The metabolism and urinary excretion of orotic acid in hyperargininaemic sheep.

The synthesis, blood plasma turnover and urinary excretion of the orotic acid in normo- and hyperargininaemic sheep was investigated. The whole-body orotate formation was evaluated indirectly by the measurement of urinary orotate excretion after blockage of pyrimidine pathway with 6-azauridine (4 hour i.v. infusion of 0.2 mg.kg-1.min-1). Simultaneous infusion of L-arginine (2.5 mumols.kg-1.min-1) significantly elevated the blood plasma arginine, ornithine and urea level, however, it did not significantly influence urinary orotate excretion. In normoargininaemia blood plasma turnover of exogenous orotic acid amounted to 4.9 min and 67% of this compound was eliminated through the kidneys. The renal clearance of orotic acid amounted to 21.7 ml.min-1.kg-0.75. Hyperargininaemia elevated blood plasma turnover to 8.2 min, and diminished the renal clearance of this metabolite to 13.7 ml.min-1.kg-0.75. These results indicate that hyperargininaemia and hyperornithinaemia do not change the whole body synthesis of orotic acid in sheep but they can affect renal excretion of this metabolite, particularly at the rate of tubular secretion close to saturation.

Urinary excretion of purines in sheep with experimental orotic aciduria.

Urinary excretion of uric acid, hypoxanthine, allantoin, and urea was measured in sheep (Polish Merino, about 20 kg b.w.) with experimental orotic aciduria. The 240 min infusion of 6-azauridine solution into the jugular vein induced a highly significant increase of urinary orotic acid, uric acid and hypoxanthine excretion. No differences were found in relation to excretion of allantoin and urea in examined sheep. It was calculated that renal clearance of uric acid and hypoxanthine increased significantly in response to 6-azauridine infusion. Intravenous infusion of sodium orotate evoked a highly significant elevation of renal urate clearance. No significant change in renal urea clearance was observed. The data suggest that competition between the renal transport of orotate and actively transported purine compounds (uric acid and hypoxanthine) occurs.

[Effect of volatile fatty acid concentration in the rumen on blood flow in the mesenteric vessels of sheep]. / Wplyw stezenia LKT w przedzoladkach na przeplyw krwi w naczyniach krezkowych u owiec.

The studies were performed on sheep with chronic rumen fistulae and implanted electromagnetic recorders of blood flow in the anterior mesenteric vein and the anterior mesenteric artery. The animals were fed the diet consisting of sugar beet, urea and mineral salts (diet I) or sugar beet and mineral salts (diet II--nitrogen deficient). The diet caused an increase of blood flow in the mesenteric artery and the mesenteric vein: this increase reached the highest level after 2 hours since the application of the diet. There was noted a positive correlation between the changes of blood flow in the mesenteric vessels and the volatile fatty acid concentration in the rumen. The composition of the diet, differing by a protein level, did not influence significantly the differences in blood flow in the mesenteric vessels. It was suggested that an increase of blood flow in the mesenteric vessels was caused by fermentation of carbohydrates in proventriculi, and hence an increased concentration of VFA in the content attaining the duodenum, stimulation of chemoreceptors in the rumen mucosa and increased activity of cholinergic system in internal organs of the abdominal cavity.

The depressive action of ammonium chloride on the hepatic blood flow in sheep.

Using the 133Xe clearance method it is shown that NH4Cl infusion into the anterior mesenteric vein decreased capillary blood flow in the liver. Phentolamine completely and propranolol partially prevented the depressive action of NH4Cl on hepatic blood flow. NH5Cl infused into the jugular vein provoked a slight increase in the hepatic blood flow. The adrenaline-like action of ammonium ion on the blood circulation in the liver region is discussed.