Adrenal-dependent change in vascular reactivity in stroke-prone spontaneously hypertensive rats

Tail arteries from stroke-prone spontaneously hypertensive rats (SHRSP) exhibit oscillatory contractions in response to norepinephrine. This type of oscillatory behavior does not occur in tail arteries from normotensive Wistar-Kyoto rats (WKY). We have shown that the traits of norepinephrine-induced oscillatory activity and high blood pressure are genetically associated in SHRSP, suggesting that oscillatory activity is a primary vascular abnormality that contributes to hypertension in this strain. In the present experiments, two approaches were used to test the hypothesis that adrenal mineralocorticoids modulate expression of this genetically determined vascular abnormality in SHRSP. First, the effect of adrenalectomy on blood pressure and oscillatory activity was determined in SHRSP that underwent bilateral adrenalectomy 3 weeks before experimentation. Second, the effect of deoxycorticosterone acetate (DOCA)-salt treatment on blood pressure and oscillatory activity was determined in 1) rats with no genetic background for oscillatory activity (WKY) and 2) progeny of SHRSP x WKY (F₁ rats). Helically cut tail artery strips from all rats were mounted in isolated tissue baths for isometric force recording. Vessels were exposed to norepinephrine (6 x 10^-10 to 6 x 10^-6 M) for 20 minutes at each concentration. Oscillatory activity was defined as the sum of the phasic contractile amplitudes for all oscillations occurring during the final 10 minutes of norepinephrine incubation. Adrenalectomy markedly decreased blood pressure and oscillatory activity in SHRSP. DOCA-salt treatment caused by hypertension in both WKY and F₁ rats, but oscillatory activity was observed in tail arteries only from rats with a genetic background that favors the development of oscillatory activity (F₁ rats). These results suggest a role for adrenal mineralocorticoids in modulation of this vascular abnormality in SHRSP.