ISSN:
1435-1463
Keywords:
Norepinephrine release
;
guinea pig atrium
;
muscle relaxants
;
presynaptic inhibition
;
muscarine receptors
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The influence of nondepolarizing muscle relaxants (MR) on the resting and electrically evoked release of tritiated norepinephrine (3H-NE) was investigated, in the absence and presence of 10−4 mol/l cocaine, in the in vitro right atrium preparation of guinea pigs (g.p.) preloaded with3H-NE. In the absence of MR both resting and stimulated3H and3H-NE release remained relatively constant throughout the experiment and the ratios of the evoked release of3H during consecutive stimulation periods (i.e. S2/S1, S3/S2) were close to unity. None of the MR had any effect on resting3H release. Atropine (3× 10−7 mol/l), gallamine (7×10−5 mol/l), and pancuronium (2×10−6 mol/l), but not d-tubocurarine (5×10−6 mol/l) significantly increased stimulated release of3H-NE. The effect of MR on resting or evoked release of3H-NE was not influenced by 10−4 mol/l cocaine. In the presence of atropine gallamine and pancuronium did not affect the release of3H-NE. This finding indicates that the effect of MR was mediated via presynaptic muscarinic receptors. Muscle relaxants and atropine inhibited these receptors and removed the tonic inhibitory effect of acetylcholine (ACh) released from the parasympathetic nerve endings on the release of NE from the sympathetic nerve. This was substantiated by the finding that in the present of cholinesterase inhibition, when the effect of endogenous ACh was amplified and thereby the cholinergic tone was dominant, the total release of3H-NE evoked by stimulation was much lower and muscle relaxants and atropine were much more effective to enhance3H-NE release. Gallamine and pancuronium also increased the force of contraction of the electrically stimulated atria. These findings indicate that the acceleration of the heart rate observed with gallamine and pancuronium in anesthetized man is due to increased release from, and not the inhibition of reuptake of NE by the sympathetic nerve endings of the right atrium.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01260502
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