5-Hydroxytryptamine initiates pulsatile urea excretion from perfused gills of the gulf toadfish (Opsanus beta)

M. Danielle McDonald, Patrick J. Walsh, Chris M. Wood

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


When stressed, toadfish become ureotelic and excrete almost all of their nitrogenous waste in 1-3 daily pulses of urea-N across the gills. Intravascular injections of 5-hydroxytyptamine (5-HT; serotonin) and analogues also elicit marked excretory pulses of urea-N from toadfish in vivo, suggesting that 5-HT release is the proximate trigger for spontaneous pulses. However it is unclear whether 5-HT is acting on the gills directly or elsewhere to cause the effect indirectly. A perfused whole gill preparation which maintained normal pressure relationships and stable vascular resistance was employed to address this question. Bolus injections into the ventral aortic perfusate of either 5-HT (1, 10μmolkg-1) or the specific 5-HT2 receptor agonist α-methyl 5-HT (1, 10μmolkg-1) elicited rapid urea-N pulses from perfused toadfish gills. The effective doses, the post-injection delays (5.5±1.3min, range=2-22), the percent occurrences (57-85%), and the magnitude of the induced urea-N pulses (615.4±131.3μmol-Nkg-1, range 66.0-2634.0), were all similar to those previously reported when these agents were injected in vivo. Bolus injections of 5-HT and α-methyl 5-HT also elicited a biphasic response in ventral aortic pressure, reflecting an initial rapid short-lived vasodilation and a subsequent longer-lasting vasoconstriction. These events were similar to those which have been recorded to occur at a greater frequency during spontaneous urea-N pulsing in vivo. Neither the urea-N pulsing nor the cardiovascular responses to 5-HT were inhibited by the 5-HT2A receptor subtype blocker, ketanserin (pre-injection with 10μmolkg-1 plus 33μmolL-1 in the perfusate). Overall, these results provide strong support for the idea that the proximate stimulus for natural urea pulsing in vivo is 5-HT mobilization, acting directly in the gills.

Original languageEnglish (US)
Pages (from-to)30-37
Number of pages8
JournalComparative Biochemistry and Physiology - A Molecular and Integrative Physiology
Issue number1
StatePublished - Sep 2012


  • α-Methyl 5-HT
  • 5-HT
  • Blood pressure
  • Ketanserin
  • Serotonin
  • Urea transporter
  • Vascular resistance

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Physiology


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