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Two endogenous receptors for the potent smooth muscle-stimulating peptide neuromedin U (NmU) have recently been identified and cloned. Pharmacological, binding, and expression studies were conducted in an attempt to determine the receptor(s) involved in the smooth muscle-stimulating effects of NmU. The NmU peptides caused a concentration-dependent contraction of canine isolated urinary bladder. NmU did not have this same effect in the urinary bladder from rat, guinea pig, rabbit, mouse, or ferret. Although NmU had no effect on canine uterus it did cause contraction of canine stomach, ileum, and colon. As well as causing contraction of canine bladder in vitro, NmU administered systemically resulted in a significant increase in urinary bladder pressure in vivo. High-affinity binding sites for NmU were identified in canine bladder. The four NmU peptides porcine NmU-8, rat NmU-23, human NmU-25, and porcine NmU-25 displaced (125)I-NmU-25 binding with similar K(i) values (0.08-0.24 nM). A different binding profile was revealed in human embryonic kidney-293 cells transiently expressed with the canine NmU-2 receptor where porcine NmU-8 (K(i) = 147.06 nM) was much less potent than the other NmU peptides. Using TaqMan, expression of NmU-1 was detected in human urinary bladder, small intestine, colon, and uterus. Expression of NmU-2 was much lower or absent in these human tissues and undetectable in canine bladder and stomach. The results of this study reveal significant species differences in the activity of NmU. The contractile activity in human and canine smooth muscle seems to be mediated by the recently cloned NmU-1 receptor.

The effects of the angiotensin type 1 (AT(1)) receptor antagonist, eprosartan, were studied in a model of severe, chronic hypertension. Treatment of male spontaneously hypertensive stroke prone rats (SHR-SP) fed a high-fat, high-salt diet with eprosartan (60 mg/kg/day i.p.) for 12 weeks resulted in a lowering of blood pressure (250 +/- 9 versus 284 +/- 8 mm Hg), renal expression of transforming growth factor-beta mRNA (1.5 +/- 0.2 versus 5.4 +/- 1.4) and the matrix components: plasminogen activator inhibitor-1 (5.2 +/- 1.4 versus 31.4 +/- 10.7), fibronectin (2.2 +/- 0.6 versus 8.2 +/- 2.2), collagen I-alpha 1 (5.6 +/- 2.0 versus 23.8 +/- 7.3), and collagen III (2.7 +/- 0.9 versus 7.6 +/- 2.1). Data were corrected for rpL32 mRNA expression and expressed relative to Wistar Kyoto (WKY) rats [=1.0]. Expression of fibronectin protein was also lowered by eprosartan (0.8 +/- 0.1 versus 1.9 +/- 0.5), relative to WKY rats. Eprosartan provided significant renoprotection to SHR-SP rats as measured by decreased proteinuria (22 +/- 2 versus 127 +/- 13 mg/day) and histological evidence of active renal damage (5 +/- 2 versus 195 +/- 6) and renal fibrosis (5.9 +/- 0.7 versus 16.4 +/- 1.9) in vehicle- versus eprosartan-treated rats, respectively. Our results demonstrated that AT(1) receptor blockade with eprosartan can reduce blood pressure and preserve renal structure and function in this model of severe, chronic hypertension. These effects were accompanied by a decreased renal expression of transforming growth factor-beta1, plasminogen activator inhibitor-1, and several other extracellular matrix proteins compared with vehicle-treated SHR-SP.

1. The effect of carvedilol on renal function, structure and expression of TGF beta and the matrix proteins fibronectin, collagen I and collagen III, was evaluated in spontaneously hypertensive stroke-prone (SHR-SP) rats fed a high fat, high salt diet. 2. Carvedilol treatment for 11 to 18 weeks did not alter systolic blood pressure in SHR-SP rats, however, it resulted in a significant reduction in heart rate. 3. Carvedilol treatment reduced renal fibrosis and total, active and chronic renal damage to levels approaching those of WKY rats on a normal diet. 4. Urinary protein excretion was higher in SHR-SP rats (51+/-10 mg day(-1)) than WKY rats (18+/-2 mg day(-1)) and this was further increased when SHR-SP rats were fed a high fat, high salt diet (251+/-120 mg day(-1)). Treatment with carvedilol resulted in significantly lower urinary protein excretion (37+/-15 mg day(-1)). 5. The expression of TGF beta mRNA was significantly higher in SHR-SP rats compared to WKY rats and a further increase was observed when rats were fed a high fat, high salt diet. Renal TGF beta expression was significantly reduced by treatment with carvedilol. The expression of fibronectin and collagen I and collagen III mRNA showed a pattern similar to that observed with TGF beta mRNA expression. Collagen I mRNA expression followed a pattern similar to renal fibrosis. 6. These data indicate that carvedilol can provide significant renal protection in the absence of any antihypertensive activity and that the mechanisms involved in this action may include reduced expression of profibrotic factors such as TGF beta.

