Decrease in plasma volume from intra-abdominal trauma in rats is prevented by H1 but not by H2 histaminergic blockade.

Intra-abdominal surgery causes plasma extravasation which, in the rat, is prevented by combined histaminergic H1 and H2 blockade. We evaluated the relative importance of H1 and H2 blockade in this situation. Cloralose-anaesthetized Wistar rats were subjected to a standardized abdominal trauma. Mean arterial pressure (MAP), heart rate (HR) and haematocrit (Hct) were monitored and plasma volume (PV) was determined before and 1 h after the trauma. Compared to non-traumatized rats (n = 8), the trauma decreased PV and increased Hct (n = 8). MAP decreased during the actual trauma, whereas HR remained stable throughout. In animals given cimetidine 25 mg kg-1 i.v. just prior to the trauma (n = 8), PV, Hct and MAP changed, as in the non-blocked rats. In contrast, pyrilamine, 10 mg kg-1, completely prevented the decrease in PV and the increase in Hct (n = 7), but not the decrease in MAP. The findings suggest that a histaminergic H1 mechanism is of importance for the plasma loss elicited by intra-abdominal trauma.