Bovine Somatotropin Increases Hepatic Phosphoenolpyruvate Carboxykinase mRNA in Lactating Dairy Cows,

Abstract

Somatotropin (ST) increases milk production and through coordinated changes in hepatic glucose synthesis and amino acid metabolism in dairy cows. The objective of this study was to determine the effects of ST on hepatic mRNA expression for phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC), enzymes that are critical to the synthesis of glucose in liver and hepatic mRNA expression for carbamylphosphate synthetase I (CPS-I), argininosuccinate synthetase (AS), and ornithine transcarbamylase (OTC), critical enzymes of the urea cycle. Eighteen cows were randomly allocated to 2 treatment groups and received either recombinant bovine ST (Posilac; Monsanto, St. Louis, MO) or saline injections at 14-d intervals during a 42-d period. Expression of mRNA was determined using Northern blot analysis. Nuclei, isolated from liver biopsy samples, were used to determine effects of ST on transcription rate of PEPCK. Milk production was increased with ST (37.3 vs. 35.1+/-0.6 kg/ d). Plasma NEFA was increased with ST (299 vs. 156+/-34 microM). There were no differences in the expression of CPS-I, AS, and OTC mRNA with ST. Expression of PEPCK and IGF-I mRNA were increased with ST but PC mRNA was unchanged. The data indicate increased PEPCK mRNA in cows given ST and indicates a greater capacity for gluconeogenesis from gluconeogenic precursors that form oxaloacetate. The effects of ST to elevate PEPCK mRNA expression require chronic administration and involve increased transcription of the PEPCK gene.

Metabolic, productive and reproductive responses to postpartum short-term supplementation in primiparous beef cows

“…Consequently, there is an increase in hepatic glucose synthesis rate, and thus an increase in circulating glucose concentrations (Reynolds et al, 2003). Thus, changes in circulating glucose or neoglucogenic precursor concentrations promote changes in the glucose homeostatic system (Velez & Donkin, 2004;Karcher et al, 2007). Insulin is one of the main hormones that regulate blood concentrations of this metabolite (Coffee, 1998;Drackley et al, 2001).…”

“…Cow BCS was recorded at 0, 7 and 22 days (before, during and at the end of the nutritional treatment) according to a scale validate in Uruguay by Vizcarra et al (1986) (scale 1-8;Vizcarra et al, 1986), as well as cow and calf BW using a digital scale. Blood samples were collected weekly from 7 days before the initiation of the nutritional treatment (day -7) to day 49 of experiment, early in the morning, by jugular venipuncture using 10 mL Vacutest ® tubes (Vacutest Kima, Arzergrande, Italy) with heparin.…”

Gluconeogenesis in dairy cows: The secret of making sweet milk from sour dough

“…Further exploration of control of PC and PEPCK with feed restriction and bovine somatotropin (bST) administration indicates that PC, but not PEPCK, is elevated during feed restriction (66) and PEPCK, but not PC, is elevated with bST (73). These data highlight the uniqueness of the bovine species with regard to control of glucose metabolism.…”

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising fromin vivostudies

“…Similarly, when glucose demand is experimentally increased such as after phlorizin treatment (that blocks glucose transport, inducing glucose loss in urine) during lactation, overall hepatic glucose production and gluconeogenesis increase (128,152) and AA potentially increase in importance as precursors for glucose production (128) . In contrast, when metabolism is strongly partitioned towards protein anabolism such as after growth hormone infusion in lactating cows, increased milk production and gluconeogenesis (157) do not result in increased utilisation of AA for energy (and lactose production) because they are consequentially spared for protein synthesis (158,159) . In ruminants, this vitally important plasticity in gluconeogenic precursors (i.e.…”