Objective: Eprosartan is a selective angiotensin II type I receptor antagonist approved for the treatment of hypertension. In the present studies, eprosartan's ability to provide end-organ protection was evaluated in a model of cardiomyopathy and renal failure in stroke-prone rats (SP)., Methods: SP were fed a high fat (24.5% in food) and high salt (1% in water) diet (SFD). Eprosartan (60 mg/kg/day) or vehicle (saline control) (n = 25/group) was administered by intraperitoneally-implanted minipumps to these SP on the SFD for 12 weeks. Normal diet fed SP and WKY rats (n = 25/group) were also included for comparison (i.e. served as normal controls). Mortality, hemodynamics, and both renal and cardiac function and histopathology were monitored in all treatment groups., Results: Eprosartan decreased the severely elevated arterial pressure (-12%; P < 0.05) produced by SFD but did not affect heart rate. Vehicle-treated SP-SFD control rats exhibited significant weight loss (-13%; P < 0.05) and marked mortality (50% by week 6 and 95% by week 9; P < 0.01). Eprosartan-treated SP-SFD rats maintained normal weight, and exhibited zero mortality at week 12 and beyond. Eprosartan prevented the increased urinary protein excretion (P < 0.05) that was observed in vehicle-treated SP-SFD rats. Echocardiographic (i.e. 2-D guided M-mode) evaluation indicated that SP-SFD vehicle control rats exhibited increased septal (+22.2%) and posterior left ventricular wall (+30.0%) thickness, and decreased left ventricular chamber diameter (-15.9%), chamber volume (-32.7%), stroke volume (-48.7%) and ejection fraction (-22.3%), and a remarkable decrease in cardiac output (-59.3%) compared to controls (all P < 0.05). These same parameters in eprosartan-treated SP-SFD rats were normal and differed markedly and consistently from vehicle-treated SP-SFD rats (i.e. treatment prevented pathology; all P < 0.05). Cardiac-gated MRI data confirmed the ability of eprosartan to prevent cardiac pathology/remodeling (P < 0.05). Histopathological analysis of hearts and kidneys indicated that eprosartan treatment significantly reduced end-organ damage (P < 0.01) and provided corroborative evidence that eprosartan reduced remodeling of these organs. Vehicle-treated SP-SFD rats exhibited a 40% increase in the plasma level of pro-atrial natiuretic factor that was reduced to normal by eprosartan (P < 0.05)., Conclusion: These data demonstrate that eprosartan, at a clinically relevant dose, provides significant end-organ protection in the severely hypertensive stroke-prone rat. It preserves cardiac and renal structural integrity, reduces cardiac hypertrophy and indices of heart failure, maintains normal function of the heart and kidneys, and eliminates premature mortality due to hypertension-induced end-organ failure.

Although secondary hyperparathyroidism is a common complication of chronic renal failure, few studies have examined the characteristics of parathyroid hormone (PTH) binding to the kidney or the regulation of the PTH receptor in chronic renal disease. In this study we measured PTH binding to the PTH-1 receptor in renal cortical membranes from normal rats and from rats with experimentally induced chronic renal failure. In normal rats, analysis of saturation binding experiments using 125I PTH-related peptide (chicken, cPTHrP) revealed apparent Kd and Bmax values of 1.16 +/- 0.14 nmol/l and 338 +/- 22.7 fmol/mg, respectively. Three weeks following induction of renal failure there was no change in the affinity of the PTH-1 receptor (Kd = 1.51 +/- 0.24 nmol/l) but the Bmax was reduced by 45% (183 +/- 32.5). In normal rats which had undergone thyroparathyroidectomy, the Kd was unchanged (1.17 +/- 0.09) while the Bmax increased to 459 +/- 31 fmol/mg. We conclude that chronic renal failure is accompanied by a downregulation of renal PTH-1 receptors., (Copyright 2001 S. Karger AG, Basel)

