Comparative activities of growth hormone and luteinizing hormone in the direct stimulation of local release of progesterone from microdialyzed ovine corpora lutea in vivo.

摘要

In experiment 1 (single corpus luteum model), on day 7 after oestrus, 3 microcapillary dialysis membranes were surgically implanted into the cyclic corpus luteum of 5 ewes. Each microdialysis line was continuously infused with Ringer's solution. Serial fractions were collected every 30 min for 35 h on days 8-9, following a preperfusion period of 10-12 h. A 16-h perfusion with growth hormone (10 鎔/ml) increased progesterone release to 300% of the baseline value throughout the infusion (P<0.001). A3-h perfusion with oxytocin also stimulated progesterone release to approximately 200% of the baseline value (P<0.01). When oxytocin was infused following growth hormone infusion, no additional effect was observed. In experiment 2 (a multiple corpus luteum model), 4 ewes were superovulated, and multiple corpora lutea formed thereafter were implanted with the microdialysis system on day 7 after GnRH injection. Infusions with growth hormone or LH on days 9-10 at doses of 2.5, 5 or 10 鎔/ml for 4 h, twicewith an 8-h interval, similarly induced a clear increase of progesterone release. The 2nd growth hormone infusion had a greater stimulatory effect than the 2nd LH infusion at all doses tested (P<0.05). Furthermore, the 2nd infusion with growth hormone at5 and 10 鎔/ml induced a higher increase of progesterone release than the 1st infusion (P<0.05), while LH, at any of the doses, stimulated progesterone release to a similar extent during the 1st and 2nd infusions. The finding that growth hormone, like LH, directly stimulates the local release of progesterone within the corpus luteum in cyclic and superovulated ewes in vivo strongly suggest that it, like LH, is an essential luteotropic pituitary hormone in ewes.