The 5-hydroxytryptamine content of rabbit hearts and its release during in vitro perfusion

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Abstract
Rabbit hearts were perfused in vitro at constant pressure by the Langendorff technique. After 30 min perfusion, hearts from untreated animals contained significantly more 5-HT than those from animals pretreated with heparin. The cardiac 5-HT content of the non-heparinized group decreased during a further 55 min perfusion and the amount lost from the hearts was equal to that recovered from the perfusion fluid. In contrast, the 5-HT content of hearts from heparinized animals did not change significantly during this period, and no 5-HT could be detected in the perfusates. Investigation of the distribution of 5-HT within the hearts from heparinized animals disclosed a significantly greater concentration of 5-HT in the right atrium than in the rest of the heart. It is concluded that the small, perfusion-resistant store of 5-HT within hearts from heparinized rabbits represents the true endogenous 5-HT content in this species, but that much higher values may be obtained unless care is taken to exclude a contribution from blood platelets.