Basal lipolytic activity of subcutaneous and omental adipose tissue of precalving dairy cows with different body condition score

The adipose tissue of dairy cows plays an important role during the transition period. Recent research indicates a selective mobilization of adipose depots during negative energy balance. Therefore, we investigated the influence of the size of the adipocytes and the adipose depot (omental versus subcutaneous) on the basal lipolytic activity of adipocytes from precalving dairy cows with different body condition score (BCS). Five pregnant dairy cows (BCS 2,75-4,25) were euthanized (approximately 12 days before expected day of calving) and immediately after euthanasia, samples of subcutaneous (at right side of the tail base) and omental adipose tissue were transferred to sterile falcon tubes containing culture medium (KREBS ringer bicarbonate hepes + 3% BSA at 38°C). Adipose tissue fragments were minced using very sharp scissors and approximately 100 mg adipose tissue explants were incubated in 3 ml culture medium at 38°C on a shaker. After 3 hours of incubation, samples of the medium were taken for glycerol analysis using free glycerol reagent (Sigma). Results are expressed as nmol glycerol release per 3 hours per million adipocytes. The number of adipocytes was determined as described by DiGirolamo et al. (1971). Briefly, adipose tissue fragments were digested using collagenase (Sigma), the diameter of 300 adipocytes was determined microscopically and the number of adipocytes was calculated using the density of lipids (0,915 g/ml) and the average volume of the adipocytes. Statistical analysis was performed using a mixed effect linear model with cow as random factor, diameter of the adipocytes and adipose depot as fixed factors and glycerol release as dependent variable. The diameter of the adipocytes was on average 103,84 μm (range 87,65-120,98). The average glycerol release was 583 nmol/106adipocytes/3h (range 236-1428). The mixed effect linear model revealed a significant effect for the diameter of the adipocytes on the glycerol release (β=26,7; P 0,1). The basal lipolytic activity of adipose tissue increases significantly with increasing size of the adipocytes independently of the adipose tissue depot (subcutaneous versus omental) in precalving dairy cows.