Nephrectomized Rabbits Research Articles

The influence of the progression of secondary hyperparathyroidism on the set point of the parathyroid hormone-calcium curve

The influence of secondary hyperparathyroidism (2 HPT) on the set point of the parathyroid hormone (PTH)-Ca(2+) curve is controversial. In vitro experiments have shown an increase in the set point. However, clinical studies with hemodialysis patients have provided a variety of results (increases, decreases and no changes in the set point have been reported). The present study was designed to investigate the influence of the progression of 2 HPT on the set point of the PTH-Ca(2+) curve. The PTH-Ca(2+) curve and the expression of parathyroid calcium receptor (CaR mRNA) and vitamin D receptor (VDR mRNA) have been studied in normal rabbits (group I, n=9) and in nephrectomized rabbits (group II, n=18) at two stages after inducing 2 HPT: 2-3 weeks (group IIA) and 5-6 weeks (group IIB). In group I, the set point of the PTH-Ca(2+) curve was 1.63+/-0.03 mM. A progressive hypocalcemia was detected during the evolution of 2 HPT (groups IIA and IIB). Rabbits from group IIA had a significant (P<0.001) decrease in the set point to values of 1.45+/-0.02 mM. However, the set point increased significantly in group IIB (P<0.001) to 1.56+/-0.03 mM. CaR mRNA was similarly decreased in groups IIA (39+/-12%) and IIB (48+/-7%). No changes were detected in VDR mRNA. In conclusion, a reduction in the set point of the PTH-Ca(2+) curve in response to decreased extracellular Ca(2+) was detected in the early phases of 2 HPT. However, with the progression of 2 HPT the set point tended to increase even though extracellular Ca(2+) was markedly decreased. The increase in the set point in the course of 2 HPT seems to be a complex process that cannot be fully explained by changes in parathyroid CaR mRNA or VDR mRNA.

Capillary leakage of a macromolecular MRI agent, carboxymethyldextran-Gd-DTPA, in the liver: pharmacokinetics and imaging implications.

Capillary leakage of a macromolecular contrast agent, Carboxymethyl Dextran-Gd-DTPA (CMD-Gd-DTPA) was characterized in a highly permeable system, the liver, to assess its potential as a blood pool marker. Its elimination kinetics in hepatic lymph were compared in nephrectomized rabbits with that of a tracer of extra cellular fluid space, Gd-DOTA. Four parameters were defined: volume of distribution, normalized initial leakage rate (ILRn), maximum ratio of lymph and plasma concentrations (max Cl/Cp), and the time to obtain this maximum ratio. The effect of this leakage was studied on MR images by comparing liver contrast enhancement after injection and after almost total removal of the contrast agent from the blood by exchange transfusion. Capillary leakage of CMD-Gd-DTPA was detected in lymph. Compared to Gd-DOTA, it was slower (ILRn = 0.36 10(-5) l min-1 for CMD-Gd-DTPA and ILRn = 2.6 10(-5) l min-1 for Gd-DOTA), less abundant (max Cl/Cp was 80% for CMD-Gd-DTPA and 100% for Gd-DOTA). Liver enhancement remained stable, which indicated that the leakage did not modify the enhancement induced by the intravascular fraction of the contrast agent. These results obtained in a highly permeable capillary model indicate that this agent can be used as a selective blood pool enhancer.

Doxorubicin treatment of rabbit renal VX-2 carcinoma: nephrotoxicity, serum parameters and weight.

Serum electrolytes, creatinine, urea, protein, albumin, bilirubin and glucose were examined every 4 days until time of death in rabbits with VX-2 carcinoma implanted in one kidney. The rabbits were treated with doxorubicin, nephrectomy or combinations thereof and observed for up to 1 year. Rabbits treated with doxorubicin only showed a slight creatinine rise initially, but over time creatinine reached almost the same concentration as that in nephrectomized rabbits receiving equivalent doses of doxorubicin. Creatinine concentrations increased significantly above the normal range following nephrectomy combined with doxorubicin. Doxorubicin nephrotoxicity in rabbits occurs at lower doses than previously reported. In all rabbits the parameters except creatinine remained stable within the established normal ranges, except for the last 4 days before time of death in the animals with metastatic disease. Weight loss was the best parameter for making a prognosis for an individual rabbit, since peak weight was noted 16-20 days before death. In experimental work with VX-2 carcinoma, weight is thus the most important indicator of the time at which rabbits not responding to treatment can be put to death to avoid unnecessary suffering before the end of the experiment.

