A method for studying acute insulin secretion and glucose tolerance in unanesthetized and unrestrained rats. The effect of mild stress on carbohydrate metabolism.

A technique is described for glucose infusions and for frequent sampling of small quantities of blood in unrestrained and unanesthetized small laboratory animals. Under pentobarbital anesthesia, polyethylene catheters were implanted into the jugular vein and the aorta, and distal ends were exteriorized on the back of the neck of 250-gm. rats. Five to seven days following surgery the rats regained weight and were in a normal anabolic state, despite indwelling catheters. On the day of the intravenous glucose tolerance test (ivGTT), the exterior ends of the indwelling jugular and aortic catheters were connected to specially prepared extension catheters, through which a glucose pulse was given and frequent blood samples in small quantities were collected, respectively. During the entire procedure, the animals were resting quietly, unrestrained and unanesthetized. In another group of similar rats with indwelling catheters, ivGTT was performed after they were restrained in plastic restrainers. During the ivGTT, serum glucose levels were significantly higher in the restrained rats than those observed in the control rats. The mean glucose disposal rate (K) of 2.2 +/- 0.2 was significantly slower in restrained rats than the K of 3.0 +/- 0.3 in unrestrained rats. Following the glucose pulse, insulin secretion was significantly lower in restrained rats than that observed in the unrestrained rats. These observations emphasize the importance of controlling the modifying effects of mild stress on glucose tolerance and insulin secretion.