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First published online May 13, 2004
Journal of Experimental Biology 207, 2003-2010 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00957
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Dogmas and controversies in the handling of nitrogenous wastes: 5-HT2-like receptors are involved in triggering pulsatile urea excretion in the gulf toadfish, Opsanus beta

M. Danielle McDonald* and Patrick J. Walsh

Division of Marine Biology and Fisheries, NIEHS Marine and Freshwater Biomedical Science Center, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, 33149-1098, USA

* Author for correspondence (e-mail: dmcdonald{at}rsmas.miami.edu)

Accepted 23 February 2004

When injected arterially, serotonin (5-hydroxytryptamine; 5-HT) has been shown to elicit naturally sized urea pulse events in the gulf toadfish, Opsanus beta. The goal of the present study was to determine which 5-HT receptor(s) was involved in mediating this serotonergic stimulation of the pulsatile excretion mechanism. Toadfish were surgically implanted with caudal arterial catheters and intraperitoneal catheters and injected with either 8-OH-DPAT (1 µmol kg–1), a selective 5-HT1A receptor agonist, {alpha}-methyl-5-HT (1 µmol kg–1), a 5-HT2 receptor agonist, or ketanserin, a 5-HT2 receptor antagonist (0.01, 0.1, 1 and 10 µmol kg–1) plus {alpha}-methyl-5-HT. 8-OH-DPAT injection did not mediate an increase in urea excretion, ruling out the involvement of 5-HT1A receptors in pulsatile excretion. However, within 5 min, {alpha}-methyl-5-HT injection caused an increase in the excretion of urea in >95% (N=27) of the fish injected, with an average pulse size of 652±102 µmol N kg–1 (N=26). With {alpha}-methyl-5-HT injection there was no corresponding increase in ammonia or [3H]PEG 4000 permeability. Urea pulses elicited by {alpha}-methyl-5-HT were inhibited in a dose-dependent fashion by the 5-HT2 receptor antagonist ketanserin, which at low doses caused a significant inhibition of pulse size and at higher doses significantly inhibited the occurrence of pulsatile excretion altogether. However, neither 8-OH-DPAT nor {alpha}-methyl 5-HT injection had an effect on plasma cortisol or plasma urea concentrations. These findings suggest the involvement of a 5-HT2-like receptor in the regulation of pulsatile urea excretion.

Key words: serotonin, ketanserin, serotonin receptor, {alpha}-methyl-5-HT, 8-OH-DPAT


Related articles in JEB:

SPECIAL COLLECTION: DOGMAS AND CONTROVERSIES IN THE HANDLING OF NITROGENOUS WASTES
Kathryn Phillips
JEB 2004 207: i. [Full Text]  



This article has been cited by other articles:


Home page
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K. Phillips
SPECIAL COLLECTION: DOGMAS AND CONTROVERSIES IN THE HANDLING OF NITROGENOUS WASTES
J. Exp. Biol., May 15, 2004; 207(12): i - i.
[Full Text]


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