Contractile responses to field stimulation of intramural nerves of arteries and veins taken from rabbits made hypertensive by partial constriction of the abdominal aorta have been related to the carotid artery pressure. The increase in contraction of cephalic and short saphenous veins with rise in carotid artery pressure can be accounted for by an increase in sensitivity of the alpha-adrenergic receptor. The neurogenic contraction of the ear artery increased with carotid artery pressure rise. Changes in some of the extraneuronal factors that influence transmitter distribution and disposition in the tunica media were examined. In hypertensive animals, the percentage of released adrenergic transmitter entering the vessel wall might be expected to decrease due to an increase in medial thickness. However, this percentage was not significantly altered in the ear artery probably due, in part, to a concomitant increase in medial permeability to the transmitter. Extraneuronal transmitter disposition factors, i.e. extraneuronal uptake, monoamine oxidase, and catechol-O-methyltransferase activity are directly related to the wet weight of the vessel wall. Thus, their contribution to transmitter disposition would be expected to increase with increase in vessel wall thickness and tend to reduce the response to sympathetic activity. As the contractile response increased in the hypertensive vessels despite such changes, the increase in effector cell mass and density of neuronal terminal plexus, shown previously to increase with hypertension, are more important than these other considerations.

This chapter describes the effectiveness of adrenergic transmitter concentrations in synaptic clefts of differing dimensions. The dimensions of the adrenergic neuromuscular synapse show considerable variation in different tissues. In the arterial tree, the synaptic cleft size appears to diminish with vessel diameter. The shortest neuromuscular distance ranges from approximately 20,000 Å in the elastic arteries to 1000 Å in the smaller arteries, and arterioles. The differing patterns of transmitter distribution and concentration have functional correlates in the contractile responses to nervous activity. In elastic arteries for example, there is no evidence of any special contractile effect, or response resulting from transmitter action on cells closest to the nerve elements. Effector response is the sum total of local transmitter effects on the individual smooth muscle cells in the vessel wall. In muscular arteries, such as the ear artery of the rabbit, there are two phases of response associated with two modes of transmitter excitation.

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Journal Article On the blockade of neural and exogenous noradrenaline Get access J A Bevan, J A Bevan Department of Pharmacology, UCLA, School of Medicine, Los Angeles, California 90024, USA Search for other works by this author on: Oxford Academic Google Scholar C Su, C Su Department of Pharmacology, UCLA, School of Medicine, Los Angeles, California 90024, USA Search for other works by this author on: Oxford Academic Google Scholar B Ljung B Ljung Department of Pharmacology, UCLA, School of Medicine, Los Angeles, California 90024, USA Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 25, Issue 1, January 1973, Pages 78–79, https://doi.org/10.1111/j.2042-7158.1973.tb09121.x Published: 12 April 2011 Article history Received: 10 October 1972 Published: 12 April 2011

A quantitative study of monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) has been made on homogenates of adult rabbit thoracic aorta. Most of the activity of both enzymes is located in the tunica media. The ratio of adventitia/media distribution of COMT is considerably less than the corresponding ratio for MAO. The specific activities of MAO and COMT change in parallel through the greater part of the transmural profile obtained on 24 μ cryostat sections. The specific activity of COMT drops significantly in sections that include endothelium and subendothelial media, where no decrease in MAO is noted. Subcellular distribution studies indicate the presence of MAO in mitochondrial and microsomal fractions, compared to the predominantly microsomal and cell sap localization of COMT.

Studies of the release of the adrenergic transmitter in the rabbit pulmonary artery have been carried out in vitro. At a stimulation frequency of 10 per second, the release was 52.9 pg per gram wet weight per pulse. The mean number of nodes or varicosities per gram wet weight of artery was 9.3×107. If 80% of the released transmitter is taken up by tissues in the artery wall, these values correspond to the average release of approximately 400 molecules ofl-norepinephrine per node per pulse. The transmitter concentrations in the region of the muscle in the outermost lamina of the vessel during sympathetic activity are discussed in relation to the spatial dimensions of the neuroeffector cleft. The release of the total contents of a vesicle on the average every 7 or 8 pulses from each node is consistent with these requirements.

Journal Article Release of [3H]noradrenaline from vasoconstrictor nerves Get access C Su, C Su Department of Pharmacology, UCLA School of Medicine, Los Angeles, California 90024, U.S.A. Search for other works by this author on: Oxford Academic Google Scholar J A Bevan J A Bevan Department of Pharmacology, UCLA School of Medicine, Los Angeles, California 90024, U.S.A. Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 19, Issue 9, September 1967, Pages 625–626, https://doi.org/10.1111/j.2042-7158.1967.tb09603.x Published: 12 April 2011