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Annual variations in the plasma thyroxine level in Microcebus murinus.

A Petter-Rousseaux

    General and Comparative Endocrinology
    |September 1, 1984
    PubMed
    Summary

    Plasma thyroxine (T4) in mouse lemurs shows significant seasonal changes, peaking in summer and dropping in November. Long daylight hours appear to drive this T4 increase, similar to testosterone patterns.

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    Area of Science:

    • Endocrinology
    • Animal Physiology
    • Seasonal Biology

    Background:

    • The study investigates the annual variation in plasma thyroxine (T4) levels in Microcebus murinus (mouse lemurs).
    • Understanding these variations is crucial for comprehending the physiological adaptations of this species to environmental changes.
    • Previous research suggests photoperiod influences hormone levels in various species.

    Purpose of the Study:

    • To document the annual cycle of plasma thyroxine (T4) in Microcebus murinus.
    • To identify potential environmental factors, specifically photoperiod, influencing T4 levels.
    • To compare the annual variation of T4 with that of testosterone in the same species.

    Main Methods:

    • Plasma samples were collected from Microcebus murinus throughout the year.
    • Thyroxine (T4) levels were measured using established immunoassays.
    • Data were analyzed to determine annual patterns and correlations with photoperiod and testosterone levels.

    Main Results:

    • Plasma T4 exhibited significant annual variation, with averages ranging from 30 to 68 ng/ml between February and July.
    • T4 levels markedly decreased to 6 ng/ml by November.
    • A positive correlation was observed between long photoperiods and increased plasma T4, mirroring testosterone patterns.

    Conclusions:

    • Plasma thyroxine levels in Microcebus murinus display a pronounced annual rhythm.
    • Extended photoperiods are identified as a key environmental cue stimulating the summer increase in T4.
    • The annual T4 variation does not show phase opposition to testosterone variation in this species.

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