Beta-adrenergic-induced local angiotensin generation in the rabbit hind limb is dependent on the kidney.

Evidence was sought for beta-adrenergic-induced increase in femoral vascular angiotensin production in sham-operated and nephrectomized rabbits. Systemic blood pressure and right femoral blood flow were monitored in anesthetized rabbits. Arterial and femoral venous plasma angiotensin II (Ang II) and angiotensin I (Ang I) were measured by radioimmunoassay after high-performance liquid chromatography. Isoproterenol, 1 and 10 nmol/min, was infused intrafemoral arterially, reducing femoral vascular resistance by 47 +/- 5% and 60 +/- 6% in the sham-operated group, and by 50 +/- 6% and 63 +/- 4% in the nephrectomized group, respectively. The hemodynamic effect of isoproterenol was blocked by 2 mumol/kg propranolol injected intravenously plus 0.2 mumol/min infused intrafemoral arterially, indicating that the effect was beta-adrenergically mediated. In the sham-operated group, arterial Ang II and Ang I levels were increased, respectively, by 85 +/- 16% and 103 +/- 23% with the low dose of isoproterenol, and by 121 +/- 13% and 563 +/- 126% with the high dose of isoproterenol. The apparent femoral Ang II secretion rate was increased by 3.2-fold and 4.4-fold, and the apparent femoral Ang I secretion rate increased by 4.3-fold and 21.2-fold, with the low and high dose of isoproterenol, respectively. Propranolol abolished or markedly attenuated the increased arterial angiotensin levels and the increased femoral angiotensin secretion rates. Neither the low nor the high dose of isoproterenol caused any increase in plasma levels or the apparent femoral secretion rates of the angiotensins in the nephrectomized group. Low plasma levels of Ang I and Ang II remained in the nephrectomized group, representing some locally generated angiotensins.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertrophy of renal mitochondria.

Compensatory renal hypertrophy leads to an increase in the size and metabolic capacity of renal tubular cells. Increased transport and metabolic activities must be sustained by an augmented rate of energy production, which is largely dependent on mitochondrial processes. Although previous studies have suggested that mitochondria proliferate in the hypertrophying cell, the data to support this have not been convincing. This study was designed to determine whether the mitochondria of the hypertrophied renal proximal tubular cell undergo hypertrophy or proliferation. Flow cytometric analysis of proximal tubular cells obtained from the kidneys of uninephrectomized rabbits revealed an increase in cell size and RNA content compared with control cells but showed no change in DNA content and nuclear size and no evidence of entry into the S/G2/M phases of the cell cycle. Histomorphometric analysis of cortical proximal tubules revealed that although cytoplasmic volume increased, mitochondrial density remained constant, indicating that mitochondrial volume increases in proportion to the increase in cell volume. By day 14, mitochondrial volume had increased 66% above control values. Electron microscopic examination of isolated S2 proximal tubules from 5/6 nephrectomized rabbits with maximal hypertrophy revealed mitochondrial cristae which appeared to be more densely packed than that in normal cells. The size of the functional mitochondrial pool per cell was determined by rhodamine-123 fluorescence. This increased within 24 h of uninephrectomy, peaked at approximately 80% above control levels at 5 days, and remained elevated throughout the 16 days of observation. The initial increase (days 1 and 2) occurred before a measurable increase in mitochondrial volume occurred and presumably reflects an increase in mitochondrial membrane potential.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo comparison of renal and femoral vascular sensitivity and local angiotensin generation.

