The Effects of Estrogen on the Expression of Clock Genes in the Brain and Peripheral Tissue of Female Rats Undergoing Jet Lag
Estrogen has a direct effect on circadian rhythms, but the consequences of these effects had not been well established. Disruption of endogenous rhythms as occurs in jetlag or shift work leads to serious health issues. These perturbations could either be worsened or ameliorated in women by the presence of estrogen. The aim of our study is to determine the role of the estrogen in the entrainment of clock gene rhythms in the suprachiasmatic nucleus (SCN), the site of the master clock, following disruption of circadian rhythms. We compared the effects of estrogen (150 μg of estradiol benzoate in sesame oil) to oil on the clock gene rhythms of ovariectomized female rats. We performed RT-PCR to analyze the effect of the hormone of the expression of the clock gene Per2 from animals killed at 4 times of day either before jetlag, or two days after a six hour phase advance of the light/dark (LD) cycle. We found no significant effects of estrogen or jetlag on Per2 mRNA expression in the SCN. However, we saw a significant effect of time on the Per2 expression in the SCN in all groups of animals such that Per2 expression was lowest at time point 16. Additionally, we saw the amplitude of the gene is higher at time point 12 when the animals are treated with oil compared to estrogen in a 12:12 L:D cycle. Further studies will examine clock gene rhythms in peripheral tissue and compare these rhythms to the SCN.