Factors influencing the acid-base changes in the air-pouch exudate following carrageenan induced inflammation in rats

The interactions between the acid-base variables that contribute to exudate acidosis were studied in the subcutaneous air-pouch after carrageenan injection in rats. We studied the concurrent changes of exudate gases (P-CO2 and P-O2), main ions ([Na+], [K+], [Ca2+], [Mg2+], [Cl-] and [Lac(-)]), inorganic phosphate (Pi) and albumin in acutely inflamed rats (4, 8, 12, 24 and 48 h of inflammation). A notable hypercapnia was found in the exudate after only 8 h (exudate P-CO2 = 64.3 +/- 2.9 mm Hg) but this hypercapnia decreased after 48 h (32.9 +/- 12.7 mm Hg), coincident with the greatest increase in exudate cells. With respect to the metabolic acid-base variables, the most important changes found were a parallel decrease in the strong ion difference ([SID]) and exudate pH, as well as increases in the exudate weak acid buffers ([A(TOT)]) due to albumin and inorganic phosphate (P-i) increases. However, after 12 h, the exudate acidosis was stable at around pH 7. A similar acid pH was obtained after 24 h of inflammation when the carrageenan solution injected was previously adjusted to a physiological pH (7.4). This pH, analogous to that of the exudate, was the result of compensation by the acid-base independent variables, a fact which suggests that acid pH may be a beneficial condition for cells taking part in inflammatory processes.