Document Detail

Is urea pulsing in toadfish related to environmental O2 or CO2 levels?
MedLine Citation:
PMID:  17196858     Owner:  NLM     Status:  MEDLINE    
The neurochemical, serotonin (5-hydroxytryptamine; 5-HT) is involved in the regulation of toadfish pulsatile urea excretion as well as the teleost hypoxia response. Thus, the goal of this study was to determine whether environmental conditions that activate branchial chemoreceptors also trigger pulsatile urea excretion in toadfish, since environmental dissolved oxygen levels in a typical toadfish habitat show significant diel fluctuations, often reaching hypoxic conditions at dawn. Toadfish were fitted with arterial, venous and/or buccal catheters and were exposed to various environmental conditions, and/or injected with the O(2) chemoreceptor agonist NaCN or the 5-HT(2) receptor agonist alpha-methyl-5HT. Arterial PO(2), as well as ammonia and urea excretion were monitored. Natural fluctuations in arterial PO(2) levels in toadfish did not correlate with the occurrence of a urea pulse. Chronic exposure (24 h) of toadfish to hyperoxia was without effect on nitrogen excretion, however, exposure to hypoxia caused a significant reduction in the frequency of urea pulses, and exposure to hypercapnia resulted in a reduction in the percentage of nitrogen waste excreted as urea. Of toadfish exposed acutely to hypoxia, 20% pulsed within 1 h, whereas none pulsed after normoxic or hypercapnic treatments. Furthermore, 20% of fish injected intravenously with NaCN pulsed within 1 h of injection, but no fish pulsed after injection of NaCN into the buccal cavity. To test whether environmental conditions affected 5-HT(2) receptors, toadfish were injected with alpha-methyl-5HT, which elicits urea pulses in toadfish. No significant differences in pulse size occurred among the various environmental treatments. Our findings suggest that neither the environmental conditions of hypoxia, hyperoxia or hypercapnia, nor direct branchial chemoreceptor activation by NaCN play a major role in the regulation of pulsatile urea excretion in toadfish.
M Danielle McDonald; Kathleen M Gilmour; John F Barimo; Peter E Frezza; Patrick J Walsh; Steve F Perry
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2006-11-23
Journal Detail:
Title:  Comparative biochemistry and physiology. Part A, Molecular & integrative physiology     Volume:  146     ISSN:  1095-6433     ISO Abbreviation:  Comp. Biochem. Physiol., Part A Mol. Integr. Physiol.     Publication Date:  2007 Mar 
Date Detail:
Created Date:  2007-02-20     Completed Date:  2007-04-10     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  9806096     Medline TA:  Comp Biochem Physiol A Mol Integr Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  366-74     Citation Subset:  IM    
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, 33149-1098, USA.
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MeSH Terms
Anoxia / physiopathology
Batrachoidiformes / physiology*
Carbon Dioxide / blood,  pharmacology*
Chemoreceptor Cells / drug effects
Ornithine / metabolism
Oxygen / blood,  pharmacology*
Partial Pressure
Receptors, Serotonin / drug effects,  physiology
Serotonin / analogs & derivatives,  pharmacology
Sodium Cyanide / administration & dosage,  pharmacology
Urea / metabolism*
Reg. No./Substance:
0/Receptors, Serotonin; 124-38-9/Carbon Dioxide; 143-33-9/Sodium Cyanide; 22965-81-7/alpha-methylserotonin; 50-67-9/Serotonin; 57-13-6/Urea; 7006-33-9/Ornithine; 7782-44-7/Oxygen

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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