Renal dopamine and changes in dopamine receptor ligand binding during high sodium intake.

This study was designed to measure changes in plasma levels of atrial natriuretic peptides (ANP), urine volume (UV), urinary excretion of dopamine (UDAV) and sodium (UNaV), and dopamine (DA) receptor affinity (Kd) and binding sites (Bmax) in kidneys of rats drinking normal saline for a period of 7 days. The saline intake significantly increased UV, UNaV, plasma ANP, UDAV, and its primary metabolite dihydroxyphenyl acetic acid (DOPAC) for the period of 7 days. Bmax increased significantly 1 day after the initiation of saline intake, however, the increase appeared to be transient since measurements of Bmax made after 7 days of saline intake were not significantly different from the control group. No changes in Kd were observed. These results indicate that renal DA contributes to maintenance of Na balance during increased Na intake and that renal DA receptors undergo transient changes during this period

Evidence from functional and autoradiographic studies for the presence of tubular dopamine-1 receptors and their involvement in the renal effects of fenoldopam.

Evidence from receptor-ligand binding and biochemical studies seems to suggest the possible existence of tubular dopamine DA-1 receptors in the rat kidney. However, it is not yet clear whether these putative tubular DA-1 receptors are involved in the functional renal responses elicited during the administration of DA and DA receptor agonists. In the present study we have examined the renal effects of several doses of selective DA-1 receptor agonist fenoldopam in pentobarbital-anesthetized rats in an attempt to unmask a direct tubular DA-1 receptor-mediated diuresis and natriuresis. Additionally, we have performed receptor-ligand binding and autoradiographic studies to examine the presence and localization of DA-1 receptors in various regions of the rat kidney. At the highest dose studied (2 micrograms/kg/min), fenoldopam produced diuresis and natriuresis, which was accompanied by a significant decrease in blood pressure and also a significant increase in glomerular filtration rate. At 1 micrograms/kg/min, the diuretic and natriuretic effects of fenoldopam were observed in the absence of any changes in blood pressure and glomerular filtration rate, but there was a significant increase in renal blood flow. However, at 0.5 micrograms/kg/min, fenoldopam-induced natriuresis and diuresis was not accompanied by any changes in blood pressure, renal blood flow or glomerular filtration rate, implying a direct tubular effect. These effects of fenoldopam appear to be mediated via activation of DA-1 receptors, because they were antagonized by the selective DA-1 antagonist SCH 23390.(ABSTRACT TRUNCATED AT 250 WORDS

Anatomical localization of the binding and functional characterization of responses to dopexamine hydrochloride in the rat mesenteric vasculature.

Dopamine receptors of the DA1 subtype have been identified in mesenteric blood vessels, stimulation of which leads to vasodilation. In this study, we have determined the anatomical localization of dopexamine-hydrochloride-binding sites and carried out functional characterization of responses to this DA1-receptor and beta 2-adrenoceptor agonist in rat mesenteric vasculature. Autoradiographic studies showed the presence of [3H]-dopexamine-binding sites in all the different layers of the mesenteric artery. The DA1 receptor antagonist, SCH 23390 (IC50 = 4.9 mumol/l), and the beta-adrenoceptor antagonist, propranolol (IC50 = 6.0 mumol/l), inhibited the binding of dopexamine. The inhibitory effect of these compounds on dopexamine binding was selective for different regions of the mesenteric artery. Also, dopexamine produced concentration-related increases in cAMP formation in membrane particles from superior mesenteric artery and its main branches. The presence of both SCH 23390 and propranolol was required to completely abolish dopexamine-induced increases in cAMP formation. In functional studies, dopexamine (1 and 3 micrograms/kg/min) produced dose-related increases in mesenteric blood flow (23 and 38%, respectively) which were accompanied by concomitant decreases in the calculated mesenteric vascular resistance. As seen with increases in cAMP, the vascular responses to dopexamine could be completely abolished only by prior treatment with both SCH 23390 and propranolol. These results suggest that in mesenteric vasculature of rat dopexamine binds primarily to DA1 receptors and beta 2-adrenoceptors. The activation of these receptors by dopexamine leads to vasodilation which is mediated by an increase in the intracellular levels of cAMP

Biochemical, autoradiographic and pharmacological evidence for the involvement of tubular DA-1 receptors in the natriuretic response to dopexamine hydrochloride.

Dopexamine hydrochloride (DPX) is a dopamine analog and it possesses agonistic action at DA-1 receptors and beta 2-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 degrees 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 beta 2-adrenoceptors in glomerulus and to beta 2-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 microgram/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 beta 2-adrenoceptors in glomerulus and to beta 2-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 beta 2-adrenoceptors and (3) DPX produces natriuresis and diuresis by selectively activating DA-1 receptors located on renal tubules

BRAIN MORPHOLOGICAL ANALYSIS OF OBESE ZUCKER RAT: MODEL OF METABOLIC SYNDROME.

Metabolic syndrome (MetS) is a disorder characterized by the development of insulin resistance, with subsequent hyperinsulinemia, that increases the risk of cerebrovascular and cardiovascular diseases. Obesity is probably a risk factor for Alzheimer’s disease and vascular dementia and is associated with impaired cognitive function. The obese Zucker rat (OZR) represents a model of type 2 diabetes exhibiting a moderate degree of arterial hypertension and hyperlipidemia. To clarify the possible relationships between MetS and brain damage, the present study has investigated brain microanatomy of OZRs compared with their littermate controls lean Zucker rats (LZRs). Male OZRs and LZRs of 12 weeks of age were used. Their brain was processed for analysis of nerve cell number by neuronal specific nuclear protein (NeuN) immunohistochemistry and phosphorylated neurofilament (NFP) immunoreactive axons analysis. The possible occurrence of astrogliosis was investigated by processing brains for immunohistochemical analysis of glial fibrillary acidic protein (GFAP). In frontal cortex and hippocampus of OZRs reduced number of neurons was related to a decrease of Neu-N expression compared to LZRs. A significant increase in the size and number of GFAP immunoreactive astrocytes was also observed. These findings suggest that OZRs developed as an animal model of type 2 diabetes, may also represent a model for assessing the influence of MetS on brain. This could clarify the pathophysiology of neurological injury reported in obese individuals and/or affected by MetS