Effect of splanchnic denervation on plasma vasopressin (PAVP) and FOS immunoreactivity in response to intragastric hypertonic saline in conscious rats

Studies have suggested peripheral control of PAVP release in the rat, however the afferent pathway mediating this response is unclear. We recently demonstrated that intragastric Hypertonie, but not isotonic, saline increases PAVP without affecting plasma osmolality (POSM). Additionally, fos immunoreactivity was increased in several central nuclei, including the nucleus tractus solitarius (NTS), area postrema (AP), lateral parabrachial (LPBN), supraoptic (SON) and paraventricular (PVN) nuclei. To test whether peripheral control is mediated via splanchnic afférents, we examined the effects of bilateral splanchnic denervation (SDx) on the PAVP and fos immunoreactivity response to intragastric hypertonic saline. Sham (n=7) or SDx (n=6) rats received a five minute intragastric infusion of hypertonic saline (600 mOsm/L; 0.59 ml/min.). In sham rats, hypertonic saline increased PAVP (2.7 ±0.5 to 4.6 ±0.4 pg/ml; P < 0.05) without changing POSM, and fos immunoreactivity was observed in the NTS, AP, LPBN, SON and PVN nuclei. The SDx group showed similar increases in PAVP (2.2 ±0.4 to 4.7 ±0.6 pg/ml; P < 0.05) in absence of changes in POSM. However, fos immunoreactivity was reduced in the NTS and AP, while levels in the LPBN, SON and PVN were unaffected. These results indicate that peripheral control of PAVP docs not involve splanchnic afférents, although the splanchnic nerve may contain peripheral osmoreceptor afferent projections to the NTS and AP.