Is Ammonia Excretion Affected by Gill Ventilation in the Rainbow Trout Oncorhynchus mykiss?

Publication date: Available online 10 January 2020Source: Respiratory Physiology & NeurobiologyAuthor(s): Junho Eom, Sandra Fehsenfeld, Chris M. WoodAbstractAmmonia (NH3 + NH4+) is the major nitrogenous waste in teleost fish. NH3 is also the third respiratory gas, playing a role in ventilatory control. However it is also highly toxic. Normally, ammonia excretion through the gills occurs at about the same rate as its metabolic production, but the branchial transport mechanisms have long been controversial. An influential review in this journal has claimed that ammonia excretion in fish is probably limited by diffusion rather than by convection, so that increases in ventilation would have negligible effect on the rate of ammonia excretion. Why then should elevated plasma ammonia stimulate ventilation? The diffusion-limitation argument was made before the discovery of Rhesus (Rh) glycoproteins and the associated metabolon in the gills, which serve to greatly increase branchial ammonia permeability under conditions of ammonia loading. Therefore, we hypothesized here that (i) in accord with the diffusion-limitation concept, changes in ventilation would not affect the rate of ammonia excretion under conditions where branchial Rh metabolon function would be low (resting trout with low plasma ammonia levels). However, we also hypothesized that (ii) in accord with convective limitation, changes in ventilation would influence the rate of ammonia excretion under conditions where diffusi...
Source: Respiratory Physiology and Neurobiology - Category: Respiratory Medicine Source Type: research