The role of ANG II on renal and cardiac gene expression of matrix proteins was studied in rats with progressive renal disease. Induction of renal failure by five-sixths nephrectomy of Sprague-Dawley rats resulted in hypertension (163 +/- 19 vs. control pressures of 108 +/- 6 mmHg), proteinuria (83 +/- 47 vs. 14 +/- 2 mg/day), and increased renal expression of fibronectin, thrombospondin, collagen I and III, transforming growth factor-beta (TGF-beta), and plasminogen activator inhibitor-1 (PAI-1) mRNA. Treatment with the ANG II receptor antagonist, eprosartan (60 mg. kg(-1).day(-1)), lowered blood pressure (95 +/- 5 mmHg) and proteinuria (19 +/- 8 mg/d) and abrogated the increased TGF-beta, fibronectin, thrombospondin, collagens I and III, and PAI-1 mRNA expression. An increase in left ventricular weight was observed in five-sixths nephrectomized rats (0.13 +/- 0.01 vs. 0.08 +/- 0.01 g/100 g body wt), a response that was inhibited by eprosartan treatment (0.10 +/- 0.01 g/100 g). Left ventricular expression of TGF-beta and fibronectin was also increased in rats with renal disease; however, the small decreases in expression observed in eprosartan-treated rats did not reach statistical significance. These data suggest that eprosartan may be beneficial in progressive renal disease and that the mechanism of action includes inhibition of cytokine production in addition to antihypertensive activity.

The effect of the angiotensin-converting enzyme inhibitor captopril on clusterin mRNA was examined in partially nephrectomized male rats. Urine protein excretion was measured 3, 7, and 28 days after removal of five sixths of the renal mass. Nephrectomy caused a progressive increase in clusterin mRNA levels in the remnant kidney. Maximal clusterin mRNA levels occurred 7 days after nephrectomy and declined 28 days after nephrectomy. Captopril, 250 mg/ml in drinking water, prevented the injury-induced increase in clusterin mRNA at 7 and 28 days. Captopril had no effect on clusterin in sham-operated rats. As expected, the urine protein excretion increased progressively after nephrectomy, and this was attenuated by administration of captopril in the drinking water. Therefore, clusterin is a marker of renal injury which, along with proteinuria, is modulated by angiotensin-converting enzyme inhibition.

Evidence suggests that transforming growth factor beta 1 (TGF-beta 1), a multifunctional cytokine, induces renal extracellular matrix production and glomerular hypertrophy. The aim of the present study was to investigate the effect of captopril on the expression of TGF-beta 1 mRNA in a rat model of chronic renal failure: five-sixths nephrectomy. Chronic renal disease was induced by removal of the right kidney and ligation of three blood vessels supplying the left kidney. Sham-operated animals were used as controls. RNA was extracted from the viable remnant kidney of rats 1 day and 1 and 2 weeks following five-sixths nephrectomy and from the kidneys of rats who underwent sham surgery. TGF-beta 1 mRNA was induced within 24 h of partial nephrectomy, similar to that reported for early-onset genes. Subsequently, TGF-beta 1 mRNA expression continued to increase over the next 2-4 weeks. The upregulation of TGF-beta 1 correlated with the degree of proteinuria. Both the increase in TGF-beta 1 mRNA and proteinuria were abrogated by captopril treatment. In addition, no change in expression of ALK-5 or type II TGF-beta receptors following five-sixths nephrectomy was observed. These data suggest that captopril may protect against development of glomerulosclerosis and proteinuria by reducing TGF-beta 1 expression and hence matrix production.

The present study demonstrates that the nitric oxide synthase inhibitor, aminoguanidine, can attenuate the proteinuria observed in a predominantly noninflammatory model of chronic renal disease in the rat. These data suggest that nitric oxide synthase may be involved in progressive renal disease.

