Biomedical subjects
S K Mujais
Publications and source records attributed to S K Mujais.
New membranes: the promise of ingenuity.
Explore the source record for details and available documents.
Chronic tubulo-interstitial nephritis: saga of the ubiquitous.
Explore the source record for details and available documents.
Nephrologic beginnings: the kidney in the age of Ibn Sina (980-1037 AD).
Explore the source record for details and available documents.
Response patterns of the cortical collecting tubule Na:K pump to potassium loading.
Explore the source record for details and available documents.
Effects of aldosterone on rat collecting tubule N-ethylmaleimide-sensitive adenosine triphosphatase.
Acidification in the collecting tubule is thought to be mediated by a proton-translocating adenosine triphosphatase (ATPase), and is modulated by aldosterone. Using an enzymatic microassay, we measured N-ethylmaleimide (NEM)-sensitive ATPase activity in isolated tubules obtained from control rats and rats receiving aldosterone by osmotic minipumps (5 micrograms/100 gm/day for 7 days). In control animals, enzyme activity was higher in cortical than in outer medullary collecting tubules (259 +/- 36 vs. 111 +/- 16 pmol/mm/hr, P less than 0.005, respectively). Prolonged aldosterone administration resulted in an increase in enzyme activity in the outer medullary collecting tubule (274 +/- 39 pmol/mm/hr, P less than 0.005), with no change in the cortical collecting tubule (255 +/- 47 pmol/mm/hr). These findings suggest that prolonged enhancement of acidification by mineralocorticoids is mediated by different mechanisms in the two segments of the rat collecting tubule. Whereas in the outer medullary segment an increase in the activity of NEM-sensitive ATPase facilitates the chronic enhancement in acidification, high basal enzyme activity in the cortical segment and institution of favorable voltage condition by mineralocorticoid treatment may obviate the need to increase enzyme activity.
Profile of the uremic neutrophil.
Explore the source record for details and available documents.
Dissociation between the hypotensive effect of thiazides and plasma divalent cations.
Explore the source record for details and available documents.
Regulation of renal Na-K-ATPase: effects of aldosterone in phosphate depletion.
Explore the source record for details and available documents.
Plasma catecholamine responses to physiologic stimuli in normal human pregnancy.
The dynamic response of the sympathoadrenal system was evaluated during and after pregnancy in 13 healthy women with a protocol that compared cardiovascular parameters and plasma catecholamine levels during the basal state, after postural maneuvers, and following isometric exercise. Plasma epinephrine and norepinephrine levels were similar during and after gestation when the women rested on their sides, but heart rate was greater in pregnancy. Ten minutes of supine recumbency produced minimal changes, but attenuation of the anticipated increases in heart rate and plasma norepinephrine levels during standing and isometric exercise were observed during pregnancy. In contrast, alterations in plasma epinephrine appeared unaffected by gestation. Plasma renin activity and aldosterone levels were, as expected, greater during pregnancy; however, increments in response to upright posture were similar in pregnant and postpartum women. To the extent that circulating catecholamines may be considered indices of sympathoadrenal function, these data suggest that normal pregnancy alters cardiovascular and sympathetic nervous system responses to physiologic stimuli.
Regulation of renal Na+-K+-ATPase in the rat: role of increased potassium transport.
The purpose of this study was to characterize the alterations in collecting tubule Na+-K+-ATPase activity produced by sustained increments in dietary potassium in the rat and to evaluate the role of aldosterone in their generation. In adrenal-intact animals, feeding a high-potassium diet (10-fold that of control) or administration of a high physiological dose of aldosterone (5 micrograms X 100 g-1 X day-1), which simulates the delivery rate of this hormone during potassium loading (both for 7 days), caused marked increments in Na+-K+-ATPase activity in the cortical collecting tubule (CCT) but had no effect on the enzyme in the inner stripe of the medullary collecting tubule (MCT). A significant increase in enzyme activity was also observed after smaller dietary potassium increments (2.5 and 5 times the control) and after 4 (but not 2) days of dietary potassium load. In adrenalectomized rats provided with physiological replacement doses of corticosterone and aldosterone (0.8 micrograms X 100 g-1 X day-1), Na+-K+-ATPase activity in both CCT and MCT was similar to that of adrenal-intact controls but remained unchanged after 7 days on the potassium-enriched (10-fold) diet. In contrast, adrenalectomized animals receiving the high physiological dose of aldosterone displayed an increase in Na+-K+-ATPase activity of CCT comparable with that of adrenal-intact animals, whereas the enzyme activity in the MCT was unaffected. In conclusion, 1) following chronic potassium loading Na+-K+-ATPase activity increases significantly in the CCT with no change in its activity in the inner stripe of the MCT.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of renal Na-K-ATPase in the rat: effect of uninephrectomy.
