THE EXCRETION OF ACID IN UNILATERAL RENAL DISEASE IN MAN

Acquired distal renal tubular acidosis in man

Distal renal tubular acidosis (dRTA) may complicate renal transplantation, liver cirrhosis, and obstructive uropathy. Indeed, its occurrence may be an early clue to an episode of rejection of the graft or to obstructive uropathy. The mechanism in most patients with dRTA is impaired distal secretion of protons. In some patients, however, back leak of protons from tubular lumen to blood may abolish distal tubular ability to maintain urine to blood proton gradients. In patients with obstructive uropathy the spectrum of tubular acidosis is widened by the occurrence of additional defects in tubular secretion of potassium and impairment of hydrogen ion secretion secondary to hypoaldosteronism. Hyperkalemia is also seen in "voltage dependent" states such as following the administration of lithium and amiloride. Hyperkalemia per se is conducive to acidosis by a combination of extrarenal and several intrarenal mechanisms.

Distal renal tubular acidosis: pathogenesis and classification

Distal renal tubular acidosis results from ineffective addition of hydrogen ions to the lumen of the distal nephron. The syndrome is manifested by hyperchloremic metabolic acidosis often associated with hypokalemia. More recently, it has been recognized that hyperkalemia rather than hypokalemia can be a dominant feature of some cases of distal renal tubular acidosis. It has been generally accepted that all cases of this syndrome ultimately resulted from a similar mechanism. The prevailing view was that the abnormality underlying distal renal tubular acidosis was that of inability to either generate or maintain a steep pH gradient across the distal nephron. Recent advances in our understanding of the process of distal acidification have provided evidence that different mechanisms can alter distal hydrogen ion secretion. In this article, the significance of the various indices of urinary acidification and their use in the characterization of the mechanism underlying distal renal tubular acidosis are revised. A classification of distal renal tubular acidosis on the basis of mechanism is presented. The importance of plasma potassium and renal potassium excretion in the evaluation of patients with distal renal tubular acidosis is emphasized.

Structural and functional adaptation after reduction of nephron population

This review of adaptive changes in renal structure and function in subjects with reduced renal mass has two primary goals. One is to provide a description of the remarkable compensatory increases in glomerular filtration rate (GFR), and renal blood flow, at the level of individual nephrons, and the alterations in water and electrolyte transport by tubular epithelium. These processes preserve fluid and electrolyte balance in subjects with progressive renal failure, until whole kidney GFR is reduced to about 20 percent of normal, and provide the basis for conservative clinical medical management. The other aim is an attempt to provide an understanding of the mechanisms involved in compensatory adaptation, since this information, in addition to amplifying our understanding of renal transport processes, helps to elucidate the functional limitations placed on subjects with renal insufficiency. An attempt has been made to analyze both clinical observations and relevant experimental models and an effort has been made to correlate renal function with different patterns of renal injury.

Individual renal clearances determined at renal vein catheterization

Renal para-aminohippurate (PAH) clearances were predicted in 16 kidneys of eight hypertensive patients with renal artery stenosis, pyelonephritis, or obstructive nephropathy, without individual ureteral catheterization. Predictions of left or right kidney clearance (CL or CR) were based on roentgenographic renal frontal areas (A), on total PAH clearances (CT), and on individual PAH extractions (E) measured at renal vein catheterization according to the formula (formula: see text). When these patients underwent ureteral catheterization for diagnostic reasons, individual PAH clearances were measured and ranged from 22 to 286 cm3/min. After correction for differences in total PAH clearance on the two occasions, predicted and individually measured values corresponded closely along a line of identity. The 95% confidence limit (+/- 2 SEM) for predictions of individual PAH clearance was approximately +/- 38 cm3/min and for percet of total PAH clearance distributed to left or right kidney, +/- 6%. Individual renal PAH clearances can therefore be predicted at renal vein catheterization with acceptable error. Thus, the substantially invasive procedure of ureteral catheterization is not required to ascertain left and right kidney PAH clearance in patients already at risk from renal disease.

Independence of hydrogen ion secretion and transport of other electrolytes in turtle bladder

The relationship between hydrogen ion secretion and the transport of other electrloytes was examined in the isolated urinary bladder of the water turtle. Symmetrical solutions which were free from exogenous carbon dioxide and bicarbonate bathed the two surfaces of the preparation, and the spontaneous electrical potential of the bladder was nullified by a voltage clamp. Active transport of sodium from mucosal to serosal medium was confirmed by simultaneous bidirectional flux measurements and found to be slightly, but not significantly, greater than the short-circuit current. In the absence of sodium in the bathing solutions, the normal potential difference across the bladder reversed and the current required to nullify this reversed potential difference had the same magnitude as the simultaneously measured rate of hydrogen ion secretion. The results indicate that, under these experimental conditions, the bladder transports sodium and hydrogen ion actively, but that chloride movement does not contribute to the short-circuit current. The rate of secretion of hydrogen ion was not affected by replacement of the sodium in the bathing media by cesium, or by inhibition of sodium transport by dinitrophenol. Acidification continued when chloride in the solutions was replaced by sulfate, or when potassium or calcium was removed from the solution bathing the mucosal surface. Secretion of hydrogen ion by the turtle bladder is not dependent on the simultaneous transport of other electrolytes across the bladder.