Effects in mice of testosterone and dihydrotestosterone on platelet aggregation in injured arterioles and ex vivo.

Mice were implanted subcutaneously with placebo pellets, or with pellets containing either testosterone (T) or dihydrotestosterone (DHT). Eight to 19 days later platelet aggregation was produced in pial or mesenteric arterioles by injuring their endothelium with a noxious light/dye stimulus. The onset of platelet aggregation was significantly shortened in the mesenteric arterioles of male mice following implantation of 1.0 mg T or 0.1 mg DHT. However no effect was observed in females, nor did T or DHT alter aggregation in pial arterioles of either sex. Ex vivo studies showed that sodium arachidonate produced greater aggregation of platelets in plasma from testosterone treated males compared with controls. No effect of testosterone was observed ex vivo in platelets from females. These ex vivo results paralleled in vivo data from mesenteric vessels, but not from pial vessels. Moreover DHT failed to influence aggregation ex vivo in either sex. Thus enhanced aggregation observed in vivo in mesenteric arterioles of androgen treated males may not reflect direct action of androgen on the platelet. Rather enhanced aggregation may reflect hormonal action on endothelium or adjacent tissue. In addition to the preceding studies we tested the hypothesis that testosterone's action was due to its conversion to estradiol. This was considered because our data with T and mesenteric vessels resembled that previously reported by us with estradiol. However only minimal elevations in plasma estradiol levels resulted from testosterone treatment.