Microvascular Recruitment Is an Early Insulin Effect That Regulates Skeletal Muscle Glucose Uptake In Vivo

  1. Michelle A. Vincent1,
  2. Lucy H. Clerk1,
  3. Jonathan R. Lindner1,
  4. Alexander L. Klibanov1,
  5. Michael G. Clark2,
  6. Stephen Rattigan2 and
  7. Eugene J. Barrett1
  1. 1Divisions of Cardiovascular Medicine and Endocrinology and Metabolism, Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, Virginia
  2. 2Department of Biochemistry, University of Tasmania, Hobart, Tasmania, Australia
  1. Address correspondence and reprint requests to Eugene J. Barrett, MD, PhD, Department of Internal Medicine, Box 801410, University of Virginia Health Sciences Center, Charlottesville, VA 22908. E-mail ejb8x{at}virginia.edu

Abstract

Insulin increases glucose disposal into muscle. In addition, in vivo insulin elicits distinct nitric oxide synthase-dependent vascular responses to increase total skeletal muscle blood flow and to recruit muscle capillaries (by relaxing resistance and terminal arterioles, respectively). In the current study, we compared the temporal sequence of vascular and metabolic responses to a 30-min physiological infusion of insulin (3 mU · min−1 · kg−1, euglycemic clamp) or saline in rat skeletal muscle in vivo. We used contrast-enhanced ultrasound to continuously quantify microvascular volume. Insulin recruited microvasculature within 5–10 min (P < 0.05), and this preceded both activation of insulin-signaling pathways and increases in glucose disposal in muscle, as well as changes in total leg blood flow. Moreover, l-NAME (Nω-nitro-l-arginine-methyl ester), a specific inhibitor of nitric oxide synthase, blocked this early microvascular recruitment (P < 0.05) and at least partially inhibited early increases in muscle glucose uptake (P < 0.05). We conclude that insulin rapidly recruits skeletal muscle capillaries in vivo by a nitric oxide-dependent action, and the increase in capillary recruitment may contribute to the subsequent glucose uptake.

Footnotes

  • AGVG, arterial glucose concentration minus venous glucose concentration; CEU, contrast-enhanced ultrasound; eNOS, endothelium nitric oxide synthase; l-NAME, Nω-l-nitro-arginine-methyl ester; NOS, nitric oxide synthase; nNOS, neuronal NOS.

    • Accepted February 26, 2004.
    • Received October 15, 2003.
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