Paul Ernsberger's blog

NAASO Meeting 2005, Vancouver

First off, there was:

Magnetic resonance imaging of visceral and subcutaneous fat distribution in genetic obesity of SHROB rats and dietary obesity of overfed SHR

Wan, D.P., Johnson, D.H., Johnson, J.L., Koletsky, R.J., Flask, C. and Ernsberger, P.

Magnetic resonance imaging (MRI) is a noninvasive method that can be used to identify, map and quantify fat depots in living subjects. We sought to map the distribution of abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) in two models of obesity in the rat, one genetic and one dietary-induced. We hypothesized that the relative distribution of VAT and SAT may differ between these models, and metabolic disturbances may track with the relative proportion of VAT rather than just overall adiposity. The spontaneously hypertensive obese rat (SHROB) has a naturally occurring knockout of the leptin receptor and served as the genetic model. The spontaneously hypertensive rat (SHR), genetically identical to SHROB with the exception of the obesity-inducing mutation, was used as the lean control and was fed normal chow (4.05 kcal/g). The dietary obese model was obtained by feeding SHR a dietary supplement (1.59 kcal/mL) consisting of 24% sucrose, 8% polycose, and 8% cream supplemented with appropriate micronutrients, until a 20% increase from baseline weight was achieved. Female rats were tested at around 8 mo of age and anesthetized with enflurane. Images were acquired as T1-weighted spin echo water-cancelled scans (TE 13ms, TR 1240 ms) with 4 averaged passes on a 1.5 Tesla clinical MRI and rodent-sized coil. The acquisition was coronal with 2 mm thickness and 0.78 mm x 0.78 mm in-plane resolution. The MRI sequence data were collected by using standard software (Analyze). The peritoneum was manually traced in each slice to delineate the VAT and SAT, and organs and other non-adipose tissue were removed from the visceral area by lower-bound thresholding. In regions of poor fat-tissue contrast, adipose tissue areas were delineated manually. In lean SHR control, 22.8 mL of total adipose tissue could be divided into 13.7 mL (60.1%) of VAT and 9.1 mL (39.9%) of SAT (1.5:1 VAT:SAT ratio). In the dietary obese SHR, 85.2 mL total was measured comprising 53.3 mL (62.6%) VAT and 31.9 mL (37.4%) SAT (1.7:1 VAT:SAT). In the genetically obese SHROB model, 274.6 mL of total was calculated, with 113.4 mL (41.3%) VAT and 161.2 mL (58.7%) SAT (0.7:1 VAT:SAT). Although total VAT volume was markedly higher in the genetically obese model, the VAT:SAT ratio of the dietary obese model was markedly higher. This predicts that despite a lower total adipose tissue volume compared to genetic obesity, dietary obesity may be more closely associated with metabolic derangements, a conclusion supported by physiological data.