Renal excretion of inulin, creatinine and ferrocyanide, at normal and reduced clearance levels in the dog

Unilateral renal ischaemia in rats induces a rapid secretion of inflammatory markers to renal lymph and increased capillary permeability

A better understanding of the inflammatory process associated with renal ischaemia-reperfusion (IR) injury may be clinically important. In this study we examined the role of the kidney in production of inflammatory mediators by analysing renal lymph after 30 min unilateral occlusion of renal artery followed by 120 min reperfusion, as well as the effect of IR on size selectivity for proteins in both glomerular and peritubular capillaries. All measured mediators increased dramatically in renal hilar lymph, plasma and renal cortical tissue samples and returned to control levels after 120 min reperfusion. The responses were differentiated; interleukin-1β, monocyte chemoattractant protein-1 and leptin were markedly increased in plasma before reperfusion, reflecting an extrarenal response possibly induced by afferent renal nerve activity from the ischaemic kidney. Tumour necrosis factor-α was the only mediator showing elevated lymph-to-plasma ratio following 30 min reperfusion, indicating that most cytokines were released directly into the bloodstream. The IR-induced rise in cytokine levels was paralleled by a significant increase in high molecular weight plasma proteins in both lymph and urine. The latter was shown as a 14- to 166-fold increase in glomerular sieving coefficient of plasma proteins assessed by a novel proteomic approach, and indicated a temporarily reduced size selectivity of both glomerular and peritubular capillaries. Collectively, our data suggest that cytokines from the ischaemic kidney explain most of the rise in plasma concentration, and that the locally produced substances enter the systemic circulation through transport directly to plasma and not via the interstitium to lymph.

Pharmacokinetic aspects of measurement of glomerular filtration rate in the dog: a review

Glomerular filtration rate (GFR) is estimated by means of clearance, defined as the volume of plasma that has been cleared of a particular substance per unit time. Glomerular filtration rate may be estimated by measuring the renal clearance of a filtration marker using data from both urine and plasma or by plasma clearance using only plasma data. Several alternative pharmacokinetic models are used for the calculation of clearance using various filtration markers with slightly different pharmacokinetic properties. The purpose of this article is to discuss how the choice of marker and pharmacokinetic model may influence estimated GFR values and to elucidate commonly used methods and reported GFR values in the dog.

Renal function in conscious dogs: potential effect of gender on measurement

Conscious dogs were studied to determine the repeatability of and the agreement between conventional inulin clearance (CIn), a urineless or alternative inulin clearance (CInALT), and endogenous creatinine clearance (CCr). Although, the repeatability of the three clearance methods was satisfactory, tests of agreement within gender indicated that CInALT and CCr were not interchangeable numerically with CIn in either males or females. CInALT was significantly higher than CIn in females, and CIn was significantly higher than CCr in both genders. Between genders, there were no significant differences in individual clearance methods, plasma creatinine (PCr), or electrolytes and osmolality. However, urinary osmolality, U/P inulin and U/P creatinine were significantly higher in males. Over the normal range of clearances studied it was not possible to substitute one clearance method for the other regardless of gender. However, the enhanced repeatability of CIn and CInALT in the females suggests that their use in experimental renal studies may be more desirable than males.

Pharmacokinetics in the rat and the dog of a nonionic nitroxide contrast agent for magnetic resonance imaging

Nitroxides are paramagnetic stable free radicals that have demonstrated effectiveness as contrast agents in proton magnetic resonance imaging (MRI). The pharmacokinetics and metabolic fate, determinants of the time course of MRI contrast enhancement, of a new nonionic pyrrolidine nitroxide derivative, TAP (2,2,5,5-tetramethylpyrrolidine-1-oxyl-3-carbonic acid-(2,3-dihydroxy-1-hydroxymethyl)-amide), were evaluated in the rat and the dog. A biexponential decline of the blood concentration of TAP was observed in both species after intravenous administration of 0.1- and 2.5-mmol/kg doses. The clearances in the rat, estimated after the low and high doses (15.4 +/- 2.0 and 15.3 +/- 1.4 mL/min.kg, respectively), were about twofold higher than those observed in two beagles (7.4 and 7.1 mL/min.kg for Dog #1 and 6.3 and 6.0 mL/min.kg for Dog #2). The hydroxylamine of TAP, formed by a one-electron reduction of the nitroxide moiety, was the only metabolite observed. This bioreduction of TAP has implications for its use as a MRI contrast agent because the diamagnetic hydroxylamine lacks contrast enhancing activity. In both animal species, the urinary recoveries of the dose as unchanged TAP and its hydroxylamine were essentially complete for the 24-h urine collections (92 to 98% and 83 to 95% for the rats and the dogs, respectively). Anticipated conjugative metabolism of the hydroxyl-containing side chain of TAP was not observed. Renal excretion of unchanged TAP was the predominant route of elimination, as renal clearance was estimated to be between 47 and 89% of total clearance in the dogs. Bioreduction in vivo was slower than that expected from the observed reduction of TAP in vitro in ascorbic acid solution and in rat liver and kidney homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of the oxime HI6 in dogs

