Douglas C. McFarland

A micromethod for plasma uric acid determinations in companion birds.

A simple inexpensive method is described for determining plasma uric acid levels in companion birds. Plasma uric acid concentrations in 33 healthy parakeets were determined by a modification of the uricase spectrophotometric procedure utilizing 50 microliters of plasma. The mean uric acid level in parakeets was 5.60 mg/dl blood plasma, with no significant difference between males and females. In White Leghorn chickens, however, the mean level of uric acid in plasma was 7.19 mg/dl in males and 3.05 mg/dl in females. This method may be useful for the diagnosis and study of gout in small birds.

Purine metabolism in high and low uric acid lines of chickens: de novo uric acid synthesis in isolated hepatocytes and phosphoribosylpyrophosphate amidotransferase activities.

Abstract The de novo biosynthesis of uric acid was examined in isolated hepatocytes from the high and low uric acid lines of chickens. Rates of incorporation of radiolabeled glycine into uric acid by hepatocytes from the high uric acid (HUA) line were approximately 3.6-fold greater than found in low uric acid (LUA) control hepatocytes. Uric acid synthesis rates in these cells were positively correlated with plasma uric acid levels (r = +0.77; P < 0.01). The activity of phosphoribosylpyrophosphate (PRPP) amidotransferase was measured in acetone powder preparations from liver and kidney tissues of the HUA and LUA lines. Activities in kidney tissues were about 21% lower than those found in livers. PRPP amidotransferase activities in liver and kidney tissues did not correlate significantly with plasma uric acid levels. The increased synthesis of uric acid in the HUA line may be the result of the increased PRPP synthetase activities and PRPP pool sizes previously reported for these tissues.

Purine metabolism in high and low uric acid lines of chickens: phosphoribosylpyrophosphate (PRPP) synthetase activities and PRPP pool sizes.

Abstract Phosphoribosylpyrophosphate synthetase activities were examined in liver and kidney tissues of two genetic lines of chickens selected for their plasma uric acid levels. Previous work demonstrated that the high uric acid line (HUA) has significantly greater de novo uric acid synthesis rates in kidney tissue compared to the low uric acid line (LUA). In addition, xanthine dehydrogenase activity in liver and kidney tissues was significantly higher in the HUA compared to the LUA line. The activity of PRPP synthetase, which provides a key substrate for the rate limiting step in de novo purine biosynthesis, was found to be significantly elevated (P < 0.05) in liver and kidney tissues of the HUA line. The mean value of kidney PRPP synthetase activity was 30.2 ± 0.7 nmole PRPP and 19.1 ± 1.6 nmol PRPP produced/mg protein/hr, respectively, for the HUA and LUA lines. The PRPP pool size in kidney tissue was also significantly higher in the HUA line. The mean level of PRPP was 319.8 ± 37.2 pmole/g of wet tissue compared to 176.7 ± 12.4 pmole PRPP/g of wet tissue in the LUA line. The mean values of liver PRPP synthetase activities were 11.4 ± 0.6 nmole PRPP and 9.0 ± 0.4 nmole PRPP produced/mg protein/hr, respectively, for the HUA and LUA lines. The PRPP pool size in liver tissues was significantly higher in the HUA line as well. The mean level of PRPP was 550.7 ± 72.5 pmole/g of wet tissue compared to 313.6 ± 31.4 pmole PRPP/g of wet tissue in the LUA line. The enzyme from the HUA birds does not differ from controls with respect to Michaelis constants, inhibition phenomena, and phosphate activation. The increased PRPP synthetase activity found in HUA tissues may be due to structural alterations of the molecule resulting in an enzyme with a greater V max, an increase in the amount of enzyme protein, or a lowered level of a nondialyzable inhibitor.

Purine metabolism in high- and low-uric acid lines of chickens: hypoxanthine/guanine phosphoribosyltransferase activities.

Abstract The activity of hypoxanthine/guanine phosphoribosyltransferase (HGPRT) was examined in the livers and kidneys of two genetic lines of chickens selected for different plasma uric acid levels. Previous work demonstrated that the high-uric acid line (HUA) had significantly greater de novo uric acid synthesis rates in kidney tissue compared to the low-uric acid line (LUA). In addition, phosphoribosylpyrophosphate (PRPP) synthetase and xanthine dehydrogenase activities in livers and kidneys were significantly higher in the HUA compared to the LUA line. PRPP pool sizes were also significantly higher in both livers and kidneys of HUA birds. HGPRT activities in livers of HUA birds were significantly (P < 0.05) greater than in LUA birds. The mean value of liver HGPRT was 7.36 ± 0.25 pmole inosine-5′-monophosphate (IMP) and 6.05 ± 0.27 pmole IMP produced/μg protein/hr, respectively, for the HUA and LUA lines. There were no significant differences (P > 0.05) in kidney HGPRT activities between the two groups. The mean value of kidney HGPRT was 52.87 ± 1.62 pmole IMP and 50.72 ± 1.62 pmole IMP produced/μg protein/hr, respectively, for the HUA and LUA line. Elevated liver HGPRT may serve to enhance the regeneration of PRPP in the HUA liver. Elevated liver PRPP synthetase and PRPP pool size suggest an increased flux through the de novo purine biosynthetic pathway in HUA birds. The resulting additional pyrophosphate from the glutamine PRPP ami-dotransferase reaction would stimulate recovery of PRPP and spare the system from a substantial loss of energy.