Plasma progesterone levels in guinea-pigs actively immunized against prostaglandin F2alpha, hysterectomized or treated with intra-uterine indomethacin.

Five guinea-pigs actively immunized against a prostaglandin F2alpha(PGF2alpha)-bovine serum albumin conjugate showed elongated oestrous cycles. During these, corpora lutea were maintained in a functional secretory state as indicated by plasma progesterone levels. The results are compatible with the view that the PGF2alpha antibodies neutralized the PGF2alpha released from the uterus and thus prevented its normal luteolytic effect. Similar patterns of progesterone secretion were observed in two hysterectomized animals and in two animals with intra-uterine implants of indomethacin.