Human beings must adapt both to novel, unfavourable conditions and to circumstances of physical or psychological isolation. The initial response to stress depends fundamentally on the activation of the HPA axis. In regaining homeostatic equilibrium,
melatonin plays a role due to its synchronising and anti-stress properties. To study the role of
melatonin and the pineal gland in the organic and/or behavioural response to acute or chronic stress, 311 children were divided into two large groups: 1) Control Group - 121 healthy children classified, in turn, into 4 control subgroups, one for each pathology being studied; 2) Problem Groups, classified as traumatic stress (n=58), surgical stress (n=38), psychic stress (n=64) and febrile stress (
n=30), according to pre-established clinical criteria. These groups were sub-classified according to the degree (low or high) and duration (acute or chronic) of the stress. This study used a case controlled, cross sectional design. Serum
melatonin was measured by radioimmunoassay (RIA). In all the situations of acute stress,
melatonin increased at a rate directly proportional to the severity and/or duration of the stress-causing stimulus. In contrast, in chronic stress, i.e. the Affective Deprivation Syndrome (or Psychological
Dwarfism) with or without non-organic
failure to thrive, resulted in the opposite response with a significant reduction of
melatonin. In conclusion, in acute stress an increase in the bioavailability of
melatonin could contribute to maintaining homeostatic balance. The lack of an appropriate response to acute stress could make some groups of patients (Affective deprivation syndrome with or without growth failure) predisposed to suffer depressive symptoms associated with a wide range of neurological, endocrinological or immunological consequences.