VIP innervation: sharp contrast in fetal sheep and baboon adrenal glands suggests differences in developmental regulation

Immunocytochemical technique and light microscopy were used to ascertain th e relationship between vasoactive intestinal polypeptide (VIP) and tyrosine hydroxylase in fetal sheep and fetal baboon adrenal cortices and medullae at 85% of gestation. VIP immunostaining was extremely robust in fetal sheep adrenal cortical neurofibers and cells while weak in fibers and nonexisten t in cells of fetal baboon. Also, tyrosine hydroxylase-immunopositive cells , present throughout the adrenal cortices of both fetal sheep and baboons, were heavily innervated by VIP-immunoreactive neurofibers in fetal sheep, b ut not in fetal baboons. Adrenal cortical VIP-immunopositive fibers occurre d in greater (P<0.05) frequency in fetal sheep than in fetal baboons (14.82 +/-3.10 vs. 0.84+/-0.26 fibers/field), were larger in diameter (2.93+/-0.34 vs. 0.93+/-0.07 mu m) and ran for longer distances in the plane of section (127.85+/-5.16 vs. 74.53+/-4.93 mu m). VIP immunogenicity in cells (gangli on and chromaffin) and fibers was robust in fetal adrenal medulla of sheep while nonexistent in baboons. VIP fibers in fetal sheep medulla were smalle r in diameter compared to fetal sheep cortex (1.22+/-0.13 vs. 2.93+/-0.34 m u m, P<0.05), but not compared to extrinsic nerve fibers (1.30+/-0.09 mu m) . We hypothesize that in fetal sheep of this age, medullary neurofibers der ive primarily from extrinsic sources while cortical fibers arise from corti cal ganglion cells. We conclude that at 85% of gestation the potential for VIP neural control of paracrine (e.g., glucocorticoid/catecholamine) intera ctions in both adrenal cortex and medulla is much greater in fetal sheep co mpared to fetal baboons. (C) 2000 Elsevier Science B.V All rights reserved.