Hypertension induced by repeated stress: possible participation of sympathetic-adrenomedullary catecholamines

Several groups of male Wistar rats weighing 250-300 g were subjected to immobilization stress (IMO) for various intervals (2.5 h to 19 h daily omitting weekends for a total of 2 to 15 weeks). Blood pressure (BP) was measured with the aid of indirect cuff pressure method under routine conditions once weekly during the whole period of immobilization and in some groups also for 10 weeks after the end of this period. It was found that BP significantly increased after 2 weeks of 2.5 h IMO daily and progressively increased later on. There was an indirect relationship between the duration on individual intervals of IMO and the period which was necessary to develop a significant increase of BP. Adrenal medullectomized animals showed a significantly less increase of BP than normal ones during 16 weeks course of IMO. The level of adrenaline and noradrenaline was significantly increased in animals having 24-hour rest after 39th IMO compared to controls, the blood being taken by chronically implanted cannula in a tail artery.