Proteins and Steroids in Early Pregnancy: General Considerations

Abstract

There are many relations between steroids, more specifically steroid hormones, and proteins. To evaluate the relevance of these interactions tor early pregnancy, it may be useful to list at first these most important phenomena:

• 1. Adenotropic Hormones. The production of steroid hormones is under the control of the pituitary. The pituitary hormones are either peptides (e.g. corticotropin) or proteins. Of relevance in our context are the gonadotropins, glycoproteins consisting of two sub-units with different functions — one binding to the membrane receptor, the other entering the cell and being responsible for the physiological action. Pituitary control of steroid hormone synthesis and release is important for the cooperation of various hormones in the sexual cycle, resulting in ovulation, as well as for the development of early pregnancy.

• 2. Enzymes of Biosynthesis. Steroid hormones are the end-products of a biosynthetic pathway involving many enzymes. Cholesterol may be regarded as the common starting material, since cholesterol is present abundantly in biological membranes of all cells (it is, of course, produced from acetyl-CoA in a long sequence of reactions). For the conversion of cholesterol to progesterone, four enzymes are needed; even more are necessary for the biosynthesis of estrone. It must be kept in mind that steroid hormones are not stored in the hormone-producing tissue; thus the control of biosynthesis is the way of controlling hormone production.