Short-term fasting does not affect hypothalamic insulin expression in female rats

Abstract

We previously reported that six-hour fasting increased insulin expression in the hypothalamus of male rats [1]. Given the gender-related differences in response to metabolic stressors [2], the goal of this study was to examine whether short-term fasting also affects hypothalamic insulin expression in female rats. The female rats in proestrus or diestrus were either exposed to the six-hour fasting or had ad libitum access to food. Proestrus and diestrus were chosen due to the highest and the lowest circulating levels of sex hormones, respectively. The insulin concentration in serum, cerebrospinal fluid, as well as the hypothalamic protein isolates was determined using RIA. Quantitative PCR was performed on cDNA transcribed from the total hypothalamic RNA. Following six hours of fasting, circulating insulin concentration was decreased. However, both the cerebrospinal fluid and hypothalamic insulin levels remained unchanged regardless of the estrus cycle phase. Moreover, hypothalamic insulin mRNA expression was unaffected by fasting in both examined phases of the estrus cycle. The aforementioned results suggest that, contrary to the findings in male rats, fasting affects neither insulin mRNA expression nor insulin content in the hypothalamus of female rats in proestrus and diestrus.