Some regulatory properties of purine biosynthesis de novo in long-term cultures of epithelial-like rat liver cells

De novo synthesis of purine nucleotides and some regulatory properties of this pathway were studied in cultured epithelial-like rat liver cells. It was found that the physiological 5-phosphoribosyl 1-pyrophosphate (P-Rib-PP) concentration in these cells is limiting for purine synthesis de novo. Increase of P-Rib-PP availability, achieved by activation of P-Rib-PP synthetase at high P_i concentration, resulted in acceleration of purine synthesis. The effects of increasing cellular ribose 5-phosphate (Rib-5-P availability, by methylene blue-induced acceleration of the oxidative pentose phosphate pathway, on P-Rib-PP availability and on the rate of the novo purine synthesis were also studied. It was found that at the P_i concentration prevailing in the tissue at extracellular physiological P_i concentration, Rib-5-P availability is saturating for P-Rib-PP generation and therefore also for purine synthesis.     

Development of the neural apparatus of the human pancreas in prenatal ontogeny

In human embryos, prefetuses and fetuses from 6 to 40 weeks of development 82 preparations of the pancreas have been studied; 39 series of slices of the human embryos have been impregnated after Bielschowsky-Boeke. For the first time the nerves grow into the pancreas anlage in embryos of 16 mm long (6 weeks). The main sources supplying the pancreas with the nerves in the period studied are nervus vagus, celiac, hepatic, splenic, right adrenal, superior mesenteric and intermesenteric plexuses. Three stages in formation of the innervational apparatus of the pancreas are distinguished during the intrauterine development. The first stage is characterized by beginning of the nerve growing into the pancreas anlage. For the second stage an increased development of the intraorganic innervational apparatus and appearance of the all main sources of the organ's innervation are specific. The third stage is characterized with an increased differentiation of receptor zones in various parts of the pancreas. The development of the pancreatic innervational apparatus by the time of birth is not completed.     

Biogeochemical approaches to assessment of East Asian ecosystem sensitivity to acid depositon

We used the critical load (CL) concept to calculate ecosystem response to acid deposition in East Asia. The calculation of critical loads to assess the sensitivity of ecosystems to acidic deposition was made using a biogeochemical approach, which took into consideration both rates of biogeochemical cycling and temperature responses. On the basis of these data the soil-biogeochemical mapping has been carried out for the area of East Asia and the CL values for acid-forming compounds have been calculated using modified steady-state mass balance (SSMB) equations. In the north-eastern ecosystems of the Asian part of Russia these values of critical loads for N [CL(N)] and S [CL(S)] compounds are shown to be less than in Europe due to peculiarities of climate, soil and vegetation. The minimum values of both CL(N) and CL(S) are <50 eq/ha/yr (which occur in 8.3% and 40.5% of this area for N and S, correspondingly) and the maximum values are >300 eq/ha/yr. These values are occasionally lower than for corresponding European ecosystems. For the south-eastern ecosystems of the northern part of Thailand the minimum values are <200 eq/ha/yr and maximum values are >700 eq/ha/yr. The minimum CL values (<200 eq/ha/yr) occur in more than 75% of the studied Thai area.