Dynamics of microvascular oxygen pressure during rest-contraction transition in skeletal muscle of diabetic rats. Am J Physiol Heart Circ Physiol 283: H926-H932, 2002. First published May 16, 2002 10.1152/ajpheart.00059.2002.-Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (Q O2). In control (C; n ϭ 6) and streptozotocininduced diabetic (D: n ϭ 6, plasma glucose ϭ 25.3 Ϯ 3.9 mmol/l and C: 8.3 Ϯ 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular PO2 [PmO 2 , which reflects the dynamic balance between O2 utilization (V O2) and Q O2] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. PmO 2 data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, PmO 2 at rest was lower (C: 31.2 Ϯ 3.2 mmHg; D: 24.3 Ϯ 1.3 mmHg, P Ͻ 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 Ϯ 1.8 s; D: 7.6 Ϯ 2.1 s, P Ͻ 0.05) and with a reduced mean response time (C: 31.4 Ϯ 3.3 s; D: 23.9 Ϯ 3.1 s, P Ͻ 0.05). PmO 2 exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 Ϯ 1.1 mmHg, P Ͻ 0.05), which was absent in C muscles. These results indicate an altered V O2-to-Q O2 matching across the rest-exercise transition in muscles of D rats. streptozotocin diabetes; oxygen uptake kinetics; exercise intolerance; muscle oxygen delivery; phosphorescence quenching PULMONARY GAS EXCHANGE DYNAMICS (i.e., oxygen uptake, V O 2 kinetics) at exercise onset are slowed profoundly in diabetic patients (5, 23). Slowed V O 2 kinetics in response to a given metabolic challenge will mandate generation of a greater O 2 deficit and exacerbate intracellular perturbations of phosphocreatine, free ADP, and P i , for example, that accelerate glycogenolysis and utilization of finite glycogen reserves (33). This phenomenon is likely to contribute to the reduced exercise tolerance that is present in the diabetic condition.