Characterization of opioid peptides from maternal and fetal sheep adrenal glands

Enkephalin immunoreactive material from adrenal glands was characterized both in maternal and fetal sheep at various gestational ages. Whole gland extracts from both maternal and fetal sheep contained three major peaks of Enk immunoreactivity corresponding to apparent molecular weights of 10,000, 2800, and less than 1200 daltons. The majority of maternal adrenal Enk immunoreactivity was found in medullary tissue, although cortex also contained low but detectable amounts. This was also the case in newborn lambs and 139 day fetuses, where adrenal cortex was sufficiently developed to allow extraction and quantitation of opioid material. In fetuses at mid-gestation (70–80 days), adrenal medullary Enk immunoreactivity was approximately 75% of maternal values. Met-Enk and Leu-Enk content in 139 day fetal medulla were 70 and 76% of maternal values respectively, while newborn Met- and Leu-Enk medullary content were similar to maternal values. The molar ratio of Met-Enk to Leu-Enk was approximately 4:1 in both maternal and fetal adrenal medulla, and 2:1 in adrenal cortex, suggesting different synthetic processing of opioid peptides in the two tissues. The early appearance of significant levels of adrenal medullary Enk immunoreactivity and subsequent development paralleling that of catecholamines suggest a predominant role for adrenal enkephalins in regulation of fetal cardiovascular function early in gestation.