ULTRADIAN AND CIRCADIAN RHYTHMS IN THE PLASMA CONCENTRATION OF CORTISOL IN SHEEP

• DOI: 10.1677/joe.0.0810135
• Publication Date: 2008-12-11T22:22:29Z
• Authors: W. J. FULKERSON; B. Y. TANG
• Keywords: 0301 basic medicine; Periodicity; 03 medical and health sciences; Sheep; Hydrocortisone; Radioimmunoassay; Animals; Female; Circadian Rhythm

Three Merino ewes, adapted for about 3 weeks to their environment, were bled at 10 min intervals through a jugular venous cannula. Radioimmunoassay of plasma samples cortisol revealed marked diurnal variations with peak levels just after midnight and lowest values in the afternoon. This rhythm appeared result from changing amplitude associated distinct ultradian (frequency 0·8–1·2 cycles/h) level cortisol. Calculation daily rate secretion hormone profiles gave mean value 8·49 mg. Arguments are put forward favour this method obtaining true