Clusterin is a multifunctional glycoprotein associated with development and tissue injury. Because renal function decreases with advancing age in the obese Zucker rat, clusterin mRNA expression was examined in the kidney of young adult Zucker rats and compared with age-related changes in renal clusterin mRNA expression in Fischer 344 (F344) rats. Renal clusterin mRNA levels in the obese Zucker rat were 2.5-fold higher by 3 mo of age and fourfold higher at 5 mo of age compared with the lean strain. In comparison, renal clusterin mRNA in 12-mo-old F344 rats was twofold higher than in 3-mo-old animals and was tenfold higher at 24 mo of age. Clusterin mRNA was positively correlated with urinary protein excretion and negatively correlated with creatinine clearance in Zucker rats. Clusterin was increased in select nephrons of the obese Zucker rat kidney and in 24-mo-old F344 rat kidney as assessed by in situ hybridization. Increased expression of clusterin mRNA occurred mostly in the tubular epithelium of dilated, convoluted proximal tubules. These data indicate that renal clusterin mRNA levels increase as a function of age and that age-related increases in renal clusterin and the associated tubular abnormalities are accelerated in obese Zucker rats.

The prevention of phosphate retention in chronic renal disease may reduce both renal osteodystrophy and disease progression. We evaluated the expression of the sodium-dependent phosphate transporter, NaPi-2, and the response to phosphonoformic acid (PFA) in rats with 5/6 nephrectomy-induced renal failure. Partial nephrectomy resulted in a significant proteinuria and reduced renal function. In addition, there was an approximately 50% reduction in the expression of NaPi-2 mRNA. Treatment of rats for 48 hr with PFA (0.6% in glucose drinking fluid) had no effect on NaPi-2 mRNA; however, PFA resulted in a significant increase in fractional phosphate excretion in both normal (7 +/- 0.5% vs. 3 +/- 0.2%) and uremic (60 +/- 4% vs. 36 +/- 4%) rats. Plasma phosphate concentration was higher in uremic rats (2.5 +/- 0.1 mM) compared with normal rats (1.9 +/- 0.04 mM) but not in uremic rats treated with PFA (2.1 +/- 0.04 mM). These data suggest that PFA can increase renal phosphate excretion independent of changes in phosphate transporter expression and prevent phosphate retention.

Administration of endothelin to inactin-anesthetized rats resulted in a significant renal vasoconstriction as evidenced by a reduction in both renal plasma flow and glomerular filtration rate. Infusion of the novel nonpeptide endothelin ETA/ETB receptor antagonist, (+/-)-SB 209670, [(1RS-2SR,3RS)-3-(2-carboxymethoxy-4-methoxy-phenyl)-5 -(prop-1-yloxy)indane-2-carboxylic acid], significantly attenuated the renal vascular effects of endothelin-1. Intravenous administration of cyclosporine A (50 mg/kg) caused a significant reduction in renal plasma flow and glomerular filtration rate and urine flow and a dramatic increase in renal vascular resistance. Concomitant infusion of (+/-)-SB 209670 abolished the cyclosporine A-induced reduction in renal plasma flow and glomerular filtration rate and attenuated the cyclosporine A-induced fluid retention. The data indicate that endothelin is involved in the acute renal effects of cyclosporine A.

SB 203220, [(E)-alpha-[[2-butyl-1-[(4-carboxy-1-naphthalenyl)-methyl]-1H- imidazol-5-yl]-methylene]-2-thiophene-propanic acid], is a novel nonpeptide angiotensin II receptor antagonist with significant oral activity. In the present study, we compared the cardiovascular and renal effects of SB 203220 and captopril in rats with chronic renal failure induced by 5/6 nephrectomy. Preliminary studies indicated that SB 203220 (600 ppm in the diet) and captopril (250 mg/l in drinking water) significantly attenuated the pressor activity of exogenous angiotensin II and angiotensin I, respectively. After 5/6 nephrectomy, significant hypertension was observed such that at 6 weeks, systolic blood pressure had reached 176 +/- 9 mm Hg. Both SB 203220 (128 +/- 18 mm Hg) and captopril (131 +/- 7 mm Hg) significantly attenuated the hypertension. Urinary protein excretion increased progressively after renal ablation (from 7 to 124 mg/day), and this was attenuated by both SB 203220 (32 +/- 7 mg/day) and captopril (42 +/- 6 mg/day). Assessment of serum creatinine and urea nitrogen indicated that SB 203220 but not captopril resulted in maintenance of renal function, close to that observed in control rats. Both SB 203220 and captopril attenuated the renal and left ventricular hypertrophy associated with 5/6 nephrectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The effect of the novel beta-adrenoceptor antagonist and vasodilator, carvedilol (SK&F 105517, approximately 70 mg kg-1 daily in the food), and captopril (approximately 38 mg kg-1 daily in the drinking fluid) on the progression of chronic renal failure in rats was studied. 2. Six weeks following partial renal ablation, the urinary protein excretion of the carvediol- (60 +/- 21 mg day-1) and captopril-treated (35 +/- 9 mg day-1) animals was less than 50% that of control rats (133 +/- 27 mg d-1). 3. Serum creatinine (Scr) and urea nitrogen (SUN) concentrations of the carvedilol-(Scr, 0.63 +/- 0.09 mg dl-1; SUN, 11.3 +/- 1.2 mg dl-1) and captopril-treated (Scr, 0.82 +/- 0.05 mg dl-1; SUN, 14.1 +/- 1.5 mg dl-1) animals were also significantly (P < 0.05) lower than that observed in control animals (Scr, 1.4 +/- 0.3 mg dl-1; SUN, 19.2 +/- 3.9 mg dl-1), indicating that glomerular filtration rate was improved by both drugs. Plasma renin activity was significantly (P < 0.05) higher in captopril-treated rats (24.7 +/- 4.6 ng angiotensin I ml-1 h-1) than in either carvedilol-treated (7.9 +/- 1.4 ng angiotensin I ml-1 h-1) or control animals (7.4 +/- 1.0 ng angiotensin I ml-1 h-1). 4. Histological examination of the kidneys demonstrated a significantly reduced glomerular hypertrophy and glomerulosclerosis in those animals receiving carvedilol or captopril compared to controls. 5. Serum carvedilol concentration measured every 6 h for 24 h was variable and ranged on average from 57 +/- 13 ng ml-1 at 16 h 00 min to 121 +/- 31 ng ml-1 at 03 h 00 min. These data indicate that the rats probably had 24 h systemic exposure to carvedilol.6. The present study indicates that carvedilol is effective in attenuating the progression of chronic renal failure in rats.

