Posttranslational processing of opioid pro-opiomelanocortin products in piglets

We have measured levels of β-lipotropin, β-endorphin, and N-acetyl-β-endorphin in the plasma, cerebrospinal fluid (CSF), and caudal medullary brain containing the respiratory-related portion of the nucleus tractus solitarius (NTS) of 2.5 ± 1.0- (SD) and 38.2 ± 3.7-day-old naive uninstrumented piglets. Time of day, ambient atmosphere, temperature, handling, sound, light, and nutritional status were kept constant. Experimental procedure included decapitation and rapid collection, processing, and freezing of tissues until analysis by radioimmunoassay. Young, compared with older piglets, have higher measured levels of β-lipotropin in the plasma and CSF and of N-acetyl-β-endorphin in all three body compartments. Although measured levels of β-endorphin-like immunoreactivity are also higher in the plasma and CSF of the young group, the calculated level of β-endorphin is higher only in the CSF. In the NTS, both the measured and calculated active endorphin appear higher in the older group, but this difference is not significant. Excess β-endorphin in the CSF of neonates may explain the relative immaturity of their respiratory functions at birth.