Thomson SC, Rieg T, Miracle C, Mansoury H, Whaley J, Vallon V, Singh P. Acute and chronic effects of SGLT2 blockade on glomerular and tubular function in the early diabetic rat. Am J Physiol Regul Integr Comp Physiol 302: R75-R83, 2012. First published September 21, 2011 doi:10.1152/ajpregu.00357.2011.-Tubuloglomerular feedback (TGF) stabilizes nephron function from minute to minute and adapts to different steady-state inputs to maintain this capability. Such adaptation inherently renders TGF less efficient at buffering long-term disturbances, but the magnitude of loss is unknown. We undertook the present study to measure the compromise between TGF and TGF adaptation in transition from acute to chronic decline in proximal reabsorption (Jprox). As a tool, we blocked proximal tubule sodium-glucose cotransport with the SGLT2 blocker dapagliflozin in hyperglycemic rats with early streptozotocin diabetes, a condition in which a large fraction of proximal fluid reabsorption owes to SGLT2. Dapagliflozin acutely reduced proximal reabsorption leading to a 70% increase in early distal chloride, a saturated TGF response, and a major reduction in single nephron glomerular filtration rate (SNGFR). Acute and chronic effects on Jprox were indistinguishable. Adaptations to 10 -12 days of dapagiflozin included increased reabsorption by Henle's loop, which caused a partial relaxation in the increased tone exerted by TGF that could be explained without desensitization of TGF. In summary, TGF contributes to long-term fluid and salt balance by mediating a persistent decline in SNGFR as the kidney adapts to a sustained decrease in Jprox.dapagliflozin; hyperfiltration AN ONGOING DISTURBANCE IN salt transport anywhere along the nephron will eventually be compensated by a combination of changes in glomerular filtration of salt, salt transport elsewhere along the nephron, and salt intake to fulfill the requirement for long-term balance. The kidney cannot obviate this requirement, but exerts some control over how it is achieved. Tubuloglomerular feedback (TGF) is one mechanism that the kidney can employ to influence how the response to an outside disturbance is compensated. TGF senses the amount of fluid and salt reaching the macula densa and evokes counterbalancing changes in single nephron glomerular filtration rate (SNGFR), thereby reducing the impact that an outside disturbance in proximal reabsorption would otherwise have on distal delivery. The usual way to measure the effectiveness of TGF is by in vivo micropuncture, which is most adapted to studying the TGF responses to events that occur on a time scale of several minutes (17). TGF responses over periods of 1-2 h have been partially characterized using carbonic anhydrase inhibitors to perturb proximal reabsorption (3). But little is known about the influence of TGF over the compensatory response to an outside disturbance lasting several days, which is the critical time frame over which the kidney regulates salt balance and blood pressure (5).The present studies were performed to...

In patients with chronic kidney disease, metabolic acidosis can occur as a result of insufficient ammoniagenesis within the damaged kidney. This, in turn, can bring about a variety of sequella that have their basis in hormonal and cellular abnormalities that effect stunted growth, loss of muscle and bone mass, and negative nitrogen balance. Cellular mechanisms accounting for these findings are reviewed. In bone, metabolic acidosis causes direct dissolution of bone; ostoeclastic activity is increased while osteoblastic activity is suppressed. In muscle, branched-chain amino acid oxidation is increased and the ubiquitin-proteasome pathway is activated: muscle wasting results. Even a modest degree of metabolic acidosis can be harmful and can initiate a series of maladaptive responses that are not easily reversed, although there is evidence that alkali therapy can be beneficial in reversing these responses.

Objective Older adults with chronic kidney disease have a high rate of uncontrolled hypertension. Home monitoring of blood pressure (BP) is an integral part of management, but requires that patients bring records to clinic visits. Telemonitoring interventions, however, have not targeted older, less technologically-skilled populations. Methods Veterans with stage 3 or greater chronic kidney disease and uncontrolled hypertension were randomized to a novel telemonitoring device pairing a Bluetooth-enabled BP cuff with an Internet-enabled hub, which wirelessly transmitted readings (n= 28), or usual care (n= 15). Home recordings were reviewed weekly and telemonitoring participants were contacted if BP was above goal. The prespecified primary endpoints were improved data exchange and device acceptability. Secondary endpoint was BP change. Results Forty-three participants (average age 68 years, 75% white) completed the 6-month study. Average start-of-study BP was 147/78mmHg. Those in the intervention arm had a median of 29 (IQR 22, 53) transmitted BP readings per month, with 78% continuing to use the device regularly, whereas only 20% of those in the usual care group brought readings to in-person visits. The median number of telephone contacts triggered by the wireless monitoring was 2 (IQR 1, 4) per patient. Both groups had a significant improvement in systolic BP (P< 0.05, for both changes); systolic BP fell a median of 13 mmHg in monitored participants compared with 8.5mmHg in usual care participants (P for comparison 0.31). Conclusion This low-cost wireless monitoring strategy led to greater sharing of data between patients and clinic and produced a trend toward improvements in BP control over usual care at 6 months.

