Heterogeneity of follicle stimulating hormone: control and physiological function.

The existence of a heterogeneous population of follicle stimulating hormone (FSH) was described many years ago. Other pituitary glycoproteins, such as thyroid stimulating hormone (TSH) and luteinizing hormone (LH) as well as placental human chorionic gonadotrophin (HCG) also exhibit heterogeneity. Because FSH plays a significant role in a variety of ovarian activities such as follicular maturation, selection of the dominant follicle and ovulation, the possible role of subpopulations of FSH with distinct physicochemical characteristics is of great interest. After a great deal of investigation, the physiological significance of this biochemical phenomenon has yet to be fully understood. Investigators have employed immunoassays, in-vitro bioassays and radioreceptor assays to study the biological activity of the individual isoforms of FSH. As more information has accumulated, it has become clear that some of the initial assumptions used to interpret data may be incorrect. This review is provided to update the reader with available information on the topic as it relates to FSH and to point out issues that require re-evaluation in this area.