MINERALOCORTICOID RECEPTORS IN SHEEP KIDNEY AND PAROTID STUDIES IN NA+ REPLETE AND NA+ DEPLETE STATES

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Abstract
1. As an adrenalectomized sheep becomes progressively more Na+ deplete, its salivary electrolyte secretion becomes increasingly sensitive to exogenous aldosterone administration. 2. Alteration in mineralocorticoid receptor affinity or concentration is a possible mechanism whereby this sensitivity could be expressed at a molecular level. 3. Binding sites with a high affinity for aldosterone (Kd 37°C∼5 × 10-10 M) have been demonstrated in sheep kidney and parotid. 4. Renal binding sites were examined in detail, and shown to have affinity characteristics appropriate for mineralocorticoid receptors (aldosterone>deoxycorticosterone>dexamethasone>cortisol>progesterone>oestradiol > dihydrotestosterone). 5. No difference in mineralocorticoid receptor affinity or concentration could be shown between Na+ replete and Na+ deplete sheep, in either kidney or parotid gland. 6. Accordingly, the molecular mechanisms whereby parotid sensitivity is mediated remain as yet undefined.

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