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 HI mechanism is of importance for the plasma loss elicited by intra-abdominal trauma.