The current study was designed to determine the cardiovascular effect of centrally administrated melittin, a phospholipase A2 (PLA2) activator, and the mediation of central thromboxane A2 (TXA2) and its receptors in normotensive conscious rats. Studies were performed in normotensive male Sprague Dawley rats injected intracerebroventricularly (i.c.v.) with melittin. Melittin (1.5, 3.0, 6.0 microg/5.0 microl; i.c.v.) caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR). Maximal effects were observed 5-10 min after 3.0 microg dose of melittin. In order to test the mediation of central TXA2 and its central receptors in the cardiovascular effect of melittin, the rats were pretreated with furegrelate (500.0 microg; i.c.v.), a TXA2 synthesis inhibitor, and SQ-29548 (8.0 microg; i.c.v.), a TXA2 receptor antagonist, 15 min prior to melittin (3.0 microg). Furegrelate or SQ-29548 partially inhibited the pressor effect and bradycardia elicited by melittin. In conclusion, our findings show that centrally administered melittin increases MAP and decreases HR in conscious rats. Moreover, according to our findings, central TXA2 and its receptors may in part mediate melittin-induced cardiovascular effects.
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