[Effect of mannitol on oxygen consumption of the renal cortex of rats]

We have determined the oxygen consumption (QO2) in renal cortical tissue from controls and from rats which received in vivo and infusion of mannitol (600 mM) in order to study the metabolic changes which occurred in the tissue. QO2 was significantly higher (+20%, p less than 0.01) in slices from animals which received the infusion than in those from non-infused animals, when incubated in mannitol containing solutions; these slices had tubules with their lumens open. When the slices were incubated in solutions without mannitol or obtained from animals not infused with mannitol, the QO2 was lower and the tubules appeared histologically with the lumen closed. A short (2 min) exposure to 2 mM ethacrinic acid inhibited QO2 only in slices from mannitol infused animals incubated in mannitol containing solutions. Similar exposures to 1 mM ouabain inhibited QO2 both in slices from infused and from non-infused animals and independently of the composition of the incubation media. We suggest that the higher QO2 found in those slices which had their tubular lumens open, as well as the specific inhibitory effect of ethacrinic acid on the excess QO2 of such slices, might relate to transport processes, linked to tissue metabolism, and only present in tubules which have their lumens open. Such active transport process may correspond, for example, to the coupled transcellular Na+ and Cl- transport. The effects of mannitol on the tissue water content is discussed.