Abstract

This study was designed to investigate the effects of constant darkness and light on changes of serum cholesterol, insulin and glucose levels in healthy male rats. In this study, healthy male rats (n = 30) were divided into 3 groups of tens and kept at various light/dark conditions: Control 12:12 light/dark (LD); constant darkness (DD), and constant light (LL) groups for 2 weeks. Blood samples were obtained from retro-orbital sinus before start of experiment and on the 7^th and 14^th days of the experimental period. The serum cholesterol and glucose levels were measured by the enzymatic method and insulin levels were measured using insulin kit by enzyme-linked immunosorbent assay (ELISA) method. The results of the study showed that the levels of serum cholesterol and glucose on the 7^th and 14^th days of the experimental period in DD group significantly decreased compared to the LD and LL groups (p < 0.05). On the 14^th day of experiment, we observed significant decrease of serum insulin level in the constant darkness group compared with the two other groups (p < 0.05). The study showed that on the 7^th and 14^th days of experiment, constant light significantly increased serum glucose level without having any significant effects on serum cholesterol and insulin levels. Also, the long period of time (14 days) was found to be more effective in the serum of these metabolic parameters changes than the short period (7 days).

Key words: Constant darkness, light, cholesterol, glucose, insulin, healthy male rats.

Abbreviation

SCN, Suprachiasmatic nucleus; LD, control group; LL, constant light group; DD, constant darkness group; ELISA, enzyme-linked immunosorbent assay; LDL, low-density lipoprotein; FDP, fructose-1, 6-diphosphatase; PFK,phosphofructokinase; SNS, sympathetic nervous system; PNS, parasympathetic nervous system.