Food related intravenous insulin self-administration in normal and diabetic rats

A chronic cardiac catheter was used to provide evidence for the ability of rats to perform intravenous insulin self-administrations. All rats tested rapidly learned to press a lever delivering a solution of regular insulin. The insulin self-injection, lasting several weeks, indicated a pattern specific to this hormone which differed from that of saline self-administration. On the average the daily amount of self-injected insulin was fivefold that of saline. Ninety percent of the daily insulin intake (versus 50% of the saline) were periprandially injected at the time of the meal and particularly just after the meal. The periprandial self-injected insulin positively correlated with the meal size. Fasted rats exhibited an immediate drop in the amount of the self-administered insulin. Upon discontinuation of the insulin delivery, the rats continued to press the inoperant lever with the same previously established meal-related pattern. Under insulin self-administration, the daily food and water intake did not increase and the body weight gain was not different from that of controls. In diabetic rats, previously trained on insulin self-injection, the transitory increase in the daily insulin intake was observed which later stabilized to a level lower than the pre-diabetic one. Results are discussed in relation to the reinforcing property of insulin and to neuroendocrine mechanism of food intake.