On the mechanism of activation of the hypothalamo-pituitary-adrenal reaction to changes in the environment (the ‘alarm reaction’)

Abstract

The amount of circulating noradrenaline increases considerably in parallel with an improvement in cardiovascular haemodynamics in adrenalectomized rabbits after intravenously injected hydrocortisone. In view of this finding, that as well as a constant regulation with negative retroaction of the corticotrophic-releasing factor-adrenocorticotrophic hormone (ACTH)—cortisol system, there exists an externally controlled servomechanism from nervous system activity related to the environment. Hydrocortisone favours passive avoidance, extinction and facilitates the activity of the chohnergic inhibiting system; ACTH facilitates active avoidance and catecholaminergic activation. It has already been demonstrated that stimulation of the inhibiting system or inhibition of the activating system released noradrenaline from the peripheral nerves of an adrenal ectomized animal. It therefore seems that the early release of ACTH after aggression is capable of favouring locomotor activity in ‘flight or fight’. If the latter is effective, there is a return to the previous behavioural and endocrine balance. On the other hand, if ‘flight or fight’ should be ineffective, there arises a vicious circle with positive retroaction, because secondary secretion of glucocorticoids will maintain inhibition and considerable activity in the noradrenergic system. The significance of the alarm reaction and the secondary release of the mineralocorticoids are discussed as well as the central mechanism of allegedly psychosomatic, illness. Aggression, as well as the lesion it induces, causes a reaction from the organism subjected to aggression. This is a non-specific reaction to which Selye (1936) has drawn attention. This reaction sets the central nervous system in action, which activates the vegetative nervous system and the endocrine system through the hypothalamus and the pituitary gland. In the vegetative system and the vasomotor changes related to it, the alarm syndrome has to be understood as a way to induce flight or fight, which allows the organism to move away from the aggressor. When this behaviour is impossible or ineffective the vasomotor reaction is threatened and it is depressed or inhibited (Laborit, 1952). Resuscitation techniques involving central or peripheral inhibitors, such as lytic cocktails, neuroplegy or neuroleptanalgesia, derive from this concept. The neuro-endocrine significance of the alarm reaction is still not understood and resuscitation techniques are quite empirical in relation to it.