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Abstract
Melatonin is a neuromodulatory hormone with diffuse effects through several eurbendocrine axes. It appears that melatonin exerts an effect on hypothalamic-ituitaty-end-organ systems related to prolactin, thyroid, insulin, growth hormone, drenal, and reproductive dynamics. Behavioral and emotional effects have also een proposed to be related to changes in melatonin secretory pattems. However, till many of these results need strong support. Since reports of the effects of melatonin on the endocrine system in man are cant and inconsistent, our study is conducted to clarify the link between melatonin d physical stress from one point of view, melatonin and light from another point d melatonin and endocrine functions from a third point of view. Rats of both exes were classified into 16 groups, melatonin was administered in a dose of 0.4 g / kg b.w daily at 10.00 A.M. p.o. for 30 days to 8 groups of them, of which 4 were kept in constant illumination of 1000 lux light intensity for 30 days, 4 oups were kept in dark for the same period. Of these 8 groups, 4 groups were ubjected to 90 minutes period of immobilization stress just prior to scarifying by ing al1 four limbs to metal mounts attached to a board. All were controlled by imilar groups sharing the same conditions. In the 30th day, blood samples were collected and sera were separated and ubjected to assay of the following hormones: TSH, T4, LH, FSH and insulin. Serum TSH, T 4, LH and FSH were measured by ELISA method, while serum nsulin was determined by RIA technique. 1- Nocturnal illumination significantly raised both TSH and T4 levels only in non-treated, non-stressed male and female rats and didn’t affect them in all.