THE EFFECT OF RELAXIN ON COLLAGEN-METABOLISM IN THE NONPREGNANT RAT PUBIC SYMPHYSIS - THE INFLUENCE OF ESTROGEN AND PROGESTERONE IN REGULATING RELAXIN ACTIVITY

The aim of this study was to examine the effects of relaxin on collage n content, solubility, and composition in the rat pubic symphysis. Non pregnant, female Sprague-Dawley rats were bilaterally ovariectomized a nd either unprimed or primed with estrogen or progesterone alone, or a combination of estrogen and progesterone. One week later these animal s were given increasing doses of a synthetic human (gene-2) relaxin (0 -100 mu g) before being killed 16 h later. Their pubic symphysial tiss ues were then removed and analyzed for collagen content and solubility , whereas collagen composition was determined by SDS-PAGE. Relaxin adm inistration significantly increased the length(140 +/- 6%) and weight( 170 +/- 9%) of the interpubic fibrocartilage in estrogen-primed rats ( n = 15). At the same time, it decreased the total collagen content by 68 +/- 6%, without altering the proportions of collagen types, which w ere predominantly type I (85%) and type II collagen (15%). Relaxin adm inistered alone reduced the total collagen content by 64 +/- 4% but ha d no effect on collagen solubility or composition. Progesterone abolis hed the effects of relaxin in estrogen-primed rats. It is concluded th at relaxin has a potent effect on the amount of collagen in the rat pu bic symphysis that is enhanced by estrogen and antagonized by progeste rone. The changes in the extracellular matrix within the pubic symphys is induced by relaxin may be important in the modifications that this tissue undergoes during pregnancy.