Photoperiodic and light spectral conditions which inhibit circulating concentrations of thyroxine in the male hamster |
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Authors: | M K Vaughan G C Brainard R J Reiter |
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Institution: | 1. Department of Cellular and Structural Biology, The University of Texas Health Science Center at San Antonio, San Antonio, TX, USA;2. Department of Neurology, Jefferson Medical College, Philadelphia, PA, USA |
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Abstract: | Adult male Syrian hamsters were exposed daily for 12 weeks to 11 h/day of cool white fluorescent light (350 +/- 50 microW/cm2) followed by an additional 3 h of near ultraviolet (339-317 nm), blue (435-500 nm), green (515-550 nm), yellow (558-636 nm) or red (653-668 nm) light at an irradiance of 0.2 microW/cm2 or to total darkness. Animals exposed to the wavelengths between 558-668 nm (yellow or red half peak bandwidths) or those receiving a total of 13 h of darkness/day had suppressed circulating levels of thyroxine (T4), a depressed free T4 index (FT4I) and a higher T3/T4 ratio compared to animals receiving a total of 14 h of white light (350 +/- 50 microW/cm2). These results suggest that specific wavelengths of light can affect the neuroendocrine-thyroid axis. |
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