1. Six weeks following partial nephrectomy in rats, significant increases in serum urea nitrogen and serum creatinine concentration and a significant decrease in creatinine clearance were observed. 2. Measurement of systolic blood pressure by tail plethysmography indicated that animals that had undergone partial nephrectomy were hypertensive. 3. Compared to sham-operated animals, there were 4 fold increases in both urinary protein excretion and urinary endothelin excretion. 4. There was a significant correlation between urinary protein and urinary endothelin excretion (r = 0.77). There was also a correlation (r = 0.65) between urinary endothelin excretion and systolic blood pressure. 5. Plasma endothelin concentrations were not different in sham-operated and partially nephrectomized rats. 6. The data indicate that there is an increased renal endothelin production in rats with chronic renal failure.

The aim of the present study was to determine the effect of a calcium channel blocker on renal function, urinary endothelin excretion and endothelin receptor number in rats. Administration of cyclosporine resulted in a significant impairment of renal function when measured by either [14C]inulin or 24 h creatinine clearances. This nephrotoxicity was associated with statistically significant (P less than 0.05) increases in urinary endothelin excretion and renal endothelin receptor number. Treatment with nifedipine attenuated cyclosporine A-induced renal dysfunction and reduced urinary endothelin excretion. The data provide further evidence of a role for endothelin in cyclosporine A-induced nephrotoxicity.

Measurement of endothelin receptors by binding assay was performed in rats treated with cyclosporine A (CYA). Cyclosporine A administration at 50 mg/kg i.p. for 4 days resulted in renal function impairment as indicated by a significant increase in serum creatinine concentration (from 0.46 +/- 0.02 to 0.61 +/- 0.03 mg/dl. P less than 0.01) and a significant decrease in 24 h creatinine clearance (from 0.65 +/- 0.04 to 0.41 +/- 0.02 ml/min per 100 g, P less than 0.01). Renal endothelin (ET) receptor density was significantly higher in CYA-treated rats (312 +/- 34 vs. 196 +/- 26 fmol/mg protein, P less than 0.01). These data support the possible involvement for endothelin in the increased renal vascular resistance associated with CYA-induced nephrotoxicity.

