Specific Radioimmunoassay of Chorionic Gonadotropin During Implantation in Rhesus Monkeys

Abstract

Antisera to the β subunit of ovine luteinizing hormone were generated in ten rabbits. Using antiserum H-26, we have developed a sensitive radioimmunoassay (RIA) for macaque chorionic gonadotropin (mCG) in which neither circulating nor urinary gonadotropins of pituitary origin cross-react. With this specific assay, we have measured mCG concentrations in both peripheral blood and urine specimens collected during the menstrual cycle in which rhesus monkeys conceived. Serum progesterone levels were measured concurrently. MCG in serum and urine was first measured from the 21st to 25th day of the fertile cycle or 8 to 12 days after the estimated day of conception. Mean concentrations of serum progesterone were significantly elevated within 24 to 48 hr after the appearance of mCG in serum. These findings demonstrate that the attaching blastocyst or the developing syncytiotrophoblast either already possesses or rapidly attains the capacity to secrete mCG. The presence of mCG at the time of implantation probably maintains the viability of the corpus luteum and temporarily enhances progesterone secretion immediately following implantation.