Experiments were conducted to compare the relative importance of the local renin-angiotensin systems in the rabbit renal and femoral vascular beds and their functional role in hemodynamic regulation. Angiotensin I (Ang I) (0.15 microgram/kg i.v.) elevated mean arterial blood pressure by 18 +/- 1 mm Hg in the renal experimental group and 19 +/- 1 mm Hg in the femoral experimental group; it decreased renal blood flow by 35 +/- 3% but increased femoral blood flow by 31 +/- 8%. All these effects were blocked by intravenous administration of captopril (2 mg/kg bolus injection plus 1 mg/kg/hr). Captopril also lowered mean arterial pressure by 17 +/- 3 and 16 +/- 2 mm Hg in the renal and femoral experimental groups, respectively, and it increased renal blood flow by 32 +/- 10% but reduced femoral blood flow by 21 +/- 4%. As a result, renal vascular resistance was decreased by 36 +/- 5%, but femoral vascular resistance remained unchanged. After captopril, plasma angiotensin II (Ang II) levels were decreased and Ang I levels increased in the two groups. The renal venous-arterial difference of Ang I was increased by captopril, but the femoral venous-arterial difference of Ang I was not, suggesting greater generation of Ang I in the kidney. In a separate group of bilateral nephrectomized rabbits, plasma Ang II levels as well as mean arterial pressure, femoral blood flow, and femoral vascular resistance were not changed by intravenous administration of captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic responses to atrial natriuretic factor in nephrectomized rabbits: attenuation of the circulatory consequences of acute volume expansion.

We investigated the hemodynamic responses to three doses of atrial natriuretic factor [human atrial natriuretic factor-(99-126)] (ANF) in nephrectomized rabbits anesthetized with ketamine and acepromazine. The influence of the different doses of the peptide on the hemodynamic consequences produced by acute volume expansion (0.9% NaCl, 1.4 ml/kg/min for 60 minutes) was also studied. All three dosages of ANF (0.001, 0.01, and 0.2 micrograms/kg/min for 20 minutes) significantly reduced blood pressure. With the lowest dose, the hypotensive effect was associated with reduction in systemic vascular resistance and no significant change in heart rate, stroke volume, central venous pressure, and hematocrit. In contrast, the intermediate and high doses, which resulted in markedly higher plasma levels, caused a significant decrease in heart rate, central venous pressure, and stroke volume; a slight rise in hematocrit; and no change in systemic vascular resistance. Volume expansion produced by saline infusion in an additional group of nephrectomized rabbits increased central venous pressure and decreased hematocrit. When ANF infusion was associated to volume expansion, each dosage of ANF was able to reduce the rise in central venous pressure, while only the higher dosage attenuated the progressive fall in hematocrit caused by volume expansion. Plasma volume, measured at the end of volume expansion was lower in the group treated with the highest dose of ANF than in the control animals (28.2 +/- 9 vs. 35.1 +/- 3 ml/kg, p less than 0.05). We conclude that 1) ANF induces significant hemodynamic effects independently from its renal action.(ABSTRACT TRUNCATED AT 250 WORDS)

The Role of the Capillary Wall in Restricting Diffusion of Macromolecules

In 5 nephrectomized rabbits the peritoneal clearance of neutral dextrans from plasma to dialysate decreased from 7.8 to 3.3 microliters/kg/min as molecular mass increased from 17,000 to 43,000 daltons, and was relatively constant at 2.8 microliters/kg/min from 49,000 to 97,000 daltons in accord with prior studies. The clearance from dialysate to plasma was measured by determining the distribution volume, which averaged 72 ml/kg, and the plasma concentration 5 h after intraperitoneal instillation. Inward clearances ranged from 11.4 to 19.9 microliter/kg/min, did not correlate well with solute size and were significantly higher than outward clearances. The data suggest that while the capillary wall is the major barrier to macromolecule transfer, absorption can bypass vascular capillaries and occur via the lymphatics. It is suggested that lymphatic flow rate from the peritoneum exceeds 16 microliter/kg/min.

