Weber, Martina: Endocrine activity of adipose tissues as influenced by energy intake in the periparturient cow. - Bonn, 2016. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Martina Weber}},
title = {Endocrine activity of adipose tissues as influenced by energy intake in the periparturient cow},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2016,
month = feb,

note = {With the onset of lactation, dairy cows have to mobilize body reserves, mainly in form of fat, to cover the energy output via milk. Homeorhetic adaptations, achieved via the orchestrated actions of hormones, are necessary to ensure the nutrient drain towards the mammary gland. In contrast to the well examined hormones, e.g. growth hormone and prolactin, which are knowingly involved in the metabolic control during the transition period, the role of messenger molecules originating from adipose tissue (AT) (i.e. adipokines), their receptors as well as the role of other receptors and enzymes present in different adipose tissue depots was only scarcely investigated in dairy cows. The aim of this thesis was to characterize the serum concentration of three adipokines as well as the mRNA abundance and the protein expression of related factors in two different adipose tissue depots which are potentially involved in glucose and lipid metabolism during late gestation and early lactation. In addition, different amounts of concentrate as well as a dietary supplementation with nicotinic acid were tested for potential effects on the target variables. Using blood samples as well as samples of subcutaneous (SCAT) and retroperitoneal adipose tissue (RPAT) obtained from 20 pluriparous cows, the time course of 3 adipokines and of the mRNA abundance of eight different target genes as well as their potential relationship were characterized. Neither the amount of concentrate, nor the supplementary niacin had any influence on the variables examined herein. The adipokine apelin remained fairly constant and might thus not be suitable to predict insulin sensitivity during the transition period. Resistin increased towards parturition and returned to pre-calving levels within one week after parturition. Since this observation substantiates recently published results, resistin may qualify as a biomarker for metabolic adaptations. Receptors involved in the regulation of lipolysis, i.e. hydroxycarboxylic acid receptor 1 (HCA1, a receptor for lactate) and 2 (HCA2, a receptor for BHBA and niacin) and tumor necrosis factor α receptor 1 (TNFR1), showed different mRNA expression patterns between SCAT and RPAT and point to an AT depot-specific lipolytic regulation. The serum lactate concentrations were likely too low to activate the receptor and no correlation was observed between lactate and HCA1 mRNA abundance. The decreased HCA2 mRNA after parturition points to a lipolytic regulation at the level of receptor quantity, rather than via its endogenous ligand BHBA. The mRNA of the adiponectin receptors 1 (AdipoR1) and 2 (AdipoR2) decreased after parturition supporting a link to the reduced insulin sensitivity characteristically observed around calving. The higher AdipoR1 mRNA abundance and the higher correlation between AdipoR1 and AdipoR2 mRNA in RPAT point to a tissue-specific regulation of insulin sensitivity. The decreased mRNA of nicotinamide phosphoribosyltransferase (Nampt) and the trend for a decreasing mRNA abundance of the NAD-dependent enzyme Sirtuin-1 (SIRT1) as well as the observed protein expression might contribute to the decreasing insulin sensitivity after parturition. PPARγ-co activator 1α protein expression at d 21 after parturition was higher in the animals receiving a low amount of concentrate. The highest correlation was observed between the mRNA abundances of SIRT1 and AdipoR1. This indicates a functional relationship between these factors and point to a regulatory role in glucose metabolism during the transition period. The present dissertation serves as a basis for further studies elucidating the complex regulation of the metabolic adaptations during the transition period. To substantiate the present results, the variables investigated on the level of transcription herein should be further examined on the level of protein expression or, as for SIRT1, the enzyme activity should be assessed.},
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