Abstract

The effects of ovarian extracts containing relaxin on various types of smooth muscle have been investigated. Administration of the extracts to dogs produced hypotension, bradycardia and inhibition of ureteral motility; tachyphylaxis developed to these actions. A component in the extracts caused the release of histamine in quantities sufficient to account for the hypotension. The extracts inhibited the spontaneous uterine motility of the rat but not that of the rabbit or human (in vitro). Tachyphylaxis developed to the uterine inhibitory action in vitro and in vivo. The component which produced hypotension differed from the factor which inhibited the uterus in not being inactivated by pepsin. The results of these studies have been discussed in relation to the effects of relaxin-containing extracts in man.