Disappearance of circulating anti-Xa activity after intravenous injection of standard heparin and of a low molecular weight heparin (CY 216) in normal and nephrectomized rabbits

Disappearance of circulating anti-Xa activity after intravenous injection of standard heparin and of a low molecular weight heparin (CY 216) in normal and nephrectomized rabbits

Steady flow visualization in a rigid canine aortic cast

Steady flow studies were conducted in a transparent canine aortic cast. The cast segment stretched from the aortic valve to beyond the renal arteries and included all major branches. Flow was visualized by analysis of dye streaklines. Flow rates for basal and exercising cardiovascular states were simulated. The Reynolds numbers in the ascending aorta for basal and exercising conditions were 900 and 1587 respectively. Aortic core flow was laminar in basal simulations. Disturbed flow commenced in the upper descending aorta with exercising flow rates. Separation zones existed along the inner curvature of the aortic arch and the proximal walls of the brachiocephalic, left subclavian, and coeliac arteries. Such zones may exist over a portion of the cardiac cycle. If either renal artery was occluded, then a vortex formed. This vortex is associated with high shear regions which correlate well with sites where sudanophilic lesions have been reported in cholesterol-fed nephrectomized rabbits.

Degradation of 125I-labelled prolactin in the rabbit: effect of nephrectomy and prolactin infusion.

Hyperprolactinaemia in patients with chronic renal disease undergoing dialysis has prompted the investigation of the relative roles of liver and kidney in the degradation of prolactin. Male rabbits were acutely nephrectomized, and compared with intact animals with or without prolactin infusion. Prolactin degradation was followed after intravenous injection of 125I-labelled ovine prolactin. Measurements were made of peptide-bound 125I and 125I-labelled degradation products in plasma, liver, kidney, bile, urine and muscle and total thyroid radioactivity. A significant (P less than 0.01) reduction in the metabolic clearance rate of 125I-labelled prolactin was observed due to nephrectomy, with double the accumulation of 125I-labelled peptides in the livers in this group. Prolactin infusion of nephrectomized animals had a further and larger effect than nephrectomy alone on prolactin degradation. Metabolic clearance rate significantly (P less than 0.01) decreased from 5.5 ml/min per kg in nephrectomized rabbits to 0.8 ml/min per kg with prolactin infusion. The accumulation of 125I-labelled prolactin degradation products in the blood was significantly (P less than 0.01) lower in this group of animals and the amount of peptide-bound 125I in plasma at 60 min after 125I-labelled prolactin administration was significantly (P less than 0.01) higher. Liver degradation of prolactin in the absence of exogenous hormone appears to be sufficient to maintain an approximately normal half-life for prolactin in plasma (intact t 1/2 = 6.8 min; nephrectomized t 1/2 = 8.5 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of human fibrinopeptide A in normal and nephrectomized rabbits

The distribution, elimination, and metabolism of human fibrinopeptide A (FPA) were studied in normal and nephrectomized rabbits. The activity of 125-I-labeled desamino-tyrosyl human FPA (DAT-FPA) was followed over 4 hours after i.v. administration. Results show that in normal rabbits (n=10) DAT-FPA is eliminated from plasma in four phases with half-lives of 30 sec, 3.5 min, 15 min, and 90 min. The distribution of 123-I-labeled DAT-FPA in plasma was determined in 15 control rabbits with scintigraphy over 2 hours. DAT-FPA was distributed primarily in the cardiovascular system, liver, and kidneys. In some animals minimal radioactivity was detected over the gall bladder. Radioactivity accumulated rapidly in the urinary baldder, approximately 50% being recorded after 15 min and 90% after 120 min. In the heart area radioactivity decreased with half-lives of 25 sec, 7.5 min, 25 min, and 180 min. Nephrectomized rabbits had similar initial fast distribution of DAT-FPA after administration of 125-I-labeled (n=10) and 123-I-labeled peptide (n=10). The estimated half-life of the slow component was in the order of several hours. The results of the scintigraphic and gel chromatographic studies show that FPA is primarily excreted in the urine. Previously reported half-lives of FPA reflect distribution rather than steady state conditions.

The Ototoxicity of the Aminoglycoside Antibiotics in Nephrectomized Rabbits

The Ototoxicity of the Aminoglycoside Antibiotics in Nephrectomized Rabbits

Red blood cell deformability in renal failure.

