Changes in enkephalin and neuropeptide Y-like immunoreactivity in rabbit chromaffin tissues during perinatal development.

Enkephalin-like immunoreactivity (ENK-LI), neuropeptide Y (NPY)-LI and dopamine-beta-hydroxylase (DBH)-LI were found within the chromaffin cells of both the paraaortic body and the adrenal medulla of the newborn rabbit using immunohistochemistry. Cells positive to DBH-LI were abundant in both the paraaortic body and the adrenal medulla. ENK-LI positive cells were frequent in the paraaortic body, but more sparse in the adrenal medulla. A few cells staining for NPY-LI could be detected in both organs. Some nerve fibers within these organs also contained substance P-LI and calcitonin-gene related peptide-LI. The tissue contents of ENK-LI and NPY-LI, as measured by radioimmunoassay, increased after birth in the adrenal glands and were significantly higher than the fetal levels from 1 week of age. In the paraaortic body the lowest content of ENK-LI was found around birth, whereas the content of NPY-LI was highest at that time. With advancing postnatal age, the content of ENK-LI increased, whereas the content of NPY-LI decreased. At each age, there was a higher content of ENK-LI as compared to NPY-LI in both organs. This indicates that the synthesis of ENK-LI and NPY-LI in the paraaortic body is differently regulated during perinatal development.