Over the past few years, populations of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) have increased dramatically in the waters of China, Korea, and Japan without any definitive reason. This has resulted in severe damage to fisheries in the areas. During a pilot study, we observed that the
venom of N. nomurai produced a functional cardiac depression in mice. However, the mechanism of action was not examined. In the present study, we investigated the cardiovascular effects of nematocyst-derived
venom from N. nomurai in anesthetized rats.
Venom (0.1-2.4 mg
protein/kg, i.v.) produced dose-dependent
hypotension (65+/-12% of initial at a cumulative dose of 3 mg/kg) and
bradycardia (80+/-5% of initial at a cumulative dose of 3 mg/kg). At the highest dose, this was characterized by a transient decrease in blood pressure (phase 1) followed by a return to basal level and then a slower decrease in blood pressure (phase 2).
Venom also produced a decrease in rate and force of contraction in the rat isolated atria. Interestingly,
venom induced a contraction of isolated aortic rings which was blocked by
felodipine but not by
prazosin, suggesting the contraction is mediated by
calcium channel activation. These results suggest that the negative inotropic and chronotropic effects of the
venom of N. nomurai may be due to a direct effect on the heart.