Sodium-dependent transport of inorganic sulfate by rabbit renal brush-border membrane vesicles. Effects of other ions

A Na+ gradient (extravesicular greater than intravesicular) increased the rate of inorganic sulfate (SO24-) uptake into renal brush-border membrane vesicles and energized the transient accumulation of the anion against its concentration gradient, indicating a secondary active transport system. Stimulation of SO24- uptake was specific for Na+. The anions, SO23-, S2O23-, SeO24-, MoO24-, CrO24-, and WO24-, but not HPO24-, cis-inhibited and trans-stimulated SO24- uptake, suggesting that these divalent anions shared the SO24- carrier. The Na+/SO24- co-transport and Na+. The apparent Km for SO24- was 0.6 mM at 100 mM Na+. The relationship between Na+ concentration and rate of SO24- uptake was sigmoidal. From a Hill analysis of the data a [Na+]0.5 of 36 mM and an n value of 1.6 were calculated. Comparisons of the effects of a K+ diffusion potential (inside positive), of a H+ diffusion potential (inside negative), of Na+ salts of anions of different conductances on the Na+-dependent uptakes of SO24- and D-glucose, and of the responses of a membrane potential-sensitive fluorescent probe concomitant with the uptakes indicate that Na+/SO24- co-transport was electroneutral. The simplest stoichiometry consistent with an electroneutral mechanism would be the co-transport of two Na+ and one SO24-. Na+ gradient-dependent SO24- uptake was enhanced by intravesicular Cl-. cis-Cl- inhibited the efflux as well as the influx of SO24-. These findings suggest that Cl- was an inhibitor of SO24- transport. Intravesicular K+ stimulated Na+ gradient-dependent SO24- uptake. The co-transport of Na+/SO24- appeared not to be coupled to the transmembrane flux of K+. It is hypothesized that the co-transport system contained an internal site activated by K+.

Effect of sodium concentration on aldosterone secretion by isolated perfused canine adrenal glands

Small changes in sodium concentration [( Na]) are not generally considered to have a major direct effect on aldosterone secretion. However, a marked disruption in the renin-aldosterone relationship has been observed in a variety of hypernatremic and hyponatremic states. Therefore, we evaluated the hypothesis that small changes in [Na] have a potent direct effect on angiotensin II- and potassium-stimulated aldosterone secretion. The left adrenal gland, abdominal aorta, and surrounding periadrenal tissue were surgically isolated from mongrel dogs and perfused with Ringers bicarbonate solution at a pressure of approximately 57 mm Hg. Infusion of a KCl test solution at the beginning and end of most experiments produced similar increases in aldosterone secretion, thus documenting the stability of these preparations. After a stable response was established to either a low dose of angiotensin II or a small increase in perfusate [K], the [Na] was changed by adding or removing NaCl. Changing perfusate [Na] from 152 to 139 mM during the infusion of either angiotensin II or potassium caused 20- to 25-fold increases in aldosterone secretion. Increasing perfusate [Na] from 145 to 152 mM inhibited aldosterone secretion to a greater extent during stimulation by lower doses (40-50 pg/ml) than by higher doses (80-100 pg/ml) of angiotensin II. These data demonstrate that during moderate stimulation by angiotensin II or potassium, small changes in [Na] have a powerful inverse effect on aldosterone secretion by a direct action on the canine adrenal gland.

Preoptic recess lesions, body fluid compartments, and the renin-aldosterone system

The effects of electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V) of the rat brain on body fluid distribution and the renin-aldosterone system were determined. Rats underwent either ablation of AV3V periventricular tissue or control surgeries. After recovery, animals were implanted with femoral arterial and jugular venous catheters, and sodium space and plasma volume were measured by calculating the dilution of intravenous injections of 22Na- and 125I-labeled serum albumin, respectively. Total body water was determined in separate groups of rats by desiccation. Other animals with AV3V lesions and control rats were used to measure urinary sodium excretion and plasma renin (Prenin) and aldosterone (Paldo) concentrations while volume replete and after volume depletion. Animals with AV3V lesions had expanded extracellular fluid volume and decreased plasma volume, but total body water was comparable with control-operated rats. Volume-replete and volume-depleted rats with AV3V lesions had significantly higher Prenin than control animals in similar volume states. Although Paldo was not different between groups in the volume-replete state, it was significantly greater in rats with AV3V lesions than in control animals after volume depletion. These data demonstrate that AV3V periventricular ablation results in chronic alterations in the normal body fluid distribution but does not diminish the rats' ability to increase Prenin and Paldo or decrease sodium excretion during volume depletion.

