The hormonal control of the guinea pig corpus luteum during early pregnancy.

Forty guinea pigs were divided into two groups, pregnant and nonpregnant, and were operated upon on days 10, 12, 14, and 16 of the ovarian cycle or of pregnancy. Blood was obtained from the utero-ovarian vein, and prostaglandin F2alpha (PGF2alpha), prostaglandin E (PGE), progesterone, and estrogen content was assayed by radioimmunoassay. Increased levels of PGF2alpha preceded a drop in progesterone levels in nonpregnant animals, reflecting luteolysis. In pregnant animals, the level of PGF2alpha remained low, and progesterone levels increased. PGE levels were similar in the two groups. These results suggest that the low PGF2alpha levels seen during early pregnancy are related to corpus luteum rescue.