Effects of isolation, handling and restraint on growth of rats

The effects of 3 environmental conditions on physical growth and skeletal maturation were assessed in pair-fed rats. Rats subjected to restraint from ages 28 to 80 days weighed less and were shorter than pair-fed like-sex controls; skeletal maturation was unaffected. The observations cannot be attributed to handling, as those animals were heavier than their controls, or to isolation, which was found to be without effect on any of the measurements. The adverse effects of restraint on physical growth are attributed to increased adrenal cortical activity, reflected in increased adrenal weight.