title: Influence of adipocyte size and adipose depot on the in vitro lipolytic activity and insulin sensitivity of adipose tissue in dairy cows at the end of the dry period.
abstract: The aim of the present research was to describe characteristics of adipose tissue lipolysis in dairy cows with a variable body condition score (BCS). Ten clinically healthy Holstein Friesian cows were selected based on BCS and euthanized 10 to 13 d before the expected parturition date. Immediately after euthanasia, adipose tissue samples were collected from subcutaneous and omental fat depots. In both depots, we observed an increase in adipocyte size with increasing BCS. Using an in vitro explant culture of subcutaneous and omental adipose tissue, we aimed to determine the influence of adipocyte size and localization of adipose depot on the lipolytic activity in basal conditions and after addition of isoproterenol (nonselective β-agonist) and insulin in different concentrations. Glycerol release in the medium was used as a measure for lipolytic activity. We observed that the basal lipolytic activity of subcutaneous and omental adipose tissue increased with adipocyte volume, meaning that larger fat cells have higher basal lipolytic activity independent of the location of the adipose depot. Dose-response curves were created between the concentration of isoproterenol or insulin and the amount of glycerol released. The shape of the dose-response curves is determined by the concentration of isoproterenol and insulin needed to elicit the half-maximal effect and the maximal amount of stimulated glycerol release or the maximal inhibitory effect of insulin. We observed that larger fat cells released more glycerol upon maximal stimulation with isoproterenol and this was more pronounced in subcutaneous adipose tissue. Additionally, larger fat cells had a higher sensitivity toward lipolytic signals. We observed a trend for larger adipocytes to be more resistant to the maximal antilipolytic effect of insulin. The insulin concentration needed to elicit the half-maximal inhibitory effect of insulin was within the physiological range of insulin and was not influenced by adipocyte size or adipose depot. We conclude that overconditioned cows have larger adipocytes and are predisposed to excessive mobilization of body fat due to a higher basal and stimulated lipolytic activity of large adipocytes while the antilipolytic effect of insulin is preserved.
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium. Electronic address: jenne.dekoster@ugent.be.
authors.forename: J
authors.initials: J
authors.lastname: De Koster
authors.affiliation: Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Van den Broeck
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Hulpio
authors.affiliation: Laboratory for Animal Nutrition and Animal Product Quality, Faculty of Bioscience Engineering, Ghent University, Proefhoevestraat 10, 9090 Melle, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Claeys
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Van Eetvelde
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Hermans
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Hostens
authors.affiliation: Laboratory for Animal Nutrition and Animal Product Quality, Faculty of Bioscience Engineering, Ghent University, Proefhoevestraat 10, 9090 Melle, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: Fievez
authors.affiliation: Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Opsomer
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance; D007545:Isoproterenol / Q000494:pharmacology; D007774:Lactation; D008066:Lipolysis; D009852:Omentum / Q000378:metabolism; D050151:Subcutaneous Fat / Q000187:drug effects / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; D007004:Hypoglycemic Agents; D007328:Insulin; D007545:Isoproterenol
keywords: adipose tissue; dairy cow; in vitro insulin response; in vitro lipolytic activity