Characterization of β-endorphin-related peptides in the caudal medulla oblongata and hypothalamus of the prenatal, postnatal and adult rat

A comparison was made of β-endorphin (B-END) concentrations versus post-translation products during the perinatal period in the hypothalamus and the caudal medulla oblongata. The concentration of B-END-like immunoreactivity did not differ statistically between embryonic day 21 (E21) and postnatal day 1 (P1) in either area. There were significant differences in forms, with a shift from larger precursors at E21 to smaller peptides at P1, with the predominant form of B-END being the 31 residue form at E21 in both regions. B-END varied between the two regions at P1, the 27-26 residue predominant in the hypothalamus, and the 31 residue in the caudal medulla.