Rapid and sensitive vasopressin heteronuclear RNA responses to changes in plasma osmolality

The plasma concentration of arginine vasopressin (AVP) is closely regulated by plasma osmolality. In this study, we used intronic in-situ hybridizatio n to investigate the transcriptional activity of the AVP gene in the suprao ptic nucleus (SON) and paraventricular nucleus (PVN) after intraperitoneal (i.p.) injection of hypertonic saline inducing small changes in plasma osmo lality in rats. After ip injection of 900 mOsm/kg saline (2% BW), plasma [N a] reached the highest level at 10 min (900 mOsm/kg, 146 +/- 1 mEq/l; 290 m Osm/kg, 139 +/- 1 mEq/l, P < 0.01) and maintained that level until 30 min. The expression of AVP heteronuclear (hn) RNA in the SON and PVN increased s ignificantly as early as 10 min and peaked 30 min after ip injection of the hypertonic saline. AVP hnRNA expression showed a significant increase even after a 2 mEq/L elevation in plasma [Na] concentration, and increased dose -dependently in response to the concentration of saline injection (290-900 mOsm/kg). These results demonstrate that, similar to AVP secretion, AVP gen e transcriptional activity in the SON and PVN is closely regulated by plasm a osmolality.