Acta Physiologica 43. (1973)

3. szám - PHYSIOLOGIA - Kerner J.-Sándor A.-Alkonyi I.: Physiological Variations in Carnitine Acetyl-Transferase Activity in Rat Tissues: Activity in Animals Exposed to Fasting and Cold

J. KERNER et al. of the rat, it possesses a high carnitine concentration and CAT activity (Mar­quis and Fritz 1965). Methods White male rats of 200 to 250 g body weight were used. The animals were given rat chow and tap water ad libitum and were kept at 25°C under artificial light from 7 a.m. to 7 p.m. The animals were sacrificed at midday and in studies of the diurnal rhythm 4 animals were killed every 4 hours. Before the animals were decapitated the fasted ones received nothing hut tap water for 48 hours. Animals exposed to cold were kept at -j-5°C for various periods of time. Enzyme activity was tested in the system described by Marquis and Fritz (1965). The animals were killed by decapitation and tissue specimens weighing about 60 mg were excised, weighed on the torsion balance with an accuracy of +0.2 mg, homogenized in 0.4 ml of the extracting solution in a conical centrifuge tube, allowed to stand in an ice bath for 10 minutes, and centrifuged at 4000 g at +4 °C for 15 minutes. The sediment was extracted again in the same way with 0.6 ml of the solution. The pooled supernatants were used for activity measure­ment at 25°C. The protein content of the tested supernatant was determined by the biuret reaction. As regards brown fat, it was always the interscapular tissue which was subjected to examination. Except skeletal muscle, the total weight of the organs was also determined. The data were evaluated statistically by Student’s i-test. The reagents used were CoA, citrate synthetase, malate dehydrogenase (Boehringer, Mannheim, West Germany), NAD Na-EDTA. KCN, Tris, Na-deoxycholate, K2HP04 (Reanal, Budapest, Hungary). DL-acetylcarnitine was prepared according to Friedman and Fraenkel (1957) from DL-carnitine hydrochloride (Schuchard, München, West Germany). Results Diurnal rhythm If enzyme activity is expressed in unit activity per 1 g of wet tissue, no diurnal variation was observed either in skeletal muscle or in the brown fat. In the liver, activity reached a minimum at noon, which was 40% lower than the values measured at other hours of the day both in the fed and in the starved conditions. However, the weight of the liver shows a rhythmic fluctuation depending on the hour of the day, as described by Hamprecht et al. (1969). When calculating with the overall weight of the liver, in order to reduce the variations of the results due to the different size of the animals, liver weight was expressed in terms of 100 g body weight as proposed by Hamprecht et al. (1969; normalized hepatic weight). If the quantity of CAT is referred to U/l g of tissue X liver weight/100 g body weight, no significant reduction in activity was observed at midday. Effect of fasting and cold The results obtained during fasting and cold exposure are summarized in Table I. Fasting caused an increase in activity calculated for unit weight of the liver and for the protein content of the extract. Since the loss in weight and in protein due to fasting did not affect the CAT protein, the amount Acta Physiologica Academiae Scientiarum Hungaricae 43, 1973

Next