Search

This study was undertaken to investigate the changes of ambulatory activity and dopamine turnover (DOPAC/DA ratio) in streptozotocin (STZ 60 mg/kg ip)-induced diabetic rats employing the Gunma University-type special apparatus. A significant decrease in ambulatory activity was observed during the dark phase but not during the light phase 1 month after administration of STZ. Moreover, through the precise observation during light phase, we have found out that a significant decrease compared to control periods was observed during 9:00 to 12:00, whereas increase during 12:00 to 15:00 and 5:00 to 18:00 in the diabetic rats. In addition, a significant decrease in dopamine turnover compared to control rats was seen during dark phase (20:00), when significantly decreased ambulation was observed in the diabetic rats compared to control rats. However, no difference in dopamine turnover was observed during light phase (8:00), when ambulation was not significantly different from both groups. These results may suggest that fluctuation in dopamine turnover may be closely related to the ambulatory activity in STZ-induced diabetic rats.

The effect of estrogen supplement on selective D2 receptor antagonist sulpiride induced weight gain was examined in ovariectomized (ovx.) rats. Sulpiride injection (10 mg/kg, s.c.) showed a significant increase of body weight and food consumption only in female rats. Bilateral ovariectomy completely abolished the weight gain and hyperphagia by sulpiride. Subcutaneous injection of estradiol benzoate (E2:5 micrograms/day, s.c.) for 14 days restored the effects of sulpiride on weight gain in ovx, rats and sulpiride injection with E2 supplement significantly increased the efficiency of food utilization. The present study suggested that estrogen should be involved in the induction of overweight and hyperphagia by sulpiride.

We tested the hypothesis that altered heat production ability after ovariectomy may be involved in the development of obesity. Two weeks after ovariectomy, food intake of ovariectomized (Ovx) rats was increased and body weight gain was obvious, compared with sham-operated animals. However, colonic temperature of Ovx rats was not different from that of sham-operated animals. Food intake of Ovx rats was similar with that of sham-operated rats at 8 weeks later. In this period, colonic temperature of Ovx rats was not different from that of sham-operated animals and diurnal rhythmicity was maintained. The present data suggested that changes in heat production may be not an important inducer of obesity in both the dynamic and static phases of the development of obesity after ovariectomy.

Changes of colonic temperature were investigated to examine a mechanism of hypothermia in the obese rats which received subcutaneous administration of intermediate type-insulin (8 U/day) for 8 weeks. Although diurnal rhythmicity of colonic temperature levels was maintained similarly with those of vehicle-injected controls, the overall colonic temperature levels were significantly lowered in insulin-treated animals. In the condition of cold exposure at 5 degrees C, colonic temperature levels of insulin-treated animals were immediately and significantly decreased at 60 minutes after the start of cold exposure. The data obtained herein demonstrated that hyperinsulinemia accompanying with hyperphagia should be profoundly involved in hypothermia, observed in various experimental models of obesity.