Document Detail

Developmental and diel changes in plasma thyroxine and plasma and ocular melatonin in the larval and juvenile bullfrog, Rana catesbeiana.
MedLine Citation:
PMID:  12568788     Owner:  NLM     Status:  MEDLINE    
Diel variation in plasma thyroxine (T(4)), and plasma and ocular melatonin was studied in Rana catesbeiana tadpoles and postmetamorphic froglets on 12:12 and 6:18 light/dark (LD) regimens. A progressive rise in plasma T(4) initiates metamorphosis while melatonin can modulate metamorphic progress. Changes in the phase of the rhythms of these two hormones during development might influence the hormonal regulation of metamorphosis. The hormones studied exhibited LD cycle-specific diel fluctuations except in froglet plasma T(4) and all hormones at prometamorphosis on 6L:18D. On 12L:12D, plasma T(4) and ocular melatonin peaked during the scotophase at prometamorphosis and early climax, whereas the plasma melatonin acrophase shifted from the light to the dark at climax. A nocturnal peak of plasma melatonin closely correlated with the onset and offset of dark appeared in the froglet, while the peak of ocular melatonin shifted to the light. Compared to 12L:12D, the peaks of the diel fluctuations on 6L:18D occurred later than on 12L:12D in synchrony with an earlier onset, and increase in length, of the scotophase. The phase of the hormone rhythms changed during metamorphosis in such a way that the peaks of melatonin had a different relationship to the T(4) peaks as development proceeded. On both LD cycles, the 24-h mean of plasma T(4) rose at climax and fell in the froglet whereas plasma melatonin decreased at climax and then rose to a high level in the froglet. After only minor changes during metamorphosis, froglet ocular melatonin levels decreased on 12L:12D and increased on 6L:18D. The findings indicate that the hormonal flux during metamorphosis has circadian aspects, which might explain variations in the response to exogenous hormone treatment at different times of the day and LD cycle-specific timing of development. A fall in plasma melatonin at climax appears to be as much a part of the hormonal changes of metamorphosis as a rise in plasma T(4).
Mary L Wright; Julie L Duffy; Catharine J Guertin; Christina D Alves; Mary C Szatkowski; Rachael F Visconti
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  General and comparative endocrinology     Volume:  130     ISSN:  0016-6480     ISO Abbreviation:  Gen. Comp. Endocrinol.     Publication Date:  2003 Feb 
Date Detail:
Created Date:  2003-02-05     Completed Date:  2003-09-30     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370735     Medline TA:  Gen Comp Endocrinol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  120-8     Citation Subset:  IM    
Biology Department, College of Our Lady of the Elms, Chicopee, MA 01013, USA.
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MeSH Terms
Circadian Rhythm / physiology
Data Interpretation, Statistical
Eye / chemistry
Larva / growth & development
Melatonin / analysis,  blood*
Metamorphosis, Biological / physiology*
Rana catesbeiana / blood,  growth & development*
Thyroxine / blood*
Reg. No./Substance:
73-31-4/Melatonin; 7488-70-2/Thyroxine

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

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