THE CIRCADIAN-RHYTHM OF CORTISOL IN THE SALIVA OF YOUNG-PIGS

Single and population-mean cosinor analyses document a circadian rhyth m in salivary cortisol of pigs (p < 0.001). The midline estimated stat istic of rhythm, the MESOR (M), is 1.50 +/- 0.07 ng/ml. For the group of 14 pigs studied there was a predictable variation of 64% around thi s mean in salivary cortisol within a day: the double circadian amplitu de, 2A, was 0.96 ng/ml, with a 95% confidence interval ranging from 0. 60 to 1.32 ng/ml. A measure of timing, the acrophase, phi, was 10 h 52 min from the phase reference (0030, the middle of the daily dark span of the 24-h light-dark cycle in which the pigs were kept). The 95% co nfidence interval of phi extended from 9 h 48 min to 12 h 12 min from the reference time. The chronobiologic approach provides indispensable quantitive characteristics as reference standards for future basic or applied work.