Introduction
The decline in ovarian hormones across the menopausal transition is associated with increased risk of weight gain, but the underlying mechanisms are largely unknown. Brown adipose tissue (BAT) contains uncoupling protein-1 (UCP1), which allows heat dissipation. Ovarian hormones, specifically 17β-estradiol, activate BAT via central and/or direct mechanisms. The aim of the current study was to determine the relationship between circulating ovarian hormones and BAT temperature in pre- and post-menopausal women. We hypothesised that pre-menopausal women have greater BAT activity compared to post-menopausal women, and that ovarian hormones are positively correlated with BAT temperature.
Methods and results
Seventeen participants were recruited to the following groups: women during the follicular (n=8) or luteal phase (n=6) of the menstrual cycle, and post-menopausal women (n=3). Infrared thermography was used to measure cutaneous supraclavicular (SCV) temperature as an index of BAT temperature and the manubrium (negative control). BAT temperatures were measured 5 mins prior, 5 mins during and 30 mins after cold exposure, which was elicited via hand immersion in 15°C water. Plasma blood samples were collected and used for radioimmunoassay to determine 17β-estradiol and progesterone concentrations. Anthropometric measurements (weight, height and BMI) were recorded for subsequent regression analyses. Repeated measures ANOVA, with post-hoc Fisher’s least significance test revealed that SCV temperature was lower in post-menopausal women than premenopausal women (p<0.05) in response to cold exposure. Increased SCV temperature after cold exposure correlated to 17β estradiol levels (maximum AUC, β= 4.06, R2= 0.22, p<0.01); however, an inverse relationship between age and BAT temperature (p<0.05) was also found.
Conclusion
Our current work proposes that the decrease in SCV temperature in post-menopausal women may contribute to reduced energy expenditure and increased weight gain in post-menopausal women. Further work is needed to unravel the 17β estradiol-dependent mechanisms that lead to the decline of SCV temperature across the menopausal transition.