The pharmacokinetics and pharmacodynamics of the oxime HI6 were investigated in conscious and anesthetized beagle dogs following intramuscular injection. The absorption of HI6 (100 mumol/kg) was slower in conscious dogs as compared to the anesthetized dogs, and the maximum concentrations in plasma were lower (200 instead of 300 mumol/l). In comparison, the elimination of HI6 (100 mumol/kg) was twice as rapid in the conscious dogs (ke = 0.013 instead of 0.006 min-1) as in the anesthetized animals and was equal to the elimination after injection of 50 mumol/kg (likewise in anesthesia). The more rapid elimination was accompanied by a greater renal excretion of unchanged HI6 (60% instead of 40% in 3 h). HI6 penetrated the blood-brain barrier. The concentration of the oxime in CSF increased rapidly during the absorption phase (by 30 min after injection). The maximum concentrations (1-3 mumol/l) were reached between 60 and 120 min. The peak concentrations in plasma and CSF did not correlate with each other. In the anesthetized dogs the higher dose of HI6 (100 mumol/kg) caused a steady decrease in mean blood pressure (20 mm Hg) and blood flow (50%) in the femoral artery and a fall in left ventricular pressure (20 mm Hg), lasting for at least 60 min; the lower dose (50 mumol/kg) did not cause circulatory effects. EKG, respiration, hematocrit, arterial blood gases, and pH were not influenced.

Estimation of glomerular filtration rate in conscious dogs following a bolus of creatinine. Comparison with simultaneously determined inulin clearance

The renal clearance of creatinine was measured following orogastric administration in conscious dogs. Values of creatinine clearance were compared with simultaneously determined values of inulin clearance, when urine volume, glomerular filtration rate and volume status were acutely altered by a variety of experimental manoeuvres. At urine volumes greater than 20 microliters X min-1 X kg-1, creatinine clearance was not significantly different from inulin clearance. At low urine volumes there was some evidence of creatinine reabsorption. It is concluded that the bolus creatinine technique provides reliable estimates of glomerular filtration rate and is particularly applicable to long-term studies in conscious dogs.

Influence of indomethacin on cation excretion after acute unilateral nephrectomy in dogs

Acute unilateral nephrectomy (AUN) causes functional changes in the remaining kidney. Since renal prostaglandins (PGs) may participate in this response, we investigated the effect of the PG synthetase inhibitor, indomethacin (INDO), on the function of the remaining kidney after AUN. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), filtration fraction (FF), sodium excretion, and potassium excretion were measured for 1 hr prior to and 3 hr after AUN in dogs anesthetized with sodium pentobarbital. Group I and II animals underwent AUN. A third group was sham-operated (Group III). Group I received INDO (2 mg/kg) before and 2 hr after AUN, while Groups II and III received a buffered saline vehicle. AUN alone (Group II) had no effect on GFR, ERPF, FF, or sodium excretion, while potassium excretion was increased. In animals administered INDO prior to AUN (Group I), the increase in potassium excretion was abolished, FF rose and sodium excretion, while potassium excretion was increased. In animals administered INDO prior to AUN (Group I), the increase in potassium excretion was abolished, FF rose and sodifore and 2 hr after AUN, while Groups II and III received a buffered saline vehicle. AUN alone (Group II) had no effect on GFR, ERPF, FF, or sodium excretion, while potassium excretion was increased. In animals administered INDO prior to AUN (Group I), the increase in potassium excretion was abolished, FF rose and sodium excretion was decreased. Results suggest that renal PGs participate in the compensatory response of the remaining kidney to AUN and may specifically play a role in increased cation excretion following AUN.

Clinical assessment of renal function in the dog with a reduction in nephron number

The viewpoint presented is that, because compensatory functional adjustment of the residual nephrons occurs in chronic renal disease, reduction in nephron number usually exceeds 70% before a diagnosis is made. The case that earlier diagnoses are likely if laboratory medicine values are measured and interpreted with a maximum of efficiency is then made. The laboratory data more commonly used in practice for the clinical assessment of renal function in the dog are presented and some comparisons with findings in man are made. The information originates from clinical and experimental observations of the authors, as well as from a literature review. The laboratory data presented and discussed includes glomerular filtration rate and the clearance of nitrogenous waste (urea and creatinine), plasma protein concentration, plasma osmolality, renal concentrating capacity, and urinary constituents, particularly its protein concentration and sediment (centrifuge deposit). All parameters recommended for the clinical assessment of chronic renal failure are considered qualitatively, and some are also dealt with quantitatively.

SEPARATE RENAL FUNCTION STUDIES IN DOGS WITH CHRONIC UNILATERAL RENAL ARTERY OBSTRUCTION: THE EFFECT OF HYPERTONIC UREA INFUSIONS

The left main renal artery was constricted in 41 dogs for intervals of 7 to 30 days. Separate urine collections from each kidney were then made during water diuresis and, in 28 of the dogs, during hypertonic urea diuresis.The most sensitive criteria of renal artery obstruction were combinations of urine volume and creatinine concentration ratios or of sodium and creatinine concentration ratios.To demonstrate enhanced water reabsorption by the tubules of a kidney, there is no diagnostic advantage in the use of any one over another of the ratios of urine creatinine, urea, or para-amino hippurate.The filtration fraction of the constricted kidney was the same as that of the control. Thus the simpler measurement of each kidney's endogenous creatinine clearance offers the same assessment of relative kidney function as the technically more difficult measurement of separate para-amino hippurate clearances.When, under water diuresis, the urine concentration ratios of sodium and creatinine, as well as the urine volume ratio, are diagnostic, then urea infusions tend to blunt them. Conversely, when these ratios are not diagnostic, urea infusions tend to enhance them. Thus, for the greatest efficiency in the diagnosis of renal artery obstruction, separate urine collections should be made under conditions of both water and hypertonic urea diuresis.