Interferon-gamma receptor signaling is not required in the effector phase of the alloimmune response.

BACKGROUND: Gene transcripts for the Thl cytokines interleukin (IL)-2 and interferon-gamma (IFN-gamma) are frequently detected during allograft rejection. The relative importance of these cytokines in facilitating allograft rejection is unclear. Recently, we have shown that IL-2-deficient mice reject islet allografts. In the IL-2-deficient system, IFN-gamma gene transcripts are abundantly expressed. METHODS: To determine the relative importance of IFN-gamma-dependent effector mechanisms in mediating allograft rejection, the present study utilized IFN-gamma receptor-deficient mice as islet allograft recipients. Grafts were analyzed by immunohistology, and cytokine expression was measured by competitive template reverse transcriptase polymerase chain reaction. RESULTS: IFN-gamma receptor-deficient mice reject islet allografts by a process that is T cell-dependent. Although IFN-gamma receptor signaling is absent, these mice do not show a clear Th2 type response. CONCLUSION: Although the signals evoked through the IFN-gamma receptor may play a role, they are not essential to allograft rejection.

Pressure dependent modulation of renin release in isolated perfused glomeruli.

The isolated perfused glomerulus technique was used to study pressure dependence of renin release in single, microdissected rabbit glomeruli with intact afferent arteriole and intact Bowman's capsule. Renin release from individual afferent-glomerular units was measured in 30 minute intervals while afferent arteriolar pressure was either decreased from 55 to 40 to 25 mm Hg or increased from 25 to 40 to 55 mm Hg. There was a clear, inverse relation of renin release and afferent pressure. Mean renin release rate was 3.2 times higher at 25 than at 55 mm Hg and 1.5 times higher at 40 than at 55 mm Hg. To evaluate the possible role of wall stretch in mediating this response, inner and outer afferent arteriolar diameters were measured by videomicroscopy. Outer afferent diameter remained constant between 25 and 55 mm Hg, whereas inner diameter exhibited a slight increase. Changes of afferent arteriolar wall stretch, however, did not correlate with changes of renin release. These data for the first time directly demonstrate the existence of a renin baroceptor at the level of the renal afferent arteriole. They furthermore suggest that this baroceptor is not a stretch receptor.

Control of hypertension by verapamil enhances renal damage in a rat remnant kidney model.

The effect of calcium channel blockers on the progression of renal failure is controversial. In contrast with earlier studies, we recently reported that moderately large doses of verapamil significantly accelerated chronic renal failure in the rat remnant kidney model. Studies reporting beneficial effects of verapamil were characterised by a much lower dose of verapamil and by the start of treatment immediately after renal ablation, which potentially interfered with the initial phase of remnant kidney hypertrophy. We therefore studied the effects of a high, fully antihypertensive oral dose of verapamil (100-150 mg/kg/per day; group Vera high) and a low, haemodynamically almost ineffective dose (10-15 mg/kg per day; group Vera low), on the progression of chronic renal failure in female Wistar rats with 5/6 nephrectomy. The treatment was started no earlier than 5 weeks after renal ablation, and matched groups of 20 animals were followed for 16 weeks thereafter. High-dose verapamil reduced systolic blood pressure to median values of 130-140 mmHg throughout the experimental period, whereas blood pressure in Vera low animals remained elevated at median values of 165-172 mmHg similar to non-treated rats with 172-185 mmHg median systolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of renin secretion in single perfused rabbit glomeruli.

A new technique is presented that allows the measurement of the renin secretion rate of single rabbit glomeruli during in vitro perfusion at controlled afferent arteriolar perfusion pressure. Rabbit glomeruli with intact afferent arteriole and Bowman's capsule are obtained by microdissection and cannulated with a pipette system that allows continuous afferent arteriolar pressure measurement. The renin secretion rate of 10 glomeruli, perfused at 40 mmHg, was measured in 15-min intervals with an antibody-trapping microassay. Renin secretion rate was low relative to total renin content (1.2-2.0% of content/perfusion h) and increased three- to fivefold in response to isoproterenol (10(-5) M). The afferent arteriole contracted to norepinephrine (10(-5) M) in each instance. This novel, although difficult, technique allows the study of renin release in vitro at controlled perfusion pressure, without the interfering effects of the macula densa, arterial angiotensin II, and the adrenergic nervous system. It should allow a new perspective on issues such as the pressure-flow dependence of renin release and the interaction of the afferent arteriolar endothelium with the renin-secreting juxtaglomerular cells.

Long-term enalapril and verapamil in rats with reduced renal mass.

