title: Alpha-adrenergic-mediated reflex responses to induced muscular contraction are changed with age in dogs.
abstract: Aging significantly affects reflex cardiovascular (CV) responses to induced muscular contraction in anesthetized dogs. To further investigate whether age-related changes in alpha-adrenergic-mediated responses to muscular contraction contribute to these previously reported age-related changes in CV responses associated with advanced age, hemodynamic and regional blood flow (BF) responses at baseline and during hindlimb contraction (HLC) were evaluated both before and after alpha-blockade (alpha-AB) in older (8-14 yr old) and in younger (2-3 yr old) beagles during alpha-chloralose anesthesia. alpha-AB with phentolamine resulted in significant (P < 0.05) reductions in mean arterial pressure before and during HLC, regardless of age. However, age-related differences in the systemic vascular resistance, cardiac output, and stroke volume responses to HLC, observed before alpha-AB, were eliminated after phentolamine as the result of an age-related difference in each of these responses to alpha-AB. Baseline BF (microspheres) was unchanged after alpha-AB in seven of eight abdominal organs, regardless of age. However, reductions in BF during HLC were attenuated in seven of eight abdominal organs in the younger dogs after alpha-AB, but in none of these organs in the older dogs, indicative of diminished alpha-mediated vasoconstriction in these organs in the older dogs during HLC. Furthermore, the age-related difference in the combined BF reduction to all eight abdominal organs before alpha-AB was eliminated after alpha-AB. Finally, BF increases to two of four contracting muscles, as well as the combined increase in blood flow to all four contracting muscles, were attenuated after alpha-AB, regardless of age. These results demonstrate that alpha-blockade eliminates many of the age-related differences in CV responses to HLC observed before alpha-AB and suggest that alpha-adrenergic-mediated responses to HLC change with age in beagles.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-9034.
authors.forename: G C
authors.initials: GC
authors.lastname: Haidet
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000375:Aging / Q000502:physiology*; D000818:Animals; D002320:Cardiovascular Physiological Phenomena; D004285:Dogs; D006439:Hemodynamics / Q000187:drug effects; D006614:Hindlimb / Q000098:blood supply; D009119:Muscle Contraction / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects
chemical_list: D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha