Effect of adrenal demedullation and adrenaline on hypertension development and vascular reactivity in young spontaneously hypertensive rats.

1. The effects of adrenal demedullation and subcutaneous depots of adrenaline, on hypertension development and vascular reactivity, were determined in young spontaneously hypertensive rats (SHRs). 2. Plasma adrenaline, but not noradrenaline, was significantly lower in all 16-week-old demedullated SHRs, irrespective of the time of demedullation. However, hypertension development was attenuated only in SHRs demedullated at 6 weeks of age or younger. 3. Adrenaline depots restored hypertension development in SHRs demedullated at 4 weeks, irrespective of the time of depot implantation, but were without effect in sham-operated rats. 4. Pressor responses to exogenous noradrenaline, in isolated perfused mesenteric arteries from 16-week-old demedullated and sham-operated SHRs and those treated with adrenaline depots, did not differ significantly. Maximal neurogenic pressor responses were, however, reduced in mesenteries from all demedullated rats, including those treated with depot adrenaline. Adding adrenaline to the perfusate facilitated neurogenic responses only. 5. Thus, the adrenal medulla appears to be involved in modulating sympathetic neurogenic vasoconstriction. The nature of this sympathoadrenal interaction and its role in the early development of hypertension in the SHR is unclear and is not explicable simply in terms of a facilitation of sympathetic neurogenic responses by adrenaline.