Diminished expression of renal dopamine D1A receptors in the kidney inner medulla of the spontaneously hypertensive rat.

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Dysfunctional dopamine neurotransmission and greater than normal retention of salt have been found for renal proximal tubules of the spontaneously hypertensive rat To determine whether there are differences between kidney D1A dopamine receptor distributions of spontaneously hypertensive rats and Wistar-Kyoto rats. We examined the expression of D1A dopamine receptors in kidneys of spontaneously hypertensive rats and the normotensive Wistar-Kyoto rat through Western blots and immunocytochemistry, using highly specific antipeptide antibodies directed against the receptor. The specificity of the antisera was demonstrated by Western blot studies, using proximal tubules, from Wistar-Kyoto rats. The antiserum recognized a major polypeptide with Mr of 72 kDa and a minor protein of Mr 66 kDa, which were not detected either by antigen-adsorbed or by preimmune sera. In renal cortex of both Wistar-Kyoto rats and spontaneously hypertensive rats, D1A receptors were expressed at equivalent levels. In the inner medulla of Wistar-Kyoto rat, there was diminished (by 60%) expression of D1A receptors compared with that of the renal cortex. However, the expression of D1A receptors in the inner medulla in the spontaneously hypertensive rat was even more diminished (by 83%) relative to levels found in spontaneously hypertensive rat renal cortex. Immunocytochemical studies localized the D1A receptor protein in renal cortex primarily to epithelia of tubules. Relative to renal cortex, there was an overall decrease in staining intensity in the inner medulla both of Wistar-Kyoto rats and of spontaneously hypertensive rats. Compared with that of Wistar-Kyoto rat, the intensity of staining of D1A receptors in the inner medulla of spontaneously hypertensive rats was greatly diminished, confirming the Western blot analyses. The less than normal expression of D1A receptors in the inner medulla of spontaneously hypertensive rats might be of physiologic importance in the etiology of greater than normal retention of salt and hypertension in spontaneously hypertensive rats.