N-Carbamoylputrescine, a citrulline-derived polyamine, is not a significant citrulline metabolite in rats

Citrulline, a key amino acid of the urea cycle, has been shown to play a regulatory role in protein and energy metabolism in mammals. We questioned whether N-carbamoyl-putrescine (NCP), the decarboxylated derivative of citrulline, could play a role in the biological properties of this amino acid. To evidence the presence of NCP in mammalian tissues, we developed a sensitive reverse-phase high-performance liquid chromatography (HPLC) with fluorimetric detection method with precolumn dansyl derivatization and solid-phase extraction for the determination of NCP together with polyamines in biological samples. Dansyl NCP was identified with a 5.85-min retention time. Linearity was obtained in a concentration range of 0.125 to 12.5 μM. Intraday and day-to-day relative coefficients of variation ranged from 8.9% to 12.3% and from 14% to 14.3%, respectively. Recovery rates in serum ranged from 75% to 83%. Thereafter, we used this method to search for the presence of NCP in serum, muscle, liver, jejunum, and ileum in rats after both short-term intraperitoneal injection and long-term oral citrulline supplementation. We failed to detect NCP in these animals. These data suggest that NCP is not a significant citrulline metabolite in rats.

Effect of apoE/ATP-containing liposomes on hepatic energy state

BACKGROUND/AIMS

ATP-containing liposomes partially prevent ATP depletion in the cold-stored liver. As hepatocytes can specifically bind apoE, we investigated whether the addition of apoE to large (200 nm) ATP-containing liposomes increases their uptake by the liver and further improves hepatic energy stores.

METHODS

Livers from fasted male Hartley guinea-pigs (231 +/- 3 g) were perfused for 90 min under our standard conditions (Control, n = 6) or after a single bolus addition of plain liposomes (Lip, n = 6), ATP (5 micromol)-containing liposomes (ATP-Lip, n = 6) or apoE/ATP-containing liposomes (0.8 or 8mg apoE/g phospholipids; apoE1-Lip and apoE10-Lip, respectively, n = 6 in each group). Liposome uptake and its impact on energy and nitrogen metabolism were studied.

RESULTS

At its highest concentration, apoE significantly increased liposome uptake (apoE10-Lip: - 9.17 +/- 0.69 vs apoE1-Lip: - 6.18 +/- 0.44 vs ATP-Lip: - 6.40 +/- 0.88 nmol min(-1) g(-1) P < 0.05). This was associated with a significant increase in intrahepatic ATP (apoE10-Lip: 1033 +/- 137 vs apoE1-Lip: 811 +/- 98 and ATP-Lip: 648 +/- 36 nmol g(-1); P < 0.05), which was restored to its level in non-perfused livers. Hepatic viability and nitrogen metabolism were not affected.

CONCLUSIONS

Hepatic ATP content being a key factor in the maintenance of liver graft function, apoE/ATP-containing liposomes should be useful in liver preservation for transplantation.

Cyclic guanosylmonophosphate urinary excretion in parasympathicomimetic or parasympatholytic syndromes induced by reserpine or diphemanil-methylsulfate

Parasympathetic hyperactivity is found in some infants presenting faint episodes and could be responsible of certain Sudden Infant Death Syndrome cases. Therefore it was interesting to look for a noninvasive biochemical indicator of parasympathetic activity. A parasympaticomimetic syndrome associated with muscarinic receptor stimulation, which has been followed during 48 h, was obtained in the awake rat by reserpine injection (6.25 mg/kg at T0 and T24h), and a model of prolonged parasympatholytic syndrome, by administration of diphemanil-methylsulfate (DPMS), a muscarinic receptor inhibitor, in drinking water (mean daily dosis: 150 mg/kg). Significant bradycardia and tachycardia were respectively observed. In the reserpine-treated rats we found significantly increased cyclic guanosylmonophosphate (cGMP) urinary excretion between T24h and T48h, when compared with vehicle-treated controls (+87% in one experiment, +135% in the other, when expressed in pmol/microg creatinine); norepinephrine urinary excretion between T24h and T48h was decreased (-44%); the increase in cGMP urinary excretion was not significantly modified by the NO-synthase inhibitor, L-nitroarginine-methyl-ester. In the DPMS-treated rats, we observed a significantly decreased cGMP (-20%) and increased norepinephrine urinary excretion (+61%). Thus cGMP excretion varied in opposite directions in the reserpine- and DPMS-treated rats. The link between these modifications in cGMP excretion and muscarinic receptor stimulation or blockade has still to be fully demonstrated. Urinary cGMP excretion could be tested as screening parameter in infants at risk of faint episodes associated with bradycardia.

Effect of pyridoxine on mice gastric ulcers and brain catecholamines after an immobilization stress

Fifty adult female Swiss albino mice were injected with either 1.11 mg/kg body weight pyridoxine or saline, subsequently they were all submitted to an immobilization stress with a complete fast for 17 h. At the end of this period, the animals were sacrificed, the gastric mucosa was dissected for ulcer count, and brain noradrenaline, dopamine and serotonin were determined by liquid chromatography. In addition, 26 nonstressed mice were used as controls, 16 of them being fed at libitum and 10 submitted to the same fasting period as the first two groups. In the stressed animals, the average number of gastric ulcers per mouse was twice as large in the saline-treated group than in the pyridoxine-treated group (p < 0.05). With a single exception, no ulcer was found in the non stressed controls. Brain norepinephrine content was almost identical in fasting controls and in stressed mice treated with pyridoxine; in the stressed animals treated with saline, the average norepinephrine content was higher by 15% and in the fed controls lower by 11% than in the two preceding groups. Pyridoxine treatment entailed a very significant reduction (p < 0.002) of norepinephrine variability, mainly due to the absence of high values (> or = 750 ng/g of fresh brain) which occurred only in the saline-treated group. Similar results were yielded for brain dopamine. No variations were observed for brain serotonin. These results suggest the antistress effect of pyridoxine.