Renal Tubular Water Reabsorption Research Articles

Serum sodium as a diabetes risk factor?

Electrolytes play a key role in controlling fluid status, muscle contraction, neurological function, coagulation, and acid base status, as well as multiple enzymatic reactions. Diabetes is associated with multiple significant electrolyte disorders, predominantly affecting serum sodium (Na), potassium, and magnesium.1 In healthy individuals, serum Na levels range between 135–146 mmol/L. Hyponatremia is defined as a serum Na < 135 mmol/L, typically accompanied by a low serum osmolality (<275 mosm/L). It is the most frequently seen electrolyte disorder, present in about 5% of adults and 35% of hospitalized patients.2, 3 In a New York health system analysis of 10 385 patients hospitalized with COVID-19 in 2020, hyponatremia was present in 37.5% of patients.4 Low serum Na may activate the renin-angiotensin-aldosterone system, may cause increased sympathetic nervous system tone, and may be associated with oxidative stress. Insulin, either administered therapeutically or in the setting of hyperinsulinemia from insulin resistance, increases renal tubular water reabsorption via a presumed vasopressin effect and can result in hyponatremia. Chronic kidney disease and diuretic use in hypertension further increase the risk of hyponatremia as well as other electrolyte imbalances such as hypokalemia and hypomagnesemia.7 Serum Na simply may represent the state of hydration. Might some of these mechanisms contribute to effects of even small deviations in serum Na from normal? Should we look more carefully at Na as a biomarker of outcome? Further analysis of large clinical data sets may give answers to these questions.

Comparative sequences of the canine and feline vasopressin prohormones

Vasopressin (VP, antidiuretic hormone) is synthesized as a prohormone consisting of four domains: a signal sequence, the VP nonapeptide, neurophysin II (NP II), and a C-terminal glycopeptide. It plays a key role in cardiovascular homeostasis by regulating renal tubular water reabsorption and urine production. As part of our ongoing studies of the hormonal effects of heart failure in dogs and cats, we have been determining, when not known, the nucleotide and amino acid sequences of relevant peptide hormones. This information will be used to assist in the development and selection of regions of the prohormone for further study and the selection of molecular and antibody probes. To determine the comparative nucleotide and amino acid sequences of canine and feline VP, total RNA was extracted from feline and canine hypothalamus to obtain complementary DNA (cDNA) by reverse transcriptase polymerase chain reaction (RT-PCR) using oligo-T primers. Consensus primers were designed and used for PCR of the resulting cDNA, and the PCR products were then sequenced and analyzed. Each VP sequence was compared to the VP from several mammalian species by alignment with sequences obtained from the GenBank database at the National Center for Biotechnology Information (NCBI). The complete sequence of the canine prohormone was consequently derived from raw data available from the canine Whole Genome Shotgun sequencing site at NCBI. Canine and feline VP prohormones share a high degree of homology with that of other known mammalian species in the VP hormone and NP II domains. The nine amino acid code of canine and feline VP (CYFQNCPRG) is identical to that found in human beings, cows, mice, and rats. The sequence differs by one amino acid from that of swine. The results of this study should be of help in the design and use of antibodies and molecular probes for future studies.

Antidiuretic and cardiovascular actions of prostaglandin E 2 in the rainbow trout Salmo gairdneri

The renal and cardiovascular actions of intravenous injection or infusion of prostaglandin E 2 (PGE 2) have been investigated in the anaesthetised rainbow trout, Salmo gairdneri. Amounts of 1–2500 ng PGE 2/kg body wt had a potent vasodilatory action and caused rapid dose-related decreases in dorsal aortic blood pressure. Intravenous infusion of PGE 2 was associated with a secondary tachycardia and vasoconstriction. Injection of PGE 2 resulted in transient dose-related decreases of urine production. Infusion of PGE 2 at 200 ng/min/kg rapidly decreased glomerular filtration rates by reducing the populations of filtering nephrons and later by increasing the renal tubular water reabsorption. The possible endocrine systems which may be involved in the renal responses to PGE 2 are discussed.

Effects of felodipine on renal function in animals.

