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Biomedical subjects

J Genest

Publications and source records attributed to J Genest.

At least 361 records · Page 20Linked to original sources
PubMed1976

Circadian variations of the urinary excretion of catecholamines and electrolytes.

Concomitant measurements of circadian variations in the urinary excretion of dopamine (DA), homovanillic acid (HVA), norepinephrine (NE), epinephrine (E) as well as of creatinine, sodium and potassium under controlled dietary conditions during relative physical and emotional rest in 13 volunteers have shown that maximum excretion of all these substances occurred in the afternoon period between 14:30h and 18:00h, and minimum excretion in the morning between 4:00h and 5:00h. The changes were in some cases progressive from one collection period to the other, and synchronized for NE and E. DA and HVA excretions fluctuated from subject to subject. Excretory rhythms of sodium and potassium were found to be similar to those of the catecholamines. This can be explained by diurnal changes in renal blood flow and different renal excretory mechanisms of catecholamines. None of the catecholamines correlated with the urinary volume but urinary NE and E positively correlated with urinary creatinine, urinary NE and E with urinary DA and urinary sodium with urinary E. There are some common patterns in the diurnal rhythms of catecholamines and electrolytes but their interrelationship is different for individual catecholamines.

Adult↗
PubMed1976

Purification and characterization of tonin.

Tonin was purified from rat submaxillary glands by differential centrifugation, ammonium sulphate precipitation, gel filtration on Sephadex G150, and by ion-exchange chromatography on DEAE-cellulose, phospho-cellulose, SP-Sephadex C25, and SP-Sephadex C50. Purified tonin was shown to be homogeneous by analytical electrophoresis and by analytical ultracentrifugation analysis. Purified tonin was very stable when stored in buffers of low pH values or when incubated at high temperatures in neutral solution. The molecular weight estimated by sedimentation equilibrium was 28 700. The pH optimum was near 6.8 in a 0.1 M potassium phosphate buffer. The Michaelis-Menten constant for tonin using angiotensin I as substrate was about 4 X 10(-5) M. Tonin activity was strongly inhibited by plasma. Kinetic studies using angiotensin I as substrate showed that the inhibition of tonin by plasma was of the non-competitive type.

Angiotensin II↗
PubMed1976

Mineralocorticoid secretion in essential hypertension with normal and low plasma renin activity.

In 19 control subjects, 33 patients with essential hypertension and normal plasma renin activity (PRA) and 11 patients with low PRA, secretory rates of 18-hydroxy-11-deoxy-corticosterone (18-OH DOC), 11-deoxycorticosterone (DOC) and corticosterone were measured. Patients with low PRA were significantly older and had higher arterial pressure and slightly lower plasma potassium levels than patients with normal PRA. Mean 18-OH DOC secretion rate was higher in patients with normal PRA (603 +/- 112 SEM mug/24 hr) than in control subjects (219 +/- 19) and considerably higher (P less than 0.001) in patients with low PRA (1800 +/- 472). DOC and corticosterone secretion rates were within normal limits in most hypertensive patients. Plasma aldosterone was significantly higher in the hypertensive population than in control subjects whereas no significant difference was observed between the low- and normal-renin groups. A significant (P less than 0.01) mutual positive correlation was found between the secretion rates of 18-OH DOC, DOC and corticosterone in patients with low plasma renin activity. In contrast, there was no correlation between the secretion rates of the three mineralocorticoids in control subjects and patients with normal plasma renin activity. These data suggest a biosynthetic variation of the mineralocorticoid pathways in essential hypertension.

18-Hydroxycorticosterone↗
PubMed1976

Plasma cyclic adenosine 3':5'-monophosphate response to isoproterenol and glucagon in hyperkinetic borderline (labile) hypertension.

The hemodynamic changes observed in patients with the "hyperkinetic" form of borderline (labile) essential hypertension (BEH) could be related to the hyperresponsiveness of cardiac beta-adrenergic receptors to catecholamines. The isoproterenol-induced increase in plasma cyclic adenosine 3':5'-monophosphate (cAMP) reflects the response of adenylate cyclase to beta-adrenergic stimulation, whereas a non-beta-receptor-mediated increase occurs with the administration of glucagon. Both substances were infused into 13 control subjects and 14 patients with the hyperkinetic form of BEH before and after propranolol administration. Baseline plasma cAMP concentrations were comparable in both groups. After 30 minutes of isoproterenol infusion (20 ng/kg per min) a significantly higher increase in plasma cAMP and heart rate and a smaller decrease in diastolic blood pressure were seen in this type of BEH than in control subjects. The increase in plasma cAMP and in heart rate correlated positively when all subjects were considered together. Propranolol abolished hemodynamic and humoral responses to a similar degree in both groups. The plasma cAMP responses to glucagon (200 ng/kg per min) were slightly lower in our patients with BEH than in control subjects and were not suppressed by propranolol. The data are compatible with a hyperreactivity of the beta-adrenergic receptors or of the adenylate cyclase or both in hyperkinetic BEH and could correspond to the previously observed exaggerated beta-adrenergic drive to the heart in this type of hypertension. The non-beta-receptor-mediated rise in plasma cAMP (glucagon), however, remains comparable in control subjects and BEH.

