Differentiation of noradrenergic and dopaminergic nerves in the rat kidney: evidence against significant dopaminergic innervation

Role of renal dopaminergic activity on renal sodium-water metabolism in congestive heart failure

1. The role of the renal dopaminergic system in water-sodium metabolism in heart failure remains unclear. 2. In this study, the urinary free dopamine excretion (uDA), delivery of L-dopa to renal proximal tubules (plasma L-dopa x creatinine clearance (Ccr)), and the production of dopamine in the kidney [uDA/(plasma L-dopa x Ccr)] were investigated in patients with congestive heart failure (n = 30) and in normal controls (n = 12). In both groups, endogenous Ccr, urinary excretion of sodium (UNaV), fractional excretion of sodium (FENa), plasma noradrenaline concentration (pNA) and plasma L-dopa concentration were also estimated. 3. uDA, plasma L-dopa, delivery of L-dopa and dopamine production in the kidney showed successively lower values in congestive heart failure with progression in NYHA functional class. 4. UNaV (r = 0.458, P < 0.05) and Ccr (r = 0.539, P < 0.01) positively correlated with uDA. Linear correlations were found between left ventricular ejection fraction and uDA (r = 0.574, P < 0.01), pNA (r = -0.495, P < 0.01) or plasma L-dopa (r = 0.423, P < 0.05). 5. From these findings, it was suggested that (i) uDA was clearly suppressed in patients with CHF, and (ii) the possible mechanisms of its suppression might be due to decrease of delivery of L-dopa into the proximal tubules and suppressed production of dopamine from L-dopa in the kidney.

A study of the neuronal and non-neuronal stores of dopamine in rat and rabbit kidney

The present study has examined the effects of 6-hydroxydopamine (6-OHDA) alone and in combination with pargyline, desipramine and GBR 12909 and denervation as induced by occlusion of the renal artery (RAO) on the endogenous dopamine (DA) and noradrenaline (NA) contents in rat and rabbit renal tissues; the effects of chemical denervation on catecholamine levels in the left ventricle were also studied. In rat and rabbit renal medulla and rat renal cortex, 6-OHDA and pargyline plus 6-OHDA selectively reduced NA (85-92% reduction) without a parallel decrease in DA tissue content (19-27% reduction). This 6-OHDA- and pargyline plus 6-OHDA-insensitive DA pool was found to be resistant to denervation as induced by RAO. The NA-depleting effect of 6-OHDA in these renal areas was found to be prevented by the previous administration of desipramine, but not with that of GBR 12909. In the rabbit renal cortex, 6-OHDA selectively reduced NA (90% reduction) without a parallel depletion of DA (20% reduction); previous treatment with pargyline abolished this selectivity. Again, only desipramine, but not GBR 12909, was found to prevent the NA and DA depleting effect of 6-OHDA in the rabbit renal cortex. Denervation induced by RAO was also found to produce a parallel depletion of DA and NA tissue levels in this renal area. In the left ventricle, 6-OHDA alone or in combination with pargyline produced a parallel depletion of DA and NA tissue levels (79-88% reduction) in both species. These results provide evidence against the presence of independent dopaminergic neurones in rat and rabbit kidney and suggest that in rat and rabbit renal medulla and rat renal cortex most of DA is stored in a non-neuronal compartment; in rabbit renal cortex some of the DA appears to be located in noradrenergic neurones, in a store different from that which contains NA.

Differential effect of guanethidine on dopamine and norepinephrine in rat peripheral tissues

The changes of dopamine (DA) and norepinephrine (NE) were investigated in rat peripheral tissues after guanethidine treatment (50 mg/kg i.p. five days each week) during one week (group 1, n = 10, five injections) and during 2.5 weeks (group 2, n = 8, 13 injections). Guanethidine greatly reduced NE levels in all the analyzed tissues but only partially depleted DA in kidney, bladder, stomach, intestine, lung and liver and in sympathetic ganglia. The differential pattern of changes between DA and NE induced by guanethidine suggests that peripheral DA is distributed in several neuronal or non-neuronal pools, whose presence, nature and contribution varies in the different tissues. Both noradrenergic cell bodies and small intensely fluorescent cells (SIF cells) can contribute to the DA in the superior cervical ganglion. Noradrenergic neurons seem to be the main sources of DA in seminal vesicles, vas deferens, heart and spleen. In addition to noradrenergic nerves, extraneuronal sources could account for a meaningful portion of DA in kidney, gastrointestinal tract, lung and liver. The bladder is the peripheral tissue where DA exhibits the highest resistance to the neurotoxin. Accordingly, these tissues may provide meaningful sources of non-precursor DA pools.

