Effect of removal of follicles, corpora lutea or ovaries on maintenance of pregnancy in swine.

The effects of the removal of follicles, corpora lutea (CL) or ovaries at day 108 of gestation on maintenance of pregnancy and on concentrations of progesterone, prostaglandin 2 alpha-metabolite (PGF2 alpha-M) and relaxin in maternal plasma were studied in 20 gilts. Controls were subjected to sham surgical procedures. Removal of CL or ovaries decreased progesterone and relaxin and increased PGF2 alpha-M in the maternal circulation and prematurely terminated pregnancy without causing onset of lactation. Progesterone and relaxin decreased to a lower concentration after ovariectomy than after removal of CL, probably because of incomplete extirpation of luteal tissue. Ovariectomy increased the frequency of stillbirths. These results show that the CL are the main source of progesterone and relaxin in pregnant swine and that relaxin may play a role in parturition and the onset of lactation.