Local Mammary Glucose Supply Regulates Availability and Intracellular Metabolic Pathways of Glucose in the Mammary Gland of Lactating Dairy Goats Under Malnutrition of Energy.

Jie Cai,Feng-Qi Zhao,Jian-Xin Liu,Di-Ming Wang

doi:10.3389/fphys.2018.01467

Jie Cai, Feng-Qi Zhao + Show 2 more

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https://doi.org/10.3389/fphys.2018.01467

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Abstract

As glucose is the regulator of both the milk yield and mammary oxidative status, glucose supply is considered to play important nutritional and physiological role on mammary gland (MG) metabolism. However, inconsistent results were observed from different infusion methods to evaluate the effect of glucose on MG glucose metabolism. Thus, precise method should be developed to learn how availability and intracellular metabolic pathways of glucose in the MG are altered by the direct mammary glucose supply. In addition, limited information is available on the role of mammary glucose supply in milk synthesis in lactating ruminants under an energy-deficient diet. Direct glucose supply to the MG was implemented in the current study through the external pudendal artery infusion under an energy-deficient diet. Six doses of glucose (0, 20, 40, 60, 80, and 100 g/d) were infused through the external pudendal arteries, which is the main artery to the MG, to six lactating goats fed with basal diet meeting 81% energy requirement in a 6 × 6 Latin square design. Milk and lactose yields were both quadratically increased with increased glucose infusion, whereas the milk yield changed inconsistently with the increased energy balance (EB), indicating local glucose supply, rather than EB, improved milk production. Glucose fluxes in the MG were significantly increased and correlated with mammary plasma flow. However, the ratio of lactose yield to glucose absorbed by the MG was significantly decreased. The increased glucose fluxes in the MG and changed glucose-related metabolites in milk indicated that the glucose availability and intracellular metabolic pathways was regulated by local mammary glucose. Acute glycolysis consumed the superfluous glucose and induced accumulation of oxygen radicals in the MG during over-supplied glucose conditions. The present study provided insight to optimal glucose supply to the MG during the lactation.

Highlights

Milk production is largely influenced by precursor supply to the mammary gland (MG) (Toerien et al, 2010)
Glucose is partitioned within cells, which includes the partition of glucose between lactose synthesis, glycolysis, the pentose phosphate pathway (PPP), or other metabolic pathways in mammary epithelial cells (MECs) (Zhao, 2014; Zachut et al, 2016)
Milk yield and ECM increased in a quadratic manner in response to mammary glucose supply (Pquadratic < 0.01)

Summary

Introduction

Milk production is largely influenced by precursor supply to the mammary gland (MG) (Toerien et al, 2010). Glucose is one of the most important nutrients for milk production as it is the major substrate of lactose synthesis (Zhao, 2014). Glucose did not stimulate milk yield when infused ruminally or intravenously (Vanhatalo et al, 2003; Curtis et al, 2014). Glucose is partitioned within cells, which includes the partition of glucose between lactose synthesis, glycolysis, the pentose phosphate pathway (PPP), or other metabolic pathways in mammary epithelial cells (MECs) (Zhao, 2014; Zachut et al, 2016).

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