Previous studies addressing energy turnover in fish blood have ignored the possible influence of white cells. The present investigation quantified the contribution of white and red cells to whole-blood energy turnover in trout (Oncorhynchus mykiss) before and after adrenergic stimulation. All experiments were carried out on cells kept in their native plasma. White cells were found to have an almost twenty times higher rate of oxygen consumption than red cells. Furthermore, white cells were responsible for essentially all whole-blood lactate production. Our data therefore show that white cells account for almost half of the energy turnover in trout blood. Adrenergic stimulation elicited a significant increase in total as well as ouabain-sensitive (a Na+/K+-ATPase inhibitor) red cell oxygen consumption. However, the ouabain-sensitive red cell oxygen consumption amounted to approximately 23 % of the total red cell oxygen consumption, regardless of adrenergic stimulation. Therefore, energy-consuming processes other than Na+/K+-ATPase activity are probably involved in the increased red cell oxygen uptake after adrenergic stimulation.

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