title: Diaphragm arterioles are less responsive to alpha1- adrenergic constriction than gastrocnemius arterioles.
abstract: The sympathetic nervous system has greater influence on vascular resistance in low-oxidative, fast-twitch skeletal muscle than in high-oxidative skeletal muscle (17). The purpose of this study was to test the hypothesis that arterioles isolated from low-oxidative, fast-twitch skeletal muscle [the white portion of gastrocnemius (WG)] possess greater responsiveness to adrenergic constriction than arterioles isolated from high-oxidative skeletal muscle [red portion of the gastrocnemius muscle (RG) and diaphragm (Dia)]. Second-order arterioles (2As) were isolated from WG, RG, and Dia of rats and reactivity examined in vitro. Results reveal that Dia 2As constrict less to norepinephrine (NE) (10(-9) to 10 (-4) M) than 2As from RG and WG, which exhibited similar NE-induced constrictions. This difference was not endothelium dependent, because responses of denuded 2As were similar to those of intact arterioles. The blunted NE-induced constrictor response of Dia 2As appears to be the result of differences in alpha1-receptor effects because 1) arterioles from Dia also responded less to selective alpha1-receptor stimulation with phenylephrine than RG and WG arterioles; 2) arterioles from Dia, RG, and WG dilated similarly to isoproterenol (10(-9) to 10(-4) M) and did not respond to selective alpha2-receptor stimulation with UK-14304; and 3) endothelin-1 produced similar constriction in 2As from Dia, RG, and WG. We conclude that differences in oxidative capacity and/or fiber type composition of muscle tissue do not explain different NE responsiveness of Dia 2As compared with 2As from gastrocnemius muscle. Differences in alpha1-adrenergic constrictor responsiveness among arterioles in skeletal muscle may contribute to nonuniform muscle blood flow responses observed during exercise and serve to maintain blood flow to Dia during exercise-induced increases in sympathetic nerve activity.
authors.affiliation: Department of Veterinary Biomedical Sciences, University of Missouri, Columbia 65211, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Aaker
authors.forename: M H
authors.initials: MH
authors.lastname: Laughlin
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D003964:Diaphragm / Q000098:blood supply*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply*; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D014654:Vascular Patency / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D018340:Receptors, Adrenergic, alpha-1; D019335:Nitroarginine; D009638:Norepinephrine