The effect of long-term treatment with either enalapril or high dose verapamil on survival, proteinuria, blood pressure and renal morphology was studied in female Wistar rats with markedly reduced renal mass. Four weeks were allowed for remnant kidney hypertrophy before determining the response to renal ablation of individual animals regarding proteinuria and hypertension. At this time, five groups of 18 rats were formed with equal levels of proteinuria and hypertension. Groups E1 and E2 were treated with enalapril, groups V1 and V2 with verapamil, and one group served as control. The daily food allowance was 14 g/rat of a standard rat diet, containing 30% protein and 100 mmol NaCl/kg food in groups E1 and V1. NaCl content was reduced to 20 mmol/kg food in groups E2, V2 and control. The drugs were added to the drinking water, enalapril at a dose of 0.1 g/liter, verapamil at 0.5 to 0.7 g/liter. Drug intake thus amounted to 10 to 25 mg/kg for enalapril and 50 to 140 mg/kg for verapamil. Treatment was continued for 15 weeks. Three of the 18 control rats did not survive up to 15 weeks. Mortality was lower in the enalapril treated groups with a single nonsurvivor in group E1. In contrast, mortality was higher in the verapamil treated animals with seven nonsurvivors in group V1 and eight in group V2. Blood pressure control was excellent in both enalapril treated groups. and proteinuria decreased in most animals of group E1 and all of group 22. Glomerulosclerosis did not develop in the majority of the enalapril treated animals. Despite the high dose, verapamil barely lowered blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

The angiotensin converting enzyme inhibitor enalapril in acute ischemic renal failure in rats.

The influence of the renin-angiotensin system on renal hemodynamics, tubular pressure and tubulo-glomerular feedback was investigated with the angiotensin converting enzyme inhibitor MK 421 (enalapril), in uninephrectomized rats with and without ischemia-induced acute renal failure. In animals with normal renal function proximal tubular pressure and tubulo-glomerular feedback response were lowered by enalapril long-term treatment, whereas glomerular filtration rate and renal blood flow were not influenced by the drug. After 45 and 70 minutes ischemia there was no difference between treated and untreated animals in the severely impaired glomerular filtration rate. Renal blood flow remained unaffected by the treatment. The histological damage due to ischemia (tubular casts, tubular necrosis and medullary capillary congestion) was not influenced by enalapril. As tubulo-glomerular feedback had been significantly inhibited during renin-angiotensin inhibition, its importance in mediating acute renal failure remains doubtful; other factors such as tubular obstruction and medullary congestion may be crucial.

Cyclosporine A nephrotoxicity in Goldblatt renovascular hypertension in rats.

Experiments were conducted on a renovascular model of hypertension to investigate the effect of high blood pressure and CyA nephrotoxicity combined on arteriolar and tubular morphology and renal function. A two kidney, one clip model of Goldblatt hypertension was selected in which were given 20 or 40 mg/kg/d CyA by gastric gavage for 3-4 weeks while receiving isotonic saline as drinking fluid. CyA was found to suppress feeding and drinking and, as a result, lead to volume depletion and weight loss, with a corresponding lowering of blood pressure and renal function and an increase in plasma renin. When CyA and control animals were pair-fed these effects disappeared, except for a modest depression of renal function, unaccompanied by a reduction in urinary concentrating power. Histological damage to the tubules was equally prevalent in both kidneys despite different levels of renal perfusion, suggesting that plasma concentration, rather than toxin delivery, determines tubular damage. The occurrence of arteriolopathy and glomerulosclerosis was infrequent, and if present, it was only found in the unclipped kidney and was not potentiated by CyA. Glomerular prostaglandin synthesis after substrate incubation was suppressed by CyA to an equal extent in both kidneys, clipped and unclipped.

Mannitol potentiates cyclosporine nephrotoxicity.

A possible drug interaction between cyclosporine (CyA) and mannitol was tested for in female Wistar rats infused continuously with CyA 10 mg (40-50 mg/kg BW) in 24 ml mannitol 20% daily for 3 to 4 days (group CIM). For comparison, two other groups of rats were infused either with the same amount of CyA in 24 ml NaCl 0.9% (group CINa) or with the same amount of mannitol without CyA (group M). No animal of groups CINa or M, but 6 out of 10 group CIM rats developed severe oligo-anuric acute renal failure (ARF). Histologically massive vacuolisation of proximal tubular epithelia was found in the kidneys of CIM rats with ARF, while CIM rats without ARF showed minor to moderate degrees of vacuolisation. No vacuolisation was seen in groups CINa and M. Moderate amounts of tubular inclusion bodies and microcalcifications were detected in the kidneys of CIM rats without ARF and in those of CINa rats. To elucidate the mechanism of ARF, renal blood flow, creatinine clearance and proximal tubular pressures were measured in the kidneys of another series of CIM rats infused for 48-96 hours with CyA and mannitol. Renal blood flow and proximal tubular pressures in the kidneys of animals that had not or not yet developed ARF did not differ from those in rats infused with mannitol alone despite histological alterations with minor to moderate degrees of vacuolisation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cyclosporine in rats with reduced renal mass.

