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At least 91 records · Page 5Linked to original sources
PubMed1990

Mesenteric oxygen metabolism, ileal mucosal hydrogen ion concentration, and tissue edema after crystalloid or colloid resuscitation in porcine endotoxic shock: comparison of Ringer's lactate and 6% hetastarch.

We performed an experimental trial comparing crystalloid (Ringer's lactate) and colloid (hetastarch) resuscitation in pentobarbital-anesthetized pigs. Superior mesenteric arterial blood flow (Qsma) was measured using an ultrasonic flow probe, and ileal intramucosal hydrogen ion concentration [( H+]I) was estimated tonometrically. Beginning at t = 0 min, all animals were infused over 20 min with Escherichia coli (0111:B4) lipopolysaccharide (LPS; 150 micrograms/kg). Starting at t = 0 min and continuing for the duration of the experiment (3 hr), pigs in group I (N = 9) were resuscitated with Ringer's lactate (1.2 ml/kg min), whereas animals in group II (n = 9) were infused with 6% hetastarch in saline (0.4 ml/kg min). Systemic and mesenteric hemodynamic changes induced by LPS were similar in both groups; mean arterial pressure and systemic vascular resistance index decreased (P less than .05), but cardiac index was well preserved. Central venous pressure increased (P less than .05). Superior mesenteric O2 delivery decreased significantly (P less than .05) in both groups, although mesenteric O2 uptake was unchanged. Ileal [H+]I increased (P less than .05) in both groups. Gravimetrically determined extravascular water was greater in lung (P = .03) and ileum (P = .058) in group I as compared to group II. Although crystalloid infusion was associated with greater tissue edema, this effect did not translate into a difference in systemic or regional (i.e., mesenteric) O2 uptake or greater ileal tissue acidosis.

Animals↗
PubMed2004

Predicted effects of mineral neutralization and bisulfate formation on hydrogen ion concentration for dilute sulfuric acid pretreatment.

Dilute acid and water-only hemicellulose hydrolysis are being examined as part of a multiinstitutional cooperative effort to evaluate the performance of leading cellulosic biomass pretreatment technologies on a common basis. Cellulosic biomass, such as agricultural residues and forest wastes, can have a significant mineral content. It has been shown that these minerals neutralize some of the acid during dilute acid pretreatment, reducing its effectiveness, and the higher solids loadings desired to minimize costs will require increased acid use to compensate. However, for sulfuric acid in particular, an equilibrium shift to formation of bisulfate during neutralization can further reduce hydrogen ion concentrations and compound the effect of neutralization. Because the equilibrium shift has a more pronounced effect at lower acid concentrations, additional acid is needed to compensate. Coupled with the effect of temperature on acid dissociation, these effects increase acid requirements to achieve a particular reaction rate unless minerals are removed prior to hydrolysis.

Acids↗
PubMed1986

Effect of hydrogen ion concentration on aldosterone secretion by isolated perfused canine adrenal glands.

The direct effects of changes in extracellular hydrogen ion (H+) concentration on aldosterone secretion under basal, angiotensin II- and potassium-stimulated conditions were studied in isolated, perfused canine adrenal glands. Changes in extracellular H+ concentration were induced by altering either the partial pressure of CO2 (pCO2) or the HCO3- concentration of the perfusate. Acid-base disturbances had a more pronounced effect on aldosterone secretion under stimulated than under basal conditions. Increasing H+ concentration enhanced angiotensin II- and potassium-stimulated aldosterone secretion, whereas decreasing H+ concentration markedly inhibited the secretory response to these stimuli. Because changes in H+ concentration, whether produced by varying extracellular pCO2 or extracellular HCO3- concentration, had similar effects on angiotensin II-stimulated aldosterone secretion, the data suggest that H+ concentration per se is the important determinant of the aldosterone secretory rate. Interestingly, during the immediate recovery period from pCO2-induced alkalosis under both angiotensin II- and potassium-stimulated conditions, aldosterone secretion always returned to a value significantly higher than that obtained just before alkalosis. The results of this study demonstrate that changes in extracellular H+ concentration influence the rate of aldosterone secretion, possibly via changes in intracellular pH, by a direct action on the canine adrenal gland. Therefore, when evaluating the control of aldosterone secretion, the acid-base status of the whole animal or of in-vitro adrenal tissue must be considered.

Adrenal Glands↗