The in vivo Cardiovascular Effects of the Irukandji Jellyfish (Carukia barnesi) Nematocyst Venom and a Tentacle-Only Extract in Rats

¹Ramasamy, S, ¹Isbister, G.K., ²Seymour, J.E. and ¹Hodgson, W.C. 

1 Monash Venom Group, Dept of Pharmacology, Monash University, Australia 3800, 2 Dept of Tropical Biology, James Cook University, Australia 4878.

Carukiabarnesi is a small, elusive jellyfish which can produce severe Irukandji syndrome following extensive envenoming. Difficulties in obtaining adequate specimens and pure venom samples have hindered the biochemical and pharmacological characterization of jellyfish venoms. Many previous studies have employed samples that contain an incomplete complement of clinically relevant toxin(s) and/or may be contaminated with tentacular material. However, a superior technique for the extraction of venom from the nematocysts has been developed. Using this method, a pure C. barnesi venom sample and a tentacle-only extract (devoid of nematocysts) were examined in anaesthetised rats. C. barnesi venom (50 or 100 mg/kg, i.v.) produced a pressor response (42 ± 3 mmHg and 44 ± 6 mmHg, respectively; p<0.05; n=4) and increase in heart rate (31 ± 5 and 13 ± 2 bpm, respectively; p<0.05; n=4) in anaesthetised rats. This was followed by cardiovascular collapse in some animals (1 of 4 rats receiving 50 mg/kg and 3 of 4 animals receiving 100 mg/kg). Pre-treatment of animals with prazosin (50 mg/kg, i.v.) abolished the venom (50 mg/kg, i.v.)-induced pressor response (-8 ± 3 mmHg; n=4) and tachycardia (-9 ± 4 bpm; n=4). C. barnesi tentacle-only extract (100 mg/kg; i.v.) produced a pressor response (51 ± 12 mmHg; p<0.05, one-way ANOVA; n=3) and an increase in heart rate (35 ± 1 bpm; p<0.001, one-way ANOVA; n=3). The results of the present study are consistent with the effects of human envenoming which are postulated to be a result of catecholamine release. The lack of dose dependency with the hypertensive response is suggestive of C. barnesi venom inducing release of endogenous catecholamines. Further, the cardiovascular collapse seen more frequently with the higher dose of venom may be due to myocardial depression, which is seen with severe human envenoming. In addition, for the first time, we show that the C. barnesi tentacle-only extract free of nematocyst material produces cardiovascular effects which are distinct from those caused by C. barnesi venom derived from isolated nematocysts.

Correspondence to: sharmaine.ramasamy@med.monash.edu.au