal vascular resistance, or serum potassium. dl-Propranolol, 2.0 mg/kg per min. abolished this isoproterenol-induced renin release. A moderate reduction in perfusion pressure prior to the infusion of isoproterenol resulted in a marked additional stimulation of renin release. Studies during and following ureteral occlusion demonstrated that theophylline stimulates renin release by decreasing renal vascular resistance, whereas the concomitant increase in sodium transport to the macula densa exerted an opposite effect. dl-Propranolol did not affect theophylline-induced renin secretion. It is concluded that single exogenous stimuli may activate more than one intrarenal mechanism simultaneously. Isoproterenol has a direct renin-stimulatory effect on intrarenal beta-adrenergic receptors that may be reinforced by baroreceptor stimulation. Theophylline stimulates renin via a baroreceptor mechanism, with simultaneous renin suppression via a sodium-macula densa effect.

Animals↗
PubMed1977

Slow ventricular tachycardia complicating acute myocardial infarction.

Among 200 consecutive cases of acute myocardial infarction (AMI) treated in a CCU, 117 episodes of slow ventricular tachycardia were observed in 72 patients. This figure represents a 36% rate of incidence. It is a relatively high figure because of the close monitoring to which the patient is submitted and because of the early admission to the unit. There were no significant differences of age, sex, or localization of the myocardial necrosis between patients with SVT and those without it. The different mechanisms of production described support an active origin in most of the patients for the following reasons: (1) coexistence of SVT and PVT in 51.3% of the patients; (2) identical QRS morphology in both rhythms; (3) onset of the SVT after a nonprolonged diastole in 70% of the tracings; (4) inhibition of the SVT after increase of the sinus discharge in only 14 occasions; and (5) irregular SVT rhythm in 76.9% of the recordings and ectopic mechanisms with different degrees of exit block. Because of the potential hazard of the SVT, especially if it is assumed to be of an active origin, we recommend lidocaine for patients with a sinus rate faster than 60 per minute or coexisting PVT. Atropine should be used when the sinus rate is slower than 60 per minute assuming a possible escape or passive origin.

Adult↗
PubMed1977

Renin, sodium, and vasodepressor response to saralasin in renovascular and essential hypertension.

Saralasin (1-sar-8-ala-angiotensin II), a competitive inhibitor of angiotensin II, was administered to 32 patients with renovascular or essential hypertension before (Day 1) and after (Day 2) they were mildly sodium depleted by furosemide (1 mg/kg body weight). A blood pressure lowering effect of saralasin was observed in 16 of 17 patients with renovascular hypertension on Day 2, but in only 10 of the 17 on Day 1. Of the 15 patients with essential hypertension, only the four with high renin levels exhibited a vasodepressor response on Day 2; three responded similarly on Day 1. The Average net sodium loss between the 2 days was greater for patients who responded to the drug on Day 2 (170 meq) than those who did not (129 meq) (P less than 0.05); however, there was no correlation between blood pressure response and either net sodium loss or urinary sodium excretion at the time of testing. Plasma renin activity correlated with saralasin responses (r=-0.74, P less than 0.01). Saralasin testing during a state of modest sodium depletion compares favorably with renin measurements in the detection of renin-mediated hypertension.

Adult↗
PubMed1977

Mechanisms of hypertension during the acute and intermediate phases of the one-clip, two-kidney model in the dog.

The acute and intermediate onset phases of one-clip, two-kidney hypertension were studied in six conscious dogs. Mean arterial pressure (MAP), cardiac output (CO), total peripheral resistance (TPR), serum renin concentration (SRC), plasma aldosterone (PA) and cumulative sodium and water balance were studied prior to unilateral renal artery constriction, at 2, 10, and 24 hours postconstriction, and daily thereafter for 5 days. At 2 hours postconstriction, MAP, CO, TPR, and SRC were elevated, with unchanged fluid balance. At 10 and 24 hours there was a further rise in CO accompanied by positive fluid-sodium balance, with a slight decrease in MAP, TRP, and SRC. During days 2 and 3, MAP, CO, TPR, and SRC remained elevated and stable in the presence of decreasing fluid-sodium balance to preconstriction levels. During days 4 and 5, MAP, SRC, and fluid-sodium balance remained unchanged, TPR demonstrated a secondary increase, whereas CO decreased to preconstriction values. Sequential changes in PA parallel those of SRC, but were significant only at 2 hours postconstriction. These changes suggest that the increased CO is not totally dependent on fluid-sodium balance, and that CO is not the sole determinant of elevated MAP. The temporal relationship between MAP and SRC throughout the study is consistent with renin-mediated hypertension. The secondary rise of TPR may be due to total body autoregulation and/or increased vascular reactivity to high levels of circulating angiotensin. A unitary renin-angiotensin mechanism, therefore, may be responsible for the induction and maintenance of hypertension in this experimental model.

Acute Disease↗
PubMed1977

Mechanisms of hypertension during the chronic phase of the one-clip, two-kidney model in the dog.

