Zelena, Dóra, Ludmila Filaretova, Zsuzsa Mergl, István Barna, Zsuzsanna E. Tóth, and Gábor B. Makara. Hypothalamic paraventricular nucleus, but not vasopressin, participates in chronic hyperactivity of the HPA axis in diabetic rats. Am J Physiol Endocrinol Metab 290: E243-E250, 2006. First published September 6, 2005 doi:10.1152/ajpendo.00118.2005.-Diabetes mellitus (DM), as chronic stress activates the hypothalamopituitary-adrenocortical axis. We examined whether arginine vasopressin (AVP) and the hypothalamic paraventricular nucleus (PVN) participate in DM-induced chronic stress symptoms. AVP-deficient Brattleboro or PVN-lesioned Wistar rats were used with heterozygous or sham-operated controls. The rats were studied 2 wk after a single injection of streptozotocin. The appearance of DM (enhanced water consumption and blood glucose elevation) and the chronic stress-like somatic changes (body weight decrease, thymus involution, adrenal gland hypertrophy) were not influenced by the lack of AVP. By contrast, PVN lesion significantly attenuated DM-induced thymus involution and adrenal gland hypertrophy as well as the increase in water consumption. The corticotropin-releasing hormone mRNA in PVN was diminished by DM and elevated by the lack of AVP without interaction. DM elevated the proopiomelanocortin (POMC) mRNA in the anterior lobe of the pituitary. The lack of AVP had no effect, whereas lesioning the PVN significantly diminished the elevation. The elevated basal corticosterone plasma levels detectable in DM were influenced neither by the lack of AVP nor by lesioning the PVN. Thus the lack of AVP had no influence on DM-induced chronic stress symptoms, but lesioning the PVN attenuated part of them. However, the lack of elevation in POMC mRNA after PVN lesion, together with the maintained corticosterone elevation, suggests that direct adrenal gland activation occurs in untreated DM. chronic stress; Brattleboro rats; corticosterone; proopiomelanocortin; corticotropin-releasing hormone; diabetes mellitus; hypothalamopituitary-adrenocortical axis DIABETES MELLITUS (DM) is an endocrine disorder that is quite common in developed countries (17). Inadequate insulin secretion and insulin resistance with inadequate compensatory insulin release are the main reasons for DM development. The use of toxic agents that destroy -cells in the pancreas and lead to insulin deficiency, such as streptozotocin (STZ), produces a model of DM in animals (36). The most frequent symptoms of DM are blood glucose level elevation, polyuria, polydipsia, and weight loss. However, the long-term disorder can cause many other complications, including cardiovascular, cerebrovascular, or renal ones.Long-term DM as a chronic stress may also induce a dysfunction of the hypothalamo-pituitary-adrenocortical (HPA) axis. A tight connection between HPA axis activity and blood glucose regulation is well known (9, 12). The HPA axis is responsible for the production of glucocorticoids, which are important adaptive hormones. Glucocorticoid hormones participate...