To elucidate purine degradation in contracting skeletal muscle, we analyzed changes in concentrations of adenine nucleotides, IMP, inosine, and hypoxanthine in rat extensor digitorum longus (EDL, fast - twitch) and soleus (slow - twitch) muscles stimulated simultaneously via the sciatic nerve ( 5 Hz,25V,10min). In EDL muscle, ATP concentration decreased progressively during stimulation. As ATP declined, not only IMP (from 0.09 ±0.01 to 1.72 ±0.32 μmol/g wet wt, mean ±SE), but inosine (from 0.016 ±0.003 to 0.164 ±0.019 μmol/g) and hypoxanthine (from 0.014 ±0.002 to 0.040 ±0.004 μmol/g) concentrations increased significantly. ADP and AMP concentrations remained almost unchanged. Adenylosuccinate increased very little during stimulation. Ten minutes after the end of stimulation (recovery period), IMP, inosine and hypoxanthine returned to their basal concentrations, but ATP was still lower than the basal value. In soleus muscle, there were no appreciable changes in these metabolite concentrations. The present findings indicate 1) strenuous contraction caused greater purine catabolism in fast - twitch muscle than in slow - twitch muscle and 2) inosine formation was strongly correlated with the IMP accumulation. We concluded that a small quantity of intramuscular IMP, which is the degradation product of adenine nucleotide, could get out of the purine nucleotide cycle by being converted to nucleoside and oxypurine under the condition of strenuous contraction.
The difference between the solubility of monosodium urate (Na-urate) and uric acid in urine was investigated using concentrated urine as a solvent. The solubility of uric acid increased with increasing pH and resembled a logarithmic function. On the other hand, the solubility of Na-urate as a function of pH was maximal at pH 5.6 and gradually decreased with increasing pH. These results imply that urate has a remarkable tendency to remain in a supersaturated state. However if this is disturbed, crystallization may occur and exert pathogenic effects on the body even in the case of alkaline urine. These results also provide valuable data concerning urinary management in the treatment of hyperuricosuria.
The localization of cytosol 5' -nucleotidase in chicken tissues was studied at the optical and ultrastructural level. Cytosol 5'-nucleotidase was purified from chicken liver and antibody against it was raised in a rabbit. Semi - thin sections of glutaraldehyde - fixed chicken tissues including the liver, heart, kidney, brain, and aorta were stained by the immunoenzyme technique. Staining of cytosol 5'-nucleotidase was prominent in sinusoidal cells of the liver and in capillary endothelial cells of the heart and kidney, but faint in vascular endothelium of the brain and aorta. Electron microscopic study demonstrated that the cytosol of sinusoidal endothelial cells and Kupffer cells was prominently stained, and to a lesser extent the cytosol of hepatocytes, by the use of the peroxidase - labeled Fab' of the antibody. These findings indicate that the cytosol 5'-nucleotidase is localized mainly in the cytosol of vascular endothelial cells in various tissues.
Our previous studies on murine cytidylate cyclase clarified that the activities were highest in brain among several tissues tested including liver, heart, kidney, spleen, and lung. In the present study, human brain cytidylate cyclase activities were compared with those of different types of brain tumors. The activity of cytidylate cyclase, which catalyze formation of cytidine 3',5'-cyclic monophosphate (cCMP) from cytidine 5'-triphosphate (CTP), was assessed by enzyme immunoassay (ETA) developed in our laboratory. It was shown that human normal brain had a cytidylate cyclase activity as high as those of murine brain, which could be solbilized with 0.3% (v/v) Triton X-100. There was a great variety in the enzyme activity of human brain tumors, glioblastoma shown to be low and meningioma to be high. These findings suggest that this enzyme might be used as a marker of the tumor malignancy.
We investigated the serum levels of uric acid in 70 patients under maintenance hemodialysis in comparison with the serum levels of creatinine before and after the one session of hemodialysis. There were no significant correlations between serum levels of uric acid and creatinine before hemodialysis nor between the former and the duration from the initiation of hemodialysis, although the serum uric acid levels were elevated in almost all patients (9.21±2.15mg/dl, n=70) compared with normal levels (5.32±1.15mg/dl, n=58). The mean ratios of serum uric acid to creatinine levels before hemodialysis were significantly lower (p<0.01)in the hemodialysis group (0.70±0.25) than in 58 normal control subjects (8.74±3.41) and in 58 pattients with chronic renal failure on conservative therapy (2.69±1.78). As the interval between the hemodialysis sessions was longer, the rate of elevation of serum uric acid levels from the end of one session until the next one become lower, and the rate showed a significant correlation (r=-0.517, p <0.01, n=15) with the serum creatinine levels before hemodialysis. These results indicate that some mechanism inhibits the elevation of serum uric acid level in uremia in spite of the elevation of serum creatinine level, such as a promoter to enter uric acid into cells or tissues and an inhibitor to produce uric acid in the liver.