Postnatal ontogeny of acetylated and non-acetylated B-endorphin in rat pituitary

Extracts of the anterior lobe and intermediate lobe of postnatal (P) (Day P1, P7, P14, P21, P28, P35, P42) and adult male Sprague-Dawley rats were analyzed by both a Beta-endorphin (B-END) radioimmunoassay and a radioimmunoassay for N-acetyl-B-END. In the anterior lobe, on P1, less than 2% of the adult level of B-END was present. By P42 this level had increased to 21% of adult levels. In the intermediate lobe, on P1, the B-END levels were less than 0.1% of the adult level, and by P42 this level approached approximately 45% of the adult levels. N-acetylated B-END was identified in both anterior lobe and intermediate lobe from P1 through adulthood. In the anterior lobe at P1, N-acetyl-B-END immunoreactivity contributes approximately 25% of the total B-END immunoreactivity. This level drops to less than 10% by P21, and to adult-like levels by P42 (less than 5%). On the other hand, in the intermediate lobe, the N-acetyl-B-END levels start at 70% of the total B-END immunoreactivity at P1 and by P14 reaches adult-like proportions of 90% or more of the total B-END immunoreactive material.