Plasma Relaxin Levels in Pigs with Corpora Lutea Induced During Late Pregnancy1

Abstract

Plasma relaxin levels were determined during late pregnancy and at parturition in gilts with only original corpora lutea (CL) of pregnancy or with only CL induced on day 83 (Group I) or day 103 (Group II) of gestation. Levels of relaxin were lower in gilts with only induced CL than in gilts with only original CL of pregnancy. Group I, with CL which were 30 days of age at the time of parturition, had elevated levels of relaxin 1 or 2 days preceding parturition—a secretory pattern similar to that of intact gilts. In contrast, Group II, with CL 15 days of age at the time of parturition, did not have elevated levels of relaxin preceding parturition. This study indicates that the CL of pregnancy are associated with the production and/or secretion of relaxin and that the CL may have to change or mature over at least a 15-day period in order to perform these functions.