This study has examined the temporal profile and the segmental localization along the rat nephron of the increase in Na-K-ATPase produced by uninephrectomy, and the role of the adrenal gland in the generation of the increase in enzyme activity. In adrenal-intact rats, an increase in Na-K-ATPase activity in the cortical collecting tubule (CCT) was observed at 1 wk (140 +/- 13% of sham, P less than 0.05) and sustained at 2 wk (140 +/- 8% of sham, P less than 0.05). In contrast, the enhancement of enzyme activity in the proximal convoluted tubule (PCT) was transient (at 1 wk: 164 +/- 20% of sham, P less than 0.05; and at 2 wk: 97 +/- 9% of sham, P greater than 0.5). No changes in Na-K-ATPase activity were observed in the other nephron segments studied: pars recta, medullary thick ascending limb, cortical thick ascending limb, distal convoluted tubule, and medullary collecting tubule. In adrenalectomized rats, CCT enzyme activity was lower than in adrenal-intact rats (761 +/- 84 vs. 1,984 +/- 276 pmol X mm-1 X h-1, P less than 0.001) and was not altered by uninephrectomy (849 +/- 91 pmol X mm-1 X h-1, NS). We conclude that the increase in Na-K-ATPase activity following uninephrectomy is restricted to two segments of the nephron and follows a distinctive pattern in each. In the PCT a transient enhancement in enzyme activity is observed, whereas in the CCT the increase in Na-K-ATPase is sustained and requires the presence of an intact adrenal gland.
Angiotensin II binding sites in individual segments of the rat nephron.
The sites of action of angiotensin II along the nephron are not well defined and both proximal and distal effects are suggested. Using a microassay that permits measurement of hormone binding in discrete tubule segments, we determined the binding sites of 125I-angiotensin II along the nephron of Sprague-Dawley rats. Specific binding in proximal convoluted tubule (PCT) (at 25 degrees C, pH 7.4) was linearly related to tubule length and saturable, with an apparent maximal binding capacity of approximately 300 amol X cm-1. Binding specificity was verified in competition experiments that revealed significant (P less than 0.001) and comparable competition for radioligand binding by angiotensin II and angiotensin precursor, metabolite, and analogues, whereas unrelated peptides of similar size (bradykinin, ACTH [1-10]) were without effect. The profile of specific angiotensin II binding along the nephron was: PCT, 216 +/- 13; pars recta, 86 +/- 14; medullary thick ascending limb of Henle's loop, 46 +/- 8; cortical thick ascending limb of Henle's loop, 77 +/- 8; distal convoluted tubule, 49 +/- 10; cortical collecting tubule, 15 +/- 1; medullary collecting tubule, 32 +/- 7 amol X cm-1. These results indicate the presence of specific angiotensin II binding sites in all tubule segments studied, but binding capacity was highest in the proximal convoluted tubule, in agreement with transport studies that localize the effects of the hormone in this segment.
Intact ability to lower urine pH in nonacidotic adrenalectomized rats.
Distal acidification was assessed in adrenalectomized (ADX) rats in which the development of acidosis was prevented by oral supplementation with NaHCO3, with or without glucocorticoid replacement. Totally corticosteroid-deficient nonacidotic rats were capable of lowering their urine pH in response to Na2SO4 infusion from a baseline of 7.47 +/- 0.22 to 4.83 +/- 0.1 (p less than 0.001). A similarly intact ability to lower the urine pH was also demonstrated in glucocorticoid-replaced mineralocorticoid-deficient rats. Absolute ammonium excretion was lower in ADX animals compared to controls (0.79 +/- 0.08 vs. 0.46 +/- 0.06 microEq/min, p less than 0.01) but when corrected for the difference in GFR, ammonium excretion was the same in ADX and adrenal-intact rats. During bicarbonate loading and at similar blood and urine pH, and bicarbonate concentrations, the U-B pCO2 gradient was similar in mineralocorticoid-deficient and adrenal intact rats (44 +/- 5.1 vs. 36 +/- 2.6 mm Hg, respectively). Amiloride administration to mineralocorticoid-deficient rats led to a reduction in the U-B pCO2 gradient from 30 +/- 4.5 to 10 +/- 3.0 mm Hg (p less than 0.002). These results indicate that the ability to lower the urine pH and raise the urine pCO2 is intact in the nonacidotic ADX rat; ammonium excretion in this model is reduced in proportion to the observed reduction in GFR, and amiloride administration inhibits acidification in ADX rats. The data strongly suggest the presence of a major site of aldosterone-independent, sodium-dependent acidification mechanism likely located at the level of the cortical collecting tubule.
Transport and renal effects of general anesthetics.
Explore the source record for details and available documents.
Marked proteinuria in hypertensive nephrosclerosis.
Heavy proteinuria in patients with essential hypertension raises the question of underlying primary renal disease. While malignant hypertension may be associated with proteinuria in the nephrotic range, it is generally held that protein excretion in benign nephrosclerosis is almost invariably less than 0.5-1.0 g/24 h. We report 18 patients with biopsy-proven hypertensive nephropathy and heavy proteinuria, of which only 6 had malignant hypertension. In the remaining 12 patients with benign nephrosclerosis, protein excretion reached up to 6.5 g/24 h, and nephrotic range proteinuria was present in 3 patients. All patients with heavy proteinuria suffered from long-standing moderate or severe, poorly controlled hypertension and were azotemic. We suggest that hypertensive nephrosclerosis be included in the differential diagnosis of massive proteinuria accompanying azotemia in poorly controlled hypertensives.