EFFECTS OF ACUTE HYPOTENSIVE HEMORRHAGE ON ARGININE-VASOPRESSIN GENE-TRANSCRIPTION IN THE RAT-BRAIN

To determine whether hypotensive hemorrhage has an effect on arginine vasopressin (AVP) gene expression, 16 ml/kg of arterial blood was draw n over 10 min in conscious unrestrained rats. Mean arterial blood pres sure (MABP) and heart rate (HR) were measured, and the rats were decap itated before and 10 min, 1, 3, 6, 9, 12, and 24 h after the initiatio n of hemorrhage. The hypothalamic or cerebro-hypothalamic tissue was u sed to measure AVP mRNA by Northern blot analysis, and the trunk blood to measure plasma AVP, osmolality and hematocrit. Hemorrhage brought about rapid and transient decreases in MABP and HR accompanied by tran sient increases in plasma osmolality and AVP. Hematocrit decreased aft er the bleeding and reached a stable level 6 h after hemorrhage and th ereafter. AVP mRNA was detected in the hypothalamus and not in the ext rahypothalamic cerebral brain tissue under basal and posthemorrhage co nditions. AVP mRNA in the cerebro-hypothalamic tissue increased by 1.8 -fold at 6 h and 2.1-fold at 9 h after hemorrhage. These results indic ate that AVP mRNA in the brain increases 6 h after increased AVP relea se in response to hypotensive hemorrhage.