Effects of Felodipine on the dog kidney: a lithium clearance study.
Journal - Scandinavian journal of clinical and laboratory investigation (ENGLAND )
This study was performed in order to investigate the possible influence of sympathetic nerve activity on the effects of the dihydropyridine calcium antagonist felodipine on absolute and fractional reabsorption rates of sodium and water in proximal and distal tubular segments in the dog kidney. Clearance of 51Cr-EDTA was used as a measure of glomerular filtration rate (GFR). GFR, urinary excretion rates of sodium and water, and lithium clearance (C-Li) were used for assessing the absolute and fractional tubular reabsorption rates. Felodipine infusion into the right renal artery increased renal vascular conductance (renal blood flow divided by renal arteriovenous pressure gradient) significantly (by 9%) while GFR remained unchanged. Calculated absolute proximal reabsorption rates remained unchanged while distal sodium reabsorption rate increased significantly from 2.1 +/- 0.3 to 2.7 +/- 0.4 mmol min-1. Sodium clearance (C-Na) increased from 0.22 +/- 0.08 to 0.40 +/- 0.07 ml min-1. The alpha-adrenergic blockade with phentolamine did not affect renal haemodynamic or excretory variables, nor did it influence the haemodynamic response to felodipine. After alpha-adrenergic blockade felodipine caused an increase in C-Na from 0.28 +/- 0.06 ml min-1 to 0.63 +/- 0.04 ml min-1, which was significantly greater than that measured after felodipine alone. The distal load (C-Li) was not significantly different from that obtained after felodipine alone, but distal sodium reabsorption rate increased less significantly after alpha-adrenergic blockade. The results suggest that felodipine, by its effect on tubular flow and/or composition, activates local alpha-adrenergic reflex mechanism(s), which stimulates distal sodium reabsorption, thereby attenuating the natriuretic effect.
|ISSN : ||0036-5513|
|Mesh Heading : ||Absorption Animals Dogs Felodipine Female Glomerular Filtration Rate Kidney Kidney Tubules Kinetics Lithium Male Receptors, Adrenergic, alpha Renal Circulation Sodium blood supply drug effects metabolism drug effects physiology drug effects metabolism|
|Mesh Heading Relevant : ||pharmacology physiology metabolism|
Hemodynamic and functional changes during renal venous stasis in dog kidneys.
Journal - Danish medical bulletin (DENMARK )
The effect of renal venous pressure (RVP) elevation on renal hemodynamics and tubular function was studied in neurolept anaesthetized dogs. Renal blood flow (RBF) was measured electromagnetically. Clearance of 51Cr-EDTA was used as a measure of the rate of glomerular filtration (GFR). GFR, urinary excretion rates of sodium and water, and lithium clearance (CLi) were used for assessing the absolute and fractional reabsorption rates of sodium and water in the proximal as well as in more distal segments of the nephron. The vasoconstrictor response to RVP elevation was partly abolished by acute surgical denervation or by local application of lidocain on the renal capsule, suggesting that RVP elevation activates an adrenergic vasoconstrictor reflex comprising the spinal cord, and elicited from stretch receptors located in the renal capsule. Further studies in alpha-adrenoceptor blocked or chronic denervated kidneys and in decapsulated kidneys favour the view, that neurogenic and myogenic mechanisms significantly influence the vasoconstrictor response to RVP elevation: The neurogenic contribution to the vasoconstrictor response comprising intrarenal and extrarenal vasoconstrictor mechanisms evoked reflexly by RVP elevation; the myogenic contribution to the vasoconstrictor response comprising opposing vasodilator mechanisms due to increase in renal interstitial tissue pressure during RVP elevation. Studies carried out in intact kidneys, acutely surgically or chronically denervated kidneys or alpha-adrenoceptor blocked kidneys indicate that the increase in proximal reabsorption rates during moderate RVP elevation is due mainly to local intrarenal alpha-adrenergic reflex mechanisms, since the decrease in CLi (during constant filtered load) induced by RVP elevation was unaffected by acute surgical denervation, but completely abolished by chronic denervation of the kidney, or by local alpha-adrenoceptor blockade of the kidney.
