Effects of acute hypotensive stimuli on arginine vasopressin gene transcription in the rat hypothalamus

We investigated the baroregulation of arginine vasopressin (AVP) gene trans cription in the supraoptic (SON) and paraventricular nuclei (PVN) in consci ous rats by use of intronic in situ hybridization. Hemorrhage of 16 ml/kg b ody wt decreased mean arterial pressure (MAP) by 57% and increased both pla sma AVP (control, 1.2 +/- 0.3 pg/ml; 16 ml/kg body wt, 38.9 +/- 3.2 pg/ml) at 10 min and AVP heteronuclear (hn) RNA levels (SON, 150%; PVN, 140% of co ntrol values) at 20 min. On the other hand, hemorrhage of 7 ml/kg body wt h ad no significant effect on MAP, plasma AVP, or the AVP hnRNA levels. To be tter understand the baroregulation, we also examined the effects of sodium nitroprusside (SNP), which induces hypotension without a change in blood vo lume. The subcutaneous injection of 2 mg/kg body wt SNP, which decreased th e MAP by 60%, increased both plasma AVP (control, 1.6 +/- 0.4 pg/ml; 2 mg/k g body wt, 8.1 +/- 0.4 pg/ml) at 10 min and AVP hnRNA levels (SON, 150%; PV N, 140% of control values) at 30 min. The injection of 0.1 mg/kg body wt SN P, which reduced the MAP by 10%, failed to increase either the plasma AVP o r AVP hnRNA levels. These results indicate that AVP gene transcription incr eases rapidly after both hypotensive hemorrhage and normovolemic hypotensio n. In addition, it is suggested that the set point for AVP synthesis in the baroregulation is similar to that for AVP release.