SINOAORTIC DENERVATION ALTERS THE MOLECULAR AND ENDOCRINE RESPONSES TO SALT LOADING

Neuroanatomical and physiological evidence indicates that baroreceptors influence hypothalamic vasopressin (VP) and oxytocin (OT) neurons. We evaluated the effects of sinoaortic denervation (SAD) on the molecular and endocrine response to salt loading. Sham-operated or SAD rats were given a 2% NaCl solution to drink for 72 h. A group with limited salt water intake was included as a second control because the denervated rats consumed less salt than the controls. Plasma VP, OT and osmolality and posterior pituitary peptide content were measured. Brains were processed for evaluation of VP and OT m RNA expression using in situ hybridization with computer quantitation. Salt loading produced equivalent increases in plasma VP and OT in the control and SAD groups, however, there was a greater depletion of posterior pituitary peptides in the denervated animals. Salt loading produced significant decreases in pituitary VP and OT in the SAD animals, 69.8 +/- 8.4% and 68.3 +/- 4.0%, respectively. In the control groups, there was no decrease in VP content and a decrease in OT only in the control ad lib group. The peptide mRNA response to salt loading was also altered in the denervated rats. There was a significant increase in the area and intensity of the labeling for OT mRNA in the PVN in the SAD salt group. The control salt rats showed an increase in the SON and the salt-limited group showed no changes. For VP mRNA, the only change noted was in the SON of the salt-loaded SAD animals. These results show that chronic denervation of arterial baroreceptors augments the hypothalamic VP and OT response to salt loading. This is reflected in a greater depletion of pituitary peptides and by changes in hypothalamic message levels. The results suggest that the denervated animal is hypersensitive to salt stimuli, resulting in a greater activation of the central OT and VP axis.