Effect of hormones on collagen metabolism and collagenase activity in the pubic symphysis ligament of the guinea pig.

The ligament which forms between the pubic bones of the pregnant guinea pig offers a unique system for the study of hormonal regulation of connective tissue metabolism. During the 5 days prior to parturition the length and hydroxyproline content of the pubic symphysis increase threefold. In nonpregnant animals, ligament growth can be induced in an estrogen-primed animal only following the administration of the hormone relaxin. A further increase in length can be achieved when progesterone is also injected. Removal and culture of post-partum ligaments, which undergo a 75% reduction in length and hydroxyproline content by the fifth post-partum day, allowed the demonstration of high collagenase levels released into the media. In contrast, when ligaments from pre-partum period were cultured, low levels of collagenase were detected in the media. The rapid post-partum ligament resorption could be partially inhibited if estrogen was injected immediately following parturition, whereas progesterone or relaxin significantly impaired ligament resorption. In a corresponding fashion, when the collagenase levels of these ligaments were measured progesterone treatment was shown to inhibit collagenase activity markedly while estrogen was less effective. Relaxin however, appeared to have no direct inhibitory effect.