SALT LOADING EFFECTS ON VASOTOCIN AND NITRIC OXIDE SYNTHASE
SYSTEMS IN QUAIL.
C.Castagna*, L.Plumari, C.Viglietti-Panzica, and G.C.Panzica.
Dept. Anatomy, Pharmacology and Forensic Medicine, Univ. of Torino,
I-10126 Torino, Italy
Previous studies in mammals have shown that vasopressin
(VP) colocalizes with nitric oxide (NO) synthase (NOS) in the magnocellular
secretory system and the number of NOS-ir neurons in the paraventricular
(PVN) and supraoptic (SON) nuclei of the rat increases after salt loading,
suggesting an involvement of NO in osmoregulation. In quail and fowl no
coexistence was found between vasotocin (VT) and NOS detected by means
of the histochemical reaction for NADPH-diaphorase, although close relationship
between VT-immunoreactive (VT-ir) and NOS-ir elements has been demonstrated.
To understand if chronic stimulation of quail VT system (a condition inducing
an increase of plasma VT levels and VT mRNA transcription in the avian
hypothalamus) could result in a different pattern of coexistence among
VT and NOS we have here studied the effect of prolonged salt loading on
quail VT and NOS hypothalamic systems.
Five male quail salt loaded with NaCl 2% in drinking water for 10 days
and five untreated male quail were perfused and cryostatic sections processed
for single and double immunocytochemistry to visualize VT (antibody from
D.A. Gray) and NOS (antibody from P.C.Emson) immunoreactivity.
The salt loading treatment increases the number, the size and the density
of VT-ir cells and decreases cell staining particularly in the periventricular,
SON, and PVN regions; moreover the number and the staining of hypothalamo-hypophyseal
fibers were also decreased. These morphological results could be related
to a massive release of VT following salt loading stimulation. Little or
no effect was detected in the extrahypothalamic VT-ir cell groups. The
treatment had apparently no influence on the NOS-ir elements and the double
immunofluorescence confirmed that even after a prolonged salt loading VT-ir
elements did not show colocalization with NOS.
Present data confirm our previous histochemical studies on the distribution
of NOS and VT elements in the quail magnocellular regions and, in contrast
to mammals, they suggest that, in quail, NOS system is not affected by
alterations of the salt balance, though quail VT system is influenced by
salt loading like the mammalian VP system. The physiological significance
of the hypothalamic NO system in higher vertebrates may hence show a high
interspecific variability.
Work supported by grants from MURST.