Release of insulin-like growth factor I by the sheep placenta in vitro

This study has utilized a tissue perifusion system to examine the release of insulin-like growth factor I (IGF I) from different regions of the sheep placenta at two stages of gestation. Placentae were obtained from ewes at either 116 +/- 7 (mean +/- s.e.) or 144 +/- 1.5 days of gestation and separated into the maternal basal plate or chorionic villous tissue. At both ages, the maternal basal plate tissue released approximately three times more IGF I than the chorionic villous tissue. No difference was found between the rate of release of IGF I from the maternal basal plate at 120 and 140 days of gestation, whereas the chorionic villous tissue released less IGF I later in gestation. Maternal basal plate tissue was less responsive to a depolarizing dose of KCl than was chorionic villous tissue at either age. After acid gel chromatography, perfusate from the basal plate had three peaks of IGF immunoreactivity (corresponding to binding protein, IGF I and a form with an intermediate molecular weight). In contrast, the chorionic villous tissue released only a form with a high molecular weight, corresponding to binding protein. These results demonstrate that the sheep placenta produced IGF I, that secretion varies between different placental zones which contain different cell types and that there are maturational changes in placental IGF I secretion. The IGFs may be involved in placental growth.