title: Adrenergic facilitation of myogenic response in skeletal muscle arterioles.
abstract: The myogenic response was studied in large skeletal muscle arterioles in the presence of varying degrees of constriction with norepinephrine (NE; 3 x 10(-8) to 1 x 10(-5) M) or potassium chloride (KCl, 40-120 mM). The cremaster muscle of anesthetized rats was exteriorized into a Krebs-filled tissue bath chamber for observation of the microvasculature using a video microscopy system. The body of the rats was enclosed in an airtight Plexiglas box that was pressurized from 0 to +30 mmHg to raise intravascular pressure and elicit the myogenic response. All experiments were performed in acutely denervated muscles with propranolol (1 x 10(-6) M) present to produce beta-receptor blockade. Diameter responses of the first-order arteriole (1A) were measured with a videoimage caliper and intravascular pressure with the servo-null micropipette technique. Under basal conditions, without NE, 1A diameter increased in a passivelike fashion from 122 +/- 5.4 to 130 +/- 5.1 microns as box pressure was elevated from 0 to +30 mmHg, respectively. Addition of NE to the cremaster bath produced a dose-dependent constriction of the 1A (EC50 2 x 10(-7) M). In the presence of this adrenergic tone the 1A exhibited myogenic constriction in response to increases in box pressure. For example, topical application of 3 X 10(-7) M NE caused the 1A to constrict from 122 +/- 5.4 to 70 +/- 5.3 microns. In the presence of this adrenergic tone elevating box pressure from 0 to +30 mmHg caused additional constriction to 55 +/- 6.6 microns.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Microcirculation Research Institute, College of Medicine, Texas A & M University, College Station 77843.
authors.forename: G A
authors.initials: GA
authors.lastname: Meininger
authors.forename: J E
authors.initials: JE
authors.lastname: Faber
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D011189:Potassium Chloride; D009638:Norepinephrine