The longterm effect of cyclosporine (CyA) on chronic renal failure was studied in female Wistar rats subjected to 4/5 to 5/6 nephrectomy by partial infarction of the left kidney followed by contralateral nephrectomy. CyA was added to a standard rat diet containing 25% protein. Each rat received 14 g of food daily containing 0 (control), 1.2 (group A), 2.4 (group B), or 4.8 (group C) mg CyA. The number of rats that did not survive the whole experimental period of 20 weeks on the CyA containing diets was similar to the control. In the surviving rats no difference between groups could be detected regarding body weight, serum creatinine and creatinine clearance. Proteinuria rose progressively up to 15 weeks in the control group and similarly in groups A and B. Mean proteinuria in group C was about half the control mean at 5-20 weeks. Systolic blood pressure differed little between groups A, B and control, but was significantly lower than control in group C at 10-20 weeks. Histologically groups B and C showed significantly less glomeruli with segmental sclerosis and less hypertensive vasculopathy than groups A and control. Histological signs of tubular CyA toxicity correlated with the doses applied: inclusion bodies were more frequent in all groups while the score of vacuolisation was increased significantly in group C only. In conclusion, CyA appears not to adversely affect or - at moderately toxic dosage - even to slow down progressive glomerular sclerosis in rats with reduced renal mass.

Effect of cyclosporine A on ischemic renal failure in the rat.

The influence of cyclosporine A on renal function was investigated in unilaterally nephrectomized rats subjected to 30 or 45 min of ischemia. Acute i.v. administration of high dose CyA equivalent to 1000 mg/kg/d, did not produce a decrease in glomerular filtration or renal blood flow within 2 hours and its influence on proximal tubular pressure could be attributed to the cremophor vehicle. Chronic oral administration of 20 mg/kg/d CyA after ischemia produced no alteration in renal function after 2 or 9 days, but 40 mg/kg/d CyA lowered renal function demonstrably by 9 days. When pair-fed to eliminate CyA-induced weight loss as a cause of depressed renal function, the loss of renal function after 9 days was smaller but still evident. At this time renal cortical prostaglandin E2 and thromboxane B2 production were also reduced, but plasma renin remained unaltered because of the exclusion of volume depletion through weight loss. These kidneys showed no signs of delayed regeneration from ischemic renal injury but did show signs of tubulotoxicity, which seemed to be more apparent after longer periods of ischemia.

Morphology of cyclosporine nephrotoxicity in the rat.

Cyclosporine (CSA) nephrotoxicity was investigated in the rat. Morphologically, CSA nephrotoxicity is characterized by the following features: (a) Tubular inclusion bodies (TIB) corresponding to autolysosomes and giant mitochondria; (b) tubular vacuolization (TV) due to dilatation of the endoplasmatic reticulum; (c) tubular microcalcification (TM); and (d) tubular regeneration (TR). The morphologic features are limited to (a and b) or predominate (c and d) in the proximal tubule. CSA tubulopathy as defined above is dose dependent, independent of the route of a drug administration, develops quickly (within a week), is reversible after CSA withdrawal, is more pronounced in male than in female rats and shows no clear cut differences in various rat strains. Body weight shows a dose dependent reduction. The functional changes are usually slight. No significant correlation exists between functional changes and morphologic lesions. The type of CSA nephrotoxicity in the rat is very similar to CSA-tubulopathy in man but associated with less severe functional changes.

Acutely impaired renal function during intravenous administration of cyclosporine A: a cremophore side-effect.

The parenteral application of a cyclosporine A (CyA)-containing solution in high doses, 0.7 mg/kg/min, was associated with an acute reduction in renal blood-flow and a depression in creatinine clearance to approximately one half of control values. Exactly the same effect can be produced by the intravenous administration of the vehicle, cremophore, a polyoxyethylated castor-oil derivative. Although these observations are not of great clinical importance, since the doses of CyA used in man are much lower and the drug is generally taken orally, they are of considerable importance when studying the effects of CyA under experimental conditions. For the purpose of examining the influence of CyA on renal function, cremophore-containing solutions should be avoided.

The potassium content of heart muscle following cyclosporine.

