RELEASE OF ANGIOTENSIN IN THE PARAVENTRICULAR NUCLEUS IN RESPONSE TO HYPEROSMOTIC STIMULATION IN CONSCIOUS RATS - A MICRODIALYSIS STUDY

Angiotensin peptides are thought to act as neurotransmitters or neurom odulators in central osmoregulation. We tested the hypothesis that ang iotensin peptides are released in the paraventricular nucleus (PVN) of the hypothalamus upon local osmotic stimulation. Brain microdialysis and radioimmunoassay (RIA) techniques were used to measure the release of immunoreactive angiotensin II (irANG II) in the PVN following dire ct stimulation of this area with hyperosmotic solutions. In conscious rats, perfusion of the PVN with 0.3 M and 0.6 M NaCl in artificial cer ebrospinal fluid (aCSF) elicited concentration-dependent increases in irANG II release to 5.52 +/- 0.53, (P < 0.01, n = 8) and 9.01 +/- 1.03 pg/100 mu l, (P < 0.001, n = 7), respectively, from basal values of 3 .04 +/- 0.46 pg/100 mu l. Local perfusion of the PVN with 1.2 M glucos e in aCSF also resulted in an increased release of irANG II from 3.07 +/- 0.87 to 6.24 +/- 0.45 pg/100 mu l (P < 0.05, n = 5). Fractionizati on of angiotensin peptides by HPLC followed by RIA revealed that ANG I I (1-8) and ANG III (2-8) were released in similar amounts in the perf usate collected during 0.6 M NaCl stimulation (4.79 +/- 0.69 and 3.45 +/- 0.76 pg/100 mu l, respectively). Our results show that both, ANG I I and ANG III are released in the PVN in response to local hyperosmoti c stimulation. They support the concept that angiotensin peptides in t he PVN are involved as neurotransmitters in central osmotic control.