Cyclic nucleotide alterations in mixed leukocyte reaction: a preliminary report

Endogenous cyclic adenosine and guanosine monophosphate (cAMP, cGMP) levels were studied in human peripheral blood lymphocytes during mixed leukocyte reactions (MLR). cAMP level was consistently elevated in one-way MLR, with good correlation to 3H-thymidine uptake in these reactions. In contrast, cGMP level was practically unchanged. Irradiation of reacting cell populations resulted in inhibition of cyclic nucleotide phosphodiesterase (PDE) activity. These results suggest that metabolic alterations in cAMP may be associated with immune reactions of cellular recognition.     

Intestinal transport of thiamin and thiamin monophosphate in rat everted jejunal sacs: a comparative study using some potential inhibitors

Rat everted jejunal sacs were incubated for 15 and 30 min at 37 degrees C in oxygenated Krebs-Henseleit buffer, pH 7.4, containing 0.2 microM [3H]-thiamin (3H-T) or [3H]-thiamin monophosphate (3H-TMP) with and without 10 mM 1-phenylalanine (PAL) or 2.5 mM levamisole (LEV). The concentrations of 3H-T and its phosphoesters in sac wall and serosal fluid were determined by a radiometric method after electrophoretic separation. In separate experiments, thiamin pyrophosphokinase (TPKase) and thiamin pyrophosphatase (TPPase) activities were determined in mucosal scrapings, with and without PAL or LEV, by using a radiometric and a colorimetric method, respectively. 3H-TMP was transported partly unchanged by an active mechanism similarly to 3H-T, but less efficiently. During transport, 3H-TMP was also enzymatically transformed to thiamin (T) and thiamin pyrophosphate, which accumulated in the tissue. In the serosal fluid, the concentration of 3H-TMP exceeded that of 3H-T. Presence of PAL or LEV with 3H-T or 3H-TMP in the incubation medium reduced the serosal transport and the tissue content of T compounds. LEV caused a dose-dependent inhibition of TPKase without affecting TPPase, whereas PAL inhibited both activities to about the same extent. These results indicate that the transport of TMP involves a number of different processes similar to those responsible for T transport. The effects of PAL and LEV underline the importance of phosphorylation-dephosphorylation coupling.     

Studies on purine turnover in the camel (Camelus dromedarius) and zebu (Bos indicus)

Significantly higher hypoxanthine over uric acid ratios were found in camel plasma and urine, with respect to those of zebu. Enzyme levels of purine catabolism were markedly lower in camel than in zebu liver. Oxidation of hypoxanthine appears to be the limiting step of purine metabolism in camel liver. Any hepatic hypoxanthine appears to be actively converted into IMP in camel liver, rather than oxidized to uric acid.     

Nucleotide pool changes in coelomic cells (eleocytes) of the polychaete Nereis virens during sexual maturation

Eleocytes (a type of coelomic cell) of the polychaete Nereis virens can store large amounts of adenine nucleotides at certain times. Since eleocytes have specific functions related to gametogenesis, we tested whether the presence of these large nucleotide stores in eleocytes is specific to gender or related to specific events during gametogenesis. Nucleotide pools in eleocytes isolated at different stages of sexual maturation from N. virens were analysed using high-performance liquid chromatography. Eleocytes from immature and male animals had extremely high concentrations of both AMP and ADP (each > 10 μmol/ml of packed cell volume). In eleocytes from male animals, the high nucleotide stores were maintained throughout the maturation phase and decreased at a late stage, while in female animals the nucleotides were degraded at an early stage of maturation. In male eleocytes, the decrease in the adenine nucleotide pool may be the result of its conversion to inosine which is then released by the eleocytes and reutilized by male germ cells for nucleic acid biosynthesis, as has been suggested previously. Our study shows that the time of degradation of the adenine nucleotide pool coincides with the period of spermatogonia proliferation which involves intense nucleic acid synthesis. ATP levels (0.4–1.5 μmol/ml packed cell volume) and the guanine nucleotide pool (GTP+GDP+GMP; 0.08–0.18 μmol/ml packed cell volume) were similar in both sexes, did not change during germ cell development and were decreased only in eleocytes from prespawning females. The GTP/GDP ratios were initially higher (up to 14) in eleocytes from females compared to ratios in eleocytes from immature (4–9) and male animals (up to 8), and decreased during the maturation phase of the animals. GTP levels were correlated with those of ATP; this correlation was much closer in eleocytes from females than from males. The results further support the hypothesis that the adenine nucleotide stores in the eleocytes are maintained as a supply of purine precursors for the growing germ cells.