15–0.4 Hz, which
is the frequency interval of respiratory function; and (5) 0.4–1.6 Hz, which contains the heart beat frequency. Systemic hyperinsulinemia has been shown to affect microvascular vasomotion by increasing endothelial and neurogenic activity in skin and muscle [19,100], and that particularly the contribution of endothelial and neurogenic selleck screening library activity to microvascular vasomotion is impaired in obese, insulin-resistant individuals . Local hyperinsulinemia during cathodal iontophoresis of insulin, on the other hand, affects microvascular vasomotion by increasing myogenic activity . Similarly, rat muscle studies showed the main increase due to insulin to be myogenic . Most studies of the effect of insulin on microvascular function have been conducted Trametinib order with the euglycemic, hyperinsulinemic clamp technique, i.e., under steady-state hyperinsulinemia. However, physiologically, hyperinsulinemia is usually
transient and dynamic, such as after a glucose load and after a meal, and is then accompanied by changes in circulating concentrations of glucose, amino acids, and gut and pancreatic peptides, which are not replicated by the clamp technique. If insulin’s effects on microvascular function play a physiological role in regulating insulin-mediated glucose uptake, such effects should be demonstrable not only during steady-state hyperinsulinemia but also after a meal. In addition, any such effects would be expected to be impaired in obese (insulin-resistant) individuals as compared with (insulin-sensitive) healthy controls. Interestingly, obesity has been shown to blunt changes in microvascular vasomotion specifically in the endothelial and neurogenic domain after a mixed meal (Figure 2) . Obesity has also been shown to impair microvascular recruitment in human skeletal Tacrolimus (FK506) muscle after a mixed meal . It is presently unknown whether microvascular vasomotion and capillary recruitment may be directly related, but preliminary
data suggest that insulin-induced changes in the neurogenic domain of vasomotion are associated with insulin-induced capillary recruitment (MP de Boer, unpublished data). Finally, insulin TET is a third potential site for regulating insulin delivery . Recent in vivo and in vitro findings suggest that insulin crosses the vascular endothelium via a trans-cellular, receptor-mediated pathway, and emerging data indicate that insulin acts on the endothelium to facilitate its own TET . It is still unclear whether capillary recruitment and TET of insulin may be related or may function independently. All together, these data illustrate the importance of the microcirculation in regulating nutrient and hormone access to muscle, and raise the possibility that any impairment in capillary recruitment may cause an impairment in glucose uptake by muscle.