Developmental dynamics was investigated in the activity of glutamate dehydrogenase (GDH, E.C. 1.4.1.2.-4) and glutamine synthetase (GS, E.C. 6.3.1.2) in different parts of the digestive tract of lambs, in dependence on the age from 10 to 90 days; the goal of these investigations was to elucidate in greater detail the role of the above enzymes in nitrogen metabolism. The activity of GDH, and of the coenzymes NADH and NADPH, was followed in the digesta because simple organisms (bacteria, fungi, plants) have two glutamate dehydrogenases: they differ from each other by coenzyme specificity, unlike GDH from animal sources which can utilize both NADH coenzyme and NADPH coenzyme (Fahien et al., 1965; Frieden, 1964). The following activities of GDH and GS were found out in trials with lambs at the age of 10, 20, 30, 40 and 90 days, as to the different parts of digestive tract: in the tissues of rumen, omasum, reticulum, spleen, duodenum, jejunum, ileum, int. caecum and colon the activity of GDH (NADH) varied from 0.031 to 0.305 nkat/mg dry matter, in the digesta from 0 to 2.92 nkat/mg dry matter (Fig. 1). An investigation of GDH (NADH, NADPH) dynamics in the digesta of lambs (Figs. 1 and 2) showed the relatively high activity of GDH (NADH) in the digesta of colon at the age of 10 days and that of GDH (NADPH) in the digesta of int. caecum. The activity of GDH (NADH) was also found to be high in the digesta of int. caecum at the age of 20 days. In that period the activity of GDH (NADH, NADPH) in the digesta of rumen, omasum and reticulum was zero. The activity of GDH (NADH, NADPH) began to increase on day 40, and on day 90 the GDH (NADH) values were highest not only in the digesta of rumen, omasum and reticulum but also in the digesta of int. caecum and colon. Similarly like Palmquist and Baldwin (1966), and Chalupa et al. (1970), we observed the markedly lower activity of GDH (NADPH) in comparison with GDH (NADH). The activity of GDH (NADPH) varied from 0 to 0.563 nkat/mg dry matter; the highest values were recorded in the digesta of rumen and omasum on day 40 and in the digesta of int. caecum on day 10 (Fig. 2). The activity of GS (Fig. 3) was low in the tissues of digestive tract and in the digesta of the whole apparatus (0.0-0.251 nkat/mg dry matter), the highest values were found in the digesta of duodenum, jejunum and ileum. The results of our experiments show that there are different possibilities of NH3 utilization, by means of glutamic acid and glutamine synthesis, in the different parts of digestive tract in lambs. Before the histological evolution of rumen structure is finished and the proventriculi begin to function, ammonia utilization through GDH takes place mainly in the digesta of int. caecum and colon. A possibility of significant nitrogen utilization in the caecum was also confirmed in the experiments by Nolan et al. (1976), who found out that as much as 25 % of endogenic urea was degraded in the caecum. In that period the activity of GS in the digesta of the different parts of digestive apparatus was low. It may be related to the fact that the higher ammonia concentrations inhibit the activity of GS (Fonty et al., 1984). Until completion of the histological evolution of rumen structure is finished, the conditions for the enzymatic synthesis of glutamic acid and glutamine are created mainly in the digesta of rumen, omasum, reticulum and colon, and also in the walls and digesta of all parts of digestive apparatus.