1. Partial (5/6) renal ablation was performed in Long Evans rats treated with vehicle or a vasopressin V1-receptor antagonist, in control Long Evans rats, and in homozygous Brattleboro rats which lack endogenous vasopressin. 2. In control and vasopressin-blocked Long Evans rats, 3 weeks following partial renal ablation, systolic blood pressure was 215 +/- 5 and 199 +/- 9 mmHg and, urinary protein excretion was 54 +/- 4 and 50 +/- 3 mg day-1, respectively. 3. The pressor response to exogenous vasopressin was significantly (P less than 0.05) reduced in rats treated with the V1-receptor antagonist (ED50 mmHg 5.0 +/- 1.6 vs. 0.09 +/- 0.01 micrograms kg-1). 4. In control Long Evans and in Brattleboro rats, 3 weeks following renal ablation, systolic blood pressure was 204 +/- 10 and 191 +/- 7 mmHg, and urinary protein excretion was 97 +/- 27 and 71 +/- 5 mg day-1, respectively. 5. Histological examination of the remaining kidney tissue demonstrated significant glomerular hyalinization following renal ablation but no differences between any of the groups. 6. The data indicate that neither vasopressin nor the urinary concentrating mechanism is likely to be involved in the hypertension and proteinuria associated with partial renal ablation.

There is evidence to suggest that thromboxane synthesis inhibition will attenuate the hypertension and proteinuria associated with subtotal renal ablation. In the present study, the thromboxane receptor antagonist, daltroban, (30 mg/kg/day i.p.) or vehicle was administered to rats for 3 weeks starting 2 weeks after partial renal ablation (right uninephrectomy and ligation of approximately two-thirds of the blood supply to the left kidney). Renal ablation was associated with proteinuria and increased systolic blood pressure. Neither the proteinuria nor the hypertension was affected by daltroban administration. Histological examination of the remaining kidney demonstrated no beneficial effect of daltroban. In a second study, it was determined that, 2 weeks after renal ablation, urinary thromboxane excretion was significantly increased, and subsequent administration of daltroban for 2 weeks resulted in significant blockade of the effects of the thromboxane mimetic, U46619. In a third study, enalapril (50 mg/l in the drinking water) resulted in a significant attenuation of the proteinuria, hypertension and glomerular lesions associated with partial renal ablation. The data indicate that enalapril, but not daltroban, protects against the development of renal disease associated with reduced renal mass.

Mitochondrial carbonic anhydrase has previously been quantitated in liver mitochondria; it was not detected in guinea pig kidney cortical mitochondria. Evidence of this enzyme in rat kidney cortical mitochondria is reported. Electron microscopy showed that intact mitochondria were free of other intracellular organelles. When intact kidney mitochondria were added to isotonic 3'-(N'-morpholino) propanesulfonic acid buffer with 25 mM KHCO3 (1% labeled with 18O) the rate of disappearance of C18O16O was biphasic; this indicates that there is carbonic anhydrase within the inner mitochondrial membrane. Intact rat kidney mitochondria were assayed for carbonic anhydrase activity at 4 degrees C by the changing pH technique. The rate of CO2 hydration in the presence and absence of intact mitochondria was identical; this rate increased when Triton X-100 was added which indicates that all carbonic anhydrase is inside the inner mitochondrial membrane. Carbonic anhydrase activity was quantitated as kenz (units, ml.s-1 mg-1 mitochondrial protein) at 37 degrees C, pH 7.4, in 25 mM NaHCO3 (1% labeled with 18O) by following the rate of disappearance of C18O16O from solutions before and after addition of disrupted mitochondria. Values of Kenz for liver and kidney mitochondria from rats given free access to normal rat chow and water at neutral pH were 0.06 and 0.08 (respectively). Values of kenz for liver and kidney mitochondria from rats fed as above and with free access to water adjusted to pH 2.5 with HCl were 0.04 and 0.16, respectively. Values of kenz for rats starved for 48 h were 0.06 and 0.12 (respectively). The values of kenz remained 0.11-0.14 in liver mitochondria from guinea pigs fed normally, given dilute acid, or starved and the value was always at zero in guinea pig kidney mitochondria. Values of Kenz were measured with disrupted mitochondria by the 18O technique as a function of pH at 25 degrees C, 25 to 75 mM NaHCO3, ionic strength 0.3. From pH 7.0 to 8.0 kenz increased threefold for mitochondria from rat liver, fed rat kidney, and acid rat kidney, and increased eightfold for mitochondria from guinea pig liver. kenz was decreased similarly by increasing HCO3- in mitochondria from rat liver, fed kidney, and acid kidney; it is concluded that carbonic anhydrase in rat liver mitochondria is probably the same isozyme as in rat kidney mitochondria. The published observation that rat kidney cortices are up to 10 times as gluconeogenic from pyruvate as guinea pig kidney cortices can be explained by the presence of mitochondrial carbonic anhydrase in rat but not guinea pig mitochondria.