Comparison of the noradrenergic sympathetic nerve contribution during local skin heating at forearm and leg sites in humans.

Abstract

We investigated the role of noradrenergic sympathetic nerves in the cutaneous circulation at rest and in response to local heating. Dorsal forearm and lateral leg sites were each instrumented with 2 microdialysis fibers, 2 local skin heaters, and 2 laser-Doppler probes. All sites were heated from 33° to 42 °C. Each limb had 1 skin site treated with bretylium tosylate (BT) to block noradrenergic sympathetic neurotransmitter release and 1 site infused with lactated Ringer's (Control). During baseline (33 °C), cutaneous vascular conductance (CVC; laser-Doppler flux/blood pressure) at control (24 ± 2 %max) and BT-treated (29 ± 4 %max) sites in the leg was significantly higher than the forearm (control: 12 ± 1 %max; BT-treated: 17 ± 2 %max) (P = 0.032 and P = 0.042). At 42 °C local skin temperature, the initial peak CVC response with BT decreased compared to control at both forearm (62 ± 3 vs. 86 ± 6 %max, P < 0.01) and leg (67 ± 3 vs. 77 ± 2 %max, P = 0.035) sites. CVC at the forearm with BT was lower than that of the leg (P = 0.02). With control, plateau phase (~35 min at 42 °C) CVC was greater in the leg (98 ± 2 %max) than the forearm (89 ± 4 %max) (P = 0.027). BT reduced the peak CVC in the leg (90 ± 4 %max, P = 0.027) and in the forearm (69 ± 5 %max, P < 0.01). CVC at the BT-treated sites was reduced more in the forearm than in the legs (P < 0.01). The contribution of noradrenergic sympathetic nerves during local heating differs between leg and forearm at rest and with skin heating.