tailieunhanh - Báo cáo y học: "Absence of a serum melatonin rhythm under acutely extended darkness in the horse"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Absence of a serum melatonin rhythm under acutely extended darkness in the horse. | Murphy et al. Journal of Circadian Rhythms 2011 9 3 http content 9 1 3 JOURNAL OF CIRCADIAN RHYTHMS RESEARCH Open Access Absence of a serum melatonin rhythm under acutely extended darkness in the horse Barbara A Murphy 1 Ann-Marie Martin1 Penney Furney1 and Jeffrey A Elliott2 Abstract Background In contrast to studies showing gradual adaptation of melatonin MT rhythms to an advanced photoperiod in humans and rodents we previously demonstrated that equine MT rhythms complete a 6-h light dark LD phase advance on the first post-shift day. This suggested the possibility that melatonin secretion in the horse may be more strongly light-driven as opposed to endogenously rhythmic and light entrained. The present study investigates whether equine melatonin is endogenously rhythmic in extended darkness DD . Methods Six healthy young mares were maintained in a lightproof barn under an LD cycle that mimicked the ambient natural photoperiod outside. Blood samples were collected at 2-h intervals for 48 consecutive h 24-h in LD followed by 24-h in extended dark DD . Serum was harvested and stored at -20 C until melatonin and cortisol were measured by commercial RIA kits. Results Two-way repeated measures ANOVA n 6 time point revealed a significant circadian time CT x lighting condition interaction p .0001 for melatonin with levels non-rhythmic and consistently high during DD CT 0-24 . In contrast cortisol displayed significant clock-time variation throughout LD and DD p .0009 with no CT x light treatment interaction p .4018 . Cosinor analysis confirmed a significant 24-h temporal variation for melatonin in LD p .0002 that was absent in DD p .51 while there was an apparent circadian component in cortisol which approached significance in LD p .076 and was highly significant in DD p .0059 . Conclusions The present finding of no 24 h oscillation in melatonin in DD is the first evidence indicating that melatonin is not gated by a self-sustained circadian .