Estrogen receptors and serotonin receptors coexist in cells in a wide variety of tissues, and this critical review of the literature suggests that many of E2's effects may be medi- ated by changes in the actions of serotonin (5HT). Serot- onin is usually considered to be a neurotransmitter, but surprisingly, only 1% of serotonin in the human body is found in the CNS [4]. The remaining 99% is found in other tissues, primarily plasma, the gastro-intestinal tract, and immune tissues, where serotonin acts as a hormone regulating various physiological functions including vasodilation[5], clotting[6], recruitment of immune cells [7-9], gastro-intestinal motility,[10] and initiation of uter- ine contraction [11,12]. Serotonin also has peripheral functions in.
