Rat adrenal transplants are reinnervated: An invalid model of denervated adrenal cortical tissue

Adrenal autotransplantation is a widely used approach to investigate the po tential for neural modulation of adrenal cortical function. It is believed that regenerating adrenal transplants are not reinnervated, thereby providi ng a model to investigate adrenal function in the absence of neural modulat ion. However, the hypothesis that adrenal transplants become reinnervated h as not been directly tested. The purpose of the present study was to charac terize the time course, extent, and nature of the reinnervation of the rege nerating adrenal transplant and to assess whether the recovery of steroidog enic function and enzyme expression correlates temporally with the presence of innervation. Using immunohistofluorescent detection of tyrosine hydroxy lase (TH), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), an d vasoactive intestinal peptide (VIP), the innervation of regenerating adre nals was assessed 14-30 days after transplantation of adrenal capsules bene ath the kidney capsule in rats. Extensive reinnervation by TH-, NPY-, and V IP-positive fibres was present by 14 days after transplantation including r egions of the adrenal capsule and cortex, with only minimal reinnervation b y CGRP-positive fibres up to 30 days. TH- and NPY-positive chromaffin cells were also observed in the regenerating transplants. In addition, there was marked recovery of steroidogenic function and steroidogenic enzyme express ion up to 30 days. The finding that nerve fibres are present in the transpl ants during the re-establishment of steroidogenic function and enzyme expre ssion suggests that innervation may modulate the regeneration and functiona l recovery of adrenal transplants. In an attempt to prevent reinnervation o f transplants, adrenal capsules were autotransplanted to denervated kidneys . Immunohistochemical analysis showed that, despite extensive denervation o f the kidney tissue, the reinnervation and regeneration of the adrenal tran splants still occurred. These data demonstrate the marked capacity of the r egenerating adrenal to become reinnervated and reinforces the conclusion th at adrenal transplants are an invalid model of denervated adrenal cortical tissue.