Direct assessment of tubuloglomerular feedback responsiveness in connexin 40-deficient mice.

Participation of connexin 40 (Cx40) in the regulation of renin secretion and in the tubuloglomerular feedback (TGF) component of renal autoregulation suggests that gap junctional coupling through Cx40 contributes to the function of the juxtaglomerular apparatus. In the present experiments, we determined the effect of targeted Cx40 deletion in C57BL/6 and FVB mice on TGF responsiveness. In C57BL/6 mice, stop-flow pressure (PSF) fell from 40.3 ± 2 to 34.5 ± 2 mmHg in wild-type (WT) and from 31 ± 1.06 to 26.6 ± 0.98 mmHg in Cx40-/- mice. PSF changes of 5.85 ± 0.67 mmHg in WT and of 4.3 ± 0.55 mmHg in Cx40-/- mice were not significantly different (P = 0.08). In FVB mice, PSF fell from 37.4 ± 1.5 to 31.6 ± 1.5 mmHg in WT and from 28.1 ± 1.6 to 25.4 ± 1.7 mmHg in Cx40-/-, with mean TGF responses being significantly greater in WT than Cx40-/- (5.5 ± 0.55 vs. 2.7 ± 0.84 mmHg; P = 0.002). In both genetic backgrounds, PSF values were significantly lower in Cx40-/- than WT mice at all flow rates. Arterial blood pressure in the animals prepared for micropuncture was not different between WT and Cx40-/- mice. We conclude that the TGF response magnitude in superficial cortical nephrons is reduced by 30-50% in mice without Cx40, but that with the exception of a small number of nephrons, residual TGF activity is maintained. Thus gap junctional coupling appears to modulate TGF, perhaps by determining the kinetics of signal transmission.

The role of renin-angiotensin-aldosterone system in the progression of chronic kidney disease.

The renin-angiotensin-aldosterone system (RAAS) is a well known regulator of blood pressure (BP) and determinant of target-organ damage. It controls fluid and electrolyte balance through coordinated effects on the heart, blood vessels, and Kidneys. Angiotensin II (AII) is the main effector of the RAAS and exerts its vasoconstrictor effect predominantly on the postglomerular arterioles, thereby increasing the glomerular hydraulic pressure and the ultrafiltration of plasma proteins, effects that may contribute to the onset and progression of chronic renal damage. AII may also directly contribute to accelerate renal damage by sustaining cell growth, inflammation, and fibrosis. Interventions that inhibit the activity of the RAAS are renoprotective and may slow or even halt the progression of chronic nephropathies. ACE inhibitors and angiotensin II receptor antagonists can be used in combination to maximize RAAS inhibition and more effectively reduce proteinuria and GFR decline in diabetic and nondiabetic renal disease. Recent evidence suggests that add-on therapy with an aldosterone antagonist may further increase renoprotection, but may also enhance the risk hyperkalemia. Maximized RAAS inhibition, combined with intensified blood pressure control (and metabolic control in diabetics) and amelioration of dyslipidemia in a multimodal approach including lifestyle modifications (Remission Clinic), may achieve remission of proteinuria and renal function stabilization in a substantial proportion of patients with proteinuric renal disease. Ongoing studies will tell whether novel drugs inhibiting the RAAS, such as the renin inhibitors or the vasopeptidase inhibitors, may offer additional benefits to those who do not respond, or only partially respond, to this multimodal regimen.

The relative roles of sodium and renin in the hypertension of renal disease. An assessment based on the response to frusemide and propranolol.

