Arginine catabolism in lactating porcine mammary tissue2

Abstract

In vivo studies have shown that the uptake of plasma arginine by the lactating porcine mammary gland greatly exceeds the output of arginine in milk, but little is known about the metabolic fate of arginine in this organ. The objective of this study was to quantify arginine catabolism via arginase and nitric oxide synthase pathways in the mammary tissue of sows on d 28 of lactation. Mammary tissue slices (approximately 60 mg) were incubated at 37 degrees C for 1 h in 2 mL of Krebs bicarbonate buffer containing 0.5 or 2 mM L-[U-14C]arginine, and arginine metabolites were measured using HPLC and radiochemical techniques. Rates of arginine utilization were similar to rates of urea production. Proline, ornithine, urea, glutamate, glutamine, CO2 and polyamines (putrescine + spermidine + spermine) were formed from arginine, accounting for 46, 31, 17, 2.3, 1.5, 0.22, and 0.30%, respectively, of the metabolized arginine carbons. Relatively small amounts of arginine were utilized for nitric oxide and citrulline synthesis, with citrulline accounting for 2% of the metabolized arginine carbons. Production of all arginine metabolites increased with increasing extracellular arginine concentrations from 0.5 to 2 mM, indicating a high capacity for arginine degradation. Consistent with the metabolic findings, the activities of arginases, ornithine aminotransferase, and pyrroline-5-carboxylate reductase were high, whereas those of pyrroline-5-carboxylate dehydrogenase, ornithine decarboxylase, and nitric oxide synthases were relatively low, and there was no proline oxidase, ornithine carbamoyltransferase or pyrroline-5-carboxylase synthase activity in the mammary tissue. Our results demonstrate for the first time that proline, ornithine, and urea were the major products of arginine catabolism via the arginase pathway in lactating porcine mammary tissue and provide a biochemical basis to explain a relative enrichment of proline but a relative deficiency of arginine in sow's milk.

l-Arginine Consumption by Macrophages Modulates the Expression of CD3ζ Chain in T Lymphocytes

“…Supernatants from stimulated PM were used to measure NO production using the Griess reagent method (Molecular Probes). In addition, the extracellular concentration of L-arginine was tested in supernatants by HPLC (Dr. G. Wu, Texas A&M University, College Station, TX) as described previously (21).…”

Top-dressing 1% arginine supplementation in the lactation diet of sows does not affect the litter performance and milk composition

“…TROTTIeR et al (1997) observed that the level of arginine in sow's milk is smaller than the supply of this amino acid to the mammary gland due to its continue degradation by mammary tissue (O'QUINN et al, 2002). In the present study, crude protein or amino acid content of milk, including arginine itself, were not altered by topdressing L-arginine HCL at 1% supplementation, indicating that despite increasing arginine supply in the bloodstream, level of supplementation was not enough to exceed the threshold of arginine degradation in the mammary tissue.…”

“…Since arginine is an essential amino acid for young piglets (O'QUINN et al, 2002) and its supplementation in artificially fed neonates improved their development (KIM et al, 2004), it has been speculated about the potential ability to manipulate milk composition with arginine supplementation. TROTTIeR et al (1997) observed that the level of arginine in sow's milk is smaller than the supply of this amino acid to the mammary gland due to its continue degradation by mammary tissue (O'QUINN et al, 2002).…”

Effects of L-Arginine Supplementation on Lactating Mares and the Development of Foals

“…Arginine (Arg) is a versatile amino acid that is used by different tissues in several metabolic functions, including the production of urea, creatinine and other blood biomarkers [11,19,21]. Although the subject is significant in relation to the metabolism of animals, very few studies of the effects of Arg supplementation in horses have been carried out.…”

“…In addition, it contributes to the formation of polyamines, which are important regulators of lactogenesis and protein synthesis for the production of milk [4,11,16,18,19]. In this context, it has been demonstrated that the absorption of Arg by mammary tissue is important for angiogenesis and for the production of other amino acids during the lactation period [19,25]. In most animal species, the presence of Arg in milk is low.…”