The effects of felodipine on renal function were evaluated in dogs and rats using renal clearance, haemodynamic and micropuncture techniques. Unilateral renal arterial infusion of felodipine in anaesthetised dogs produced an ipsilateral diuresis and natriuresis without changing the mean arterial blood pressure, renal blood flow or glomerular filtration rate. In similar studies, the non-calcium antagonist vasodilator, hydralazine, produced antidiuresis and antinatriuresis. Continuous intravenous administration of felodipine in anaesthetised normotensive rats also produced a diuresis and natriuresis without changing mean arterial blood pressure, renal blood flow, whole kidney or single nephron glomerular filtration rate. Renal tubular reabsorption of water and sodium were inhibited in the distal tubule and collecting duct; neither potassium excretion nor reabsorption were affected. Bolus intravenous administration of felodipine to conscious spontaneously hypertensive rats produced dose-related decreases in mean arterial blood pressure and renal vascular resistance which were associated with increases in renal blood flow, glomerular filtration rate, urinary flow rate and sodium excretion; urinary potassium excretion was not affected. The non-calcium antagonist vasodilator minoxidil produced antidiuresis and antinatriuresis. Felodipine, a calcium-antagonist vasodilator used as an antihypertensive, possesses beneficial diuretic and natriuretic properties which are due to its direct effect on renal tubular water and sodium reabsorption.

Developmental aspects of renal tubular reabsorption of water in the lamb fetus.

Summary: The effects of intrauterine maturation on the tubular reabsorption of water by the fetal kidney was determined in 44 chronically catheterized fetal lambs divided in three groups. Fourteen fetuses were studied between 101 and 119 days, 13 between 120 and 130 days, and 17 between 131 and 142 days. The urinary flow rate increased (P < 0.01) when fetuses <120 days were compared to fetuses between 120-130 days of gestation. A 35% increase in Uosm was found in fetuses over 130 days and was paralleled by significant increases in (U/P) iothalamate and (U/P) osm ratios. An increase in (U/P) urea ratio in fetuses over 130 days correlated with an increase in (U/P) iothalamate (r = 0.87). The (U/P) ratios for Na+ and Cl− were not correlated with fetal age and did not increase during gestation. The percent of filtered water excreted (V/GFR) was high before 120 days of gestation (26.8 ± 3.04%) and remained elevated in fetuses of 120-130 days (28.7 ± 2.53%). After 130 days of gestation, it decreased significantly to 18.3 ± 2.56% (P < 0.05). Similarly, /GFR values were, respectively, 12.02 ± 1.53 and 13.18 ± 1.46 ml/min/100 ml GFR in groups of fetuses of less than 120 days and between 120-130 days; after 130 days /GFR decreased significantly to 5.82 ± 1.97 ml/min/ 100 ml GFR (P < 0.02). Cosm/GFR remained unchanged in all three groups of fetuses at 14.76 ± 2.57, 15.49 ± 1.90, and 12.51 ± 1.34 ml/min/100 ml GFR, respectively. The simultaneous significant decreases in V/GFR and /GFR without changes in Cosm/GFR in fetuses over 130 days suggest that the increase in Uosm in near-term fetuses represents an increase in free water reabsorption by the fetal kidney. Speculation: The increase in free water reabsorption by the near-term fetal kidney may represent either an increase in end-organ responsiveness to arginine vasopressin or maturation of mechanisms involved in the buildup of the osmotic gradient in the fetal medulla or both.

Renal response to secretin

The effect of Jorpes secretin on the urinary volume, pH, and excretion of sodium, potassium, chloride, bicarbonate, titratable acidity, ammonia and phosphate was studied in five healthy male volunteers with and without simultaneous aspiration of duodenal fluids. A three- to fourfold increase in urinary volume and sodium excretion occurred within the first 30 min after secretin injection and this was accompanied by a significant rise in urinary pH in each instance. Urinary bicarbonate excretion increased from 55 plus or minus 13 to 395 plus or minus 33 mueq/30 min after secretin injection. Aspiration of alkaline duodenal contents was accompanied by an even greater postsecretin increase in urinary bicarbonate excretion. No significant changes in arterial pH or blood gases were detected throughout the study. These observations are compatible with a direct effect of secretin upon the renal tubular reabsorption of water, bicarbonate, and other ions, and could account for the transient alterations in urinary pH occurring in response to a meal.

The effect of temperature on renal function in the white sucker fish, Catostomus commersonii

1. 1. The effect of temperature on urine flow, renal tubular water reabsorption and renal glucose reabsorption was investigated in the white sucker. 2. 2. Urine flow increased with increasing temperature over the range 2 to 18°C ( Q 10 = 2·21). 3. 3. Temperature did not significantly affect the proportion of filtered water which was reabsorbed and had only a slight effect on the proportion of filtered glucose reabsorbed ( Q 10 = 1·21). 4. 4. Intermittent glomerular function appears to be the means by which the rate of urine flow is controlled in the white sucker.