Twenty-seven patients with hypertension and varying degrees of renal failure were studied before and during the administration of frusemide. In 15 patients studies were repeated following the addition of propranolol. Mean exchangeable sodium was increased before the introduction of frusemide or propranolol in patients with azotemia, possibly due in part to the administration of other antihypertensive drugs, and was reduced to normal during frusemide treatment increasing slightly but significantly following the addition of propranolol. Blood pressure fell significantly with frusemide but there was no further significant fall with propranolol. The relationship of change in blood pressure to change in exchangeable sodium with frusemide did not reach significance. There was no relationship between changes in blood pressure and changes in plasma renin activity with frusemide, suggesting that the blood pressure response to frusemide is not limited by the rise in renin. The fall in blood pressure following the addition of propranolol was proportional to the dose of the drug but inversely proportional to the change in renin suggesting that renin levels are to some extent determined by the blood pressure response to propranolol rather than themselves determining that response. Serum creatinine was significantly increased during treatment with frusemide probably due to a combination of the effects of sodium depletion and the natural progression of the underlying renal disease rather than to nephrotoxicity. The further slight increase in serum creatinine following the addition of propranolol is in keeping with the reported effect of this drug on renal blood flow and glomerular filtration rate in patients without renal disease.

Electrolyte economy and its hormonal regulation in congenital chloride diarrhea.

The economy of Cl-, K+, and Mg++, extracellular volume (ECV) and plasma volume, and the role of hyperreninemia and hyperaldosteronism were explored in 22 patients with congenital chloride diarrhea. Stool volume was in significant correlation with its Cl-, Na+ and K+ content, the correlation being significantly better with Cl- content than with the Na+ content. Low fecal Cl- concentrations were seen in chronic hypochloremic contraction, but acute episodes did not cause reduction of fecal Cl- concentration from the basal level of 140--150 mmol/liter. The adequate condition (defined as normal serum electrolyte concentrations and bl;od pH, and presence of Cl- in urine) was associated with high total exchangeable Cl- and ECV. This excess Cl- and ECV roughly equalled the high daily fecal amount of Cl- and volume. Reduced ECV was accompanied by high renin activities and hyperaldosteronism, but in the adequate condition these were normal. Hyperaldosteronism caused a decrease in urinary Na+-K+ ratio and, after the age of 2--6 months, in the fecal Na+-K+ ratio. Total exchangeable K+ was normal in the adequate condition. No Mg++ depletion was present, although the patients lack Mg++ substitution. The adequate condition could be maintained with an oral supplement of NaCl, KCl and water.

Assessment of 11beta-hydroxylase activity with plasma corticosterone, deoxycorticosterone, cortisol, and deoxycortisol: role of ACTH and angiotensin.

UNLABELLED: In this study we evaluated the role of ACTH and angiotensin on regulation of activities of 11beta-hydroxylases of the adrenal cortex. The ratio of the plasma concentrations of 11 deoxycorticosterone (DOC) to plasma corticosterone (B) reflected the activity of the enzyme of the B and/or aldosterone pathways, and the ratio of plasma 11-deoxycortisol (S) to plasma cortisol (F) as the activity of the enzyme in the F pathway. In normal subjects, both ratios were significantly lower at 0800-0900 h (Doc to B, .01+/-.004, mean+/-SE, n=10; and S to F, .01+/-.003) than at 2000 h (DOC to B, .028+/-.024 and S to F, .015+/-.005). The plasma levels of DOC, B, S and F were all significantly lower at 2000-2100 h than at 0800-0900 h. In contrast 9 patients with Cushing's syndrome exhibited no diurnal change in the ratios. The ratios increased substantially following dexamethasone or metyrapone administration. A high or low salt diet and an angiotensin infusion produced no significant effect on the ratios. The plasma concentration of all four steroids was increased by more than 50% by an infusion of angiotensin. Four hours after administration of 80 mg of Lasix at 0800 h to 10 normal subjects, the ratios of DOC to B and S to F increased significantly (P less than .02), an effect possibly related to a decreased secretion of ACTH. CONCLUSIONS: 1) 11beta-hydroxylase activity of the B and/or aldosterone and F pathways appears to change in parallel with ACTH secretion, and 2) although angiotensin stimulates steroidogenesis of the pathways, it has no apparent effect on 11beta-hydroxylase activity.