A metabolism chamber for measuring oxygen consumption in the laboratory rat and mouse

Details are given for the construction and use of an inexpensive metabolism chamber to measure oxygen consumption in a relatively large group of laboratory rodents in a brief time. Metabolic rates (MR) were measured regularly in male and female Sprague Dawley rats, 11-114 days old, and mice, 100 days old. Adult mice had higher MR than rats of approximately the same age. Female rats and mice had higher MR than males at all times. To demonstrate the versatility of the metabolism chambers adult rats were injected once or for 9 consecutive days with 6-n-propyl-2-thiouracil (PTU) to inhibit thyroid function and reduce MR, or with the carboxymethylcellulose (CMC) vehicle. PTU failed to lower MR in the animals most probably because CMC vehicle tended to increase MR, an effect more prominent in males than females.