Evaluation of the impression technique by measuring interstitial oedema in rat testis

The impression method for assessment of subcutaneous oedema was evaluated in a rat testis model where the testicular interstitial fluid volume was changed both artificially by infusion of rat plasma and pharmacologically by administration of human chorionic gonadotrophin. Both the integral value and the impression force value, as measured with the impression method, changed with infused volume, and changes as small as 16 microliters (approximately 7% of the total interstitial fluid volume in a testis) could be detected. Rats were treated with a single injection of 100 i.u. human chorionic gonadotrophin in order to induce changes in the volume of interstitial fluid in the testis. Both the integral value and the impression force value seemed to reveal information on testicular interstitial fluid volume in rats treated with human chorionic gonadotrophin that was similar to data revealed by measuring the actual fluid content in the testis. Interstitial fluid volume measured morphometrically in the contralateral testis in human chorionic gonadotrophin-treated rats was significantly correlated to the impression force value (r = 0.75) and the integral value (r = 0.52). This rat testis model proved to be an interesting experimental set-up for evaluation of the impression technique.