Specific Aims) The current proposal focuses on the role of altered Na and K intake on the adrenal zona glomerulosa (ZG) synthesis of aldosterone. In rats and humans reduced Na or increased K intake enhances adrenal glomerulosa responsiveness. However, in some forms of human hypertension (non-modulators) and in the spontaneously hypertensive rat (SHR) dietary intake produces less marked effects. The normal mechanisms leading to changes in adrenal responsiveness to dietary intake and the reason for reduced effects in the SHR are not known. Two major hypotheses are to be tested: (1) enhanced aldosterone output with dietary K loading or Na restriction is secondary to increased ZG generation of AII which can activate a number of second messenger systems and new 11 Beta hydroxylase (P450cll) enzyme which is involved in the last step of aldosterone synthesis. (2) The reduced responsiveness of the SHR to AII during low Na intake is secondary to either a defect in (a) local AII formation, (b) AII signalling systems or (c) failure of AII to upregulate expression of P450cll mRNA levels.
The Specific Aims to test these hypothesis include: (1) To determine whether ZG responsiveness to dietary manipulation is mediated by changes in mRNA levels for the late pathway enzyme system. These studies will involve measuring mRNA levels and enzyme activity during chronic manipulations of dietary Na and K. Additional studies will also be performed using cultured bovine ZG cells. Studies in SHR rat will be performed to determine if the defect in this model is due to an impairment of Na modulation of P450cll mRNA.
In Specific Aim 2, the role of locally generated AII as the mediator of the change in gene activation induced by dietary Na/K manipulation will be studied. The time course changes of adrenal AII after Na/K manipulations will be evaluated in normotensive and SHR rats. Also, in cultured cells the effect of CEI and renin inhibitors on mRNA levels and activity of P450cll will be studied in cells incubated in high K+ media. (3) Another goal will be to determine whether exogenously added AII induces adrenal AII and whether AII can restore P450cII levels and activity in cells treated with CEI and renin inhibition. (4) Finally, whether locally produced AII works with cell surface AII receptors will be evaluated.
Specific Aim 3 is to evaluate whether activation of protein kinase C (PKC) is the link between the change in local AII production and gene activation of the late pathway. Specifically, the effort of dietary Na and K on the phospholipase C messenger system including inositol phosphates Ca2+ and DAG will be studied. Studies will be conducted in normal and SHR rats. Two """"""""Controls"""""""" in the studies will be used. Zona fasciculata cells and the early pathway system side chain cleavage (SCC).
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