Differential ob mrna expression in four fat depots of overfed rats

Site specific changes in ob protein mRNA expression during early development of obesity were examined in overfed rats. Rats were fed ad libitum (AL), tubefed normal intake (100%) or twice this (200%) for 2, 14 or 32 days. Ob protein mRNA was measured by Northern blot analysis in retroperitoneal (RP), perirenal (PR), inguinal (ING) and uterine (UT) adipose tissue from female Sprague Dawley rats using a 320 bp cDNA probe. At all time points ob mRNA expression was 2-fold higher in RP and UT than in ING or PR fat. Changes in response to mealfeeding were detected as early as day 20, when expression was significantly increased in RP and UT from both 100% and 200% fed rats and in PR from 200% fed rats. There were no changes in body or fat pad weights although ING cell number had increased by day 2. An effect of overfeeding was detected on day 14 when ob mRNA was significantly higher in 200%-fed than 100%-fcd rats in all depots except PR. By day 32 ob mRNA expression was 8 to 10-fold higher in 200%-fed rats than in AL rats and 2 to 4-fold higher than in 100%-fed rats. The 200%-fed rats were 160% of AL body weight, fat pads were 5-fold larger and adipocyte number had increased 5 to 6-fold. These results show differences in regional expression of ob protein mRNA. Mealfeeding caused a rapid, 2 to 3-fold increase, in ob mRNA expression and substantial obesity was required to increase it further. Ob protein mRNA level appealed to be higher in depots which exhibited adipocyte hypertrophy rather than hyperplasia. This is consistent with reports that ob mRNA levels are higher in large adipocytes than in newly differentiated cells.