M. Pavlidis et al., The effect of photoperiod on diel rhythms in serum melatonin, cortisol, glucose, and electrolytes in the common dentex, Dentex dentex, GEN C ENDOC, 113(2), 1999, pp. 240-250
Diel rhythms in serum concentrations of melatonin, cortisol, glucose, sodiu
m, chloride, and potassium were studied in the common dentex, Dentex dentex
, under different photoperiods (DD, 8L:16D, 12D:12D, 16L:8D). Photoperiod a
ffected both the diel rhythms and the absolute values of the estimated bloo
d components. Regardless of the photoperiod, melatonin titers were elevated
during the scotophase (384.3 +/- 13.9 pg/ml) compared with a mean baseline
level of 54.4 +/- 2.7 pg/ml during the photophase. Serum melatonin concent
rations reflected the prevailing photoperiod and constantly elevated melato
nin levels with no diel. rhythmicity were evident in fish held in the DD pr
otocol. A circadian-like pattern in serum cortisol was observed in fish tha
t were kept at the DD and 8L:16D protocols with cortisol peak at 18:00 h in
the night. Fish exposed to the 16L:8D regime showed highest cortisol level
s at 10:00 h, while no rhythmicity was evident under the 12L:12D protocol.
A phase shift of 4 h between the peaks of cortisol and glucose was evident
in fish exposed to the DD, 8L:16D, and 12L:12D regimes. Diel patterns of ch
anges in serum Na+ and Cl- were observed only in the fish held in the DD pr
otocol. Serum K+ values were lowest during the first part of the scotophase
under all regimes, except the 16L:8D where no diel rhythmicity was detecte
d. During the photophase, cortisol was positively correlated with glucose,
Na+, and Cl- and negatively with K+. During the scotophase, melatonin was p
ositively correlated with glucose and electrolytes. Results indicated that
cortisol may be responsible for the observed rhythmicity of glucose and tha
t melatonin may play a role in glucose and ion regulation in common dentex.
(C) 1999 Academic Press.