Mineralocorticoid receptors in sheep kidney and parotid: studies in Na+ replete and Na+ deplete states.

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. Bonding sites with a high affinity for aldosterone (Kd 37 degrees C approximately 5 x 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 greater than deoxycorticosterone greater than dexamethasone greater than cortisol greater than progesterone greater than oestradiol greater than dihydrotestosterone). 5. No difference in mineralocoticoid 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.