Beta Endorphin and Dynorphin Levels in Rat Pituitary and Hypothalamus: Age Studies

The content of immunoreactive (ir)-beta-endorphin, ir-dynorphin 1-17, and ir-dynorphin 1-8 was determined in hypothalamus, anterior pituitary, and neurointermediate lobe of rats 3-24 months of age. In the anterior pituitary ir-beta-endorphin showed a progressive rise with age (0.5 +/- 0.06 ng/tissue at 3 months to 1.02 +/- 0.23 at 24 months); a similar change was seen in ir-adrenocorticotropic hormone content of the same tissues. No age-related change in neurointermediate lobe ir-endorphin content was observed. In the hypothalamus, the ir-beta-endorphin content fell progressively from 3 to 18 months, but was restored at 24 months to levels indistinguishable from those at 3 months (16.2 +/- 4.3 ng/tissue compared with 11.3 +/- 4.0 at 24 months). The ir-dynorphin content did not change progressively over the age span examined, except in the case of anterior pituitary content of ir-dynorphin 1-17 which fell progressively between 3 and 18 months (from 1.65 +/- 0.15 ng/tissue at 3 months to 0.73 +/- 0.12). Radioimmunoassay following high-performance liquid chromatography analysis of extracts of the tissues showed little variation of the immunoreactive forms with age, with two notable exceptions. In the hypothalamic extracts from 24-month-old rats the ratio of the nonacetylated ir-endorphin to the acetylated ir-endorphin was lower than in equivalent extracts from 3-month-old rats. In anterior pituitary extracts from 3-month-old rats, ir-dynorphin 1-17 appeared as two peaks (putative 6K and 4K species) of approximately equal size.(ABSTRACT TRUNCATED AT 250 WORDS)