The role of vasopressin in chronic stress studied in a chronic mild stress model of depression.

BACKGROUND AND PURPOSE: Vasopressin plays an important role in the hypothalamo-pituitary-adrenal axis regulation as well as in stress-related disorders. A common view suggested that the role of vasopressin is especially important during chronic stresses. Here we tested the hypothesis that vasopressin-deficient rats may be more resistant to the development of chronic hypothalamo-pituitary-adrenal axis hyperactivity after chronic mild stress.

METHODS

Male vasopressin deficient Brattleboro rats were compared to their heterozygous litter mates. Chronic mild stress consisted of different mild stimuli (e.g. wet cages, restraint) for 6 week. The corticosterone changes were followed by repeated tail cutting and organs and blood were collected from decapitated rats.

RESULTS

In controls, chronic mild stress resulted in symptoms of chronic stress state characterized by typical somatic (body weight reduction, thymus involution) and endocrine changes (resting plasma ACTH and corticosterone elevation and POMC mRNA elevation in anterior lobe of the pituitary). Unexpectedly, the lack of vasopressin could not influence any chronic mild stress-induced changes.

CONCLUSION

Somatic changes and endocrine effects of chronic mild stress are similar in control and vasopressin deficient animals. This suggests that either vasopressin is not indispensable for activating the hypothalamo-pituitary-adrenal axis by chronic stress or the absence of vasopressin is compensated by other mediators (e.g. CRH) in Brattleboro rats.