Differential responses in post- and pre-ganglionic adrenal sympathetic nerve activity and renal sympathetic nerve activity after injection of 2-deoxy-D-glucose and insulin in rats

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.