Effects of sodium ion and solution tonicity on reactivities of hypertensive rat aortic strips.

Abstract

Rats were rendered hypertensive by injecting DCA and feeding 1% NaCl solution in place of drinking water. Isometric tensions developed by strips of aorta from these rats, when exposed to a low concentration of epinephrine, were compared with tensions developed by strips from normotensive controls, under conditions of varying Na ion concentration and solution tonicity. Solutions with high Na ion concentrations (hypertonic), and normal solutions rendered equivalently hypertonic by the addition of sucrose, increased the reactivities of strips from normotensive rats, but decreased the reactivities of strips from hypertensive rats, to added epinephrine. The hypertensive rat strips manifested increases in tension in these solutions even prior to the addition of epinephrine, so that the subsequent smaller responses to epinephrine may have been related to these initial tension increases. Low sodium ion concentrations in hypotonic solutions, but not in isotonic solutions, decreased the reactivities of both hypertensive and normotensive rat strips. These results are interpreted to mean that aortas from hypertensive rats are so changed structurally and functionally, that they respond differently than do normal aortas to increased sodium ion concentrations and/or hypertonic solutions, as well as to epinephrine in such solutions.