PLASMA AND TISSUE HISTAMINE CHANGES DURING HEMORRHAGIC-SHOCK IN THE RAT

We investigated the phase-associated changes in plasma histamine level s in an isobaric model of hemorrhagic shock, in an attempt to determin e whether histamine might be an etiologic factor in the onset of decom pensation. Sprague-Dawley rats were bled according to an isobaric blee ding protocol which maintained the mean arterial blood pressure at 40 mmHg until death. The status of vascular compensation for the blood lo ss was tracked by measurement of the shed blood volume (SBV) required to maintain the target pressure. Blood samples for analysis were taken at the control period and at 25% intervals of the peak shed blood vol ume (PSBV) during the compensatory and decompensatory phases. Plasma a nd tissue histamine levels were measured using a radioimmunoassay meth od. In untreated animals, plasma histamine levels at control, 75 and 1 00% of the PSBV, and after return of 25 and 75% of the PSBV were 45 +/ - 10, 48 +/- 9, 134 +/- 48, 693 +/- 351, and 994 +/- 371 nM, respectiv ely. These results show that rises in plasma histamine occurred coinci dentally with the onset of decompensation (p < .05), however, the subs equent rate of decompensation did not correlate with plasma histamine changes during decompensation. Organ histamine levels measured after h emorrhage were lower in the duodenum and colon than in unbled control animals, suggesting that parts of the intestinal tract may contribute to the elevated plasma histamine levels seen in severe hypotension (p < .05).