Release of Relaxin by a Nonluteolytic Dose of Prostaglandin F2α in in Pregnant Swine

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Abstract
Ten gilts were infused i.v. for 5 min on days 105 and 108 of gestation with 50 .mu.g prostaglandin F2.alpha. (PGF2.alpha.) in 10 ml of saline or saline alone. Plasma concentrations of relaxin and progesterone were determined in samples taken immediately before and after infusion, at 10-min intervals throughout the first hour postinfusion, at 30-min intervals throughout the next 5 h, and at 12-h intervals from day 103 of gestation through day 1 postpartum. Plasma concentrations of relaxin were increased immediately after infusion with PGF2.alpha. and peaked within 10 min postinfusion. The peak was followed by a rapid decline in plasma relaxin throughout the remainder of the first hour following infusion. Progesterone values did not change from preinfusion levels for either treatment during this time period and did not differ between treatments for the remainder of the gestation period. When compared to controls, PGF2.alpha.-treated animals were not significantly different with respect to length of gestation, duration of parturition or frequency of live births. Exogenous PGF2.alpha. can stimulate relaxin release from the corpus luteum without inducing luteolysis.