Effects of betamethasone on the stimulation of corticosterone secretion in rats.

The effects of betamethasone on the elevation of rat plasma corticosterone levels by nicotine (400 microgram/kg s.c.), urethane anaesthesia and psychological stress have been studied. Betamethasone pretreatment (5 mg/kg given in the drinking water over 24 hr) initially suppressed the response to all three stimuli but, after 24 hr, only the response to urethane remained totally suppressed. Nicotine administered at this time to the urethane anaesthetised rats caused an increase in plasma corticosterone, apparently by stimulation of the autonomic nervous system. The results suggest that, following betamethasone, there is a prolonged delay in the recovery of the specific mechanism through which urethane stimulates pituitary-adrenal function rather than a total blockade of the effects of all stressful or chemical stimuli on ACTH secretion.