Abstract
Recently, several new atypical actions of circulating oxytocin are emerging, which
may be of importance for the physiological effects of oxytocin released during stress.
However, little information is available on oxytocin response to chronic stress stimuli.
The aim of the present study is to deepen the knowledge on oxytocin secretion during
chronic and repeated stress. The main hypothesis to be tested was that oxytocin release
in response to single and to repeated or chronic stress is of different kinetics.
Adult male Sprague-Dawley rats were exposed to 2 different stress stimuli or their
combination. Restraint (immobilization) of different duration (10–120 min) and number
of repetitions (1 or 7 times) as well as chronic exposure (28 days) to cold temperature
were used. Concentrations of oxytocin in plasma and posterior pituitary were measured
by a radioimmunoassay. Concentrations of oxytocin in plasma increased significantly
in response to both single and repeated immobilization. Acute immobilization caused
rapid increase already after 10 min of restraint, while the recovery occurred only
after 24 h. Repeated restraint caused delayed onset of increased oxytocin release
and a more rapid recovery to prestress levels after 3 h. In conclusion, the results
of the present study show that though with a different kinetics, increased oxytocin
release is preserved during repeated exposure to an intensive stressor, namely immobilization
for 120 min. During repeated exposure to shorter stressors, an adaptation in oxytocin
responses may occur. This should be taken into account with respect to cardiovascular
and metabolic effects of stress-induced oxytocin.
Key words
hormone - immobilization - ambient temperature
