Schuh, Katharina: Establishment of an experimental model for dairy cows of divergent peripartal mobilization of body reserves: Profiling circulating steroid hormones and the mRNA abundance of steroid metabolizing enzymes in liver and in adipose tissue. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-64894
@phdthesis{handle:20.500.11811/9480,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-64894,
author = {{Katharina Schuh}},
title = {Establishment of an experimental model for dairy cows of divergent peripartal mobilization of body reserves: Profiling circulating steroid hormones and the mRNA abundance of steroid metabolizing enzymes in liver and in adipose tissue},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = dec,

note = {The lactation cycle of dairy cows is characterized by physiological, metabolic, and endocrine changes that also affect adipose tissue (AT) function and portion. These changes include lipogenesis during periods of nutrient excess and lipolysis during periods of energy deficit. In addition to storing and providing energy, the AT is an important endocrine organ that is considered as a major reservoir of lipophilic steroid hormones which are locally converted by steroidogenic enzymes. Besides the naturally occurring mobilization of body reserves after parturition, cows that are over-conditioned before calving (a.p.) mobilize more fat after calving (p.p.) compared to normal conditioned cows along with an increased release of lipids from AT into the circulation. Consequently, stored steroid hormones may also enter the circulation. To gain insights into how varying degrees of post partum lipolysis affects steroid metabolism in dairy cows, we compared pluriparous cows with high (HBCS, N = 19) and normal body condition (NBCS, N = 19) a.p. Differences in body condition score (BCS) and backfat thickness (BFT) were maintained throughout the entire observation period from 7 weeks a.p. until 12 weeks p.p. The metabolic status was further characterized by assessing the energy status and milk yield together with the circulating concentrations of several metabolites and metabolic hormones. The HBCS cows had consistently higher serum concentrations of fatty acids and of ß-hydroxybutyrate p.p., indicating higher body fat mobilization and ketogenesis compared to NBCS cows. The concentration of 19 steroids in blood and 17 steroids in subcutaneous AT (scAT) were quantified using a targeted metabolomics approach. Further, the mRNA abundance of five steroidogenic enzymes was assessed in liver and scAT samples collected in week -7, 1, 3, and 12 relative to calving. The concentrations of both scAT-accumulated and circulating steroids followed a comparable periparturient time course and were also influenced by parity. Increased lipolysis in HBCS cows p.p. was associated with greater concentrations of circulating androgens and progestins, which may reflect the release of these steroids from AT. Conversely, glucocorticoid concentrations were up to 3.5-fold higher in scAT of NBCS than in HBCS cows p.p.; however, the underlying mechanism of origin remains elusive and requires further validation. The results of this work indicate that local steroid conversion in bovine AT is initiated by the steroidogenic enzymes steroid 21-hydroxylase and 17-ß-hydroxysteroid-dehydrogenase type 12 (HSD17B12). The increased hepatic mRNA abundance of HSD17B12 in HBCS relative to NBCS cows 7 weeks a.p. supports the notion that HSD17B12 may be involved in lipogenic processes. The present thesis provides first insights into the complex metabolism of endogenous steroid hormones in AT and blood of dairy cows differing in the intensity of lipomobilization after parturition, and provided a sound animal model for further research in this field.},
url = {https://hdl.handle.net/20.500.11811/9480}
}

The following license files are associated with this item:

InCopyright