Clozapine reverses hyperthermia and sympathetically mediated cutaneous vasoconstriction induced by 3,4-methylenedioxymethamphetamine (ecstasy) in rabbits and rats

Abstract

Life-threatening hyperthermia occurs in some individuals taking 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). In rabbits, sympathetically mediated vasoconstriction in heat-exchanging cutaneous beds (ear pinnae) contributes to MDMA-elicited hyperthermia. We investigated whether MDMA-elicited cutaneous vasoconstriction and hyperthermia are reversed by clozapine and olanzapine, atypical antipsychotic agents. Ear pinna blood flow and body temperature were measured in conscious rabbits; MDMA (6 mg/kg, i.v.) was administered; and clozapine (0.1-5 mg/kg, i.v.) or olanzapine (0.5 mg/kg, i.v.) was administered 15 min later. One hour after MDMA, temperature was 38.7 +/- 0.5 degrees C in 5 mg/kg clozapine-treated rabbits and 39.0 +/- 0.2 degrees C in olanzapine-treated rabbits, less than untreated animals (41.5 +/- 0.3 degrees C) and unchanged from pre-MDMA values. Ear pinna blood flow increased from the MDMA-induced near zero level within 5 min of clozapine or olanzapine administration. Clozapine-induced temperature and flow responses were dose-dependent. In urethane-anesthetized rabbits, MDMA (6 mg/kg, i.v.) increased ear pinna postganglionic sympathetic nerve discharge to 217 +/- 33% of the pre-MDMA baseline. Five minutes after clozapine (1 mg/kg, i.v.) discharge was reduced to 10 +/- 4% of the MDMA-elicited level. In conscious rats made hyperthermic by MDMA (10 mg/kg, s.c.), body temperature 1 hr after clozapine (3 mg/kg, s.c.) was 36.9 +/- 0.5 degrees C, <38.6 +/- 0.3 degrees C (Ringer's solution-treated) and not different from the pre-MDMA level. One hour after clozapine, rat tail blood flow was 24 +/- 3 cm/sec, greater than both flow in Ringer's solution-treated rats (8 +/- 1 cm/sec) and the pre-MDMA level (17 +/- 1 cm/sec). Clozapine and olanzapine, by interactions with 5-HT receptors or by other mechanisms, could reverse potentially fatal hyperthermia and cutaneous vasoconstriction occurring in some humans after ingestion of MDMA.

Figure 1.

Effect of MDMA and then clozapine on body temperature and cutaneous blood flow in one rabbit (A, B, intravenous injection of drugs) and in one rat (C, D, subcutaneous injection of drugs). The traces are continuously recorded Doppler ear pinna (rabbit) and tail (rat) signals and telemetrically measured continuously recorded intraperitoneal temperature signals. In both species, administration of MDMA causes intense cutaneous vasoconstriction and increase in body temperature. Both of these effects are reversed by subsequent administration of clozapine.

Figure 2.

