Does Gender Modify the Effect of 2-Arachidonylglycerol on Platelet Aggregation in Rat Whole Blood?

Jennifer Shearer, Kathleen Kane, Hilary Carswell, Susan Coker. University of Strathclyde, Glasgow, Scotland, UK.

The endocannabinoid, 2-arachidonylglycerol (2-AG), is released from activated platelets and can modulate aggregation in man (Maccarrone et al., 2001). Cannabinoid metabolism in platelets is influenced by gender with enhanced uptake and degradation in platelets from female migraineurs (Cupini et al., 2006). This study examined the influence of gender on the effect of 2-AG, and its interaction with other agonists, on platelet aggregation in rat whole blood. Age-matched male (300-500g) and female (240-305g) Sprague Dawley rats were anaesthetised with isoflurane and the carotid artery cannulated to allow blood withdrawal. Whole blood aggregometry was used to examine the effects of 2-AG and ADP and interaction of 2-AG with ADP or 5-HT (n=6). Data are expressed in Ω as mean ± SEM and compared with repeated measure 2-way ANOVA or unpaired Student’s t-test (*p<0.05). Responses to ADP peaked at 2 min whereas those to 2-AG developed slowly over 10 min. The concentration response curve to 2-AG (75-300μM), but not that to ADP (0.1-30μM), was modified by gender. Greater aggregation to 75µM 2-AG was observed in blood from male rats compared to females (9.8±3.4 vs.1.8±2.0*). 5-HT (10µM) did not cause platelet aggregation but it potentiated the response to 75µM 2-AG. This potentiation was similar in magnitude in blood from male and female rats, albeit, that potentiation in male rats just failed to reach statistical significance (12.4±0.7 vs. 5.1±2.8 in males; p=0.054 and 7.4±1.9 vs. -0.2±0.1* in females). 2-AG prolonged and enhanced the aggregatory response to ADP at 5 min. Combination of 2-AG and ADP increased aggregation to 14.3±0.3 vs. 5.1±2.8 and 5.4±0.9 for 2-AG and ADP respectively in males and 13.6±0.9 vs. -0.2±0.1 and 8.7±2.0 in females. This potentiation was of a similar magnitude in blood from male (3.7±3.5) and female rats (5.1±2.6).

This study demonstrated that 2-AG caused platelet aggregation in rat whole blood and interacted with other agonists to modulate aggregation. Gender modified the response to 2-AG at 75µM but did not significantly affect its interaction with ADP or 5-HT.

Cupini et al. (2006) Cephalalgia. 26, 277-281.
Maccarrone et al. (2001) Eur J Biochem. 268, 819-825.