Respiration Physiology 111 (1998) 163 – 175 Skeletal muscle microcirculatory structure and hemodynamics in diabetes Casey A. Kindig a,b , William L. Sexton c , M. Roger Fedde b , David C. Poole a,b, * a Department of Kinesiology, 8 Natatorium, Kansas State Uniersity, Manhattan, KS 66506 -0302, USA b Department of Anatomy and Physiology, Kansas State Uniersity, Veterinary Medical Sciences, 1600 Denison Aenue, Manhattan, KS 66506 -5602, USA c Department of Physiology, Kirksille College of Osteopathic Medicine, Kirksille, MO 63501, USA Accepted 10 November 1997 Abstract Within skeletal muscle, insulin-dependent (Type 1) diabetes produces straighter, narrower capillaries. To test the hypothesis that these microvascular alterations would be associated with impaired capillary hemodynamics, intravital microscopy techniques were used to study the in vivo spinotrapezius muscle microcirculation of age-matched control (C) and streptozotocin (STZ) induced diabetic (D) rats. D rats exhibited a marked reduction in body weight (C, 266 5 g; D, 150 6 g; P 0.001). At resting sarcomere lengths (i.e. 2.7  m), the additional capillary length arising from tortuosity and branching was less in D muscle (C, 10.5 0.8%; D, 5.3 1.0%, P 0.01). Capillary diameter was reduced in D muscle (C, 5.4 0.1  m; D, 4.6 0.1 m; P 0.001), and was positively correlated (r =0.71) with the decreased proportion of capillaries sustaining flow (C, 85 5%; D, 53 3%; P 0.001). Within those ‘flowing’ capillaries, red blood cell (RBC) velocity and flux were reduced 29 and 43%, respectively in D muscle (both P 0.05). This reduced calculated O 2 delivery by 57% per unit tissue width and 41% per unit muscle mass. Capillary ‘tube’ hematocrit was unchanged from control values (C, 0.22 0.02; D, 0.22 0.02). We conclude that, in the diabetic state, microvascular remodeling is associated with a reduced proportion of ‘flowing’ capillaries and a reduction in RBC velocity and flux in these vessels such that skeletal muscle O 2 delivery is markedly reduced. © 1998 Published by Elsevier Science B.V. All rights reserved. Keywords: Blood, red cell flux; Capillary, muscle, geometry; Disease, diabetes; Mammals, rat; Muscle, spinotrapezius 1. Introduction Muscle function is dependent upon adequate blood flow and substrate exchange at the micro- circulatory level. Therefore, structural alterations * Corresponding author. Tel.: +1 913 5324529; fax: +1 913 5324557; e-mail: Poole@vet.ksu.edu 0034-5687/98/$19.00 © 1998 Published by Elsevier Science B.V. All rights reserved. PII S0034-5687(97)00122-9