Diurnal and seasonal variation of cholecystokinin peptides in humans

• Cholecystokinin (CCK) was determined in plasma obtained from 10 female (aged 23.4 ± SD 2.3 years) and nine male (aged 22.0 ± SD 1.4 years) healthy volunteers. Blood samples were drawn three times (8.00 a.m., 12 noon and 8.00 a.m.) on each of two sessions, one in the winter (November-December) and one in the summer (April-July). The participants had fasted (and were nicotine-free) since midnight preceding the sampling. A standardized breakfast was served after the first sampling. CCK was determined by radioimmunoassay. The area under the curve 0-24 h (AUC)CCK Winter was lower than AUCCCK Summer (F1:17 = 4.73, P = 0.0440) in the whole group of volunteers. On comparing the CCK concentrations within each session, there was an overall difference in winter (F2:36 = 14.81, P < 0.0001) as well in summer (F2:36 = 18.39, P < 0.0001). Post hoc comparisons yielded a difference between the 8.00 a.m. and 12 noon concentrations on the first day in winter (t = -3.96, P = 0.0009) as well as in summer (t = -4.64, P = 0.0002). The difference between the summer and winter AUCsCCK correlated with the difference between AUCs for temperatures in summer and winter (r = 0.58, P = 0.0089). The correlation was accounted for by the females (r = 0.73, P = 0.0171). The results are in accord with a diurnal and a seasonal variation of CCK in human plasma. © 2006 Elsevier Ltd. All rights reserved.

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