Effect of splanchnic nerve section and compensatory adrenal hypertrophy on rat adrenal neuropeptide content

The neuropeptides which have been immunolocalised within the adrenal cortex have a role in regulating steroidogenesis and adrenal blood flow, but little is known of the mechanisms which regulate adrenal neuropeptide content. The present studies were designed to investigate the regulation in the rat of three adrenal neuropeptides, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY) and substance P (SP), looking at the effects of splanchnic nerve section and also investigating the effects of unilateral adrenalectomy on the neuropeptide content of the contralateral adrenal following 9 days of compensatory growth. Splanchnic nerve section, followed by a 10-day recovery period, caused a significant increase in immunoreactive NPY (irNPY) and irSP content, but had no effect on irVIP in the capsular/zona glomerulosa portion of the rat adrenal gland. In the inner zone/medullary fraction, however, irVIP was significantly decreased, while irNPY and irSP were unaffected by splanchnic nerve section. Unilateral adrenalectomy had no effect on the contralateral adrenal content of any of the peptides, although the left adrenal gland increased in size by around 60% 9 days after removal of the right adrenal. These data suggest that NPY and SP in the rat adrenal capsule/zona glomerulosa and VIP in the inner zones/medulla, are regulated, directly or indirectly, by splanchnic nerve activity, but that VIP in the outer cortex, and NPY and SP in the inner zones are regulated by another mechanism, which is, at present, unclear. These data do not support a role for VIP, NPY or substance P in the adrenal hypertrophic response to unilateral adrenalectomy in the rat.