ISSN:
1432-1912
Keywords:
Dopexamine
;
DA-1 Receptors
;
β2-Adrenoceptors
;
Renal function
;
Heart failure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Dopexamine hydrochloride (DPX) is a dopamine analog and it possesses agonistic action at DA-1 receptors and β2-adrenoceptors. It also is a weak agonist at DA-2 receptors. In the present study, we have examined the anatomical localization of DPX binding sites in rat kidney and their functional significance in terms of the renal effects of this compound. In receptor-ligand binding studies, [3H]-DPX was found to bind specifically to sections of rat kidney in a time (maximum binding at 60 min), temperature (optimal temperature 25°C) and concentration (highest specific/non-specific ratio at 2 nmol/l) dependent manner. Autoradiographic studies revealed the presence of [3H]-DPX binding sites in renal tubules, glomerulus and various layers of small and large blood vessels. Inhibition studies with SCH 23390, ICI 118,551 and 1-sulpiride showed that DPX binds primarily to DA-1 receptors in tubules, only to β2-adrenoceptors in glomerulus and to β2-adrenoceptors, DA-1 and DA-2 receptors in blood vessels. Also, DPX caused concentration related increases in cyclic AMP levels in rat kidney membrane particles, which could be completely abolished by a combined presence of SCH 23390 and propranolol suggesting that both binding sites of DPX are linked to adenylate cyclase. In functional studies DPX (1 μg/kg min for 30 min) produced a modest fall in blood pressure, pronounced tachycardia and slight but significant increase in renal blood flow (11%). These responses were accompanied by increases in urine output (97%), urinary sodium excretion (89%), and fractional excretion of sodium (132%). There was no change in glomerular filtration rate. Propranolol pretreatment abolished DPX-induced hypotension and tachycardia but seemed to potentiate the natriuretic responses to DPX. On the other hand, SCH 23390, a DA-1 receptor antagonist completely abolished DPX-induced hypotension, natriuresis and diuresis without affecting tachycardia. These results indicate that (1) DPX binds predominantly to DA-1 receptors in renal tubules, to β2-adrenoceptors in glomerulus and to β2-adrenoceptors, as well as DA-1 and DA-2 receptors in renal blood vessels (2) DPX stimulates cAMP formation in the kidney by activating both DA-1 and β2-adrenoceptors and (3) DPX produces natriuresis and diuresis by selectively activating DA-1 receptors located on renal tubules.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00180672
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