Validation of the internal reference technique for microdialysis measurements of interstitial histamine in the rat

The internal reference technique (IRT) was compared with the no net flux me thod (NFM) as a microdialysis calibration technique for sampling of interst itial histamine in the rat. Microdialysis catheters (polyacrylonitrile, 50 kD cut off) were inserted in liver, muscle, subcutaneous tissue and in an i nduced adenocarcinoma. Estimated relative recovery with IRT ranged from 23/-2% in-liver to 30+/-3% in subcutaneous tissue with and without tumor (p<0 .05). By using the NFM-technique we found similar recovery as compared to t he IRT in all tissues studied. Interstitial histamine was up to 3-fold high er than the mean plasma histamine concentration (54+/-2 nmol/l). Subcutaneo us tissue (177+/-39 nmol/l) and subcutaneous tumor (165+/-29 nmol/l) exhibi ted high histamine while liver (65+/-14 nmol/l) and liver tumor (75+/-7 nmo l/l) had low interstitial histamine concentrations. In conclusion, the IRT was validated against the NFM as a rapid method for histamine measurements in situ in the rat.