Adult↗
PubMed1976

Effects of ACTH on steroid metabolism.

Metabolic clearance rates (MCR) of aldosterone, cortisol, DOC, corticosterone, and progesterone were simultaneously measured by constant infusion in 8 control subjects before and during an ACTH infusion (12.5 U/4 h). Plasma levels of aldosterone and cortisol, the heat-labile plasma protein-bound fraction of aldosterone, and hepatic blood flow as estimated by the fractional clearance of indocyanine green, were concomitantly determined. The mean MCR of aldosterone, cortisol, and DOC increased to a peak value of 26%, 23%, and 22%, respectively, above baseline values. The increase was already significant (P is less than 0.001) 30 min after the beginning of the ACTH infusion. In contrast, no consistent changes occurred in the MCR of corticosterone and progesterone or in hepatic blood flow. ACTH induced a marked fall in the heat-labile plasma protein-bound fraction of aldosterone. Plasma levels of aldosterone and corsitol increased by 190 and 250%, respectively. A significant negative correlation (r=-0.423, P is less than 0.01) between the MCR and the heat-labile protein-bound fraction of aldosterone was observed. We suggest that competitive interactions in the protein binding properties of various steroids account for the selective effect of ACTH on the MCR of aldosterone, cortisol, and DOC.

Adrenocorticotropic Hormone↗
PubMed1976

Dissociation of plasma renin activity and aldosterone in essential hypertension.

Plasma renin activity (PRA) and plasma aldosterone (PA) were measured in 401 and 98 patients, respectively, with mild essential hypertension after overnight recumbency and on a 135 mmol/day sodium diet. The mean PRA values declined with each increasing decade of age, whereas the mean PA concentrations did not, and those PRA and PA values determined simultaneously were not correlated, suggesting that PA concentrations are inappropriately elevated relative to the PRA in patients with essential hypertension in the older decades of age.

Adolescent↗
PubMed1976

Effects of beta-adrenergic blockade on plasma cyclic AMP and blood sugar responses to glucagon and isoproterenol in man.

In healthy humans glucagon infusion resulted in a significant increase in blood sugar and in plasma cyclic AMP. No discernible hemodynamic effects were found. Isoproterenol infusion on a mole per mole basis in the same subjects induced a significant, although less pronounced rise in plasma cyclic AMP, heart rate, and a fall in diastolic blood pressure but had no effect on blood sugar. Propranolol administration abolished the hemodynamic effects of isoproterenol and significantly decreased the response of plasma cyclic AMP; the same blocking dosage had little effect on plasma cyclic AMP changes induced by glucagon wheras the response in blood sugar was significantly reduced. These data in vivo are compatible with the in vitro demonstration of separate receptors for glucagon and isoproterenol.

Adult↗
PubMed1975

Arterial hypertension and neurofibromatosis: renal artery stenosis and coarctation of abdominal aorta.

A 10-year-old girl had arterial hypertension, generalized neurofibromatosis, coarctation of the abdominal aorta and multiple stenoses at the origin of each renal artery. After resection of the stenotic areas and reimplantation of the renal arteries in the aorta, her arterial pressure decreased substantially. However, hypertension recurred and radiologic follow-up 4 1/2 years later showed distinct progression of the coarctation and renewed stenosis of all renal arteries at their origin. The stenotic areas showed eccentric intimal proliferation, frequently bulging into the lumen, with small nodular aggregates of smooth muscle cells and proliferation of fibrous tissue containing spindle-shaped nuclei in a palisading pattern. Hypertension associated with neurofibromatotic vascular disease has been described in 47 other patients in the literature. These patients have been young (mean age, 14 years) and predominantly male. In contrast to fibromuscular dysplasia, in which 95% of all stenoses are found in the distal two thirds of the renal arteries, in vascular neurofibromatosis more than 50% of the stenoses are found at the origin.

Adolescent↗
PubMed1975

Hypertension with renal arterial stenosis: humoral, hemodynamic and histopathologic factors.

