Factors regulating the synthesis and secretion of corticosteroid-binding globulin (CBG) in the young pig

This study examined the in vitro production of corticosteroid-binding globulin (CBG) by liver collected from pigs at various ages following birth, the effects of various hormone treatments on the in vitro hepatic release of CBG, and the relationship between the hormone effects and postnatal development. Liver was collected from pigs (n=20) immediately following euthanasia on 3, 10, 20, 30 or 40 days of age. Liver slices (200 mg) were incubated for 12 and 24 hours with either cortisol (10^-7 M), estradiol (10^-8 M), progesterone (10^-7 M), or thyroxine (10^-7 M) prepared in 0.5% ethanol. A single blood sample was collected upon euthanasia for determination of plasma CBG levels. The amount of CBG released per unit weight of liver slices and in circulation was measured using an enzyme-linked immunosorbent assay (ELISA) procedure. The percentage of cell's dying and the amount of total protein released were measured to compare with CBG concentration. Cell death was higher (P<0.05) on days 3, 10, and 20 than on days 30 and 40. Addition of 0.5% ethanol to the media did not affect the release of total protein or CBG. The release of total protein did not change (P>0.10) with age. Plasma CBG levels increased (P<0.05) on day 30 and CBG levels measured in media from liver slices decreased (P<0.01) on day 20. Hormone treatment had no apparent effect on the release of CBG by the cultured liver. Consequently, the release of CBG per unit weight of liver decreased (P<0.01) on day 20. CBG release from hepatic tissue may be regulated in a different manner from that of other proteins. The absence of a hormone treatment effect on the release of CBG from liver slices may indicate that regulation of CBG release from the liver may be primarily related to age.