Although the cause of hypertension among individuals with obesity and insulin resistance is unknown, increased plasma insulin, acting in the kidney to increase sodium reabsorption, has been proposed as a potential mechanism. Insulin may also stimulate glucose uptake, but the contributions of tubular insulin signaling to sodium or glucose transport in the setting of insulin resistance is unknown. To directly study the role of insulin signaling in the kidney, we generated inducible renal tubule-specific insulin receptor-KO mice and used high-fat feeding and mineralocorticoids to model obesity and insulin resistance. Insulin receptor deletion did not alter blood pressure or sodium excretion in mice on a high-fat diet alone, but it mildly attenuated the increase in blood pressure with mineralocorticoid supplementation. Under these conditions, KO mice developed profound glucosuria. Insulin receptor deletion significantly reduced SGLT2 expression and increased urinary glucose excretion and urine flow. These data demonstrate a direct role for insulin receptor-stimulated sodium and glucose transport and a functional interaction of insulin signaling with mineralocorticoids in vivo. These studies uncover a potential mechanistic link between preserved insulin sensitivity and renal glucose handling in obesity and insulin resistance.

Acute increases in K intake decrease Na‐Cl cotransporter (NCC) phosphorylation and NCC‐mediated Na reabsorption. This decrease in NCC phosphorylation, coupled with increased distal delivery of Na and enhanced ENaC activity, is one mechanism to augment kaliuresis. We sought to dissect the role of adaptation to a high K diet in which the plasma K concentration was unchanged between a normal and high K diet. To test this, we measured thiazide‐sensitive electrolyte excretion in acutely fasted mice fed a chronic normal or high K diet with and without the addition of benzamil, an ENaC antagonist.We placed C57Bl/6J mice on either a normal (0.7% w/w) or high (5% w/w) K diet for 1 week. We fasted mice, performed an intraperitoneal injection of either 30 mg/kg hydrochlorothiazide to inhibit NCC, 1.4 mg/kg benzamil to inhibited ENaC, or both, and collected urine for 4 hours. After a washout period, we sacrificed mice after an acute fast for tissue analysis. We measured plasma aldosterone concentration from a separate, similarly treated group of normal or high K‐fed mice.Mice demonstrated decreased thiazide‐induced Na excretion on a high K diet compared to a normal K diet, yet thiazide‐induced K excretion remained unchanged (0.138 +/− 0.017 vs. 0.109 +/− 0.006 μmol/min, normal vs. high K diet, respectively, p=0.28) and significantly higher than vehicle. Aldosterone was significantly higher in the high K diet‐fed group (141 +/− 13 vs. 516 +/− 171 pg/ml, normal vs. high K diet, respectively; p<0.05). Benzamil increased urine flow on the high K (1.03 +/− 0.05 μl/min, p<0.05) but not normal K diet (0.42 +/− 0.19 μl/min, p=0.2) compared to vehicle (0.46 +/− 0.11 μl/min), congruent with increased ENaC‐mediated Na reabsorption. Plasma K concentrations in acutely fasted mice were no different between mice on normal or high K diets (4.98 +/− 0.22 vs. 4.53 +/− 0.17 mmol/L, normal vs. high K diet, respectively, p=0.2). Membrane preparations of kidney lysate blotted for total and phosphorylated NCC were not significantly different on a normal vs. high K diet. The increase in K excretion in high K diet‐fed mice after thiazide administration suggests that NCC activity is not significantly diminished. The decrease in thiazide‐induced Na excretion may be explained by an aldosterone‐mediated increase in ENaC activity with a chronic, high K diet. These data provide evidence that both NCC phosphorylation and activity are not tonically suppressed with high K adaptation in the absence of elevated plasma K concentrations. ENaC activity is also increased on a high K diet in the absence of elevated plasma K. Furthermore, plasma K‐mediated regulation of NCC phosphorylation may be relevant for short‐term, rather than chronic K adaptation.Support or Funding InformationJMN receives support from the NIH (1K08 DK114567‐01). JMN was previously supported by an American Heart Association Postdoctoral Fellowship (16POST27770003). VB receives support from the NIH (1R01 DK091565).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

High fat‐fed mice recapitulate several features of the Metabolic Syndrome, including impaired sodium excretion and increased blood pressure. In this model, post‐thiazide sodium excretion is increased compared to low fat‐fed controls, providing evidence that increased Na‐Cl co‐transporter (NCC)‐mediated transport may contribute to both impaired sodium excretion and hypertension in the Metabolic Syndrome. We sought to test whether a chronic, high potassium diet regulates NCC differently in high fat‐fed mice compared to low fat‐fed controls.We fed high fat‐fed mice either a normal (0.7% w/w) or high (5% w/w) potassium diet for 1 week then performed an intraperitoneal injection either vehicle or 30 mg/kg hydrochlorothiazide and collected urine for 4 hours. We then switched the dietary potassium content of both groups and rechallenged the mice with the same drugs. After a washout period, we sacrificed mice for tissue analysis.While on a high potassium diet, post‐thiazide urinary sodium excretion was no different from vehicle and significantly lower than excretion on a normal potassium diet (0.164 +/− 0.024 vs. 0.026 +/− 0.005 μmol/min, normal vs. high potassium diet, respectively; p<0.001). Post‐thiazide potassium excretion was no different on either diet (0.138 +/0 0.017 vs. 0.109 +/− 0.006 μmol/min normal vs. high potassium diet, respective; p = 0.28) and higher than vehicle. Urine flow rate was no different while on either normal or high potassium diet after vehicle or thiazide injection. Membrane preparations of whole kidney lysate blotted for both total and phosphorylated NCC were not significantly different in high fat‐fed mice on a normal vs. high potassium diet. High fat‐fed mice do not demonstrate the high potassium diet‐induced repression of NCC phosphorylation that is well‐documented in low fat‐fed mice, and have detectable, albeit diminished sodium excretion. These data support a role for attenuated repression of the potassium‐NCC axis in engendering impaired sodium excretion and hypertension in this model of Metabolic Syndrome.Support or Funding InformationJMN receives support from the NIH (1K08 DK114567‐01). JMN was previously supported by an American Heart Association Postdoctoral Fellowship (16POST27770003). VB receives support from the NIH (1R01 DK091565).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.