Veterinary/zoology session

The HDC-KO mouse has no histamine bio-synthesis genetically. Histamine is one of the most general mediators in both humans and animals. The complete absence of histamine leads therefore to several modifications in phenotypic features of HDC-KO mice. The aim of the experiment was to compare the digestive physiology of the HDC-KO (Semmelweis University) and the normal so called Balb/c (Charles River Hungary Ltd.) mice by measuring the transit time and apparent digestibility of major nutrients. The live weight of mice and their feed and drinking-water consumption were also detected.

For the transit time measurement, chromium(III)-oxide (Reanal, Budapest) as indicator was added to the diets at a concentration of 0.3 per cent. The nutrients’ digestibility was determined by using the total (faeces) collection method, lasting for 9 days. Nutrients of normal diet for lab rodents (CRLT/N, Charles River) such as organic matter, crude protein, ether extract, crude fibre and N-free extract were highly digested by both mouse strains (n=8/group). The digestibility differed insignificantly (P>0.05). HDC-KO mice the nutrients of histamine-free diet (<0.6 nmol histamine, Altromin, Germany) digested somewhat higher (P>0.05) than the control animals (n=6/group). Comparing the mouse strains, the digestibility of nutrients in histamine-free diets was higher in both groups than that of normal diet, occasionally the differences were significant (P<0.01).

The faecal concentration of chromium(III)-oxide ingested by the normal diet has been changed in the similar way in both groups, reaching the maximum values (844 and 781 mg/kg, normal and HDC-KO, respectively) 4 hours after beginning the feeding, then decreased continuously to about the initial level (21 and 25 mg/kg, normal and HDC-KO, respectively) in 33 hours. In the case of histamine-free diet, the transit time has slightly been different in the two mouse groups as well as in what was observed in the normal diet. The chromium(III)-oxide reached the maximum values in 8 hours in HDC-KO and in 24 hours in normal mice (1840 and 2450 mg/kg, HDC-KO and normal, respectively), and has considerable level in the faeces even at 48 hours (534 and 209 mg/kg, normal and HDC-KO, respectively).

Considering the digestibility and transit time, the HDC-KO mice consuming normal diet do not differ from the normal ones because histamine is taken up by the food. The histamine-free diet slowed the transit time in the intestine and consequently improved the digestibility of nutrients. The reduced transit time is due to the low (<1%) dietary crude fibre content.