Reversal of high-fat diet-induced obesity in female rats.

The purpose of the present study was to test whether the degree of obesity or the duration of the obese state affects the reversibility of diet-induced obesity. This was accomplished by initially feeding adult female Wistar rats either a low-fat diet (Chow) or one of two high-fat diets (HFDs; 30 and 60% of total calories as dietary fat; 30% HFD and 60% HFD, respectively). Fifty-four days, reversal 1 (R1), or ninety-seven days, reversal 2 (R2), later the HFDs were substituted with the low-fat control diet in subgroups of rats. Animals from all groups were sampled at three intervals: the start of R1 (R1 start), and the completion of R1 (R1 end) and R2 (R2 end). At the end of each interval the 60% HFD-fed group had increased body weight, carcass lipid content, and retroperitoneal and parametrial white adipose tissue (RWAT and PWAT) pad weight, fat cell diameter, and fat cell volume, but not fat cell number (FCN), compared with the other groups. The 60% HFD-fed rats also exhibited a marked and persistent hyperphagia that continued even as most of the indexes of obesity approached their maximal values (R1 end). The 60% HFD group had a transient increase in RWAT and PWAT lipoprotein lipase activity that followed the development of most obesity indicators. A clear intermediate level of obesity did not develop in the 30% HFD-fed group. Instead, these animals had nonsignificant increases in these measures of adiposity, making it impossible to test whether the severity of the obesity affected its reversibility in age-matched groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of diabetes and insulin on photoperiodic responses in Siberian hamsters.

Short day pineal melatonin secretion patterns cause gonadal regression in Siberian hamsters, an effect due to alterations in gonadotropin secretion that ultimately affects the gonads. An analogous endocrine response sequence may underlie short day (melatonin)-induced decrease in body weight (fat) in this species. A potential mediating hormone for this effect of melatonin may be insulin. The purpose of the present experiments was to determine whether alterations in insulin status might affect the photoperiodic control of body weight (fat) and reproductive condition. Insulin was controlled by inducing experimental diabetes mellitus via injections of streptozotocin across several days, followed by treatment with one of two doses of long-lasting insulin. Both insulin doses normalized urinary glucose, but not body weight in long days. Seven weeks of short day exposure caused gonadal regression in all groups regardless of insulin status. The magnitude of the short day-induced decrease in body weight and carcass lipid was directly related to long day baseline body weights; however, the body weight nadir reached was similar among the groups. A 'regulation' of seasonally appropriate body weight (fat) is implied by these findings.