On the origin and prenatal development of the bovine adrenal gland

Decisive steps of bovine prenatal adrenal development were investigated in 46 embryos and fetuses using histological, electron microscopical, immuno-, enzyme and lectin histochemical methods. About day 30, the intermediate me soderm between the cranial mesonephros and coelomic cavity is segmentally o rganized. It consists of proliferating tissue complexes that are connected to the coelomic cavity by vestigial nephrostomial tubules. This segmental o rganization soon disappears, however, due to longitudinal fusion of the tis sue complexes into a continuous joined blastema. This blastema of intermedi ate mesodermal (nephric) origin becomes positive for alkaline phosphatase a t about 30 days, and slightly later also for acetylcholinesterase. The most cranial portions of this common blastema represent the adrenocortical anla ge, the following portions the gonadal rete blastema. A reevaluation of the comparative anatomical record revealed that a nephric origin of adrenocort ical or interrenal cells is a general feature of all vertebrates and that t he erroneous assumption of the lateral plate-derived coelothelium as precur sor of the adrenocortical (interrenal) blastema should be definitively aban doned. The first adrenomedullary precursor cells become visible in the bovi ne adrenal primordium at day 35. At 50 days, both components (medullary and cortical precursors) are present as interpenetrating plates and strands be tween large sinusoid vessels and exhibit a strong MIB-1 activity, indicativ e of a high proliferation rate. About day 60 the cellular proliferation slo ws down in some of the adrenocortical precursor cells, and the separation i nto a visible cortex and medulla is initiated. From about day 80 on, the me dullary tissue coalesces into a large, continuous area in the interior of t he gland, surrounded by a narrow cortical glomerulo-fasciculata that become s positive for 3 beta-hydroxysteroid dehydrogenase at about day 90. Autonom ous nerves penetrate the blastemal region as early as day 31. When the sepa ration into cortex and medulla starts, the nerves are more concentrated in the latter. From 130 days on, nerve fascicles reach the interior of the org an not only from its medial side, but also from the capsule surrounding the gland. The penetrating bundles traverse the zona glomerulo-fasciculata wit hout ramification and split off at the border to the medulla. Here, in the outer zone of the medulla, they constitute a particularly dense plexus, whe reas in the central medulla a less dense innervation is observed. Up until 90 days, cells with the characteristic features of primordial germ cells ar e present within the confines of the adrenal gland.