Jl. Soengas et al., DOSE-DEPENDENT EFFECTS OF ACUTE MELATONIN TREATMENTS ON BRAIN CARBOHYDRATE-METABOLISM OF RAINBOW-TROUT, Fish physiology and biochemistry, 18(4), 1998, pp. 311-319
The levels of glycogen, lactate, acetoacetate and beta-hydroxybutyrate
in brain as well as glycogen and lactate levels in liver, and glucose
levels in plasma were evaluated in rainbow trout, Oncorhynchus mykiss
, injected with ethanol/saline (5/95; v/v) alone (controls) or contain
ing melatonin at three different doses 0.25, 0.5 and 1 mg kg(-1). The
results obtained demonstrate, for the first time in a teleost fish, th
e existence of changes in brain carbohydrate and ketone body metabolis
m due to melatonin treatment. Thus, a clear dose-dependent decrease wa
s observed in brain and liver glycogen levels, whereas a clear dose-re
sponse increase was observed in brain for lactate, acetoacetate and be
ta-hydroxybutyrate levels, and in plasma for glucose levels. CO2 produ
ction from glucose was also tested in brains of pooled fish and these
rates were not altered by melatonin treatment. Altogether, these resul
ts suggest that melatonin may play an indirect role, possibly through
alterations in insulin physiology, in the regulation of carbohydrate a
nd ketone body metabolism in brain of rainbow trout.