Postnatal Development of ACTH and a-MSH in the Medulla Oblongata of Rat: c -MSH Is the Predominant Peptide

ALESSI, N. E. AND P. QUINLAN. Postnatal development of ACTH and a-MSH in the medulla oblongata of rat: a-MSH i.s the predominant peptide. PE PTIDES 6: Suppl. 2, 137-141, 1985.-ACTH and a-MSH levels were measured by radioimmunoassays in extracts of the caudal medulla oblongata of developing rats on postnatal (P) days 1-42 at 7 day intervals, and in adult rats. From PI to adulthood, ACTH increased > ! 1-fold from 7.2_ + 1.9 fmol to 82.4_+ 12.6 fmol per medulla section (mean_+ S.E.M.). In comparison, a-MSH increased >7-fold from 68.75_+ 11.0 fmol to 491 _+97.8 fmol during this time period. ACTH/p.g of soluble protein decreased during postnatal development from 0.006_+0.01 to 0.005_+0.001 fmol//zg of protein and a-MSH increased from 0.06_+0.01 fmol//zg of protein to 0.11 -+0.009 fmol//xg of protein between P1 and P7, decreased to 0.015_+0.003 fmol/#g of protein by P42 and increased to 0.03-+0.006 fmol/protein per unit protein by adulthood. These data indicate a significant shift in the levels of a-MSH detected during development with a decrease in the concentration of material occurring from early postnatal development (P1-P7) to adulthood, which does not appear to be solely related to a regional increase in protein. These studies, as well as radioimmunoassays for ACTH and a-MSH in combination with sizing chromatography of pooled extracts at P1. P7 and the adult, demonstrated the predominance of a-MSH at all ages.