Amiloride prevents the metabolic acidosis of a KCl load in nephrectomized rats

1. Counter movements of K+ and H+ across cell membranes were studied in nephrectomized KCl-loaded rats. In one group of animals, the movements of K+ and H+ were determined during and after a KCl load, and in another group, amiloride was used in order to evaluate Na+ participation in K+/H+ exchange. 2. After a KCl load at constant Pco2, 79% of infused K+ left the inulin space, half of which was in exchange for H+. As a result, blood pH fell from 7.40 ± 0.01 to 7.30 ± 0.01 (mean ± sem; P < 0.001). 3. During KCl infusion, the K+/H+ exchange ratio varied between 1.3 and 6.8, showing that the coupling ratio is not fixed. 4. Amiloride did not change blood pH and plasma [K+], but prevented the metabolic acidosis produced by the KCl load without affecting K+ entry into the non-inulin space. Therefore, K+ and H+ movements became completely dissociated. 5. The results indicate that KCl activates an amiloride-sensitive H+ extrusion from the cells. This finding is compatible with the view that Na+/H+ exchange participates in the metabolic acidosis produced by a KCl load.

Fluctuations in intracellular pH associated with vasopressin stimulation

Intracellular pH (pHi) was estimated in paired hemibladders isolated from Dominican toads (Bufo marinus) by the tissue distribution of [14C]5,5'-dimethyl-2,4-oxazolidinedione and [3H]inulin. Tissues were incubated with isotopes for 30 min to correlate changes in pHi with the approximate time of peak vasopressin (VP)-induced water flow. At serosal pH 7.1 in the presence of an osmotic gradient, the intracellular hydrogen ion concentration [( H+]i) after 30 min of VP (20 mU/ml) stimulation was 8.29 +/- 0.23 X 10(-8) M (pHi 7.08) compared with 5.19 +/- 0.46 X 10(-8) M (pHi 7.28) in unstimulated paired controls (n = 5, P less than 0.001). The cyclic AMP (cAMP) analogue 8-(p-chlorophenylthio)-cAMP (10(-5) M) mimicked the VP effects. A similar change was observed at serosal bath pH 8.2, where [H+]i was 1.67 +/- 0.06 X 10(-8) M (pHi 7.78) with VP vs. 1.11 +/- 0.04 X 10(-8) M (pHi 7.95) in matched controls (n = 8, P less than 0.001). In all cases, the hydroosmotic response was associated with a significant decrease in inulin space. When the osmotic gradient was eliminated with Ringer solution or isotonic sorbitol in the mucosal bath, VP produced a smaller decrease in pHi (approximately 0.08 pH units) at both serosal pH. 31P-nuclear magnetic resonance spectra showed a similar downward trend in pHi with cell swelling. When vasopressin was removed from the bath, pHi and inulin space in stimulated hemibladders returned to pretreatment values within 30 min, and the tissues were again capable of a maximum hydroosmotic response if rechallenged with the hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubular reabsorption delay of amino acids in the rabbit kidney

Estimates were obtained both with a rapid-transient technique and under steady-state conditions of the average time required for filtered solutes in the intact rabbit kidney to cross tubular epithelium from tubular lumen into the peritubular inulin space. This interval, defined as the transepithelial passage time, was relatively short (about 15 s) for glucose, in agreement with earlier results in the dog. In contrast, several amino acids required an average transepithelial passage time of about 40 s. Values for aspartate could only be obtained when its large basolateral uptake was inhibited by excess succinate. The long transepithelial passage time may be due to the slow extrusion of reabsorbed amino acids across basolateral cell membranes. This hypothesis was supported by the extent of tissue accumulation of amino acids during reabsorption. Even though basolateral transfer may thus limit the linear rate of movement of filtered amino acids across the epithelium, the step determining fractional absorption from the lumen is situated at the brush border.

Uptake of cytidine by isolated, perfused mouse liver

Mouse livers were perfused at 22 °C with an oxygenated salts medium containing [5−3H]cytidine and [carboxyl-14C]inulin. The cellular uptake of cytidine was determined from the 3H content of liver samples less that present in the extracellular (inulin) space of the samples. Time courses of cytidine uptake were biphasic with initial phases which were approximately linear for 15 s and had time zero values that approximated the extracellular space. Rates of cytidine uptake derived from the initial phase of uptake evidently represented rates of membrane transport because (i) initial rates were saturable, and (ii) cytidine uptake was blocked by the nucleoside transport inhibitor, nitrobenzylthioinosine (NBMPR). Treatment of mice with the 5′-monophosphate of NBMPR (> 0.2 mg/kg, injected i.p.) 30–40 min prior to the perfusion also blocked cytidine entry into livers. An apparent half-saturation constant of about 10−3 M and a maximum rate of about 1 μmol∙g−1∙min−1 were estimated for the NBMPR-sensitive transport of cytidine into mouse liver cells.

Changes in Vascular Ionic Composition at Different Stages of DOC-Salt Hypertension in the Rat

1. Sequential changes in the ionic composition of the aorta and skeletal muscle were followed during 1, 2 and 4–6 weeks in 30 rats given deoxycorticosterone (DOC) and salt supplemented with potassium chloride. Twenty-one rats, drinking water, were used as controls. 2. Twenty-five per cent of the test rats were hypertensive after 1 week, 60% after 2 weeks and 100% after 4–6 weeks. 3. Muscle potassium fell in all test rats by an average of 15%. In contrast, aortic potassium fell by 19% only in those rats which did not develop hypertension after 1 week. 4. Total and non-inulin sodium and water of the aorta were normal in rats which remained normotensive after 1 or 2 weeks and high in those which became hypertensive during the same period. 5. Total sodium and water content of the aorta were also high in rats which were hypertensive at 4–6 weeks. However, because of simultaneous expansion of the inulin space, non-inulin fractions were normal in this group. 6. Results suggest that vascular ionic changes participate in the pathogenesis of DOC-salt hypertension through more than a single mechanism.

Sodium balance during pregnancy in the rat

The purpose of this study was to quantitate sodium balance during gestation in the rat (3 wk) to determine the time course of salt retention and to define the distribution of the retained salt. We have found that while sodium retention appears to begin during the 2nd wk, the bulk of retention occurs during the 3rd wk when the rat excretes only 67% of that ingested. Compared to that of nonpregnant, control rats, net retention for all of gestation was 9.8 meq. Despite a significantly higher sodium intake in pregnant rats, neither urinary nor fecal sodium excretion was different in pregnant and control rats. Fifty-nine percent of the retained sodium was found in the products of conception. Inulin space was increased by term from 19.7 to 25.4% of nonconceptus body weight. In pregnant rats a net retention of 6.3 meq of potassium was noted, 55% of which was found in the products of conception. We conclude that the rat retains sodium and potassium during pregnancy, predominantly in the third trimester. Over half of these salts are found within the conceptus products.