Royal jelly (RJ) has a variety of reported biological activities, including vasorelaxation and blood pressure–lowering effects. Although functional foods are positively used for health, the effects of RJ on the cardiovascular system in healthy individuals have not been well studied. Therefore, we investigated the mechanisms underlying the vasorelaxation effects of RJ in healthy control rats to evaluate whether the peripheral circulation was increased.

We used fresh RJ to examine the vasorelaxation effects and related mechanisms in Wistar rats using organ bath techniques. Furthermore, we measured changes in tail blood circulation, systolic blood pressure (sBP), and heart rate (HR) after the oral administration of RJ to control rats and nitro-l-arginine methyl ester (l-NAME)–treated rats (0.5 mg/ml dissolved in distilled drinking water for 1 week). Concentrations of acetylcholine (ACh) in the RJ were measured using a commercial kit.

RJ caused vasorelaxation of isolated rat aortas and superior mesenteric arteries, and this effect was inhibited by atropine (10⁻⁵ M, 15 min) or L-NAME (10^-4 M, 20 min) and endothelium-denuded arterial ring preparations. Oral RJ increased tail blood flow and mass in control rats 1 h after treatment without affecting velocity, sBP, or HR. These effects were not observed in L-NAME–treated rats. RJ contained approximately 1000 μg/g of ACh.

The present study demonstrated that RJ is composed of muscarinic receptor agonist(s), likely ACh, and induces vasorelaxation through nitric oxide (NO) production from the vascular endothelium of healthy rats, leading to increased tail blood circulation. Thus, fresh RJ may improve peripheral circulation in healthy individuals.