Peritoneal Potassium and pH Measurement in Early Diagnosis of Acute Mesenteric Ischemia in Rats

The value of potassium, pH and D-dimer levels in early diagnosis of acute mesenteric ischemia: an experimental study on rats

INTRODUCTION

The aim of this randomized controlled experimental study was to evaluate the efficacy of potassium, pH and D-dimer levels in blood, as well as potassium and pH levels in peritoneal lavage fluid, in the early diagnosis of acute mesenteric ischemia.

MATERIAL AND METHODS

This study was conducted at the Istanbul University Center of Experimental Medicine after having received approval from the Istanbul University animal testing ethics committee. Male albino Wistar rats (n = 24; 250 to 350 g) were divided into two control groups and two ischemic groups. Levels of potassium, pH, and D-dimer in blood and levels of potassium and pH in peritoneal lavage fluid were analyzed for 1 h and 2 h after the induced acute mesenteric ischemia procedure. The degree of ischemic injury was determined using the histopathological damage score in tissue samples taken from the terminal ileum.

RESULTS

Ischemic groups had statistically significant differences in potassium and pH in blood and peritoneal lavage fluid compared to non-ischemic groups (p < 0.05). There was no significant difference between control and ischemic groups in terms of D-dimer and histologic grading results after 1 h (p = 0.132, p = 0.475 respectively), while there was a significant difference between control and ischemic groups after 2 h (p < 0.05).

CONCLUSIONS

The levels of potassium, pH, and D-dimer could be useful in daily practice for the early diagnosis of acute mesenteric ischemia.

The Acidic Tumor Microenvironment as a Driver of Cancer

Acidic metabolic waste products accumulate in the tumor microenvironment because of high metabolic activity and insufficient perfusion. In tumors, the acidity of the interstitial space and the relatively well-maintained intracellular pH influence cancer and stromal cell function, their mutual interplay, and their interactions with the extracellular matrix. Tumor pH is spatially and temporally heterogeneous, and the fitness advantage of cancer cells adapted to extracellular acidity is likely particularly evident when they encounter less acidic tumor regions, for instance, during invasion. Through complex effects on genetic stability, epigenetics, cellular metabolism, proliferation, and survival, the compartmentalized pH microenvironment favors cancer development. Cellular selection exacerbates the malignant phenotype, which is further enhanced by acid-induced cell motility, extracellular matrix degradation, attenuated immune responses, and modified cellular and intercellular signaling. In this review, we discuss how the acidity of the tumor microenvironment influences each stage in cancer development, from dysplasia to full-blown metastatic disease.

Acidosis inhibits rhythmic contractions of human thoracic ducts

Lymph vessels counteract edema by transporting interstitial fluid from peripheral tissues to the large veins and serve as conduits for immune cells, cancer cells, and pathogens. Because edema during inflammation and malignancies is frequently associated with acidosis, we tested the hypothesis that acid-base disturbances affect human thoracic duct contractions. We studied, by isometric and isobaric myography, the contractile function of human thoracic duct segments harvested with written informed consent from patients undergoing esophageal cancer surgery. Human thoracic ducts produce complex contractile patterns consisting of tonic rises in tension (isometric myography) or decreases in diameter (isobaric myography) with superimposed phasic contractions. Active tone development decreases substantially (~90% at 30 vs. 7 mmHg) at elevated transmural pressure. Acidosis inhibits spontaneous as well as noradrenaline- and serotonin-induced phasic contractions of human thoracic ducts by 70-90% at extracellular pH 6.8 compared to 7.4 with less pronounced effects observed at pH 7.1. Mean tension responses to noradrenaline and serotonin - averaged over the entire period of agonist exposure - decrease by ~50% at extracellular pH 6.8. Elevating extracellular [K+ ] from the normal resting level around 4 mmol/L increases overall tension development but reduces phasic activity to a level that is no different between human thoracic duct segments investigated at normal and low extracellular pH. In conclusion, we show that extracellular acidosis inhibits human thoracic duct contractions with more pronounced effects on phasic than tonic contractions. We propose that reduced phasic activity of lymph vessels at low pH attenuates lymph propulsion and increases the risk of edema formation.

Extracellular acidosis and very low [Na+ ] inhibit NBCn1- and NHE1-mediated net acid extrusion from mouse vascular smooth muscle cells

AIM

The electroneutral Na⁺ , HCO3- cotransporter NBCn1 and Na⁺ /H⁺ exchanger NHE1 regulate acid-base balance in vascular smooth muscle cells (VSMCs) and modify artery function and structure. Pathological conditions - notably ischaemia - can dramatically perturb intracellular (i) and extracellular (o) pH and [Na⁺ ]. We examined effects of low [Na⁺ ]_o and pH_o on NBCn1 and NHE1 activity in VSMCs of small arteries.

METHODS

We measured pH_i by 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-based fluorescence microscopy of mouse mesenteric arteries and induced intracellular acidification by NH4+ prepulse technique.

RESULTS

NBCn1 activity - defined as Na⁺ -dependent, amiloride-insensitive net base uptake with CO₂ /HCO3- present - was inhibited equally when pH_o decreased from 7.4 (22 mm HCO3-/5% CO₂ ) by metabolic (pH_o 7.1/11 mm HCO3-: 22 ± 8%; pH_o 6.8/5.5 mm HCO3-: 61 ± 7%) or respiratory (pH_o 7.1/10% CO₂ : 35 ± 11%; pH_o 6.8/20% CO₂ : 56 ± 7%) acidosis. Extracellular acidosis more prominently inhibited NHE1 activity - defined as Na⁺ -dependent net acid extrusion without CO₂ /HCO3- present - at both pH_o 7.1 (45 ± 9%) and 6.8 (85 ± 5%). Independently of pH_o , lowering [Na⁺ ]_o from 140 to 70 mm reduced NBCn1 and NHE1 activity <20% whereas transport activities declined markedly (25-50%) when [Na⁺ ]_o was reduced to 35 mm. Steady-state pH_i decreased more during respiratory (ΔpH_i /ΔpH_o  = 71 ± 4%) than metabolic (ΔpH_i /ΔpH_o  = 30 ± 7%) acidosis.

CONCLUSION

Extracellular acidification inhibits NBCn1 and NHE1 activity in VSMCs. NBCn1 is equivalently inhibited when pCO₂ is raised or [HCO3-]_o decreased. Lowering [Na⁺ ]_o inhibits NBCn1 and NHE1 markedly only below the typical physiological and pathophysiological range. We propose that inhibition of Na⁺ -dependent net acid extrusion at low pH_o protects against cellular Na⁺ overload at the cost of intracellular acidification.