Changes in progesterone secretion following treatment with transforming growth factor alpha (TGF-alpha) during the follicular phase of the sheep oestrous cycle.

The effects of transforming growth factor alpha (TGF-alpha) on ovarian steroid secretion were investigated. Three crossbred ewes synchronized for oestrus with ovarian autotransplants were infused with TGF-alpha (30 micrograms in 12 h) via the ovarian artery for 12 h before withdrawal of progestagen pessary. Three ewes were used as controls. Jugular and ovarian venous blood samples were taken at intervals of 10 min at two stages during the follicular phase (21-27 h and 38-42 h after pessary withdrawal) and every 2 h from 44 to 86 h. Plasma LH and FSH concentrations, and ovarian secretion rates of inhibin, androstenedione, oestradiol and progesterone were determined using radioimmunoassays. LH pulse amplitude increased in ewes treated with TGF-alpha in the early follicular phase (0.92 +/- 0.25 micrograms l-1 in controls versus 3.10 +/- 0.35 micrograms l-1 in TGF-alpha treated ewes; P < 0.05) and remained high in the late follicular phase. Plasma FSH concentrations were high during the follicular phase in ewes treated with TGF-alpha (P < 0.05). The infusion of TGF-alpha had no significant effect on the ovarian rate of secretion of androstenedione and, although the secretion rates of oestradiol and inhibin were consistently lower in TGF-alpha-infused ewes, the differences were not significant. The ratio of secretion of androstenedione to oestradiol was greater during the follicular phase in TGF-alpha-treated ewes (P < 0.05), suggesting that the efficiency of aromatization had been impaired.(ABSTRACT TRUNCATED AT 250 WORDS)