The acid-base responses of gills and kidneys to infused acid and base loads in the channel catfish,Ictalurus punctatus

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Abstract
Acid and base loads infused into the dorsal aorta of the freshwater channel catfish (Ictalurus punctatus Rafinesque) were excreted by both gills and kidneys. The gills excreted 2-3 times as much as the kidneys. After a 2 mmol. kg-1 load of NaHCO3, the gills excreted 50% of the net OH- load in the first 5 h, while the kidneys excreted 18% in the first 6 h. After a 2 mmol. kg-1 load of NH4Cl, the gills excreted 32% of the load in 6 h, and 16% was excreted renally in 20 h. There was no evidence of tissue damage after either NaHCO3 or NH4Cl infusions, whereas infusion of 2 mmol. kg-1 HCl or 1 mmol. kg-1 of L(+)-lactic acid caused significant kidney damage and extensive tissue necrosis within 24 h. After both NaHCO3 and NH4Cl infusions, the majority of the load had been transferred to the intracellular compartment within 2 h. From there it was excreted slowly, presumably by transfer back through the extracellular compartment. Due to the relative compartment volumes and buffer values, the change in intracellular pH was less than 0.05 units, while the blood pH was changed by as much as 0.3 units.