The effects of food restriction and exercise on site-specific differences in adipocyte volume and adipose tissue cellularity in the guinea-pig. 2. Intermuscular sites.

Two intermuscular adipose depots, the popliteal mass (POP) and the fat under the gluteus superficialis muscle ( GLS ) were studied in guinea-pigs maintained under three different regimes of diet and exercise. Eleven different sites in POP and four sites in GLS were defined using associated muscle and fascia as 'landmarks'. Samples of twenty to twenty-five adipocytes from each site were removed and their mean volume measured; a consistent pattern of distribution of larger and smaller adipocytes within POP and GLS was found in all animals. The correlation between the volume of adipocytes from sites between the same pairs of muscles was substantially greater than the correlation between the volume of adipocytes from comparable sites between different muscles, whether the sites were within the same fat mass (POP) or in different fat masses (POP and GLS ). The volume of adipocytes from the edge of the fat mass correlated more closely with those from the edge of the same or a synergistic muscle than with the volume of cells from the centre sites or edge sites from an interface with another muscle. These effects were most pronounced in exercised animals and weak or insignificant in sedentary ad lib.-fed animals. The volume of adipocytes from edge sites correlated with the gross weight of the adjacent muscles in exercised animals only. It is concluded that muscle activity has a local effect on the volume of adjacent adipocytes. It is suggested that the mechanism involved is mechanical rather than biochemical.