Studies on the glomerular filtration rate of rainbow trout (Salmo gairdneri).

ABSTRACT Variations in the glomerular filtration rate (G.F.R.) and the renal tubular reabsorption of water are probably important factors in the homoiostatic mechanisms-associated with the euryhalinity of the rainbow trout (Salmo gairdneri). The observed reduction in urine flow after the adaptation of rainbow trout to sea water can be largely accounted for on the basis of the reduced G.F.R. Intraperitoneal injections of mammalian preparations of vasopressin, oxytocin and vasopressin/oxytocin into freshwater trout significantly increased the G.F.R. The intraperitoneal injection of aldosterone into freshwater fish had no detectable effect on G.F.R. The similar administration of corticosterone significantly reduced the G.F.R. to 73 % of the intact freshwater control value.

Adrenal steroid inhibition of vasopressin release from the neurohypophysis of normal subjects and patients with Addison's disease.

There is a large body of evidence to indicate that adrenal steroids decrease distal renal tubular reabsorption of water. A popular view is that this effect may be due to antagonism of the action of vasopressin on the renal tubules (1), but others (2) have postulated that corticoids may exert a direct effect on permeability of the renal tubular cells to water. Recent studies in patients with combined anterior and posterior pituitary insufficiency (3) suggested that adrenal steroids increase free water excretion by suppressing release of vasopressin from hypothalamic portions of the neurohypophysis. Further investigation of this preliminary hypothesis in normal subjects and in patients with Addison's disease forms the basis of this report.'

Contralateral renal function after unilateral renal vein ligation.

The effect of increased pressure in one kidney, produced by ligation of its vein, on contralateral renal function was investigated in eight anesthetized dogs. Kidney function was determined under the same experimental conditions in five dogs, but without renal vein ligation. For the latter group, renal function, on the average, remained reasonably stable. After left renal vein ligation, findings for the right kidney were as follows: a) decreased urine flow, amounting maximally to 9.5–41.4% of control flows; b) slight increase of questionable significance in creatinine clearance; c) inconstant changes in PAH clearance; d) increase in urine osmolality to hypertonic values; e) decrease in solute-free water clearance; f) slight rise of questionable significance in total solute clearance; and g) either no change or inconstant changes in excretion rates Na+ and K+. The data indicate that the oliguria resulted solely from increased renal tubular reabsorption of water, suggesting liberation of antidiuretic hormone as the possible mechanism. Direct nervous influences on tubular reabsorption of water cannot, however, be presently ruled out.

Renal mechanisms in coincident Addison's disease and diabetes insipidus: effects of vasopressin and hydrocortisone.

Concurrent primary failures of adrenocortical and posterior hypophyseal functions, with coincident syndromes of diabetes insipidus and Addison's disease, to our knowledge, have not been described heretofore. The case reported here has clinical interest, therefore, in that the concurrence is uncommon. It also has physiologic interest, in that the defects of water excretion characteristic of the two syndromes are, in some respects, disparate. These renal dysfunctions were demonstrated in our patient and the effects thereon of adrenocortical (hydrocortisone) and posterior hypophyseal (vasopressin (Pitressin)) hormones were determined. The data make it seem unlikely that the adrenal hormone has a specific action on renal tubular reabsorption of water.

Study of the quantitative relationship between antidiuretic hormone and renal tubular reabsorption of water

Study of the quantitative relationship between antidiuretic hormone and renal tubular reabsorption of water

THE CONTROL OF THE RENAL EXCRETION OF WATER

1. The administration of the posterior pituitary antidiuretic hormone by constant intravenous infusion has been used to examine the two characteristic actions of the hormone; namely, the facilitation of the active renal tubular reabsorption of water distally in the nephron and the inhibition of the renal tubular reabsorption of sodium proximally. 2. Experimental evidence was obtained which indicates that variations in the excretion of water and electrolyte involve the integration of these two actions with obscure variables which are discemible in the experimental data but are not subject to definition at this time. 3. Graded antidiuresis in the animal with diabetes insipidus, when normally hydrated, was only obtained in the range of 0.001 to 0.005 unit (pressor) per hour. This range of hormone administration was also found to be physiologically active in the normal animals. These observations together with others permit the placing of the normal rate of liberation of the antidiuretic hormone in a10 to 15 kilo dog in the range of 0.001 to 0.005 unit per hour.