In 46 hypertensive patients with unilateral renal arterial stenosis, peripheral and renal venous plasma renin activity, juxtaglomerular cell count and granularity and systolic pressure gradient across the stenosis were determined. After corrective surgery and a mean postoperative observation period of 4.3 years, 18 patients were completely relieved of hypertension (good responders), 14 had a substantial reduction in arterial pressure (fair responders) and 14 remained hypertensive (poor responders). Analysis of plasma renin activity in both renal veins indicated that a ratio (stenotic/nonstenotic side) greater than 2.0 correctly predicted a favorable surgical result in all cases. Peripheral plasma renin activity was greater than normal in 65 percent of good responders, in 50 percent of fair responders and in one nonresponder. The prognostic accuracy of a pressure gradient greater than 40 mm Hg was 78 percent; no patient with a gradient of less than 40 mm Hg benefited from surgery. An increased juxtaglomerular cell count on the affected side predicted a successful operative result in 88 percent, as did increased granularity in 85 percent of cases. Renal venous renin ratio correlated positively (r =0.738, P less than 0.001) with the pressure gradient across the stenosis. The renal venous plasma renin activity of the affected side also correlated positively (r = 0.771, P less than 0.001) with the absolute count of granular cells in the juxtaglomerular apparatus. Plasma renin activity in both renal veins is the most reliable predictor of operative outcome. The addition of juxtaglomerular cell count or pressure gradient across the stenosis increases prognostic accuracy only slightly. The close mutual correlations between renal venous renin ratio, pressure gradient and juxtaglomerular cell count support the experimental evidence of a causal relation between the hemodynamic effects of the arterial lesion and the humoral and histologic changes observed in hypertension with renal arterial stenosis.

Adult↗
PubMed1975

Aldosterone and renin in essential hypertension.

A review of some recent laboratory findings indicates definite disturbances in aldosterone metabolism and regulation in patients with mild essential hypertension: (a) a significant mean increase in plasma aldosterone concentration in patients with mild and stable essential hypertension, in contrast to the absence of any difference in patients with labile borderline essential hypertension when in a normotensive phase, compared with control subjects; and (b) a significant mean decrease in metabolic clearance rate of aldosterone, associated with a 12% decrease in hepatic blood flow and an increased binding of aldosterone to a transcortin-like plasma globulin. The secretion rate of 18-hydroxy-11-deoxycorticosterone is above the upper range of normal in 60% of patients with mild, uncomplicated essential hypertension. The incidence of low-renin hypertension, when age and race are taken into account, is much lower than previously assumed. Unless measurements are repeated over a long period, one or two low values of plasma renin cannot be considered a permanent marker indicating a special category of patients with essential hypertension. Tonin, a new enzyme discovered by Boucher, which forms angiotensin II directly from a plasma protein, from the tetradecapeptide substrate and from angiotensin I, is present in most tissues, but in highest concentration in the submaxillary gland. This enzyme is under the control of beta-adrenergic receptors.

18-Hydroxydesoxycorticosterone↗
PubMed1975

Plasma progesterone and aldosterone in pregnancy.

Plasma progesterone, aldosterone and renin activity were measured simultaneously in seven women during normal pregnancy. Beginning at the 2nd trimester and until approximately 4 weeks before delivery there was a constant increase in plasma progesterone concentration. There was a significant correlation between weight gain and duration of pregnancy and between weight gain and plasma progesterone concentration. There was also an increase in plasma aldosterone concentration although this was less consistent than that of progesterone. And there was a significant correlation between plasma progesterone and aldosterone concentrations and between the progesterone/aldosterone ratio and duration of pregnancy and weight gain.

Adolescent↗
PubMed1975

Urinary homovanillic acid, dopamine and norepinephrine excretion in patients with essential hypertension.

Urinary excretion of dopamine, norepinephrine and homovanillic acid was measured in normotensive subjects and in patients with either labile of stable hypertension under conditions controlled for posture, sodium and potassium intake and time of day. Mean homovanillic acid excretion was 313.5 plus or minus 77.7 (SE) mug/4h in the normotensive patients. Mean values for the patients with labile or stable hypertension were significantly greater, at 2506 plus or minus 476 mug/4 h (P smaller than 0.001) and 795 plus or minus 170 mug/4 h (P smaller than 0.01), respectively. Urinary excretion of dopamine and norepinephrine tended to be elevated in patients with labile hypertension when compared with values in the control subjects and the patients with stable hypertension. The data are compatible with the hypothesis of adrenergic hyperactivity in labile hypertension and underline the biochemical heterogeneity of essential hypertension. Because the overlapping of values between control subjects and patients with labile hypertension was minimal, it is proposed that an elevated valve for urinary homovanillic acid could be used as a biochemical marker to identify the patients with labile hypertension.

Adolescent↗