Daily cycle of melatonin in different tissues of dybowski’s frog (Rana dybowskii)

Abstract

ABSTRACT This study is the first to analyse the daily cycle of melatonin in Dybowski’s frogs (Rana dybowskii), a species with economic importance in north-eastern China. The concentrations of melatonin in the serum, whole brain, and liver, skin, and retinal tissue samples collected from Dybowski’s frogs were measured using high-performance liquid chromatography every 4 h over a 24 h cycle. A significant melatonin peak (P< 0.05) was observed at 00:00 in the serum samples (203.25 ± 5.06 ng/L). This peak was synchronised with peak melatonin concentrations in the retinal (1513.25 ± 3.15 ng/L), liver (49.34 ± 3.67 ng/L), and whole brain (426.85 ± 6.85 ng/L) tissue samples, although melatonin concentrations in skin tissue samples peaked at 12:00 (270.02 ± 4.60 ng/L). Therefore, the time of day should be considered when examining the physiological status of this frog, given the potential effects of fluctuating daily melatonin concentrations on physiological variables.