The potassium content of cardiac muscle was examined after 9 or 22 days of cyclosporine A administration in normal rats and rats exposed to either renovascular, Goldblatt hypertension or renal ischemia. Cyclosporine A did not result in any alteration in cardiac muscle potassium compared to untreated rats in either group, even though the animals which had been subjected to renal ischemia and cyclosporine A plasma potassium was raised compared to animals subjected just to renal ischemia. The potassium content of cardiac muscle, however, was found to be raised in the hypertrophic hearts of the Goldblatt, renovascular hypertensive animals, both with and without cyclosporine.

The role of tubuloglomerular feedback in acute impairment of renal function in obstructive jaundice.

Acute renal functional impairment not infrequently accompanies liver dysfunction and, particularly with bile duct obstruction, may be extremely severe. Recent studies suggest that tubuloglomerular feedback (TGF) activated by circulating non-electrolyte factors which occur during liver dysfunction may contribute to the intense renal vasoconstriction thought to be central to the functional renal impairment. In this study, serum from two patients with obstructive jaundice (OJ) and renal impairment, and from rats with OJ due to bile duct ligation were either dialysed or treated with furosemide, known to block electrolyte-mediated TGF. These sera, when perfused into loops of Henle in rat nephrons, induced a significant fall of 28% in stop-flow pressure, an indirect measure of glomerular capillary pressure thus implying arteriolar vasoconstriction. These findings are consistent with the hypothesis that circulating, non-electrolyte factors, which stimulate TGF, occur in cases of obstructive jaundice and that these may contribute to the renal impairment.

[Endotoxin effect on intravascular volume and kidney function in an acute experiment in the rat]. / Endotoxinwirkung auf intravasales Volumen und Nierenfunktion im Akutversuch bei der Ratte.

The effect of intravenous endotoxin (Sal. abortus equi) in a semilethal dose in rats was very individual. Animals showing a drop in creatinine clearance were termed sensitive (E II), and animals without effect on the creatinine clearance non sensitive (E I). In the sensitive animals a reduction of intravascular space by albumin loss into the extravascular space, a decrease of renal blood flow and an average fall in creatinine clearance of 40% were found. The non sensitive animals (E I), on the other hand, showed no significant change in albumin space but, in contrast to E II, their hematocrit fell, a fact interpreted as vasodilatation and inflow of fluid. In these animals (E I) no change in creatinine clearance was measured. Orthograde tubular perfusion of endotoxin through the loop of Henle elicited no tubular glomerular feedback response. In these sensitive animals (E II), the absence of tubular glomerular feedback vasoconstriction, hypovolemia and a fall in blood pressure suggest a prerenal cause for this type of acute renal failure. Additional factors responsible for acute renal failure are discussed.

Feedback regulation of nephron filtration rate during pharmacologic interference with the renin-angiotensin and adrenergic systems in rats.

Tubuloglomerular feedback has been defined as a mechanism in which changes in distal tubular sodium chloride delivery induce changes in glomerular arteriolar resistance. Experiments were performed in rats to test the hypothesis that the alterations in vasomotor activity are controlled by local hormonal mechanisms. Early proximal flow rate (EPFR), used as an index of filtration rate, was assessed at loop perfusion rates of 10 and 40 nl/min and during zero loop flow before and during intravenous administration of agents which interfere with the reninangiotensin or adrenergic systems. During infusion of the angiotensin (A) antagonists [Sar1,Ile8-]-AII or [Me2,Gly1,Ile8]-AII at doses ranging from 4.8 to 30.6 micrograms/kg . min, feedback response, expressed as percent change of EPFR during loop flow elevation from 3 to 40 nl/min, fell from a mean of 47.6 +/- 3.3% to 33.2 +/- 2.9% (P less than 0.05). Likewise, after administration of the converting enzyme inhibitor SQ 20881 in a dose ranging between 5.5 and 34.0 mg/kg, feedback response decreased from 48.5 +/- 2.1% to 25.9 +/- 1.9% (P less than 0.001) and returned to 43.1 +/- 5.1% after the inhibitory effect of SQ 20881 on the pressure response to angiotensin I had disappeared. Luminal application of [Sar1,Thr2]-AII (5mM) or of SQ 20881 (5 or 10 mM) had no effect on the feedback response. A significant reduction in the feedback response was noted also during intravenous infusion of propranolol (46.4 +/- 3.2% vs. 29.0 +/- 2.8%, P less than 0.001), whereas 6-OH-dopamine, reserpine, or phenoxybenzamine had no detectable effect. Our results are in agreement with the concept that the renin-angiotensin system may mediate feedback-induced resistance changes. In addition, circulating catecholamines may, in some unknown manner, act as modulators of the feedback response.