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.

Plasma glucose and nonesterified fatty acids response to epinephrine challenges in dairy cows during a 670-d lactation

“…This has implications for the management of cows using extended lactations; for example, Delany et al (2010) demonstrated that cows fed in excess of their requirements (in the form of a TMR) gained excess body condition and were unable to sustain milk production to 670 d, unlike their pasture-based counterparts that were able to continue milking. There may also have been variable mobilization of visceral versus subcutaneous fat depots (De Koster et al, 2016). Evidence suggests differential mobilization of adipose stores from visceral and subcutaneous tissues in lactating and nonlactating cows (Hostens et al, 2012;Drackley et al, 2014).…”

“…Evidence suggests differential mobilization of adipose stores from visceral and subcutaneous tissues in lactating and nonlactating cows (Hostens et al, 2012;Drackley et al, 2014). Further, over-conditioned cows are predisposed to excessive mobilization of body fat (De Koster et al, 2016). In light of this, farmers and herd managers will need to be aware of the body condition of cows managed for extended lactations and avoid over-feeding to avoid excess fatness.…”

Short communication: Effects of body fat mobilization on macrophage infiltration in adipose tissue of early lactation dairy cows

“…When FFA concentrations decrease afterward, ATM remain in AT to fulfill their function. Serum FFA concentration reflects the mobilization of fat from all adipose depots and this may differ between different adipose depot locations (De Koster et al, 2016). Possibly, the infiltration of ATM may be more related to the local release of adipokines and FFA within different adipose depots.…”

Symposium review: Modulating adipose tissue lipolysis and remodeling to improve immune function during the transition period and early lactation of dairy cows

“…In response to lipolysis induced by NEB in late-lactation cows, TNFA gene expression was upregulated; however, no changes were observed in the transcription of other pro-inflammatory cytokines, including IL6 and CCL2 (Contreras et al, 2016). In over-conditioned nonlactating, nongestating cows (i.e., animals with higher basal lipolysis rate; De Koster et al, 2016), the expression of IL1B (encoding IL-1β), CCL2, and IL6 and its receptor (IL6R) is upregulated, especially in visceral AT (Ji et al, 2014). Zachut (2015) characterized the AT proteome in transition cows with intense and moderate lipolysis rates at 17 d before and 4 d after parturition.…”

“…Other factors that can be hypothesized to contribute in excessive lipolysis of cows overfed during the dry period are the greater amount of adipose mass, as overfed cows will accumulate excess energy in their adipose depots , higher expression of ATGL (Ji et al, 2012), and an increase in adipocyte size. Larger adipocytes have higher levels of basal and stimulated lipolytic activity (De Koster et al, 2016). The current recommended strategy to feed cows during the dry period, in view of limiting lipolysis, is to meet but not exceed energy requirements while maximizing DMI.…”