A NOVELTY-RELATED SUSTAINED ELEVATION OF VASOPRESSIN PLASMA-LEVELS INYOUNG MEN IS NOT ASSOCIATED WITH AN ENHANCED RESPONSE OF ADRENOCORTICOTROPIC HORMONE (ACTH) TO HUMAN CORTICOTROPIN-RELEASING FACTOR (HCRF)

A comparative study of the effects of intravenously administered corti cotropin releasing factor (i.e. exogenous CRF), in the absence or pres ence of simultaneous opioid receptor blockade, versus stress (i.e. end ogenous CRF) on plasma adrenocorticotropic hormone (ACTH), cortisol an d vasopressin (AVP) was carried out in ten healthy men (mean age 35.6 +/- 9.5 years) using an intra-individual repeat setting. Three differe nt stimuli were applied blindly and in random order, one per day, in a 3-day experimental block: (1) human (h)CRF; (2) hCRF/naloxone; and (3 ) a combined multifaceted 5-min stress test. A second block, following the same protocol, was carried out 12 weeks later. Each experimental day lasted from 0700 to 1500 hours, with subjects remaining supine thr oughout. ACTH and cortisol levels each responded with significant peak s to all three stimulating conditions in both blocks while AVP levels remained unaffected by any of these stimuli. Unexpectedly, in five of the ten subjects significantly elevated AVP basal concentrations were measured throughout the first block. This phenomenon appeared to be ag e-related, being observed in younger men only (29.6 +/- 5.2 vs 41.6 +/ - 9.2 years; p = 0.03) and was not paralleled by changes in plasma osm olality or blood pressure. In the second block, AVP levels were low an d no longer different between younger and older subjects. ACTH and cor tisol curves did not differ among subgroups nor between blocks. In con clusion, plasma AVP, in contrast to ACTH, is not acutely influenced by either endogenous or exogenous CRF. However, anticipation of novelty seems to be a human-specific, stress-related stimulus for a sustained elevation of plasma AVP in young men. This novelty-related continuous elevation of AVP levels reported here neither affected basal plasma AC TH nor acted synergistically with exogenous hCRF to increase circulati ng ACTH.