EFFECTS OF PURIFIED PORCINE RELAXIN ON THE UTERUS OF GILTS DURING EARLY-PREGNANCY

Twenty-three gilts were assigned to receive a 1.0 ml injection of either saline (C) or 0.5 mg purified porcine relaxin in saline (pRLX) every 6 h on Days 6-11 of gestation. All 12 gilts assigned to relaxin treatment were pregnant on Day 11. Following hysterectomy on Day 11, mean uterine wet weight was greater (P < 0.05) in pRLX-treated gilts (1247.6 +/- 94.0 g) as compared with control animals (958.5 +/- 98.2 g). Mean uterine dry weight was 123.7 +/- 6.6 g and 111.8 +/- 8.9 g (P > 0.10) in pRLX and C gilts, respectively. Uterine volumes and circumferences were also increased (P < 0.05 and P < 0.01, respectively) by pRLX treatment, but no difference was observed between treatments in uterine length or total uterine DNA and protein content. Relaxin treatment resulted in mean plasma relaxin concentrations of 4.08 +/- 0.27 ng ml-1. Mean plasma concentrations of progesterone and PGFM (15-keto-13,14-dihydro PGF2-alpha) were not affected by exogenous relaxin. In conclusion, exogenous relaxin increased uterine size during early pregnancy in gilts. The observed uterotropic effects of relaxin appear to be primarily due to cellular hypertrophy as a result of water imbibition.