Alpha-adrenergic reactivity of the microcirculation in conscious spontaneously hypertensive rats.
The goal of this study was to determine the functional distribution of alpha 1- and alpha 2-adrenoceptors in the striated muscle microcirculation. Experiments were performed in intact conscious spontaneously hypertensive rats (SHR) that were provided with a dorsal microcirculatory chamber to allow microvascular diameter measurements. Administration of selective alpha 1- and alpha 2-agonists, phenylephrine and azepexole, respectively, induced different patterns of microvascular constriction. alpha 1-Adrenoceptor stimulation showed a preferential constriction of large arteries and venules. The entire arteriolar microvasculature was sensitive to alpha 2-adrenoceptor stimulation, whereas the venular vessels did not respond to azepexole. The selective alpha 1- and alpha 2-antagonists prazosin and yohimbine showed patterns of vasodilator activity comparable to those of the corresponding agonists. The specificity of the drug-induced effects was verified by comparing their effects with those of graded hemorrhage, a non-pharmacological method for blood pressure lowering. In the range of blood pressure decreases comparable to that obtained by alpha-adrenoceptor antagonists, graded hemorrhage did not influence microvascular diameters. These results show a differential functional distribution of alpha 1- and alpha 2-adrenoceptors along the microvascular tree in striated muscle of conscious SHR.
Struijker-Boudier
H A
HA
Department of Pharmacology, Cardiovascular Research Institute Maastricht CARIM, University of Limburg, Maastricht, The Netherlands.
Messing
M W
MW
van Essen
H
H
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D006470:Hemorrhage / Q000503:physiopathology*; D006973:Hypertension / Q000235:genetics / Q000503:physiopathology*; D008297:Male; D008833:Microcirculation / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000098:blood supply*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D014661:Vasoconstriction; D014664:Vasodilation; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001381:Azepines; D018340:Receptors, Adrenergic, alpha-1; D018341:Receptors, Adrenergic, alpha-2; D010656:Phenylephrine; D015016:Yohimbine; C015603:azepexole; D011224:Prazosin