FUNCTIONAL INNERVATION OF THE ADRENAL-CORTEX BY THE SPLANCHNIC NERVE

Secretion of steroid hormones by the adrenal cortex is required to mai ntain whole body homeostasis; that is the ability to maintain blood pr essure and volume, carbohydrate, protein and fat metabolism and immune and nervous system function within normal limits is dependent on adre nocortical hormones. The premise of this report is that autonomic-endo crine interactions occurring in the adrenal cortex are required for no rmal control of steroid secretion. Under non-stress conditions when re duced steroid secretion is required, splanchnic neural activity appear s to be inhibitory, whereas during stress conditions when elevated ste roid secretion is necessary, neural activity is excitatory. The capaci ty for innervation to produce both inhibitory and excitatory effects s uggests that neural input must be encoded differentially; encoding cou ld be dependent on the neurotransmitter released or on the intra-adren al target affected. Neural input could act directly at the adrenal cel l to affect steroidogenesis or act indirectly by changing adrenal bloo d flow. An index of the role of innervation has been obtained by asses sing adrenal corticosteroid secretion after splanchnicectomy, severing the thoracic splanchnic nerve which is the major source of innervatio n of the adrenal gland. This approach has resulted in alterations in c orticosteroid secretion under nonstress and stress conditions, but in many cases has demonstrated no profound effect on in vivo steroidogene sis. It is likely that splanchnicectomy results in variable secretory responses in part due to the multiplicity of adrenal neurotransmitter systems that are regulated by the splanchnic nerve. Splanchnicectomy a lters multiple neurotransmitters at different adrenal sites. Splanchni c innervation acts as an extra-ACTH mechanism in the control of adrena l corticosteroid secretion, yet further elucidation of the physiologic al conditions under which splanchnic neural activity affects function is clearly warranted.