Catecholamine-containing, dopamine-beta-hydroxylase-immunoreactive perivascular nerve specializations in the rat kidney

Fluorescence histochemical visualization of catecholamines and immunolabeling of dopamine beta hydroxylase (DBH) were employed to study noradrenergic nerve terminals and perivascular nerve specializations in the rat kidney. Plexuses of catecholamine-containing and dopamine-beta-hydroxylase-immunoreactive nerves innervate the intrarenal arterial tree and larger intrarenal veins. Some perivascular nerve bundles have specialized segments composed of clusters of axonal enlargements that are immunoreactive for DBH and fluoresce intensely in ultraviolet light after fixation in a solution of formaldehyde and glutaraldehyde or treatment with glyoxylic acid. No fluorescent neural structures were found in denervated rat kidney sections treated with glyoxylic acid. Many such structures are associated with arteriolar branches of interlobar, arcuate, and interlobular arteries and are composed, in part, of axonal enlargements that contain mitochondria, microtubules, and one or more clusters of synaptic vesicles. These perivascular nerve specializations may be sites of axoaxonal interactions between noradrenergic axons or between these axons and other types of autonomic or sensory axons. The synaptic vesicles evidently store large amounts of catecholamine, but there is no evidence whether it is released into the surrounding tissue. These structures may be involved in changes in intrarenal innervation patterns which may occur as the rat ages. Regardless of the autonomic or sensory nature of intrarenal neural structures, close association of most such structures with arterioles suggests some neurovascular interaction.

Identification of noradrenergic nerve terminals immunoreactive for neuropeptide Y and vasoactive intestinal peptide in the rat kidney

Cryostat- and vibratome-cut sections of rat kidneys were singly or doubly labeled to visualize immunoreactive tyrosine hydroxylase (THI), dopamine beta-hydroxylase (DBHI), vasoactive intestinal peptide (VIPI), and neuropeptide Y (NPYI). Rats were perfusion fixed with 2-4% paraformaldehyde with or without 0.15% picric acid and rinsed in buffer for 18-48 hr. Single antigens were labeled with horseradish peroxidase in vibratome sections, whereas cryostat sections were used to label one antigen with peroxidase and another with a fluorophore in the same tissue section. A dense plexus of DBHI noradrenergic nerves innervates the renal arterial tree, and such nerves innervate the interlobar veins and renal calyx as well. Immunoreactive NPY is colocalized in most of these nerves, but some intrarenal noradrenergic nerves do not contain NPY but do contain VIP immunoreactivity. The distribution of NPYI nerves resembles that of DBHI nerves, whereas most perivascular noradrenergic nerves immunoreactive for VIP innervate selected arcuate and interlobular arteries. A small population of nonadrenergic, VIPI nerves innervates the renal calyx.

Adrenoceptors in the kidney: localization and pharmacology

The kidney plays a key role in the regulation of blood pressure. The sympathetic nervous system can influence many aspects of kidney function in relation to blood pressure control, e.g. renal vascular tone, intrarenal renin release and tubular reabsorption of electrolytes and fluid. The intrarenal distribution of adrenoceptors has now been studied on the basis of modern receptor ligand binding techniques combined with microscopic studies. The preferential localization of each adrenoceptor subtype within the kidney is reviewed. Furthermore, an attempt is made to describe the functional correlation of the presence of different adrenoceptor subtypes. Finally, the possible role of renal adrenoceptor abnormalities in the pathogenesis of hypertension is discussed.

Effects of dopamine on renal function in the rat isolated perfused kidney

The renal effects of dopamine, the dopamine antagonist spiperone and the combination of dopamine and spiperone were examined in the isolated perfused rat kidney preparation. Studies were carried out at constant perfusion pressure and the following were measured at 10 min intervals for 1 h: perfusate flow; GFR (3H-inulin); urine flow rate; sodium, potassium and kallikrein excretion; perfusate renin concentration; perfusate and urinary-dopamine levels. Low-dose dopamine infusion (6 X 10(-10) mol/min) resulted in significant diuresis, natriuresis and kaluresis but little change in GFR. These effects were blocked by spiperone (10(-10) mol/min) which had no significant effects when infused alone. At a higher dose (10(-8) mol/min) dopamine significantly increased urine flow alone; this too was reversed by spiperone. Dopamine had no significant effects on perfusate flow, renin release or kallikrein excretion. Perfused control kidneys excreted amounts of dopamine (328 pmol/h, s.e.m. = 57, n = 6) far in excess of kidney dopamine content (49 pmol/g, s.e.m. = 6, n = 32). Renal handling of infused dopamine was dose-related; the fraction of the administered dose taken up and/or metabolized by the kidney on the higher dose infusion was considerably less than on the lower dose (40%, s.e.m. = 3 vs. 82%, s.e.m. = 6) while more was excreted (13%, s.e.m. = 3 vs. 2%, s.e.m. = 1). These studies indicate that dopamine at low doses can produce diuresis, natriuresis and kaluresis independently of extrarenal or haemodynamic influences and not mediated by renal renin or kallikrein systems. The kidney also exhibits a saturable capacity for dopamine uptake and/or metabolism.