Vergleichende Iohexol- und Iodbestimmung in caninen und equinen Serum- und Rattenurinproben nach oraler Verabreichung von Iohexol

In the present study the iohexol content in canine and equine serum and rat urine samples was determined after oral administration of iohexol in comparison to the iodine content. The aim was to gain knowledge whether iohexol can be used as a suitable marker for assessing intestinal permeability. The examination of iohexol in urine and serum samples was carried out using solid phase extraction, followed by HPLC-analysis (Klenner 2006). A total of one hundred and sixteen serum samples of dogs and horses and thirty urine samples of rats were tested concerning their iohexol content. With the help of the measured iohexol concentration, the expected iodine proportions could be figured out in the samples. Due to difficulties in the chromatogram evaluation after the administration of very low iohexol amounts, 2.0 ml Omnipaque® 350/kg KGW per os can be recommended following Klenner (2006). When feeding the horses, the iohexol dosage should be increased in order to reach reliable and useful results. Otherwise the contrast media should be administered to fasting animals. Due to the expected high iohexol concentration in urine samples collected over a period of twenty-four hours, the dosage of 2.0 ml Omnipaque® 300 (total iohexol content 1294 mg) is sufficient in rats. The iodine analysis was carried out by means of the Sandell-Kolthoff reaction with photometric detection. Chosen urine and serum samples were divided into three groups of different concentration concerning their iohexol content. In order to transfer the iodine into a useful form for the analysis, urine and serum had to be decomposed by alkaline dry ashing. A modified method (Albers 1999) by Mitsuhashi and Kaneda (1990) was applied in changed form for the urine samples. The method by Scherer-Herr (2001) was slightly modified and used for the analysis of the serum samples. The measured amount of urinary iodine moved in different deviations above the expected values. The medium deviation resulted in thirty-two per cent plus. There was no correlation (r = 0.12) between the expected iodine content and the actual measured difference to the expected value. As well no correlation could be found between the group matching and the size of the measured difference within the different groups. Concerning the raw data, the actual measured iodine content was significant higher (p = 0.0038; r = 0.8) than the expected iodine value, measured with Wilcoxon`s signed rank test. The problems during the iodine determination in serum, relating to the sensitivity of the method could not be clarified until the end. The results of the serum analysis were, due to a constant low recovery rate, not suitable to gain reliable statements on the given iodine amount in the samples. However, a tendency for an increased iodine recovery could be observed in serum. The results which were obtained in this paper point to the fact that a possible metabolism of iohexol after oral administration cannot absolutely be excluded. Nevertheless the conducted tests are not sufficient to gain reliable results about a possible metabolization. In addition to this, further tests with a higher number of samples as well as further research of metabolites are necessary. With regard to the suitability of the test procedure for determing intestinal permeability, the ascertained differences do not seem to affect the diagnostic applicability of the test. In consideration of the increased iodine recovery, the given limit for iohexol excretion of 0.5 % of oral ingested dose in healthy control persons and patients with inflammatory bowel disease in 24 h urine (Halme et al. 1997, 2000) is exceeded in no case. Consequently, the time-consuming iodine measurement has no significant diagnostic advantage compared to the iohexol analysis under clinical conditions.