Reactivity of vascular smooth muscle in hypertensive rats.

The reactivity of vascular smooth muscle in helical strips from femoral arteries of normotensive, spontaneously hypertensive, renal hypertensive, and deoxycorticosterone acetate— (DCA-) hypertensive rats was studied. Spontaneous rhythmic contractions occurred in 25 of the 30 strips from the three groups of hypertensive rats and in only 2 of the 10 strips from normotensive rats. Strips from renal and DCAhypertensive rats had lower thresholds to epinephrine and potassium chloride (KC1) than did strips from spontaneously hypertensive and normotensive rats. Lanthanum (2.5 HIM) caused contraction of all 10 strips from spontaneously hypertensive rats but failed to cause contraction of any strip from the other three groups of rats. Strontium (5 mvc) caused contraction in 8 of 10 strips from spontaneously hypertensive rats but caused contraction in only 7 of the 30 strips from the other three groups. The optimal calcium concentration for tension development in response to a KC1 stimulus was approximately twice as high for strips from hypertensive rats as it was for strips from normotensive rats. Strips from DCA-hypertensive rats showed less tachyphylaxis to angiotensin II than did strips from the other three groups of rats. These results quantify our earlier observation that the reactivity of vascular smooth muscle from hypertensive rats is importantly different from that of normotensive rats. In addition, the study delineates individuality in vascular smooth muscle reactivity in different types of experimental hypertension. The results suggest that the cell membrane of the vascular smooth muscle in the hypertensive rat is more labile than that in the normal rat.