Blood and Muscle Metabolites: Clues to Flow

Abstract

In the previous chapter I discussed splanchnic blood flow, which can be determined by direct measures because the organ has discrete vascular connections, or the organ filters specific molecules such as inulin by the kidney. Furthermore, it is possible to measure turnovers of metabolites by measuring flow and concentration in the artery and vein that supply and drain the organ. Determination of flow characteristics and metabolite fluxes of skeletal muscle is a more intractable problem because blood supply is so diffuse. There has been only one direct and specific measurement of changes in muscle metabolite, i.e., decline and increase of muscle O₂ and lactate concentration [LA] in harbor seals during forced submersions (Fig. 3.5). The difficulty of the problem is reflected perhaps in the fact that the experiments, which were done over 40 years ago (Scholander et al. 1942), have not been repeated on other species as is the case of so many other experiments involving forced submersion. The most common method of analysis of muscle condition has been the indirect determination of changes in blood metabolites. As will be seen later in this chapter, that is the basis for the conclusions about blood flow and fuel consumption in natural dives.