Determinants of plasma leptin concentration in postmenopausal women

This investigation examined the influence of hormone replacement therapy on plasma leptin concentrations in postmenopausal women and sought to determine if a relationship existed between plasma leptin, the thermoregulatory cytokine interleukin-1 (IL-1), and basal body temperature. Twenty-two women (54-71 years of age) were studied: eight were not taking hormone replacement, seven took oral estrogen only, and seven took oral estrogen plus progestin. Morning oral temperature, plasma leptin concentration, and mononuclear cell secretion of IL-1β, IL-1 receptor antagonist (IL-1Ra), and soluble IL-1 receptor type II (sIL-1RII) were measured. Plasma leptin concentrations were not affected by hormone replacement therapy, but were inversely related to years since menopause (R=-0.48, P=0.02) and were proportional to IL-1 activity (the balance of IL-1β/IL-1Ra secretion, R=0.69, P=0.001). Moreover, morning oral temperature was positively related to plasma leptin (P=0.03), after stratifying by progestin intake. These results support the concept that basal body temperature is regulated by a network of endocrine and immune mediators that are significantly influenced by age.