Disruption of the dopamine D3 receptor gene produces renin-dependent hypertension.

Since dopamine receptors are important in the regulation of renal and cardiovascular function, we studied the cardiovascular consequences of the disruption of the D3 receptor, a member of the family of D2-like receptors, expressed in renal proximal tubules and juxtaglomerular cells. Systolic and diastolic blood pressures were higher (approximately 20 mmHg) in heterozygous and homozygous than in wild-type mice. An acute saline load increased urine flow rate and sodium excretion to a similar extent in wild-type and heterozygous mice but the increase was attenuated in homozygous mice.

Lateral parabrachial nucleus modulates baroreflex regulation of sympathetic nerve activity.

Previous studies have demonstrated that the lateral parabrachial nucleus (LPBN) is an important site for descending modulation of baroreflex control of heart rate. In the present study it was hypothesized that the LPBN neurons may also modulate baroreflex control of arterial pressure and sympathetic nerve activity. In urethan-anesthetized rats, electrical or chemical activation of the LPBN produced a significant reduction in the magnitude of the baroreflex inhibition of mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) elicited by aortic depressor nerve stimulation.

Detection of dopamine receptor D1A subtype-specific mRNA in rat kidney by in situ amplification.

In recent years, both molecular biological and immunohistochemical techniques, utilizing receptor subtype-specific probes and antibodies to cloned central nervous system dopamine receptors, have revealed their presence in a number of peripheral organs and tissues. Molecular techniques have been hindered by the low abundance of receptor mRNA in these sites, and reverse transcription-polymerase chain reaction (RT-PCR) has been utilized to address this problem. However, RT-PCR is most often employed on either isolated mRNA or microdissected tissue samples, thereby limiting interpretation of whole tissue distribution.

Localization of the dopamine D1 receptor protein in the human heart and kidney.

The dopamine D1 receptor has recently been identified in the rat heart and kidney. In the present study, using Western blot analysis and light microscopic immunohistochemistry, we examined D1 receptor protein expression in the human kidney and heart. Antipeptide polyclonal rabbit antiserum was raised against the third extracellular domain of the native receptor and affinity-purified using a protein-A column.

Vasopressin and V1-receptor antagonists modulate the activity of NTS neurons receiving baroreceptor input.

Arginine vasopressin (AVP) may act as a neurotransmitter or neuromodulator in the solitary tract nucleus (NTS). To determine whether AVP influences the activity of NTS neurons receiving cardiovascular afferent input, we used single-unit extracellular recording combined with local microinjection to test the effects of AVP and V1-receptor antagonists (antAVP) on spontaneously active NTS neurons in anesthetized rats. Phenylephrine-induced increases in arterial pressure were used to identify neurons receiving baroreceptor input.

Altered expression of delayed excitation in medial NTS neurons of spontaneously hypertensive rats.

The spontaneously hypertensive (SH) rat has an exaggerated sympathetic discharge which may result from an enhanced neuronal excitability in the central nervous system. To test this hypothesis, we examined the electrophysiological properties of neurons in the medial region of the nucleus of the solitary tract (mNTS), a central nucleus involved in the processing of baroreceptor afferent information, in SH rats and normotensive Sprague-Dawley (SD) rats. An in vitro brainstem slice preparation was used to record intracellularly from 18 neurons in 4-5-month-old SH rats and 16 neurons in 4-5-month-old SD rats.

Dopamine D1A receptors and renin release in rat juxtaglomerular cells.

Two dopamine D1-like receptors have been cloned from mammals, the D1 and D5 receptors, also known as D1A and D1B receptors, respectively, in rodents. Although D1-like receptors are known to stimulate renin release, the receptor subtype mediating this action has not been determined. We investigated D1 receptor subtype expression in rat juxtaglomerular cells obtained after enzymatic dispersion of kidney cortex and differential centrifugation.

Clinical evaluation of serial blood processing at point of care.

The Axial Separation Module (ASM), which separates whole-blood specimens serially in Axial Process Containers (APC), was evaluated for clinical performance at the University of Virginia Health Sciences Center (UVA HSC) in a community-based outpatient laboratory (North Ridge Clinic). We hypothesized that moving the task of blood separation to point of care would reduce specimen turnaround time within the main laboratory. Blood drawn into an APC was separated in the ASM at point of care at the North Ridge Clinic.

