[Neurohumoral mechanisms for vasovagal syncopes. Part I].

Vasovagal syncope is defined as a reflex loss of consciousness related to reaction to various stimuli as orthostatic stress, pain or emotions connected with loss of muscle postural tone. The aetiology of this disorder is still unknown. The imbalance between the parts of autonomic nervous system and other homeostasis-related systems as renin-angiotensin-aldosterone system, peptides as endothelin, neuropeptide Y, vasopressin, adrenomedullin and cAMP, adenosine and AMP can play an important role in the development of vasovagal syncope. In the first part of the paper the authors describe the mechanisms involved in the development of vasovagal reaction, pathophysiology of the head-up tilt test and the role of autonomic nervous system.