Figure 1.

Experimental protocol for studying the effects of 1,25(OH)₂D₃ on the development of insulin resistance in MSG-obese rats. MSG-obese rats were rendered by s.c. injection of MSG (4 g/kg/day) to newborn Wistar rats for seven successive days. (A) In protocol A, four-week-aged MSG rats were given s.c. injections of 1,25(OH)₂D₃ (1 g/kg, twice a week) for 16 weeks and an insulin tolerance test (ITT) and the euglycemic hyperinsulinemic clamp were conducted at the end of experiment to measure the incidence of insulin resistance. (B) In protocol B, the obese MSG rats were divided into three groups according to body weights and fasting plasma glucose values and were respectively treated with 1,25(OH)₂D₃ (1 g/kg, twice a week), rosiglitazone (4 mg/kg/day), or vehicle for 8 weeks.