|ISSN : ||0907-8916|
|Mesh Heading : ||Animals Denervation Diuresis Dogs Female Glomerular Filtration Rate Kidney Kidney Tubules Male Natriuresis Nerve Block Phentolamine Receptors, Angiotensin Renal Veins Venous Pressure physiology pharmacology drug effects drug effects|
|Mesh Heading Relevant : ||Renal Circulation innervation physiology physiology|
Effect of renal venous pressure elevation on tubular sodium and water reabsorption in the dog kidney.
Journal - Acta physiologica Scandinavica (ENGLAND )
This study was performed in order to quantify the effects of renal venous pressure (RVP) elevation on absolute and fractional reabsorption rates of sodium and water in proximal and distal segments of the nephron in dog kidneys. Renal blood flow (RBF) was measured electromagnetically. Clearance of [51Cr]EDTA was used as a measure of the rate of glomerular filtration (GFR). GFR, urinary excretion rates of sodium and water, and lithium clearance were used for assessing the absolute and fractional reabsorption rates of sodium and water in the proximal as well as in more distal segments of the nephron. In the kidneys with intact innervation RVP elevation to 19.9 +/- 0.1 mmHg caused significant increases in both absolute (APR) and fractional (FPR) proximal reabsorption rates from 33.4 +/- 4.2 to 38.7 +/- 2.0 ml min-1 and from 0.62 +/- 0.04 to 0.71 +/- 0.04, respectively. These responses were unaffected by acute surgical denervation of the kidneys. In contrast, chronic renal denervation or infusion of phentolamine (5 micrograms kg-1 min-1) into the renal artery eliminated the increase in APR and FPR during RVP elevation to 20 mmHg. Chronic, but not acute renal denervation depleted renal tissue content of adrenaline and noradrenaline. The results suggest that the increase in APR and FPR during RVP elevation is due mainly to local sympathetic reflex mechanisms.
|ISSN : ||0001-6772|
|Mesh Heading : ||Adrenergic alpha-Antagonists Amiloride Animals Body Water Denervation Dogs Epinephrine Glomerular Filtration Rate Kidney Kidney Tubules Lithium Mechanoreceptors Norepinephrine Sodium Venous Pressure pharmacology pharmacology metabolism drug effects metabolism physiology metabolism|
|Mesh Heading Relevant : ||metabolism physiology metabolism metabolism drug effects|
Intrarenal blood flow distribution in dog kidney determined by 99mTc microaggregates and 201Tl.
Journal - The American journal of physiology (UNITED STATES )
Intrarenal distribution of blood flow was assessed with radioactive albumin microaggregates (MA) in three cortical zones of the dog kidney. The experimentally obtained zonal fractions of total renal blood flow were compared with predicted zonal blood flow fractions obtained in a mathematical model. The maximal degree of skimming that could possibly occur in a single experiment was estimated. The analysis showed that local blood flow in the inner cortical zone was maximally underestimated by 17% because of skimming of MA, and in the outer cortical zone the blood flow was maximally overestimated by 13% with the method of radioactive MA uptake. Renal uptake of 201Tl was measured simultaneously in exactly the same locations. Paired measurements of intrarenal blood flow distribution by MA and Tl uptake methodologies showed that local blood flow assessed with MA in the inner cortical zone was significantly lower than that obtained with 201Tl and that a higher blood flow rate was obtained in the outer cortical zone with MA compared with 201Tl. This disparity could be accounted for by the effect of skimming of MA as predicted by the model.
|ISSN : ||0002-9513|
|Mesh Heading : ||Animals Blood Pressure Dogs Female Kidney Male Serum Albumin Technetium Thallium Radioisotopes anatomy & histology|
|Mesh Heading Relevant : ||Renal Circulation radionuclide imaging diagnostic use diagnostic use|