Endocrine, Reproductive, Neurophysiologic and Extraneous Activities of Estrogen in Vertebrates

Estrogens are reproductive hormones synthesized in the gonads of both male and female vertebrates. This review is geared towards uncovering some endocrine, reproductive, neurophysiologic and extraneous activities of estrogen in vertebrates. The three most  common naturally occurring estrogens are: Estrone (E1), estradiol (E2), and estriol (E3). In primates, estradiol is the most potent and predominant estrogen during reproductive years. Estrogens are synthesized primarily in the female ovaries and in small quantities in the male testes and the adrenal glands, brain, and fat of both sexes. Estrogens are steroid hormones. The adipose tissues are considered to be the major source of circulating estrogen after the gonads in both men and women. In essence, the presence of aromatase expression in a local tissue confirms extra-gonadal estrogen synthesis. In reproduction, estrogen promote secondary sexual characteristics in females and regulates maturation of sperm (spermiogenesis) in males. Neurophysiologically, estrogen promote glutamate activity in the central nervous system, facilitates dopaminergic neurotransmission but blocks gammaaminobutyric acid. Extraneously, estrogen decrease serum cholesterol and osteoporosis especially in menopausal females. However, acute estrogen droppostpartum leads to depressed mood experienced by most post parturient females. In this review, it is observed that, while serum estrogen decreases with age in females, in male it increases with age due to the extraneous synthesis of estrogen especially in the adipose tissue. Keywords: Estrogen, Female, Aromatase, Male, adipose tissue