Biochemical, metabolic, and vascular mechanisms in menopausal hot flashes

Abstract

Objective: To determine if increases in core body temperature preceding most hot flashes are caused by increased metabolic rate, peripheral vasoconstriction, or central noradrenergic activation. Design: Laboratory physiological study. Setting: University medical center. Patient(s): Fourteen healthy, postmenopausal women reporting frequent hot flashes. Intervention(s): Data were recorded for 3 hours in a temperature- and humidity-controlled room. Main Outcome Measure(s): Core body temperature, mean skin temperature, respiratory exchange ratio, sternal skin conductance, plasma 3-methoxy-4-hydroxyphenylglycol, and vanillylmandelic acid. Result(s): Twenty-nine physiologically defined hot flashes were recorded. Increases in core body temperature, measured with an ingested radiotelemetry capsule, preceded 76% of the flashes. Increased metabolic rate began after increased core temperature. Peripheral vasoconstriction did not occur. Plasma levels of 3-methoxy-4-hydroxyphenylglycol, a metabolite of brain norepinephrine, increased significantly, whereas vanillylmandelic acid, a peripheral metabolite, did not. Conclusion(s): Core body temperature elevations preceding menopausal hot flashes are not driven by peripheral vasoconstriction or increased metabolic rate, but probably by a central noradrenergic mechanism.