Open AccessJournal Article
Differential inhibiton of alpha-1 and alpha-2 adrenoceptor-mediated pressor responses in pithed rats.
I Yamaguchi,I J Kopin +1 more
TLDR
The results suggest that thePressor effects of administered norepinephrine is mediated by different receptors (alpha-2-type) than is the pressor response to stimulation of the sympathetic outflow which appears to be mediated by alpha-1-type adrenoceptors.Abstract:
The relative potencies of alpha adrenoceptor antagonists at pre- and postsynaptic receptors were assessed by comparing their effects on increments in plasma norepinephrine levels and blood pressure during stimulation of the sympathetic outflow from the spinal cord of pithed rats. Since increments in blood pressure are related to the logarithms of increases in plasma norepinephrine, the latter appear to reflect levels of the catecholamine at vascular alpha receptors. Phenoxybenzamine, dibenamine and chlorpromazine were found to block preferentially postsynaptic alpha receptors, phentolamine and tolazoline were nearly equipotent at pre- and postsynaptic receptors and mianserin and piperoxan were more potent inhibitors of presynaptic alpha receptors. Phenoxybenzamine and dibenamine were much more effective in blocking the pressor responses to sympathetic stimulation than administered norepinephrine. The opposite was true of mianserin and piperoxan, whereas phentolamine appeared to be about equipotent in blocking the pressor response to stimulation and norepinephrine. These results suggest that the pressor effects of administered norepinephrine is mediated by different receptors (alpha-2-type) than is the pressor response to stimulation of the sympathetic outflow which appears to be mediated by alpha-1-type adrenoceptors.read more
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TL;DR: The increased knowledge on the involvement of vascular adrenoceptors in many diseases like Raynaud's, scleroderma, several neurological degenerative diseases (familial amyloidotic polyneuropathy, Parkinson disease, multiple-system atrophy), some kinds of hypertension, etc., will contribute to new and better therapeutic approaches.
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Cardiovascular Regulation in Mice Lacking α2-Adrenergic Receptor Subtypes b and c
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Evidence for more than one type of post-junctional α-Adrenoceptor
TL;DR: A preliminary hypothesis is: in vivo alpha 1 is rapid in onset, short-lived, utilises internal Ca2+, prefers alkalosis and responds to short-term stimuli such as short bursts of nerve impulses or bolus injections of catecholamines; in vitro these categories of response occur but antagonists fail to define an alpha 1/alpha 2 split, suggesting that some critical factor is missing in vitro.
Journal ArticleDOI
Relationship between plasma norepinephrine and sympathetic neural activity
TL;DR: In this report a model is presented where removal processes for NE are viewed as acting in series to produce a gradient in NE concentrations from synapse to plasma, and where the relative contributions of specific vascular beds are calculated from the arteriovenous difference in plasma NE across those beds and the percentage of cardiac output distributed to them.
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