Figure 2. Chronic caffeine intake has no significant impact on sympathetic nerve system and cardiovascular system.

(a,b) Locomotor activity and heart rate changes in control and caffeine groups (n = 5). (c) Plasma catecholamine concentration on the 16^th day (n = 6). (d) Electrical field stimulation-induced mesenteric arterial contraction is similar in control and caffeine groups. Results are expressed as a percentage of the initial contraction elicited by 60 mM KCl (n = 5). (e,f) Endothelium-dependent vasodilation induced by acetylcholine (Ach) was not significantly different in control and caffeine group (n = 5). Endothelium-independent vasodilation induced by nitroglycerin (NTG) was also similar in control and caffeine group (n = 5). Results are expressed as a percentage of the maximum contraction elicited by 10⁻⁵ M phenylephrine (PE). All data are presented as means ± SEM. *P < 0.05 compared with control.