Effect of water deprivation on urinary excretion of PGE2 in the dog

We examined the influence of the state of hydration on the urinary excretion of prostaglandin E2 (PGE2) and kallikrein in the dog. Immunoreactive PGE2 and kallikrein were measured in the urine of conscious dogs during periods of water deprivation and periods of free access to drinking water and in the urine of time-control dogs that had free access to water throughout the study. During water deprivation the excretion of kallikrein did not change significantly, but PGE2 excretion increased by 50 and 75% (P less than 0.05) after 2 and 4 days, respectively, associated with reductions of body weight and urine flow and with elevation of plasma renin activity, plasma sodium, and both plasma and urine osmolality. Dehydrated dogs drank copiously when allowed free access to water, and over the following 4 days both PGE2 excretion and plasma renin activity fell significantly, associated with elevation of body weight and urine volume and with lowering of plasma sodium and plasma and urine osmolality. In contrast, if after 4 days of water deprivation the dogs were kept at a constant level of dehydration by restricting their water allotment on subsequent days to 300 ml/day, PGE2 excretion and most other variables remained at the dehydration level. In conclusion, these results suggest that renal PGE2 production is dependent on the state of hydration in the dog.

Effects of converting enzyme inhibition with captopril on renal function in normal and ACTH treated sheep

1. The effect on renal function in sheep of inhibiting converting enzyme with captopril was examined before and after 5 days ACTH administration. 2. Glomerular filtration rate, effective renal plasma flow, effective renal blood flow, mean arterial pressure and plasma sodium were all significantly increased by ACTH treatment and plasma potassium was decreased. Captopril (20 mg i.v.) had no effect on renal function or blood pressure before or after ACTH treatment, although urinary potassium excretion decreased following captopril on day 6 of ACTH treatment. 3. The increase in glomerular filtration rate and effective renal plasma flow seen with ACTH treatment in sheep does not appear to be mediated by the reninangiotensin system.

The effect of dietary sodium on the blood pressure response to dopamine infusion in the conscious rat

1. The influence of dietary sodium intake on the pressor response to intravenously infused dopamine in the conscious rat was studied. 2. Chronic sodium restriction significantly reduced the pressor response to infused dopamine, whereas high sodium diet enhanced the response. 3. Sodium intake is an important determinant of the pressor response to dopamine.

Dietary sodium intake: a determinant of postprandial plasma sodium concentration in the dog

1. The effect of dietary sodium intake on pre- and post-prandial plasma sodium concentrations and on the pattern of sodium and potassium excretion was determined in conscious female dogs, who were allowed free access to water and were fed on commercial low sodium diets supplemented with 0, 50, 100 or 250 mmol of sodium chloride/day for 6 days. 2. The preprandial plasma sodium concentration was not altered by the dietary sodium intake. However, the 4 h postprandial plasma sodium concentration was linearly related to the magnitude of dietary sodium intake, whereas the 8 h postprandial plasma sodium concentration was elevated only in dogs receiving 250 mmol of sodium/day. 3. The (0-8 h/0-24 h) ratio for urinary sodium excretion was significantly correlated with both the dietary sodium intake and the postprandial increase in plasma sodium concentration. 4. The 24 h excretion of potassium was not markedly affected by the dietary sodium intake; however, the (0-8 h/0-24 h) ratio for potassium excretion was significantly correlated with both the dietary sodium intake and the (0-8/0-24 h) ratio for sodium excretion. 5. These data indicate that: (a) postprandial increases in plasma sodium concentration need to be considered when evaluating the mechanisms involved in the daily regulation of sodium balance; (b) the daily pattern of potassium excretion is closely linked to the dietary sodium intake.

Renal and endocrine response to water deprivation in dog

Plasma and urine sodium, potassium, osmolality, aldosterone, and plasma renin activity (PRA) were measured in time controls and during control dehydration and rehydration periods in conscious dogs fed a 50 mmol NaCl diet. During 4 days of water restriction, plasma sodium and osmolality and PRA were elevated, whereas plasma potassium and aldosterone were not affected. Urinary potassium excretion was elevated above intake levels during the entire dehydration period, whereas Na excretion was only elevated during the first 2 days of dehydration. Unrestricted rehydration was associated with a marked fall in plasma sodium and osmolality, a decrease in PRA, and no change in plasma potassium or aldosterone. In addition, during the 1st day of rehydration, there was marked retention of sodium and potassium. Thus, in the dog, dehydration and subsequent rehydration cause significant alterations in sodium and potassium balance and marked alterations in PRA that are not associated with changes in either plasma aldosterone concentration or urinary aldosterone excretion.

