REGULATION OF PULSATILE SECRETION OF PROSTAGLANDIN-F2-ALPHA FROM THE OVINE UTERUS BY OVARIAN-STEROIDS

Two experiments were conducted to determine how progesterone and oestr adiol regulate pulsatile secretion of PGF2alpha from the ovine uterus. In Expt 1, ovariectomized ewes received: (1) no treatment, (2) oestra diol, (3) progesterone, or (4) oestradiol and progesterone (n = 5 ewes per treatment group) to approximate the changes in steroids that occu r during the oestrous cycle. Jugular venous blood samples were collect ed at 30 min intervals for 48 h beginning at 08:00 on day 14 of steroi d replacement. Blood samples were collected from five intact ewes at a comparable time of the oestrous cycle for comparison. The number and magnitude of pulses in 13,14-dihydro-15-keto-PGF2alpha (PGFM) in jugul ar venous blood samples were used to assess uterine secretion of PGF2a lpha. Experiment 2 was conducted as Expt 1, except that the progestero ne replacement protocol was modified to duplicate more closely the tem poral pattern of progesterone observed in intact ewes. Results were si milar in both experiments. Intact ewes averaged 4.4 +/- 0.6 pulses per 48 h blood sampling period. The frequency of pulses was less in ovari ectomized ewes (P < 0.05). The number of pulses was increased by proge sterone treatment (P < 0.01); the number of pulses in ovariectomized e wes receiving progesterone replacement was similar to that observed in intact ewes. There was a tendency for oestradiol to have a positive e ffect on the number of pulses (P = 0.12). The magnitude of pulses in i ntact ewes averaged 419 +/- 38 pg ml-1 and was much less in ovariectom ized ewes (P < 0.05) than in intact ewes. The magnitude of pulses was only partially restored by progesterone replacement (P = 0.03). No eff ect of oestradiol on pulse magnitude was observed. In conclusion, prog esterone plays an important role in regulating the number and magnitud e of pulsatile secretion of PGF2alpha from the ovine uterus. The abili ty of progesterone to completely restore the frequency of pulses but n ot the magnitude of PGF2alpha release in ovariectomized ewes indicates that ovarian secretory products other than progesterone (for example, luteal oxytocin) are not required to initiate pulsatile secretion of PGF2alpha but may be required to achieve full pulse magnitude.