Effects of chemical sympathectomy with 6-hydroxydopamine on alpha- and beta-adrenoceptors and muscarinic cholinoceptors in rat kidney

Expression of the non-neuronal cholinergic system components in Malpighian tubules of Mythimna separata and evidence for non-neuronal acetylcholine synthesis

The non-neuronal cholinergic system, widely distributed in nature, is an ancient system that has not been well studied in insects. This study aims to investigate the key components of the cholinergic system and to identify the non-neuronal acetylcholine (ACh)-producing cells and the acting sites of ACh in the Malpighian tubules (MTs) of Mythimna separata. We found that non-neuronal ACh in MTs is synthesized by carnitine acetyltransferase (CarAT), rather than choline acetyltransferase (ChAT), as confirmed by using enzyme inhibitors and high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS/MS). Fluorescence in situ hybridization revealed the presence of CarAT mRNA within MTs, specifically localized in the principal cells. Immunohistochemistry showed strong staining for A-mAChR, a muscarinic acetylcholine receptor, in the principal cells. Pharmacological analysis further demonstrated that ACh acts through A-mAChR in the principal cells to increase the intracellular Ca2+ concentration. These findings provide compelling evidence for the existence of a non-neuronal cholinergic system in the MTs of M. separata, and the principal cells play a crucial role in ACh synthesis via CarAT.

Lumbar sympathectomy reduces vascular permeability, possibly through decreased adenosine receptor A2a expression in the hind plantar skin of rats

BACKGROUND

The effect of lumbar sympathectomy for the treatment of lower limb ischemia remains a matter of controversy.

METHODS

Sprague-Dawley rats were subjected to lumbar sympathectomy, after which Evans blue dye was injected into the hind plantar skin. Extravasation of dye was measured and compared with rats undergoing sham operation. Hind plantar skin was processed for HE staining, immunohistochemistry, and Western blot.

RESULTS

In sympathectomized rats, blue stained areas in hind plantar skin and concentrations of Evans blue were significantly less than that of sham sympathectomy (control) rats, both 2 weeks and 3 months after surgery. Expression of prostaglandin E2, bradykinin, bradykinin B2 receptor, and adenosine triphosphate were not significantly different between the sympathectomized and control groups. Adenosine receptor A2a expression was significantly reduced in the sympathectomized group both 2 weeks and 3 months after surgery.

CONCLUSION

Vascular permeability in the hind plantar skin of rats decreases following lumbar sympathectomy, possibly via reduced expression of adenosine receptor A2a.

Sympathetic Denervation Accelerates Wound Contraction but Inhibits Reepithelialization and Pericyte Proliferation in Diabetic Mice

Previous studies focused on the effects of sympathetic denervation with 6-hydroxydopamine (6-OHDA) on nondiabetic wounds, but the effects of 6-OHDA on diabetic wounds have not been previously reported. In this study, treated mice received intraperitoneal 6-OHDA, and control mice received intraperitoneal injections of normal saline. Full-thickness wounds were established on the backs of mice. The wounds were sectioned (four mice per group) for analysis at 2, 5, 7, 10, 14, 17, and 21 days after injury. The wound areas in the control group were larger than those in the treatment group. Histological scores for epidermal and dermal regeneration were reduced in the 6-OHDA-treated group on day 21. The mast cells (MCs) in each field decreased after sympathectomy on days 17 and 21. The expression levels of norepinephrine, epidermal growth factor (EGF), interleukin-1 beta, NG2 proteoglycan, and desmin in the treatment group were less than those in the control group. In conclusion, 6-OHDA delays reepithelialization during wound healing in diabetic mice by decreasing EGF, but increases wound contraction by reducing IL-1β levels and the number of MCs. Besides, 6-OHDA led to reduced pericyte proliferation in diabetic wounds, which might explain the vascular dysfunction after sympathetic nerve loss in diabetic wounds.

Non-neuronal expression of choline acetyltransferase in the rat kidney

AIMS

Acetylcholine (ACh) has been shown to increase ion and water excretion in the kidneys, resulting in hypotension. However, no evidence of renal parasympathetic innervation has been shown, and the source of ACh acting on nephrons is still unknown. The aim of the present study was to identify ACh-producing cells in the rat kidney, by examining the expression of cholinergic agents and localization of an ACh-synthesizing enzyme, choline acetyltransferase (ChAT), in the kidney.

MAIN METHODS

Adult mail Sprague-Dawley rats were used in this study. Expression of mRNA of cholinergic agents, ChAT, vesicular ACh transporter (VAChT), and high-affinity choline transporter (CHT-1), in the kidney was examined by RT-PCR. Localization of ChAT mRNA and protein was examined by in situ hybridization and tyramide-enhanced immunohistochemistry, respectively.

KEY FINDINGS

RT-PCR showed the expression of ChAT, VAChT, and CHT-1. In situ hybridization demonstrated that ChAT mRNA is localized to the renal cortical collecting ducts (CCD). Immunohistochemistry showed that the ChAT-positive cells were principal cells, and that they were unevenly distributed in the tubules, and constituted approximately 15.2% of CCD in the cortex, and 3.6% and 1.5% in the outer and inner medulla, respectively. ChAT-positive immunoreactivity was localized to the apical side of principal cells, suggesting that ACh synthesis may occur in the apical compartment of these cells.

SIGNIFICANCE

These results suggest that the cholinergic effects in the nephron may be mediated at least in part by ACh originating from CCD principal cells and its expression may be locally regulated in the rat kidney.