Aldosterone and the enhanced natriuresis of hypertonic infusions in the dog

The purpose of this study was to determine whether small elevations in plasma sodium concentration (PNa) were effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in dogs fed normal sodium diets. Ten dogs fed a normal sodium diet, six DOCA-treated dogs, and four adrenalectomized dogs were given the same sodium load (2.5 mmol/kg) either as a hypertonic (1 M NaCl) or hypotonic (0.1 M NaCl) infusion. In all three groups of dogs, PNa was greater after the hypertonic than after the hypotonic infusion during most of the 22-h experiment. The dogs fed a normal sodium diet responded to the elevation in PNa (hypertonic infusion) with decreased aldosterone excretion and an exaggerated natriuresis. When aldosterone levels were maintained constant by either DOCA treatment or adrenalectomy, the exaggerated natriuresis that accompanied the hypertonic infusion was prevented. Therefore, elevation of PNa appears to be an important determinant of aldosterone secretion and, hence, of sodium excretion in conscious dogs fed normal sodium diets.

Stimulation of the efflux of L-glutamate from renal brush-border membrane vesicles by extravesicular potassium

The rate of efflux of L-glutamate from renal brush-border membrane vesicles was enhanced by Na+ and by extravesicular L-glutamate, but not by D-glutamate nor analogs of L-glutamate that do not share the Na+-L-glutamate co-transport system. These results suggest that efflux was mediated by the Na+-L-glutamate carrier. The efflux of L-glutamate was increased by extravesicular K+ or Rb+ but not by Li+, choline+, or Tris+. These findings, together with previous results showing that intravesicular K+ or Rb+ increased L-glutamate uptake and that a K+ gradient energized the concentrative uptake of the acidic amino acid in the absence of other gradients, provide evidence consistent with the hypothesis that the co-transport of Na+-L-glutamate is coupled to the transmembrane flux of K+.

Effect of hypertonic and hypotonic infusions on aldosterone in conscious sodium-depleted dogs

1. The role of the plasma sodium concentration in the regulation of aldosterone secretion and sodium excretion was investigated by comparing in 13 conscious sodium-depleted dogs the effects of the same sodium load (2.5 mmol/kg) given as either a hypertonic or hypotonic infusion. 2. The plasma sodium concentration was significantly higher and the plasma aldosterone concentration and urinary aldosterone excretion were significantly lower after the hypertonic infusion as compared with the hypotonic infusion. 3. The cumulative urinary sodium excretion during the 22 h after beginning the infusion was significantly greater after the hypertonic infusion, but this difference was not observed in five sodium-depleted dogs who were treated with deoxycorticosterone acetate before the infusions were given. 4. These data suggest that elevations in plasma sodium concentration are effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in conscious sodium-depleted dogs.

Lack of evidence for gastrointestinal control of sodium excretion in unanesthetized rabbits

Experiments were performed to determine whether unanesthetized rabbits exhibit a greater natriuresis after oral administration of a hypertonic sodium chloride solution (1.5 mmol NaCl/kg) than after the intravenous administration of the same solution. Male rabbits (New Zealand) were placed on a low sodium diet for 4 days, and on the fifth day a hypertonic NaCl solution (616 mM) was given either by stomach tube (GI) or intravenously (IV), while an equal volume of a hypotonic NaCl solution (31 mM) was given by the alternate route. The studies were repeated on each rabbit so that paired observations were obtained. No differences in plasma Na concentration, peripheral hematocrit, or urinary sodium excretion were observed between the GI and IV groups after administration of the hypertonic NaCl solution. In seven rabbits that were permitted access to food and water following NaCl administration by either route, urinary sodium excretion tended to be reduced (P = 0.08), but, again, no significant differences in plasma sodium concentration, peripheral hematocrit, or urinary sodium excretion were observed between the GI and IV routes of sodium administration. Accordingly, we could find no evidence to support the existence of a GI or portal Na receptor system that regulates urinary sodium excretion in the unanesthetized rabbit.

Haemodynamic effects of increasing extracellular potassium concentration in ACTH-induced hypertension in sheep

1. ACTH administration (20 microgram day-1 kg-1) to sheep produces hypertension associated with a raised cardiac output and hypokalaemia. 2. The aim of the present experiments was to detail the haemodynamic changes associated with restoration of the extracellular potassium concentration in sheep with ACTH-induced hypertension. 3. After 7 days of ACTH treatment potassium chloride (10 mmol/h) was infused for 3 days to restore plasma [K+] to the pre-ACTH value. 4. ACTH reduced plasma [K+] from 4.4 +/- 0.1 to 3.2 +/- 0.2 mmol/l but 3 days of potassium chloride infusion returned plasma [K+] to 4.3 +/- 0.2 mmol/l. 5. ACTH increased mean arterial pressure from 67 +/- 2 to 88 +/- 1 mmHg in the first 7 days and it remained elevated during potassium chloride infusion (91 +/- 5 mmHg on day 10). 6. Cardiac output rose with 7 days ACTH treatment from 4.9 +/- 0.2 to 6.0 +/- 0.6 l/min but fell progressively with potassium chloride infusion to 4.9 +/- 0.3 l/min on day 10. 7. These studies suggest that potassium status or extracellular [K+] may play a role in determining the haemodynamic profile associated with steroid-induced hypertension.

