Diabetic ketoacidosis develops when insulin is insuffcient to clear blood sugar into cells for energy, then the liver breaks down fat for fuel with production of ketoacids. Lower pH activates proximal tubule PEPCK expression to replenish bicarbonate and excrete acid via NHE3 as ammonia, known as, “ammoniagenesis.” Baseline female (F) rodents exhibit greater ammoniagenesis and less NHE3 activity than males (M). We examined ammoniagenesis in male (M) and female (F) ZSF1 rats, a model of obesity and diabetic kidney disease. ZSF1 rats are born lean (L) or obese (O). OM display hyperglycemia and glucosuria at 10 wk, not yet evident in OF at 18 wk. We tested three hypotheses in ZSF1 rats (n=4-6/group): 1) ammoniagenesis rate is greater in OM and OF than LM and LF, 2) LF exhibit a higher rate of ammoniagenesis than OF, and 3) the blood glucose lowering SGLT2 inhibitor empagliflozin (SGLT2i) reduces ammoniagenesis in OM. Ammoniagenesis was measured as ammonia/24 hr/tibia length because OM and OF weigh 50% more than LM and LF. Abundance of PEPCK and NHE3 was assessed by semiquantitative immunoblots. Titratable acidity (TA) was measured as classically defined. In OM, ammoniagenesis was 6X greater (P< 0.0001), and TA elevated (P=0.0003) versus LM. Ammoniagenesis was not different in OF vs LF (P=0.99). Ammoniagenesis was only 2X greater in OM vs OF (P=0.001) indicative of higher baseline ammoniagenesis in F vs M. PEPCK abundance was 2.8X greater in both OM and OF vs LM and LF (P< 0.001), and NHE3 abundance was lower by 35 and 20%, respectively, in OM and OF vs LM and LF (P< 0.003). Oral SGLT2i treatment (10 mg/d, n=5-6/group, 6 wks starting at 20 wk old) vs vehicle lowered plasma glucose 35%, doubled urine glucose excretion, but did not significantly alter ammoniagenesis, PEPCK or NHE3 abundance (but tended to reduce urine TA). These findings demonstrate that at 16 weeks, OM exhibit highly elevated ammoniagenesis and TA along with hyperglycemia. In contrast, OF do not exhibit hyperglycemia nor elevated ammoniagenesis, illustrating a resistance to diabetic ketoacidosis at 16 wk, despite obesity, higher TA (P= 0.003), higher PEPCK and lower NHE3. In 20 wk old OM ZSF1, SGLT2i treatment does not reverse ammoniagenesis despite lowering plasma glucose for 6 weeks. R01 DK083785, R25DK113659, NIH Step Up U24 DK115255,. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
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