Paracrine control of adrenocortical function: a new role for the medulla?

The classical perspective of the adrenal gland has, in general, treated the cortex and medulla as functionally independent tissues which, by chance, are located together. Recent data challenge this outlook, and there is now evidence of regulatory mechanisms which are common to both the cortex and the medulla. There is, additionally, more evidence that the products of each of these tissues may influence the function of the other. In mammals the arrangement of the adrenal gland is such that the adrenal cortex forms the outer part of the gland and totally encloses the medulla. Indeed, a close anatomical relationship, between the morphologically and functionally distinct steroid-secreting tissue and chromaffin tissue in the adrenal gland, is seen in most vertebrate groups. Why should these embryologically unrelated tissues be located together, and what is their functional link? There is a wealth of experimental evidence to support the contention that these tissues have