We evaluated the effects of exercise on the vascular constrictor responses to ?-adrenergic stimulation in the db/db mice. Twenty male db/db and their age-matched wild-type (WT) mice were exercised (1 hour/day, five days a week). Mice were anesthetized 7 weeks later, thoracic aortae were mounted in wire myograph and constrictor responses to phenylephrine (PE, 1 nM-10 µM) were obtained. Citrate synthase activity measured in the thigh adductor muscle was significantly increased in db/db mice that were exercise trained. Maximal force generated by PE was markedly greater in db/db aortae and exercise did not attenuate this augmented contractile response. Vessels were incubated with inhibitors of nitric oxide synthase (L-NAME, 200 µM), endothelin receptors (bosentan, 10 µM), protein kinase C (PKC) (calphostin C, 5 µM), cyclooxygenase (indomethacin, 10 µM) or Rho-kinase (Y-27632, 0.1 µM). Only calphostin-C normalized the augmented PE-induced constriction in db/db and db/dbexercised mice to that observed in WT (p<0.05). Cumulative additions of indolactam, a PKC activator, induced significantly greater constrictor responses in aortic rings of db/db mice compared to WT and exercise did not affect this response. Our data suggest that the augmented vasoconstriction observed in the aorta of db/db mice is likely due to increased PKC activity and that exercise do not ameliorate this increased PKC-mediated vasoconstriction.

Department of Physiology Faculty of Medicine Isfahan University of Medical Sciences Isfahan

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