The study demonstrates that the adrenal gland is innervated by both post- and pre-ganglionic sympathetic fibers which exhibit distinct response characteristics to hypoglycemia.
Differential pre- versus post-ganglionic adrenal sympathetic responses in animal hypoglycemia models; leaves open human translation and clinical relevance.
The aim of the study was to compare pre‐ganglionic adrenal nerve activity (pre‐aSNA) to post‐ganglionic adrenal nerve activity (post‐aSNA) in rats after administration of 2‐deoxy‐ d ‐glucose (2‐DG, 500 mg kg ‐1 , i.v.), which mimicks a central hypoglycaemia or to the response in pre‐aSNA and post‐aSNA to hypoglycaemia after injection of insulin (5U). Renal postganglionic sympathetic nerve recordings (rSNA) in a separate group was used as a reference. Adrenal or renal multifibre nerve activity was recorded in chloralose‐anaesthetized Wistar‐rats. Trimethaphan, a short‐lasting ganglionic blocker, was administered i.v. (10 mg kg ‐1 ) in order to test for pre‐ or post‐aSNA in the adrenal nerves. The adrenal nerves was considered to contain predominantly post or preganglionic fibres, respectively if the nerve activity in the adrenal nerve decreased (post‐aSNA) or increased (pre‐aSNA). In contrast, all renal nerves showed almost a pure postganglionic activity. Post‐aSNA responded with a tendency to increase after the 2‐DG injection. The highest value (percentage change from control) 5 min after injection was 12 ± 9%. The pre‐aSNA increased with values of 99 ± 52% at 3 min and 86 ± 31% at 5 min (percentage change from control). The activity in the rSNA was only slightly decreased after the injection of 2‐DG when compared to pre‐drug control activity. There was a significant difference between the pre‐aSNA vs. post‐aSNA at 1 min ( P < 0.05), 3 min ( P < 0.01) and 5 min ( P < 0.05). Insulin caused an increase in post‐aSNA with the maximum level of 154 ± 8% reached at 40 min compared to pre‐aSNA, which increased substantially and reached a peak value of 349 ± 43% at 50 min. RSNA was also increased with a maximum level, 160 ± 29% at 50 min ( P < 0.01). There was a significant difference in the main effect in pre‐aSNA vs. post‐aSNA. Thus, this study gives further evidence that the adrenal gland is innervated by both post‐ and pre‐ganglionic fibres with different characteristics.
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Carlsson et al. (1992) studied this question.
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