Intrarenal dopamine production and distribution in the rat. Physiological control of sodium excretion.

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial fluid (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.

Differential human renal tubular responses to dopamine type 1 receptor stimulation are determined by blood pressure status.

We performed the present studies to determine whether a proximal renal tubular dopamine D1-like receptor defect exists in human essential hypertension. Twenty-four subjects were studied (13 normotensive and 11 hypertensive) in a randomized, double-blind, vehicle-controlled study using fenoldopam, a selective D1-like receptor agonist. Subjects were studied in sodium metabolic balance at 300 mEq/d, after which the salt sensitivity of their blood pressure was determined.

Preferential release of renal dopamine into the tubule lumen: effect of chronic sodium loading.

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.

Dopamine D3 receptors in rat juxtaglomerular cells.

D2-like receptors in the kidney have been suggested to be important in the regulation of renin release but the D2-like subtype(s) expressed in juxtaglomerular (JG) cells is not known. Therefore, we determined which of the D2-like family of dopamine receptors is located in primary cultures of rat juxtaglomerular (JG) cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) identified D3 and D4 but not D2Long mRNA in JG cells (n = 3).

Transgenic mice to study the role of dopamine receptors in cardiovascular function.

Dopamine, an intrarenal regulator of sodium transport, is important in the pathogenesis of hypertension. The transduction of D1-like receptors in renal proximal tubules is defective in animal models of genetic hypertension. The defect is associated with an impaired regulation of proximal tubular sodium transport and cosegregates with hypertension in rats.

Robotics and the changing face of the clinical laboratory.

Rapid changes in healthcare coupled with parallel advances in technology have stimulated the evolution of new approaches for laboratory automation. In particular, the emergence of commercially available laboratory robotic systems offers promise for streamlining the clinical laboratory. Increasing cost-containment pressures make the application of this technology extremely attractive, and several organizations have begun to systematically integrate robotic devices into their laboratory automation schemes.

What we can learn from the selective manipulation of dopaminergic receptors about the pathogenesis and treatment of hypertension?

The natriuretic response that accompanies an acute or a chronic sodium load results, in a large part, from dopamine produced by the renal proximal tubules. This paracrine/ autocrine effect of dopamine, mediated by occupancy of renal tubular dopamine D1 receptors, is impaired in spontaneous hypertension. Disruption of the D1A receptor gene in mice increases blood pressure.

Dopamine D1A receptor regulation of phospholipase C isoform.

In LTK- cells stably transfected with rat D1A receptor cDNA, fenoldopam, a D1 agonist, increased phosphatidylinositol 4, 5-bisphosphate hydrolysis in a time-dependent manner. In the cytosol, phospholipase C (PLC) activity increased (50 +/- 7%) in 30 s, returned to basal level at 4 h, and decreased below basal values by 24 h; in the membrane, PLC activity also increased (36 +/- 13%) in 30 s, returned to basal level at 10 min, and decreased below basal value at 4 and 24 h. Fenoldopam also increased PLC-gamma protein in a time-dependent manner.

Role of the D1A dopamine receptor in the pathogenesis of genetic hypertension.

Since dopamine produced by the kidney is an intrarenal regulator of sodium transport, an abnormality of the dopaminergic system may be important in the pathogenesis of hypertension. In the spontaneously hypertensive rat (SHR), in spite of normal renal production of dopamine and receptor density, there is defective transduction of the D1 receptor signal in renal proximal tubules, resulting in decreased inhibition of sodium transport (Na+/H+ exchanger [NHE] and Na+/K+ATPase activity) by dopamine. To determine if impaired D1 receptor regulation of NHE in proximal tubules is related to hypertension, studies were performed in a F2 generation from female Wistar Kyoto (WKY) and male SHR crosses.

Dopamine receptor signaling defects in spontaneous hypertension.

Dopamine produced by renal proximal tubules acts as an intrarenal natriuretic factor by direct tubular action; this paracrine effect is influenced by the state of sodium balance. Up to 60% of sodium excretion with volume (2%-10%) expansion may be mediated by D1-like receptors. The renal paracrine effect of dopamine is impaired in genetic hypertension; this is due to defects in renal dopamine production or transduction of the dopamine signal.