A chemical that certain cells within the body produce, that affects the functions of other cells that have receptors for the hormone. There are numerous hormones in the body, some of which, such as epinephrine and norepineph-rine, are neurotransmitters. Hormones regulate cell activities that control body functions. There has been a long-held belief that estrogen, the hormone primarily responsible for female secondary sex characteristics, offered a neuropro-tective benefit for women. Recent studies, among the most extensive ever done, negate this belief.