Noradrenalin antagonizes effects of serotonin and acetylcholine in the seawater eel intestine |
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Authors: | M Ando K Kondo |
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Institution: | (1) Laboratory of Physiology, Faculty of Integrated Arts and Sciences, Hiroshima University, 730 Hiroshima, Japan |
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Abstract: | After inhibiting ion and water transport with 10-6 mol·l-1 serotonin and 10-6 mol·l-1 methacholine, a muscarinic agonist of acetylcholine, 10-5 mol·l-1 (±)noradrenaline restored the serosa-negative transepithelial potential difference and short-circuit current in a step-like manner, accompanied by an increase in water absorption across the seawater eel intestine. Such recovery by noradrenalin was not obtained after pretreatment with 10-7 mol·l-1 eel atrial natriuretic peptide. This means that the inhibitory mechanisms of serotonin and acetylcholine are different from those of atrial natriuretic peptide. Similarly, 10-7 mol·l-1 clonidine and guanabenz (2-agonists) also reversed the inhibitory action of serotonin and methacholine, but 10-7 mol·l-1 phenylephrine (1-agonists) and 10-7 mol·l-1 isoproterenol (-agonist) did not antagonize serotonin and methacholine actions. Further, the enhancement by 10-5 mol·l-1 noradrenalin was blocked by 10-4 mol·l-1 yohimbine (2-agonists) and 10-4 mol·l-1 prazosin (1-agonists), but not by 10-4 mol·l-1 propranolol (-antagonist). Although relatively high dosage is required to obtain a significant effect, and discrimination between 1- and 2- is not successful in the present study, these results suggest that noradrenalin acts on an -type receptor. The -type receptor may exist on the enterocytes, since the effects of noradrenalin are observed even in the presence of 10-6 mol·l-1 tetrodotoxin. Interestingly, the tissue resistance also increased in parallel with increase in the short-circuit current after treatment with noradrenalin in the posterior part of the seawater eel intestine.Abbreviations ACh
acetylcholine
- 5-HT
serotonin
- eANP
eel atrial natriuretic peptide
-
I
sc
short-circuit current
- MCh
methacholine
- NA
noradrenalin
- PD
transepithelial potential difference
-
R
t
tissue resistance
- TTX
tetrodotoxin
- VIP
vasoactive intestinal peptide |
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Keywords: | Active Cl- transport Noradrenalin -type receptor" target="_blank">gif" alt="agr" align="BASELINE" BORDER="0">-type receptor Acetylcholine Serotonin Tissue resistance Eel Anguilla japonica |
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