Oxygen consumed by the kidney (Q(O(2))) is primarily obligated to sodium reabsorption (T(Na)). The relationship of Q(O(2)) to T(Na) (Q(O(2))/T(Na)) may be altered by hormones and autacoids. To examine whether Q(O(2))/T(Na) depends on the mechanism of sodium reabsorption, we first evaluated the effects on Q(O(2)) and Q(O(2))/T(Na) of benzolamide (BNZ), a proximal diuretic that works by inhibiting membrane carbonic anhydrase. During BNZ infusion in anesthetized rats, Q(O(2)) increased by 50% despite a 25% decline in T(Na). However, BNZ failed to increase Q(O(2))/T(Na) when given along with the adenosine A1 receptor blocker, DPCPX, which inhibits basolateral Na-bicarbonate cotransport (NBC1), or EIPA, which inhibits sodium-hydrogen exchange (NHE). Incubating freshly harvested rat proximal tubules with BNZ also caused Q(O(2))to increase by 62%, an effect that was prevented by blocking the apical NHE3 with S3226. Blocking NBC1 or NHE3 in the proximal tubule will have opposite effects on cell pH, but both maneuvers should reduce active chloride transport. In conclusion, inhibiting membrane carbonic anhydrase in the proximal tubule increases Q(O(2)) and reduces the energy efficiency of sodium reabsorption by the kidney. This is not purely due to shifting the burden of reabsorption to a more expensive site downstream from the proximal tubule. Instead, increased cost may be incurred within the proximal tubule as the result of increased active chloride transport.

Miracle CM, Rieg T, Mansoury H, Vallon V, Thomson SC. Ornithine decarboxylase inhibitor eliminates hyperresponsiveness of the early diabetic proximal tubule to dietary salt. Am J Physiol Renal Physiol 295: F995-F1002, 2008. First published June 18, 2008 doi:10.1152/ajprenal.00491.2007.-Heightened sensitivity of the diabetic proximal tubule to dietary salt leads to a paradoxical effect of salt on glomerular filtration rate (GFR) via tubuloglomerular feedback. Diabetic hyperfiltration is a feedback response to growth and hyperreabsorption by the proximal tubule. The present studies were performed to determine whether growth and hyperfunction of the proximal tubule are essential for its hyperresponsiveness to dietary salt and, hence, to the paradoxical effect of dietary salt on GFR. Micropuncture was performed in four groups of inactin-anesthetized Wistar rats after 10 days of streptozotocin diabetes drinking tap water or 1% NaCl. Kidney growth was suppressed with ornithine decarboxylase (ODC) inhibitor, DFMO (200 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 ), or placebo. Single nephron GFR (SNGFR) was manipulated by perfusing Henle's loop so that proximal reabsorption (J prox) could be expressed as a function of SNGFR in each nephron, dissociating primary effects on the tubule from the effects of glomerulotubular balance. Alone, DFMO or high salt reduced SNGFR and suppressed J prox independent of SNGFR. Suppression of J prox was eliminated and SNGFR increased when high salt was given to rats receiving DFMO. ODC is necessary for hyperresponsiveness of the proximal tubule to dietary salt and for the paradoxical effect of dietary salt on GFR in early diabetes. This coupling of effects adds to the body of evidence that feedback from the proximal tubule is the principal governor of glomerular filtration in early diabetes. diabetic hyperfiltration; proximal tubular reabsorption; tubuloglomerular feedback; glomerulotubular balance GLOMERULAR HYPERFILTRATION is a cardinal feature of early diabetes mellitus (5). Several lines of evidence support a tubular hypothesis to explain how glomerular filtration rate (GFR) comes to be elevated in early diabetes (reviewed in Ref. 17). According to this hypothesis, hyperfiltration is rooted in a prior increase in proximal reabsorption with GFR rising secondarily via negative feedback through the macula densa. In the course of trying to determine how the initial increase in proximal reabsorption comes about, we previously discovered that it could be prevented by suppressing growth of the kidney (15), which is normally rapid in early diabetes (10). We also discovered that proximal reabsorption in early diabetes is overly sensitive to dietary salt, to the extent that, when placed on a high salt diet, a diabetic rat drops its proximal reabsorption sufficiently to activate tubuloglomerular feedback (TGF), thereby reducing single nephron GFR (SNGFR) (20, 21). Since a reciprocal effect of dietary salt on GFR is contrary to usual expectation, we refer to this phenomenon as the salt paradox. So far, the salt parad...