Despite a large number of studies, the role of melatonin on glucose metabolism is
still controversial. The aim of the present work was to further characterize the effect
of melatonin on insulin action during: i) intravenous insulin tolerance test performed
at different times of the day using melatonin, a melatonin agonist (S-20304), a melatonin
antagonist (S-20928) or in pinealectomized rats, ii) euglycemic-hyperinsulinemic clamp
performed in melatonin agonist-treated as well as in pinealectomized rats. The fall
in glycemia after the insulin injection was not significantly affected by melatonin
and melatonin agonist (S-20304) at ZT6, nor by the melatonin antagonist (S-20928)
at ZT13 nor in pinealectomized animals at ZT6 in comparison to their respective control.
Acute treatment with S-20304 or chronic suppression of melatonin by pinealectomy did
not significantly alter basal plasma glucose and insulin levels or hepatic glucose
production and whole body or individual tissue glucose utilization. These data do
not give support to a crucial role of melatonin on insulin action in normal rats.
Melatonin Agonist - Melatonin Antagonist - Pinealectomy - Glucose Production - Gluose
Utilization
