SYMPATHETIC NERVOUS-SYSTEM INFLUENCES SALT APPETITE IN 4 STRAINS OF RATS

Sodium appetite and preference were examined in four rat strains using a social stressor and drugs to block sympathetic nervous system (SNS) activity. We have studied these strains for over 14 yr in our laboratory and the SHR strain has increased blood pressure and increased sympathetic nerve activity. The F-1 crosses produce male offspring with the Y chromosome from a hypertensive or normotensive father, to examine its influence on sodium appetite. The pharmacological manipulation produces blockage of the SNS which may be partially responsible for stress induced sodium appetite. The objectives were to determine: (i) if the SNS was necessary for stress induced increased salt appetite; and (ii) if the Y chromosome from a hypertensive father increased salt intake or preference. Four strains (n = 6-8/group) of male rats were studied from 3-6 mo of age: normotensive Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and hybrid crosses between a WKY mother and SHR father (WS) and the reciprocal cross (SW). Each group consumed Purina rat chow (0.3% Na) and was given a four-bottle choice of salt water ad lib (0.0%, 0.5%, 1.0%, and 1.5% NaCl). Social stress produced by intruder males significantly increased salt intake in all groups. SHR had higher salt intake than WKY both before and after exposure to intruder stress. In general, the SHR group preferred twice the concentration of saline (1.0%) as did the WKY (0.5%). Clonidine and reserpine both reduce SNS activity and consequently reduced salt intake after stress, from 20-44% depending on the genetic background of the rat strain. The SNS was necessary for stress induced increased salt appetite and the Y chromosome from a hypertensive father did not elevate salt appetite.