Red blood cell deformability was measured in 74 cases of renal failure and diabetic nephropathy by means of a modified nuclepore membrane filter method. Low red blood cell deformability was observed in a certain proportion of the patients. In cases of renal failure only weak correlation was found between reduced red blood cell deformability and BUN as well as between reduced red blood cell deformability and creatinine level, while simultaneous changes in these variable were observed in several patients. The reduction in red blood cell deformability in cases of diabetic nephropathy slightly exceeded that in cases of renal failure and correlated with an increment in HbA1c content. The effects of uremic toxins were unclear in in vitro tests. The red blood cell deformability was impaired in nephrectomized rabbits.

Tissue distribution of ampicillin: assays in muscle tissue and subcutaneous tissue cage fluid from normal and nephrectomized rabbits.

Tissue distribution of ampicillin following a single intravenous injection was studied in normal and functionally nephrectomized rabbits. Serum concentrations of ampicillin were compared with those obtained in subcutaneous tissue cage fluid, muscle (measured by a direct agar diffusion method) and muscle tissue fluid (obtained from implanted cotton threads). Considerable differences were found. Penetration of ampicillin into rabbit muscle was rapid and the elimination half-life was similar to that of serum. Concentrations in tissue cage fluid were low as compared with muscle tissue fluid levels, and penetration and elimination was slower. Results from experiments in functionally nephrectomized rabbits showed that a steady state between serum and muscle seemed to be attained after 15-30 min. These results were used to estimate the degree of protein binding of ampicillin in muscle tissue fluid.

Flow studies in a rigid model of an aorto-renal junction A case for high shear as a cause of the localization of sudanophilic lesions in rabbits

Flow studies were made in a rigid model of an aorto-renal junction in an attempt to explain two observations made in our laboratory in cholesterol-fed rabbits. First, the area of the lesion was proportional to the area of the orifice it surrounded, and hence probably to the flow into the branch. Second, lesions developed proximal as well as distal to blind stumps of a renal artery in nephrectomized rabbits. The branch had a sharp entrance, and came off at 90°. The area ratio of the branch and distal aorta to the proximal aorta was 1.27 and steady flow at Reynolds numbers of 570–1070 was studied both with dye injections and with a hot-film anaemometer. The flow ratio was varied from 0.16 to 0.58. Secondary motions were observed in the main channel and in the side branch at all flow rates. Boundary layer separation occurred on the outer wall of the main branch and on the proximal wall of the side branch. The thickness of the boundary layer separation in the main branch depended on the flow rate ratio. Downstream from the junction the velocity profiles were highly asymmetric in both the renal artery and the distal aorta. In the plane of the junction, peak velocities were skewed towards the inner wall. The velocity profiles perpendicular to the plane of the junction were less disturbed. The calculated shear stress on the inner wall of the main branch within one diameter of the junction was much higher than that calculated for the corresponding Poiseuille flow. The magnitude of the shear stress, and its extension downstream from the junction increased as the flow into the branch increased. This correlated with previous observation by Cornhill and Roach [1] in the cholesterol-fed rabbit, that atherosclerotic lesions develip in regions of high shear If the branch was occluded, no vortex formed in it, and streamlines in the trunk were not affected. This is opposite to the observations of Malcolm and Roach [2] in glass models with a rounded junctional zone where a vortex formed at the entrance when the branch was occluded. Since blind stumps develop proximal as well as distal lesions in the cholesterol-fed rabbit [3], the entrance geometry is probably very critical.

Effect of angiotensin-converting enzyme inhibition by captopril on cardiac output, coronary blood flow, and systemic arterial blood pressure in the intact and in the bilaterally nephrectomized rabbit.

