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 drawn over 10 min in conscious unrestrained rats. Mean arterial blood pressure (MABP) and heart rate (HR) were measured, and the rats were decapitated before and 10 min, 1, 3, 6, 9, 12, and 24 h after the initiation of hemorrhage. The hypothalamic or cerebro-hypothalamic tissue was used 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 transient increases in plasma osmolality and AVP. Hematocrit decreased after the bleeding and reached a stable level 6 h after hemorrhage and thereafter. AVP mRNA was detected in the hypothalamus and not in the extrahypothalamic cerebral brain tissue under basal and posthemorrhage conditions. 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 indicate that AVP mRNA in the brain increases 6 h after increased AVP release in response to hypotensive hemorrhage.