Do circulating plasma AVT and/or cortisol levels control pulsatile urea excretion in the gulf toadfish (Opsanus beta)?

Chris M. Wood, Justin M. Warne, Yuxiang Wang, M. Danielle McDonald, Richard J. Balment, Pierre Laurent, Patrick J. Walsh

Research output: Contribution to journalArticle

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Abstract

Previous work has shown that pulsatile urea excretion at the gills of the gulf toadfish is due to periodic activation of a facilitated diffusion transport system with molecular and pharmacological similarity to the UT-A transport system of the mammalian kidney. In mammals, AVP and glucocorticoids are two important endocrine regulators of this system. The present study focused on the potential role of circulating AVT (the teleost homologue of AVP) and cortisol levels as possible triggers for urea pulses. Long-term (34-84 h) monitoring of plasma levels by repetitive sampling at 2-h intervals from chronic cannulae in individual toadfish demonstrated that circulating AVT concentrations are low (10-12-10-11 M), and show no relationship to the occurrence of natural urea pulses. In contrast, plasma cortisol levels decline greatly prior to natural pulses and rise rapidly thereafter. AVT injections into the caudal artery or ventral aorta elicited pulse events, but these were extremely small (1-10%) relative to natural pulses, and occurred only at unphysiological dose levels (10-9 M in the plasma). AVP was a partial agonist, but isotocin, insulin-like growth factor-1, and atrial natriuretic peptide were without effect at the same concentration. Artificially raising plasma cortisol levels by cortisol injection tended to reduce responsiveness to AVT. Pharmacological reduction of plasma cortisol levels by metyrapone injection elicited small pulses similar to those caused by AVT. Following such pulse events, AVT was ineffective in inducing pulses. We conclude that decreases in circulating cortisol play an important permissive role in urea pulsing, but that circulating AVT levels are not involved.

Original languageEnglish (US)
Pages (from-to)859-872
Number of pages14
JournalComparative Biochemistry and Physiology - A Molecular and Integrative Physiology
Volume129
Issue number4
DOIs
StatePublished - Jan 1 2001
Externally publishedYes

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Keywords

  • AVP
  • AVT
  • Cortisol
  • Gills
  • Gulf toadfish
  • Isotocin
  • Opsanus beta
  • Urea
  • UT-A urea transporter

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Physiology

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