Epidermal growth factor does not cross the blood-brain barrier.

To measure the passage of epidermal growth factor (EGF) through the blood-brain barrier (BBB) 125I-labeled EGF was injected intravenously into adult rats. The distribution of 125I-EGF in the blood and cerebrospinal fluid (CSF) was determined over a time period of several hours. Between 2 to 6 h a stable distribution of intact 125I-EGF in CSF was measured to be approximately 1/500 of the blood-borne EGF, an equilibrium value below those obtained by other investigators for BBB-impermeable compounds, such as inulin and bovine serum albumin. Our data indicate that 125I-EGF, although clearly detectable in the CSF, does not cross the BBB at a higher rate or in higher quantities than would be expected from its molecular size.