Stage-dependent changes in adrenal steroids and catecholamines during development in Xenopus laevis

Changes in adrenal hormones during the complete developmental cycle from egg to juvenile were investigated in the amphibian Xenopus laevis. Whole-body concentrations of the adrenal steroids corticosterone (B), and aldosterone (Aldo) were determined by radioimmunoassay and those of the adrenal catecholamines epinephrine (E), norepinephrine (NE), and dopamine (D) were determined by HPLC. In addition, the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase were immunocytochemically localized for the characterization of chromaffin adrenal cells. B and Aldo were not detectable in the whole body before hatching. B levels rose earlier than Aldo levels from stage 36 onward. B had already peaked at stage 46, whereas the largest amounts of Aldo were found at stage 54. After peaking, both steroids decreased gradually to 2.7 +/- 0.62 (B) and 0.4 +/- 0.1 (Aldo) ng/g body wt (mean +/- SEM, n = 10) in juvenile animals. E, NE, and D were detected just after hatching, when E and D showed an early peak at stage 40. E and NE increased moderately during development and demonstrated a sharp increase at the end of metamorphosis from stages 62 onward to 14.4 +/- 1.7 (E) and 34.1 +/- 4.67 (NE) ng/g body wt (mean +/- SEM, n = 6). Interestingly, D levels had a distinct pattern, because concentrations of D remained lower than those of NE and E over nearly the complete development, but showed a dramatic rise during the latest stages, reaching 707 +/- 54 ng/g body wt in juveniles. This dramatic shift in catecholamine levels was confirmed by immunocytochemistry in parallel. A large increase in chromaffin cells labeled with tyrosine hydroxylase immunoreactivity occurred in the latest developmental stages. The catabolic rates for all catecholamines in vivo were similar, which indicates that the different levels are due to various rates of synthesis. Thus, adrenal corticosteroids as well as catecholamines may have regulatory effects during premetamorphosis and metamorphic climax.