Origin of plasma insulin-like growth factor-I (IGF-I) during estrus in goats

The objective of this study was to clarify the origin of the increase in plasma insulin-like growth factor-I (IGF-I) during estrus in goats. Focusing on the uterus, the effect of estradiol-17beta (E-2) on the secretion of IGF-I was examined using ovariectomized and hysterectomized animals. A single 5 mug/kg BW of E-2 was injected intramuscularly into ovariectornized and hysterectomized goats for 3 consecutive days, and plasma IGF-I concentrations in the two groups were compared. The concentrations of IGF-I rose after the treatments in both groups. The concentrations were significantly higher from 3 to 8 days after the treatment than before the treatment in ovariectornized goats (P<0.05), and from 1 to 3 days after the treatment than before in hysterectomized goats (P<0.05). Thus higher concentrations of plasma IGF-I tended to last longer in ovariectornized than hysterectomized goats. The area under the IGF-I response curve for the 8-day period after the first injection of E-2 tended to be greater in ovariectornized than in hysterectomized goats. The results show that E-2 increases plasma IGF-I concentrations in goats, and suggest that E-2-stimulated IGF-I in plasma may originate mainly from the uterus.