摘要：Circadian variations in catecholamines (CA) in the Thoroughbred horse were investigated by determining plasma adrenaline (Ad) and noradrenaline (NA) concentrations every 2 hr by high-performance liquid chromatography with an electrochemical detector (HPLC-ED). The HPLC-ED method in the present study was sufficient for determining plasma CA concentrations. The elution of CA from alumina with a mixture of acetic acid and methanol (1:50, v/v) gave a good recovery. The detection limit for both Ad and NA was 10 pg/ml. A significant variation during the 24 hr was observed for plasma NA concentrations (P<0.01), but not for plasma Ad concentrations. From 14:00 hr to 18:00 hr, plasma NA concentrations were significantly higher than those observed from 02:00 hr to 04:00 hr (P<0.01). As a result of the cosinor analysis for individuals, a circadian rhythm of plasma concentrations of Ad and NA was demonstrated (mean ± SE, 26.3 ± 4.6 pg/ml and 66.3 ± 3.8 pg/ml; rhythm amplitude, 9.4 ± 1.4 pg/ml and 12.7 ± 1.2 pg/ml; time of trough, 02:34 hr: min ± 9.7 min and 02:54 hr: min ± 33 min for Ad and NA, respectively). The 6 hr continuous tie-stall-type restraint decreased plasma concentrations of Ad and NA and delayed their peaks by 4 hr and 2 hr, respectively. There was a significant correlation (n=48, r=0.562, P<0.001) between the circadian variations in plasma Ad and NA. In conclusion, it was found that circadian variations in plasma CA in the Thoroughbred horse were similar to those in humans. In addition, the present study suggests that the sustained stress may influence circadian variations in plasma CA.
