Glucoregulation during rest and exercise in depancreatized dogs: role of the acute presence of insulin
Wasserman, D.H.; Bupp, J.L.; Johnson, J.L.; Bracy, D.; Lacy, D.B.
American Journal of Physiology 262(5 Pt 1): E574-E582
1992
ISSN/ISBN: 0002-9513 PMID: 1590369 Document Number: 390973
To determine the effects of the presence of insulin in poorly controlled diabetes, depancreatized (PX) dogs (n = 5) were studied during rest and 150 min of exercise in paired experiments in which saline alone was infused (IDEF) and in which insulin was replaced intraportally (200 .mu.U.cntdot.kg-1.cntdot.min-1) with glucose clamped at the levels in IDEF (IR + G). PX dogs (n = 4) were also studied with insulin, but glucose was allowed to fall (IR). Insulin was not detectable, 6.+-.1 and 6.+-.2 .mu.U/ml in IDEF, IR + G, and IR. Plasma glucose was 470 .+-. 47, 480 .+-. 48, and 372 .+-. 35 mg/dl at rest in IDEF, IR + G, and IR, respectively. Levels were unchanged with exercise in IDEF and IR + G, but fell by 139 .+-. 13 mg/dl in IR. Basal glucose rate of appearance (Ra) was 7.0 .+-. 0.9, 1.3 .+-. 1.1, and 6.0 .+-. 0.7 mg.cntdot.kg-1.cntdot.min-1 in IDEF, IR + G, and IR, respectively. Exercise elicited a rise in Ra in only IDEF. The rises in Rd and metabolic clearance rate in IDEF were reduced (.DELTA.2.6 .+-. 0.7 and .DELTA.0.8 .+-. 0.3 ml.cntdot.kg-1.cntdot.min-1 at 150 min) compared with IR + G (.DELTA.5.3 .+-. 1.9 and .DELTA.1.7 .+-. 0.2 ml.cntdot.kg-1.cntdot.min-1 at 150 min) and IR (.DELTA.3.7 .+-. 1.2 and .DELTA.2.4 .+-. 0.8 ml.cntdot.kg-1.cntdot.min-1). The insulin sensitivity of glucose utilization (Rd) was elevated by .apprx.75% at 150 min. Basal glycerol was similar in IDEF and IR but was reduced by .apprx.70% in IR + G. Glycerol rose similarly with exercise in IDEF and IR. The rise was .apprx.50% lower in IR + G. In summary, in poorly controlled PX dogs 1) the capacity of exercise to stimulate Rd is intact, but largely requires insulin; 2) the role of the presence of insulin is magnified during exercise by an increased sensitivity; 3) in the absence of a change in glycemia, small amounts of insulin suppress basal and exercise-stimulated Ra and glycerol; and 4) a reduction in hyperglycemia largely offsets the attenuation of the increases in Ra and glycerol by insulin. Thus the acute presence of insulin facilitates metabolism in poorly controlled diabetes by stimulating Rd while having very little net effect in suppressing substrate mobilization, since the accompanying reduction in hyperglycemia offsets the inhibitory effects of this hormone.