Basal Gaseous Metabolism of Giant Rats

Gigantism can be produced in rats by the administration of extracts of the anterior lobe of the pituitary. 1 We have determined the basal gaseous metabolism in 4 such giant rats and have compared their metabolic rates with those of 4 control females of the same age and the same Wistar strain.

The rats were approximately 11 months old at the beginning of the metabolism determinations. Since the age of 7 months, each of the experimental animals had received daily parenteral injections of 1 cc. of a neutralized alkaline extract of fresh beef anterior lobe containing the growth promoting principle. 2 During the period of the metabolism determinations the weight range of the injected rats, before being starved, was from 350 to 530 gm. The largest of the control rats were selected in order to obviate as much as possible the effect of size per se on metabolism. Their weights ranged from 200 to 270 gm. The increased size and weight of the injected animals is apparently due to the greater bone, muscle and skin development and to the considerable increase in size of most of the viscera, especially the liver. Body fat does not appear to be increased. Despite the obvious general overgrowth, the body lengths of the injected rats averaged less than 10% more than those of the controls.

Metabolic rate determinations were made by the oxygen consumption closed circuit method at weekly intervals. Each determination represents the average rate, in several tests, over a 3 to 4 hour period, and 18 to 22 hours after the last ingestion of food. All tests included were considered satisfactory from a technical standpoint. Body surface was calculated from the formula 3 Rat 62 was sacrificed for direct measurement of the skin area, which was found to be only 4% greater than that predicted by the formula. Respiratory quotients were found to be nearly 0.72 in both the injected and control starved rats.