Effects of fasting on adipose tissue perfused in situ in young dogs

Subcutaneous adipose tissue blood flow and triacylglycerol-mobilization during prolonged exercise in dogs

In 6 dogs concentration differences for glycerol and FFA were measured between the aorta and the external pudendal vein, a vein which mainly drains subcutaneous adipose tissue in dogs, during prolonged exercise. It was found that the a-v differences increased about 2-fold for both glycerol and FFA, however great interindividual differences were found. In 4 dogs adipose tissue blood flow, glycerol and FFA a-v differences were measured simultaneously, and the mobilizations of glycerol and FFA as well as the re-esterification of FFA were calculated. After 2 h of exercise the values were in the range of 1-7 umol/(100 g.min) for FFA and glycerol mobilizations while the FFA re-esterification was in the range of 2-14 umol/(100 g.min). It was found that the FFA/albumin ratio in adipose venous blood, on average 3.6 was at a level at which the FFA mobilization has been shown to depend on the adipose tissue blood flow in isolated fat pads. In 11 dogs subcutaneous adipose tissue blood flow rose 2-fold during exercise from about 5-10 ml/(100 g.min). It is concluded that the subcutaneous adipose tissue blood flow response to exercise is equal in man and dog, that lipolysis, FFA mobilization and FFA re-esterification are increased in subcutaneous adipose tissue during exercise, and that the increase in blood flows is of importance for the enhanced FFA mobilization during exercise.

Oxygen uptake and tissue oxygen tension during adrenergic stimulation in canine subcutaneous adipose tissue

The effect of sympathetic nerve stimulation (NS) and injected noradenaline (NA) or isoprenaline (Iso) on PVO2, VO2 and PtO2 was studied in isolated canine subcutaneous adipose tissue. These effects were compared to those produced by mechanical blood flow reduction (clamping). Resting VO2 measured 13.0+/- 2.3 mumol X min-1 X 100 g-1. When blood flow was reduced by 20% or less there was no significant change of VO2. Reducing blood flow to 50% of control or less by NS caused a parallel reduction in VO2, while clamping reduced VO2 significantly less. NA gave effects similar to those of NS. After NS or NA there was a period of hyperemia and increased oxygen extraction which more than compensated for the decrease in VO2 during vasoconstriction. Such a net increase in VO2 was not produced by clamping. Control PtO2 averaged 29+/-2 mmHg. NA reduced it by 70% and clamping to the same blood flow level only by 14% (p less than 0.01). Thus, a mere reduction in blood flow has little effect on PtO2, while blood flow reduction combined with redistribution of blood flow and an increased oxygen deman can lead to tissue hypoxia.