Response of the adrenomedullary system to early postnatal stress in the Brattleboro rat.

The sympathetic-adrenomedullary system and the pituitary-adrenocortical axis are linked to each other by chemical signals transferring information between both endocrine systems. Here we addressed the question of whether the neuropeptide arginine vasopressin (AVP) is involved in this type of information transfer during early postnatal development. The impact of congenital absence of AVP on the endocrine stress response was investigated using the AVP-deficient Brattleboro rat. Under resting conditions, we failed measure a significant difference in plasma norepinephrine levels between 10-day-old AVP-deficient homozygous juveniles versus heterozygous AVP-producing littermates. Interestingly, repeated ether exposure resulted in a reduction of plasma epinephrine levels in both genotypes. In the adrenal, we detected increased levels of the epinephrine-synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT) after ether inhalation in vasopressin-deficient pups only. These data provide insight into the development of the regulation of stress-related epinephrine secretion during ontogenesis. Furthermore, our results imply that the congenital absence of AVP affects the synthesis of PNMT in response to defined stressor exposure.