Inhibition of RNA synthesis differentially affects in vitro melatonin release from the pineal organs of ayu (Plecoglossus altivelis) and rainbow trout (Oncorhynchus mykiss)

The effects of actinomycin D (RNA synthesis inhibitor) and cycloheximide (p rotein synthesis inhibitor) on melatonin release from the cultured pineal o rgan of two teleosts with or without the circadian regulation of melatonin production (ayu Plecoglossus altivelis and rainbow trout Oncorynchus mykiss , respectively) were investigated. Actinomycin D decreased melatonin releas e from the pineal organ during the dark phase but there was a significant d ifference between the two species (22.2% for ayu and 59.1% for trout as com pared with the respective control). This difference might be due to whether the circadian regulation via gene transcription of melatonin synthesis exi sts or not. On the other hand, cycloheximide decreased melatonin release to similar to1% in both species, indicating that the fish pineal organ requir es de novo protein synthesis to maintain rhythmic melatonin release. (C) 20 01 Elsevier Science Ireland Ltd. All rights reserved.