The importance of cervical spinal pathways on the adrenal secretion of catecholamines was assessed in chloralose-anesthetized cats. Partial transections of the upper cervical spinal cord were made ipsilateral (n = 21) or contralateral (n = 10) to the adrenal vein sampling catheter. Ipsilateral cuts evoked an immediate increase in the adrenal secretion of epinephrine that remained elevated at 60 min (+ 89.7 ± 27.0 ng/min, P < 0.001) and increased the epinephrine/norepinephrine secretory ratio from 1.99 ± 0.4 to 5.02 ± 0.6 by 60 min (P < 0.01) indicating a preferential augmentation of the secretion of epinephrine. The magnitude of the increase in secretion of epinephrine was well correlated with the cross-sectional area of the ipsilateral cut (rs = 0.681, P < 0.01). In contrast, partial transections of similar size made contralateral to the adrenal vein sample evoked significantly smaller increases in the adrenal secretion of epinephrine by 60 min (+ 12.7 ± 4.8 ng/min) and were not correlated with the cross-sectional area of the cut. The region of transection common to those experiments that caused the greatest increase in the secretion of catecholamines included the deep laminae (laminae V-VII) within the central gray matter as well as a portion of the dorsal columns. Transections restricted to the dorsolateral and lateral funiculi caused small and inconsistent changes in the adrenal secretion of catecholamines. Ipsilateral and contralateral cuts evoked similar effects on peripheral concentrations of catecholamines, on plasma adrenocorticotropin and on plasma angiotensin II, suggesting that the facilitatory effect of ipsilateral cuts on the adrenal secretion of catecholamines was not the result of a humoral mechanism. Arterial pressure and heart rate increased equally by 1 min and returned to prestimulus values by 5 min after transections of the ipsilateral or of the contralateral cervical cord. Electrical stimulation of the ipsilateral cervical spinal cord, caudal to the level of transection, decreased the secretion of epinephrine and arterial pressure by 1 min (-30.5 ± 9.0%, P < 0.05) suggesting the presence of an active inhibitory mechanism that persisted after transection. The results indicated that transections of pathways ipsilateral, but not contralateral, to the adrenal medulla that traverse the upper cervical spinal cord evoke a persistent increase in the adrenal secretion of epinephrine, whereas other indices of neuroendocrine or autonomic function do not reflect this tonic influence. The neural mechanism that underlies the apparent tonic inhibition of adrenomedullary function is distributed over a non-compact ipsilateral projection pathway that is not restricted to the dorsolateral or to the lateral funiculi.
Bibliographical noteFunding Information:
The excellent technical assistance of A1 Benetti is greatly appreciated. The author also thanks Carol Cornell and Pat McDermott for the biochemical determinations. This study was supported in part by NIH Grants NS26137 and DK26831.
- Adrenal medulla
- Autonomic nervous system
- Cervical spinal cord