General considerations. Sources, metabolism and excretion of oestrogen. Gradients of responsiveness. Reversibility of effects.

General Considerations

Definition and Terminology. The term ‘oestrogen’ denotes any substance which will induce cornification in the vagina of the adult mouse like that of natural oestrus. The meaning of the word ‘oestrin’ is not so easy to define exactly, or to define at all without a background of biological history. Apart from knowing that the sexual functions of the female depend on the ovary and are not controlled through its nervous connections (Knauer, 1900), our recognition of the hormonal basis of ovarian activity began with the observation by Marshall & Jolly (1905) that oestrus could be induced in spayed dogs either by the injection of extracts of ovary removed from another dog during oestrus or by implanting oestral ovaries into the peritoneum. These workers recognized that the ovary produces two different hormones, and that the secretion which causes oestrus is different from that formed later by the corpora lutea. A few years later Adler (1912) reported that oestrus could be brought on in guinea-pigs by intravenous or subcutaneous injections of extracts or press-juices obtained from whole ovaries or from corpora lutea. The next great advance was that of Allen & Doisy (1923, 1924), who discovered that liquor folliculi from the sow's ovary caused oestrus-like changes in the rat's vagina. The hormone thought to induce these changes thereafter came to be known as theelin, oestrin or folliculin. The active principle was at that time a hypothetical substance which could be recognized only by its biological effects. Later, the isolation of the hormone in crystalline form by Doisy, Veler & Thayer (1930) and also by Butenandt (1929), working independently, narrowed the meaning of the term oestrin, as used by British workers, to the single well-defined chemical compound now known as oestrone. This would not have led to terminological difficulty if other naturally produced oestrogenic compounds, including oestradiol, oestriol, equilin and equilenin (Fig.5, p. 104), had not been identified later.