Ageing alters intrahypothalamic release patterns of vasopressin and oxytocin in rats

The ageing process has been shown to have a profound impact on the hypothal amo-neurohypophysial system (HNS) and the hypothalamo-pituitary-adrenocorti cal (HPA) axis in humans as well as in rodents. Therefore, in this study, t he intracerebral and peripheral release patterns of both vasopressin and ox ytocin have been studied in aged male Wistar rats under basal conditions an d in response to ethologically relevant stressors, using intracerebral micr odialysis and chronic blood sampling techniques, respectively. Approximatel y a twofold higher basal release of arginine vasopressin (AVP) within the h ypothalamic paraventricular nucleus (PVN), but not within the supraoptic nu cleus (SON), was found in aged rats, whereas basal oxytocin (OXT) release d id not differ in comparison with young rats. With increasing age the rise i n intra-PVN release of both AVP and OXT was blunted in response to forced s wimming. In contrast, the intra-SON release of AVP was unrelated to age. Si multaneously recorded basal secretion of both AVP and OXT from the neurohyp ophysis into blood was increased in aged rats, with a blunted OXT response to swim stress. Opposed to that, plasma AVP levels remained unchanged in bo th groups. Basal plasma levels of corticotropin (ACTH) and corticosterone w ere elevated in aged rats, whereas stress-elicited ACTH and corticosterone responses were indistinguishable. These results indicate age-related change s in the HNS and HPA axis with an enhanced basal activity opposed to a blun ted response to stressors with increasing age. The increased basal release of AVP within the PVN suggests a role of intracerebral AVP in age-associate d alterations of HPA axis regulation.