After inhibition of spontaneous tone, the contraction of spirally cut strips of aorta in response to norepinephrine was studied quantitatively in normotensive rats and in 4 different types of hypertensive rats. In no instance did the aortas of hypertensive rats show hypdrresponsiveness to norepinephrine. The majority of responses were entirely normal; in a ffew instances there was decreased responsiveness. In vivo studies which fail to consider the critical effect of an altered "base-line" state in hypertension may demonstrate "hyper-respdnsiveness" which is more apparent than real.
Administration of desoxycorticosterone and NaCl resulted in an increased sodium and potassium content of the aorta in rats becoming severely hypertensive. Equivocally hypertensive animals on this regimen showed smaller increases in sodium and a decrease in potassium. Sodium restriction prevented both hypertension and changes in arterial wall chemistry from occurring in rats receiving desoxycorticosterone. Hypertension per se may be fundamentally associated with an increased potassium and sodium content in artery, as experimental renal hypertension is characterized by a similar electrolyte alteration.
The ionic composition of the aorta of the rat was studied in ‘postdesoxycorticosterone’ hypertension, ‘adrenal regeneration’ hypertension, and the hypertension which persists after excision of an ischemic kidney. The development of hypertension as a result of each of these procedures was associated with an increase in intracellular sodium and potassium content of the aorta. These findings are similar to those obtained in other forms of experimental hypertension. If similar compositional changes occur in arterioles, they may be important in the altered peripheral vascular resistance which characterizes hypertension.
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