Utilization of classical clearance methodology for the determination of diuretic mechanism and site of action is based on four kinds of observations: (1) the effects of diuretic agents on the concentrating and diluting mechanism; (2) an analysis of the pattern of anionic excretion produced by the drug; (3) determination of the action of the agent on acid excretion and on acid-base status; (4) an evaluation of the effects of the diuretic on potassium excretion. Agents (such as acetazolamide) that act in the proximal convoluted tubule cause an enhancement of solute-free water generation (CH2O), induce a phosphaturia and an increase in bicarbonate excretion, alkalinize the urine, and cause a kaliuresis. Those agents which inhibit sodium chloride transport in the loop of Henle (for example, furosemide and ethacrynic acid) reduce both CH2O and the abstraction of tubular water from the collecting duct (TCH2O). They are the most potent natriuretic agents currently available, causing increments in the excretion of sodium in the urine of 15 to 25 per cent of filtered load. Those drugs which act in the early portion of the distal convolution (the thiazides, metolazone) reduce CH2O modestly or not at all and have no effect on TCH2O. They are capable of increasing urinary sodium by 5 to 8 per cent of the filtered load. The special-purpose agents such as triamterene and spironolactone are only mildly effective as natriuretic agents. While they augment fractional sodium excretion by only 2 to 3 per cent, they are useful because of their capacity to reduce urinary potassium excretion, either by a direct renal tubular effect (triamterene) or by competitive inhibition of aldosterone (spironolactone).

Bicarbonates↗

PubMedDate not supplied

Renal effects of bumetanide.

Upon administration of bumetanide in normal human subjects, both glomerular filtration rate and effective renal plasma flow were increased, in approximately proportional amounts. Sodium excretion rose to 16 per cent of filtered load, whereas there was a chloriuresis of 23 per cent. During maximal water diuresis, the drug caused an increase in urine flow rate associated with a rise in osmolal clearance and no change in solute-free water clearance. Intravenous injection of the drug during hypertonic saline infusion into hydropenic subjects resulted in the virtual abolition of water abstraction from the collecting duct. The drug caused a modest increase in phosphate excretion but no change in the percentage of filtered bicarbonate excreted. Furthermore, neither urinary pH nor net hydrogen ion excretion was altered by the drug. The data suggest that bumetanide has its major action in the loop of Henle but that it also inhibits sodium transport in the proximal tubule. In addition, the nature of the proximal action does not appear to be related to a carbonic anhydrase inhibitory effect. These latter observations regarding the proximal action of the drug were verified by micropuncture studies performed in the dog.

Bicarbonates↗

PubMedDate not supplied

Combined effect of bumetanide and metolazone in normal volunteers.

Bumetanide 1 to 2 mg or metolazone 2.5 mg were administered by mouth separately and then in combination to eight normal men and women in order to determine whether a sequential blockade of sodium reabsorption with diuretic agents that act at different sites within the nephron leads to a supra-additive diuretic effect. All three treatment regimens resulted in a significant weight loss and increased urine volume and the excretion of sodium, potassium, and chloride. A prolonged diuretic effect lasting up to 48 hours after administration occurred with metolazone alone. Although absolute and fractional chloride and potassium excretion and urine volume were higher after combined therapy (P less than .05 or better) than after either drug alone, absolute sodium excretion after combination therapy was higher than excretion after bumetanide (P less than .05) but not after metolazone. The percent of fractional sodium excretion after both drugs was greater than after either drug alone (P less than .05). However, excretion of chloride, sodium, potassium, and fluid on the combined therapy day was less than the sum of excretion on each single drug therapy day. Thus, the combination of bumetanide and metolazone did not have a supra-additive effect in normal subjects.

Body Weight↗

PubMedDate not supplied

Effects of elevated lead and cadmium burdens on renal function and calcium metabolism.

To assess the pathophysiologic significance of increased body burdens of lead and cadmium, detailed renal function studies and evaluation of calcium, phosphorus, and vitamin D metabolism were carried out in 38 industrial workers exposed to lead and cadmium for 11 to 37 yr. Body burden of lead, as assessed by x-ray fluorescence measurement of tibia lead content, was elevated in 58% of the men and, when assessed by excretion of lead after Ca-EDTA infusion, was elevated in 36%. Liver or kidney cadmium burden, as assessed by neutron activation analysis, was elevated in 31%. Creatinine clearance was normal in all workers. One worker was hyperuricemic and two were proteinuric; three had increased beta 2 microglobulin excretion and one had diminished urinary acidifying ability. Maximal urinary concentrating ability was abnormal in a significant fraction, i.e., 52% of the men. Individuals with a high lead burden had a slight decrease in mean serum phosphorus but no accompanying phosphaturia. There was no abnormality of serum calcium. Twenty-two percent of subjects were hypercalciuric and two had low vitamin D levels, but these abnormalities bore no relation to heavy metal burden. In this carefully characterized group of men with chronic lead and calcium exposure, definite, if subclinical, effects on renal function and serum phosphorus but not calcium or vitamin D metabolism were demonstrable.

Adult↗

PubMedDate not supplied

Effect of myeloma light chains on phosphate and glucose transport in renal proximal tubule cells.

Primary cultures of cells derived from the rat proximal tubule were exposed to up to 200 microM lambda- or kappa-light chain obtained from myeloma patients. Light chains inhibited the uptake of both phosphate and glucose by the cells while albumin had no effect. The half-maximal inhibitory concentration (IC50) of both the lambda- and kappa-light chains on phosphate transport were similar, 34 and 35 microM respectively. The IC50 of the kappa-light chain on glucose transport was 360 microM. The inhibitory effect of light chains was dose-dependent (r = 0.90, p < 0.01 for the lambda-light chain and r = 0.93, p < 0.001 for the kappa-light chain, on phosphate transport; and r = 0.93, p < 0.001 for glucose transport). Dixon and Line-weaver-Burk plot analyses were characteristic for noncompetitive inhibition. The inhibition constant 89 microM for phosphate uptake derived from the Dixon plot was similar to the IC50 calculated from the dose-response curves. These findings indicate that light chains, at concentrations found in the tubule fluid of a typical myeloma patient, are potent inhibitors of phosphate and glucose transport in proximal tubular cells, and that direct cell toxicity is a major mechanism of light chain nephrotoxicity.

Animals↗