Evidence for a peritubular-to-luminal flux phosphate in the dog kidney

The possible presence of a direct influx of phosphate into the tubular lumen of the dog kidney was examined by two different techniques. A 0.3-ml bolus of 32PO4 and [3H]inulin was injected into the renal artery of dogs with and without phosphate loading. The mean urinary transit time (TT) for PO4 was consistently less than the TT for inulin in nonphosphate-loaded dogs. Following phosphate loading the TT for phosphate approached but did not equal the TT for inulin. In contrast, after microinjections of 32PO4 and [3H]inulin into proximal tubules, the urinary TT of PO4 was significantly longer than the TT of inulin. The application of 32PO4 and [3H]inulin to the surface of the left kidney was associated with a greater recovery of 32PO4 from the left kidney compared to that from the right kidney. The recovery of [3H]inulin was proportional to the glomerular filtration rate for both kidneys. Application of the 32PO4 and [3H]inulin to the surface of a muscle resulted in an equal recovery of phosphate and inulin from both kidneys. The results demonstrate the presence of a detectable tubular influx of phosphate.

Partial purification and properties of diglyceride kinase from Escherichia coli

Diglyceride kinase (diacylglycerol kinase, E.C. 2.7.1.-), an enzyme localized in the inner membrane of Escherichia coli, has been purified about 600-fold. The purified enzyme exhibits an absolute requirement for magnesium ion; its activity toward both lipid and nucleotide substrates is stimulated by diphosphatidylglycerol or other phospholipids. Adenine nucleotides are much better substrates for the enzyme than are other purine or pyrimidine nucleotides. The purified enzyme preparation catalyzes the phosphorylation of a number of lipids, including ceramide and several ceramide and diacylglycerol-like analogs. The broad lipid substrate specificity of diglyceride kinase suggests that this enzyme may function in vivo for the phosphorylation of an acceptor other than diacylglycerol.

Isolation and characterization of the liponucleotides of Saccharomyces cerevisiae

The liponucleotide fraction of Saccharomyces cerevisiae was isolated from cells grown on tritiated uracil and identified as CDPdiacylglycerol on the basis of (1), its behavior as a single compound upon DEAE-cellulose and thin-layer chromatography; (2), its extreme lability to mild alkaline methanolysis; and (3), its hydrolysis by the CDPdiacylglycerol hydrolase of Escherichia coli to yield tritiated 5'-CMP. At most, only about 5% of yeast liponucleotide could be dCDPdiacylglycerol, in contrast to the presence of nearly equimolar amounts of CDP-and dCDPdiacylglycerols in E. coli. Although no CDPceramide could be detected in the liponucleotide fraction of this organism, the possibility still exists that it may be an intermediate in the biosynthesis of sphingolipids in systems yet to be examined.

Effect of parathyroid hormone secretion on sodium reabsorption by the proximal tubule

To determine if an increase in the endogenous secretion of parathyroid hormone could decrease sodium reabsorption by the proximal tubule, the ionized calcium concentration of blood perfusing the parathyroid gland of eight unilaterally thyroid parathyroidectomized dogs (TPTX) was reduced by infusion of an isotonic sodium citrate plus sodium chloride solution into the blood supply of the parathyroid gland. The fractional clearance of phosphate increased significantly (+9.3 +/- 2.8 ml/min per 100 ml GFR), while fractional sodium reabsorption by the proximal tubule decreased (-.06 +/- .02; P less than .025). In seven normal control dogs that received isotonic sodium chloride infusion, neither fractional sodium reabsorption by the proximal tubule nor the fractional clearance of phosphate was significantly altered. In five bilaterally TPTX dogs that received a sodium citrate plus sodium chloride infusion, sodium reabsorption by the proximal tubule was not significantly altered. There were no significant changes in glomerular filtration rate or renal plasma flow in any of these groups. The data demonstrate that alterations in endogenous parathyroid hormone secretion can play a significant role in the regulation of sodium reabsorption by the proximal tubule.

Role of parathyroid hormone in the phosphaturia of extracellular fluid volume expansion

Role of parathyroid hormone in the phosphaturia of extracellular fluid volume expansion. Acute expansion of the extracellular fluid volume increases the urinary excretion of phosphate. The present study examined the importance of increased plasma parathyroid hormone concentration in the phosphaturia accompanying acute extracellular fluid volume expansion (ECVE). Infusion of a calcium-free Ringer's solution into dogs was associated with increased urinary phosphateexcretion and serum immunoreactive parathyroid hormone concentration (iPTH), the latter being significantly correlated with a decrease in plasma ionized calcium concentration. Prevention of the fall in plasma ionized calcium concentration by infusion of a calcium containing Ringer's solution prevented the increase in serum iPTH but the magnitude of the phosphaturia was not affected.