CSF acid-base regulation and ventilation in iso- and hypocapnic Hacetate acidosis.
Intravenous infusion in conscious rabbits of Hacetate decreases both arterial CO2 partial pressure PaCO2 and cerebrospinal fluid (CSF) HCO3- more than observed with HCl or HNO3 infusion. These acids did not affect CSF HCO3- in isocapnic conditions, and this study asks whether Hacetate infusion will do so. Arterial, central venous, and cisterna magna catheters were implanted in pentobarbital-anesthetized rabbits and all subsequent measurements were performed in the conscious state. Hacetate was infused intravenously over 6 h to decrease plasma HCO3- the same amount in a group allowed to decrease its PaCO2 in response to the acid (hypocapnic) and one in which PaCO2 was maintained at control levels (isocapnic). CSF HCO3- decreased significantly in isocapnia, although the change was less than in hypocapnia. Stoichiometrically by 6 h the measured CSF HCO3- change was balanced by an increase in acetate in hypocapnia and the sum of an increase in acetate and a decrease in chloride in isocapnia. Mechanistically, net acetate entry into CSF appears to involve an exchange for chloride as proposed for NO3-/Cl- and a process that lowers CSF HCO3-. This process could be competitive replacement of HCO3- by acetate in the CSF production mechanism or nonionic diffusive entry of Hacetate into CSF with subsequent titration of HCO3-. The decreases in CSF HCO3- result from the acetate mechanism and the hypocapnic effect on Cl- and HCO3-. The greater ventilatory response results from the greater CSF acidification or a specific effect of acetate per se.
D000085:Acetates / Q000134:cerebrospinal fluid; D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000134:cerebrospinal fluid / Q000139:chemically induced / Q000503:physiopathology*; D000818:Animals; D001639:Bicarbonates / Q000134:cerebrospinal fluid; D002245:Carbon Dioxide / Q000378:metabolism; D002628:Chemoreceptor Cells / Q000502:physiology; D011817:Rabbits; D012119:Respiration
D000085:Acetates; D001639:Bicarbonates; D002245:Carbon Dioxide