The mechanism of the chronic phase of one-clip, two-kidney hypertension was investigated in 23 dogs. Mean arterial pressure (MAP), renal hemodynamics, and arterial and renal venous plasma renin activity (PRA) were studied before and at 1 and 3 months after graded, unilateral renal artery constriction. In the dogs that demonstrated sustained hypertension, the magnitude of changes in MAP, renal hemodynamics, PRA, and renal renin secretion correlated with the severity of renal artery constriction. In dogs with severe constriction (group 3, 78-86% renal blood flow reduction), MAP and arterial PRA were significantly elevated throughout. In groups 1 and 2 (0% and 50-56% renal blood flow reduction, respectively), although MAP remained significantly elevated, arterial PRA decreased to baseline values by 3 months. In group 3, there was an initial, apparent redistribution of ipsilateral renal blood flow, and prolonged reductions in ipsilateral renal plasma flow (RPF) and glomerular filtration rate accompanied by significantly increased creatinine clearance (CCreat) in the untouched kidney. Similar but less marked renal hemodynamic changes occurred in the other hypertensive dogs. All hypertensive dogs, regardless of degree of renal artery constriction, demonstrated significantly increased ipsilateral renal renin secretion and contralateral renin suppression. In three dogs that were studied 6, 12, and 16 months postconstriction, the high rate of ipsilateral renin secretion persisted throughout. Ipsilateral nephrectomy consistently resulted in rapid amelioration of the hypertension. These findings are in accord with a renal-dependent and probably renin-mediated mechanism for the maintenance of high blood pressure in the chronic phase of the one-clip, two-kidney dog model.

Animals↗
PubMed1976

Detection of renovascular hypertension: saralasin test versus renin determinations.

Angiotensin blockade was established in hypertensive patients with the competitive inhibitor saralasin and the blood pressure response was compared to prior renin determinations. Two patients with subsequently confirmed renovascular hypertension had normal peripheral renin and non-lateralizing renal vein renin ratios, yet both showed a clear-cut lowering of blood pressure after administration of the blocking agent, indicating the presence of renin-mediated hypertension. Thus, direct in vivo testing with saralasin appears to offer certain advantages over renin determinations.

Angiotensin II↗
PubMed1976

Renovascular hypertension: does the renal vein renin ratio predict operative results?

Renal vein renin ratios from 56 hypertensive patients who were operated upon for unilateral stenosis of a main renal artery were compared to blood pressure response to a corrective operation. In patients with renal vein renin ratios greater then 2.0, the upper limits of normal for essential hypertension (95 per cent confidence limits), the cure/improvement rate approximated 90 per cent. However, in patients operated upon despite lesser ratios the cure/improvement rate was also high--83 per cent in our series and 57 per cent in collected reports from the literature. Thus, the test may be falsely negative in a high percentage of patients. Renal vein renin ratios would appear to be most useful in confirming but not necessarily in denying the functional significance of a renal artery stenosis.

Adult↗
PubMed1976

Ultrastructure of simian eosinophils.

The ultrastructure of eosinophil granulocytes has been studied in the bone marrow and nasal mucosa of the monkey. Both the mature eosinophils and their precursors, including the form and dimensions of their granules, were generally similar to those of man and rodents. Unusual features in the marrow were the occasional presence of an irregular substructure in granules without interna, or of cytoplasmic vacuoles containing material apparently derived from granule breakdown. In the nasal mucosa, eosinophils were present in both the epithelium and in the sub-epithelial tissues. The lattice arrangement of the eosinophil internum had a spacing of up to 5-4 nm, with sometimes a secondary repeat of 2-7 nm, and suggested a more complex crystal structure than that of man and rodents.

Animals↗
PubMed1975

Saralasin bolus test. Rapid screening procedure for renin-mediated hypertension.

The angiotensin-blocking agent, saralasin, was given by rapid intravenous (bolus) injection to 21 hypertensive patients. A marked depressor response (average blood-pressure decrease of 30 mm Hg systolic and 20 mm Hg diastolic at 10 minutes after injection) was noted in 13 patients, of whom 11 had renovascular hypertension and 2 had high-renin essential hypertension. No change from prebolus blood-pressure was apparent at 10 minutes in 8 control patients with essential hypertension and normal or low peripheral plasma-renin activity. In all patients, blood-pressure response to saralasin bolus (10 mg) correlated with blood-pressure response to subsequent infusion of saralasin (10 microgram/kg/min). Blood-pressure response to rapid intravenous injection of saralasin--the "saralasin bolus test"--has many characteristics of an ideal screening procedure for renin-mediated hypertension.

Adult↗
PubMed1975

Operative morbidity and mortality in renovascular disease.

There were 104 major complications (13.1%) and 34 deaths (5.9%) among 502 patients with evidence of renovascular disease who underwent 577 operative procedures. The operative mortality rate in patients with atherosclerotic renovascular disease was 9.3% vs 3.4% with fibromuscular hyperplasia. Important determinants of renovascular operative mortality are (1) cause of disease, (2) presence of coronary artery disease, (3) presence of bilateral renal functional impairment, (4) the complexity of the renal operative procedure, and (5) concurrent extrarenal surgery.

Adult↗
PubMed1975

Renovascular occlusive disease. Results of operative treatment.

The blood pressure response to operative treatment in 502 patients with renal artery stenosis and coexisting hypertension was as follows: 51% cured, 15% improved, and 34% failure. The operative mortality was 5.9%. Patients with unilateral fibromuscular disease had a favorable blood pressure response (79.8%) more frequently than the patients with unilateral atherosclerosis (63.4%). In patients with bilateral stenosis, a favorable result occurred in 56%. The anatomic failure rate due to thrombosis of arterial reconstructions, as well as the operative mortality, varied considerably between institutions. If preoperative diagnostic studies demonstrated significant functional disparity between kidneys, and if the operation was anatomically successful, then approximately 80% of these patients were benefited by surgical intervention.

Arteriosclerosis↗