The purpose of this study was to investigate the hemodynamic responses, mainly cardiac output and regional blood flow, to converting enzyme inhibition by captopril in the intact and nephrectomized rabbit. Twenty-one New Zealand white rabbits anesthetized with pentobarbital has systemic arterial blood pressures measured and cardiac output and regional blood flow determined by the microsphere method. Captopril (1--3 mg/kg) significantly reduced cardiac output in the intact but not in nephrectomized rabbits. In both the intact and nephrectomized animals, captopril was associated with small but not significant decreases in blood pressure and no significant change in total peripheral vascular resistance or heart rate. Regional blood flow was reduced, but the fractional distribution of cardiac output to the myocardial, lung (bronchial), hepatic, and splanchnic (small intestine) circulations was unchanged after captopril. These data suggest that the reduction in cardiac output induced by converting enzyme inhibition may be attributed to a fall in venous return that in turn may be dependent on renal factors.

Pressor effect of tonin in anephric animals.

Tonin was injected intravenously to normal rats without effect on blood pressure. Twenty-four hours after bilateral nephrectomy, tonin produced a dose-dependent pressor effect in rats which was abolished by the angiotensin antagonist [Sar1-Ala8]-angiotensin II. Vascular response to angiotensin II was slightly increased after nephrectomy. Plasma angiotensin II increased significantly after injection of tonin and disappeared biexponentially with a half-life of less than 1 min for the fast component and 9 min for the slow component. The change in plasma angiotensin II correlated with the elevation in mean blood pressure. No difference in inhibitory power of plasma on tonin activity could be shown between intact and nephrectomized rats. In vitro, the initial velocity of generation of angiotensin II by tonin acting on plasma increased after addition of semipurified rat renin substrate and was significantly greater in plasma of nephrectomized rats. In nephrectomized rabbits, but not in intact ones, a dose-dependent pressor effect was produced by tonin. These data demonstrate the in vivo production of angiotensin II by tonin in an animal model with elevated substrate levels. Together with the in vitro data, these results suggest a role for substrate concentration in the expression of tonin enzymatic activity in vivo.

Uterine and renal renin release after ligation of the uterine arteries in the pregnant rabbit

Uteroplacental ischemia is associated with uterine renin release in pregnant nephrectomized rabbits. In the present study, uterine and renal renin release after uteroplacental ischemia were investigated in 10 Australian white rabbits at 24 to 28 days' gestation. Pentobarbital was administered, and both uterine arteries were ligated close to their origins. Blood samples were taken for plasma renin activity (PRA) determinations from the femoral artery, uterine vein, and right renal vein before ligation and at 30 and 60 minutes after ligation. Mean arterial blood pressure (MAP) was monitored throughout. In five additional pregnant rabbits renal blood flow (RBF) was measured with an electromagnetic flowmeter. The preligation uterine vein-artery PRA difference was not significant (1.9 ± 1.1 ng/ml/hr). Postligation uterine vein-artery PRA was 11.4 ± 3.2 at 30 minutes and 6.6 ± 1.9 ng/ml/hr at 90 minutes (p < 0.02). Preligation renal vein-artery PRA was 32.3 ± 10.5 ng/ml/hr (p < 0.02) and did not change significantly after ligation. MAP remained stable and RBF was unchanged after uterine artery ligation. These observations confirm the finding that the kidney is the primary source of renin in the normal pregnant rabbit and demonstrate that following acute uteroplacental ischemia there is significant uterine renin release even when the kidneys are intact.

The 125I-Hippuran renogram in rabbit kidneys after graded warm ischaemia.

125I-Hippuran renography was performed after temporary renal arterial clamping in contralateral nephrectomized rabbits. Mean renograms for the experimenttal groups were calculated for 0, 1, 1 1/2, 2, 2 1/2 and 3 h of warm ischaemia. The appearance phase, the 1 min uptake phase and excretion ratio were evaluated. The kidney function was monitored by serum-creatinine. Warm ischaemia of 1, 1 1/2 and 2 h resulted in a late maximum peak and delayed excretion, and for the last group in an accumulation curve. The uptake capacity was normal for these groups. Protracted ischaemia of 2 1/2 and 3 h affected also the appearance and uptake phase resulting in a slower and decreased Hippuran uptake of 50% and 34% respectively. Duration of warm ischaemia and changes in the renogram were well correlated. A normal uptake phase predicts restitution of the kidney function and 100% survival.