Characteristics of postsynaptic alpha1 and alpha2 adrenergic receptors in canine vascular smooth muscle

Abstract

A previous study suggested the existence of 2 distinct postsynaptic .alpha.-adrenergic receptors in canine intralobar pulmonary arteries (IPA) and veins. The present study, performed using rings of canine IPA and dorsal metatarsal vein (DMV), was designed to characterize the factors affecting the postsynaptic .alpha.- and .alpha.-receptors of these blood vessels. The responses of IPA and DMV to norepinephrine (NE), transmural nerve stimulation, phenylephrine (PE), guanabenz and clonidine were obtained in the presence and absence of alterations in pH, extracellular Ca2+ sulfhydryl bond reduction and oxidation, and destruction of adrenergic nerves with 6-hydroxydopamine. The data demonstrate the folowing: .alpha.2-receptors are inactivated by changes in pH above or below pH 7.4, contain a labile disulfide group, are suceptible to modulation by increases and decreases in Ca2+, and appear to be decreased by destruction of adrenergic nerves, and the NE and PE sensitve .alpha.1-receptors are insensitive to alterations in pH, refractory to disulfide reduction by dithiothreitol, slightly susceptible to modulation by Ca2+ and increased by destruction of adrenergic nerves. The 2 subtypes of postsynaptic .alpha.-adrenergic receptors differ in their properties and susceptibility to modification by alteration of the physiological environment.