Progesterone-binding globulin and progesterone in guinea-pigs after ovariectomy, abortion and parturition

The level of progesterone in the serum of pregnant guinea-pigs which continued their pregnancies after ovariectomy on Day 30 fell and then rose again. In contrast, progesterone-binding globulin (PBG) was apparently not affected. PBG did however fall in guinea-pigs which aborted and also after parturition. It is apparent therefore that high PBG levels were associated with continued pregnancy. The half life of PBG was found to be approximately 2 days.