THE ROLE OF RELAXIN IN GLYCODELIN SECRETION

Glycodelin is a glycoprotein named for its unique carbohydrate structu re. Glycodelin is produced by the secretory endometrium during the lat e luteal phase and returns to baseline during menses of the ensuing cy cle, whereas in conceptive cycles it rapidly increases. Although proge sterone and possibly estradiol are required for glycodelin production, they are not directly involved in the synthesis and release of this p rotein. Their role may be development of the endometrial secretory gla ndular elements, whereas other factors are required to initiate and ma intain glycodelin secretion. The pattern of relaxin secretion during t he luteal phase and early pregnancy is similar to that of glycodelin, but their profiles have not been determined simultaneously. To investi gate the relationship of relaxin and glycodelin, two studies were cond ucted. In the first study, relaxin, glycodelin, and ovarian steroids w ere measured in daily serum samples from nonconceptive and conceptive natural cycles. Profiles of relaxin and glycodelin were closely associ ated, with the onset of relaxin preceding glycodelin secretion by 1-2 days in nonconceptive cycles, and the pregnancy-associated increases i n each hormone differing by about 2 days. The second study tested the hypothesis that relaxin stimulates glycodelin secretion. Samples were obtained from patients injected with human relaxin for 28 days. In sub jects demonstrating ovarian cyclicity, glycodelin secretion was elevat ed, but it was not detected in subjects without ovarian cyclicity or i n placebo-treated control subjects. This study reveals a close tempora l and quantitative relationship between relaxin and glycodelin profile s in the late luteal phase and early pregnancy. It also demonstrates t hat relaxin administration can stimulate glycodelin production from a developed endometrium. This is the first report of a nonsteroidal ovar ian factor that controls glycodelin secretion, and these results sugge st a function for relaxin during early pregnancy. Glycodelin is a pote nt inhibitor of sperm zona pellucida binding by virtue of its extensiv e carbohydrate structure, but it is normally at a nadir in the periovu latory period. The data demonstrate that relaxin can stimulate glycode lin secretion throughout the menstrual cycle, including the periovulat ory period, when relaxin-induced glycodelin secretion could have a con traceptive effect.