Group data (means and SE) in rabbits showing the effect of intravenous MDMA and then clozapine (1 and 5 mg/kg) or olanzapine on body temperature (A) and ear pinna blood flow (B). Data points at time 0 are means and SE of the preinjection control period. Two rabbits in the MDMA-no treatment group were killed 45 min after MDMA. Numbers of rabbits: see Results for number of rabbits in MDMA-no treatment group; n = 7 for clozapine 1 mg/kg; n = 5 for clozapine 5 mg/kg; n = 6 for olanzapine 0.5 mg/kg. Symbols for analysis by repeated measures ANOVA and Fisher's PLSD comparison in A: ^##significantly greater than pre-MDMA control temperature value (no treatment group, F_(12,144) = 77.44; p < 0.0001; clozapine 1 mg/kg group, F_(12,60) = 17.61; p < 0.001; clozapine 5 mg/kg group F_(12,48) = 3.68; p < 0.01; olanzapine group, F_(12,60) = 33.48; p < 0.001); ^**significantly greater than pre-MDMA control value (F values as above; p < 0.0001 for no treatment group; p < 0.001 for clozapine 1 mg/kg group); ^••significantly <30 min post-MDMA value (F values as above; p < 0.001 for clozapine 5 mg/kg group; p < 0.0001 for olanzapine group); ns, not significantly different from pre-MDMA control value (F values as above; p > 0.05 for clozapine 5 mg/kg group; p > 0.05 for olanzapine group). Symbols for analysis by factorial ANOVA and Fisher's PLSD comparison in A: ^††significantly <60 min post-MDMA temperature in MDMA-no treatment rabbits (F_(3,26) = 17.503; clozapine 1 mg/kg group, p < 0.001; clozapine 5 mg/kg group, p < 0.0001; olanzapine group p < 0.0001). Symbols for analysis by repeated measures ANOVA and Fisher's PLSD comparison in B: ^##significantly less than pre-MDMA ear pinna blood flow control value (no treatment group, F_(12,144) = 28.26; p < 0.0001; clozapine 1 mg/kg group, F_(12,72) = 13.28; p < 0.0001; clozapine 5 mg/kg group, F_(12,48) = 18.29; p < 0.0001; olanzapine group, F_(12,60) = 14.57; p < 0.0001); ^**significantly less than pre-MDMA control value (F values as above; p < 0.0001 for no treatment group; p < 0.0001 for olanzapine group); ^§§significantly greater than pre-MDMA control value (F values as above; p < 0.01); ^••significantly >15 min post-MDMA value (F values as above; p < 0.0001 for clozapine 5 mg/kg group; p < 0.0001 for clozapine 1 mg/kg group; p < 0.01 for olanzapine group); ns, not significantly different from pre-MDMA control value (F values as above; p > 0.05 for clozapine 1 mg/kg group; p > 0.05 for olanzapine group). Symbols for analysis by factorial ANOVA and Fisher's PLSD comparison in B: ^††significantly >60 min post-MDMA ear pinna blood flow in MDMA-no treatment rabbits (F_(3,26) = 17.503; clozapine 5 mg/kg group, p < 0.0001; clozapine 1 mg/kg group, p < 0.001; olanzapine group, p < 0.0001).

Figure 3.

Effect in one anesthetized rabbit of MDMA and then clozapine on ear pinna sympathetic nerve activity (A), integrated (30 sec bins) ear pinna sympathetic nerve activity (B), body temperature (C), and arterial pressure (D). The circled numbers (1–4) in A correspond to the circled numbers on the x-axis in D, indicating the experimental period during which the nerve recording was made. The 10 min time base bar in D also applies for B and C.

Figure 4.

Group data (means and SE) in rats showing effect of subcutaneous MDMA and then Ringer's solution or clozapine on body temperature (A), tail blood flow (B), and superior mesenteric blood flow (C). Data points at time 0 are means and SE of the preinjection control period. Numbers of rats: n = 6 for MDMA and Ringer's solution; n = 5 for MDMA and clozapine for temperature and tail flow studies; n = 4 for mesenteric flow study. Symbols for analysis by repeated measures ANOVA and Fisher's PLSD comparison in A: ^##significantly greater than pre-MDMA control temperature (Ringer's solution group, F_(15,75) = 15.52; p < 0.0001; clozapine group, F_(15,60) = 19.82; p < 0.001); ^**significantly greater than pre-MDMA control value (F values as above; p < 0.0001); ^••significantly <100 min post-MDMA value (F values as above; p < 0.0001); ns, not significantly different from pre-MDMA control value (F values as above; p > 0.05). Symbols for analysis by factorial ANOVA and Fisher's PLSD comparison in A: ^††significantly <150 min post-MDMA temperature in MDMA and Ringer's solution group [F_(1,9) = 10.66; p < 0.01). Symbols for analysis by repeated measures ANOVA and Fisher's PLSD comparison in B: ^##significantly less than pre-MDMA tail flow (Ringer's solution group, F_(15,75) = 3.33; p < 0.01; clozapine group, F_(15,60) = 16.62; p < 0.001); ^**significantly less than pre-MDMA control value (F values as above; p < 0.01); ^••significantly >100 min post-MDMA value (F values as above; p < 0.0001); ^§§significantly greater than pre-MDMA control value (F values as above; p < 0.001). Symbols for analysis by factorial ANOVA and Fisher's PLSD comparison in B: ^††significantly >150 min post-MDMA tail flow in MDMA and Ringer's solution group (F_(1,9) = 10.66; p < 0.01). Symbols for analysis by repeated measures ANOVA and Fisher's PLSD comparison in C: ns, not significantly different from pre-MDMA mesenteric flow value (Ringer's solution group, F_(15,60) = 0.61; p > 0.05; clozapine group, F_(15,45) = 4.03; p > 0.05); ^§§significantly >90 min (preclozapine) mesenteric flow value (F values as above; p < 0.001).