Adaptation to restraint in the rat.

Use of telemetry in physiological research is still in early stages. Cardiovascular studies planned for gravitational work during the next few years on primates or squirrel monkeys depend on restraint devices. Two rat cardiovascular experiments (US Space Lab SLS I and SLS II) use unrestrained rats for resting cardiovascular measurements (chronic intravascular cannulas and implanted blood flow probes), but employ semi-restrained animals for microcirculatory investigations. Prior to weightlessness, these instrumented rats will be exposed a number of times to semi-restraint. In order to ascertain if there is adaptation to restraint (decreased toward normal of plasma stress hormones), the rats were exposed 18 times to restraint chambers, but the level of stress hormones stayed elevated.