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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0799v1 86/7/1526    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Takagi, M. Articles by Katoh, K. PubMed PubMed Citation Articles by Takagi, M. Articles by Katoh, K.

Changes of activity and mRNA expression of urea cycle enzymes in the liver of developing Holstein calves¹

M. Takagi^*, T. Yonezawa^*, S. Haga, H. Shingu, Y. Kobayashi, T. Takahashi^*, Y. Ohtani^*, Y. Obara^* and K. Katoh^*,2

^* Department of Animal Physiology, Graduate School of Agricultural Science, Tohoku University, 1-1 Amamiyamachi, Sendai, Miyagi, 981-8555, Japan; and and National Institute of Livestock and Grassland Science, Ikenodai, Tsukuba, Ibaraki, 305-0901, Japan

² Corresponding author: kato{at}bios.tohoku.ac.jp

Urea is an important reutilizable nitrogen source for the ruminant and is mainly synthesized through the urea cycle in the liver. The cycle is undertaken by 5 enzymes: carbamoyl phosphate synthetase (CPS), ornithine transcarbamoylase (OTC), arginino-succinate synthetase (AS), argininosuccinate lyase (AL), and arginase. The purpose of this study was to investigate changes in the activity of the enzymes and mRNA expression, given that previous observations have indicated an increase in plasma urea concentrations with age in Holstein calves. First, plasma concentrations of metabolites and hormones were determined in calves at 1, 3, 8, 13, and 19 wk of age (n = 4, weaned at 6 wk of age). The plasma concentration of urea drastically increased after weaning (P < 0.001). The plasma concentration of glucose was lowest at 8 wk. The plasma concentration of IGF-I gradually increased with age, although those of NEFA, glucagon, and cortisol decreased (P < 0.001). Concentrations of triglyceride, -amino nitrogen, growth hormone, and insulin did not change significantly with age of the calf. Next, using the liver tissues taken from calves at 2, 13, and 19 wk of age (n = 4 to 6 at each time point, weaned at 6 wk of age), we measured the activity and mRNA expression of the enzymes by biochemical methods and quantitative reverse transcription-PCR, respectively. The activities of CPS (P < 0.001), OTC (P = 0.001), and AS (P = 0.015) increased with age, whereas AL (P = 0.003) decreased. Although mRNA expression was decreased with age for AL (P = 0.002) and arginase (P = 0.007), no significant change was observed for CPS, OTC, or AS mRNA expression. We conclude that the increased urea production in the liver may be explained not only by an increase in the activities of the urea cycle enzymes, but also by increased ammonia production by rumen fermentation and gluconeogenesis from amino acids around weaning time.

Key Words: calf • development • liver • mRNA • urea cycle enzyme • weaning