Testosterone is the primary substrate in the male body for the synthesis of estrogen (etradiol), the principal female sex hormone. Estrogens presence may be unusual in men, it is structurally very similar to testosterone. With a slight alteration by the enzyme aromatase, estrogen is produced in the male body. Aromatase activity occurs in various regions of the male body, including adipose, liver, gonadal, central nervous system and skeletal muscle tissues. In large amounts however it does have potential to cause many unwanted effects including water retention, female breast tissue development (gynecomastia) and body fat accumulation. In the context of the average healthy male, the amount of estrogen produced is generally not very significant to one’s body disposition, and may actually have a beneficial in terms of cholesterol levels.
We must however not be led into thinking that estrogen serves no benefit, as it is actually a desirable hormone in many regards. Athletes have known for years that estrogenic steroids are the best mass builders, but it is only recently that are we finally coming to understand the underlying mechanisms that make this the case. This is manifested through increases in glucose utilization, growth hormone secretion and androgen receptor proliferation.
Estrogen may play a very important role in the promotion of an anabolic state by affecting glucose utilization in muscle tissue. This occurs via an altering of the level of available glucose 6-phosphate dehydrogenase, an enzyme directly tied to the use of glucose for muscle tissue growth and recuperation. More specifically, G6PD is a vital part of the pentose phosphate pathway, which is integral in determining the rate nucleic acids and lipids are to be synthesized in cells for tissue repair. During the period of regeneration after skeletal muscle damage levels of G6PD are shown to rise dramatically, which is believed to represent a mechanism for the body to enhance recovery when needed. Estrogen is directly tied to the level of G^PD that is to be made available to cells in this recovery window.
Estrogen may also play an important role in the production of growth hormone and IGF-1. IGF-1 (insulin like growth factor) is an anabolic hormone released in the liver and various peripheral tissues via the stimulus of growth hormone. IGF-1 is actually responsible for the anabolic activity of growth hormone such as increased nitrogen retention/protein synthesis and cell hyperplasia (proliferation).