P2Y receptors present in the native and isolated rat glomerulus

Extracellular ATP can mobilize intracellular calcium in rat glomeruli by interacting with P2Y receptors. However, the identity of the receptor subtypes involved is not known. In the present study, we have used RT-PCR to identify mRNAs for specific P2Y receptor subtypes expressed in the rat glomerulus: mRNA for P2Y1, P2Y2, P2Y4 and P2Y6 receptors was detected. Functional expression of P2Y1 and P2Y2/P2Y4, but not P2Y6, receptors in intact glomeruli was confirmed by measuring the relative stimulation of the inositol phosphate pathway induced by selective agonists of a particular receptor subtype. Finally, we have used available polyclonal antibodies to confirm the expression of P2Y1 and P2Y2 in the glomerulus, in mesangial cells and glomerular epithelial cells (podocytes), respectively; but we could not demonstrate P2Y4 or P2Y6 receptor expression by this means. In a separate series of experiments, we have examined the possibility that intra-renal sympathetic nerve terminals are a source of extracellular ATP and that this would be supported, though not excluded, by supersensitivity to ATP following denervation. Nucleotide-induced stimulation of the inositol phosphate pathway was measured in both control rats and rats that had been sympathectomized by intraperitoneal injection of 6-hydroxydopamine. The response to norepinephrine was measured as a positive control. In the sympathectomized rats, the effect of norepinephrine was significantly enhanced, whereas ATP-induced inositol phosphate production was unaffected, being similar in both groups of animals.

Neuroreceptor mRNA expression in the rat mesenteric artery develops independently of innervation

Studies in autonomic targets have shown that nerves may be required for the development and maintenance of postsynaptic receptor populations. We have examined this relationship in the rat mesenteric artery, assessing mRNA expression levels for a range of neuroreceptors after neonatal sympathectomy, using 6-hydroxydopamine or antisera directed against nerve growth factor, and sensory denervation, using capsaicin. Total RNA was extracted from 28 day old rats and reverse transcription-polymerase chain reaction was performed, using primers specific for the alpha1(A,B,D)- and alpha2(A,B,C)-adrenergic, neurokinin (NKI-NK3), muscarinic (M1-M5) and P2X purinergic (P2x1-7) receptor families. Results showed no decreases in mRNA expression of any of the specific receptor subtypes after either sympathetic or sensory denervation. Small increases in mRNA expression were detected following sensory denervation for some of the receptor subtypes. We conclude that neither sympathetic nor sensory nerves are mandatory for the expression of mRNA of a range of neuroreceptors in the mesenteric vascular bed of the rat.

A critical period for the role of thyroid hormone in development of renal alpha-adrenergic receptors

Adrenergic input influences renal cell replication/differentiation and the development of excretory function. Kidney cells make adrenoceptors before the arrival of the majority of nerve terminals, and the current study examines whether thyroid hormone plays a role in receptor development. Propylthiouracil (PTU) was given to pregnant and neonatal rats from gestational d 17 through postnatal d 5, a treatment that obtunds thyroid hormone levels throughout the first 2-3 wk postpartum. The PTU group showed significant deficits in the number of alpha1-receptors, and values resolved to normal in parallel with hormone level recovery. The effects were not secondary to alterations in cell differentiation or growth. as the period of receptor abnormalities did not correspond to that of growth inhibition. Similarly, the effects were selective for the alpha1-receptor, as no comparable effects were seen for total membrane protein or for alpha2-receptors. The role of thyroid hormone in alpha1-receptor ontogeny involved a critical developmental window; later in development neither treatment with PTU nor with large doses of thyroid hormone had any impact on alpha1-receptors. Studies of mRNAs encoding the alpha1-receptor subtypes indicated that hypothyroidism targets the alpha1a-subtype, which has been implicated in the transduction of neurotrophic signals; alpha1a-receptor mRNA also showed the largest proportional developmental increase compared with those encoding other alpha1-subtypes. Accordingly, thyroid hormone is likely to set the stage for the subsequent trophic control of renal development by neural input, and hypothyroidism during this critical window can be expected to result in abnormal renal functional development and increased perinatal risk.

Tissue-specific regulation of fat cell lipolysis by NPY in 6-OHDA-treated rats

The effects of neuropeptide Y (NPY), peptide YY (PYY), [Leu31, Pro34]NPY, and NPY (13-36) on adipocyte lipolysis have been studied in subcutaneous (inguinal) and visceral (parametrial) rat adipose tissues. A 48-h fasting period and chemical sympathectomy were used to evaluate the regulation of Y1 and Y2 pathways in rat adipocytes. NPY, PYY, and [Leu31, Pro34]NPY significantly inhibited fat cell lipolysis by about 25% in both tissues (p < or = 0.05). This inhibition was achieved mainly through the Y1 pathway. No significant response to NPY (13-36) was observed, suggesting a lack of involvement of the Y2 pathway in the antilipolytic effect of NPY and PYY. The 48-h fasting period led to the loss of the Y1 inhibitory effect previously observed in control rats. On the other hand, the chemical sympathectomy induced a 35% increase of fat cell lipolysis (p < or = 0.05). The latter involved the Y2 pathway as stimulated by NPY (13-36), and was observed in the parametrial tissue exclusively. These results suggest that: a) rat Y receptors reported to exhibit Gi responses can also express Gs-like responses, and b) visceral and subcutaneous adipose tissues exhibit specific regulation of fat cell lipolysis.

Ontogeny of beta-adrenoceptor/adenylyl cyclase desensitization mechanisms: the role of neonatal innervation

The ability of adrenergic stimulation to elicit desensitization of the beta-receptor/adenylyl cyclase signaling cascade is not an inherent property of cells but rather is acquired during the period in which sympathetic innervation develops. This study examines whether innervation provides the signal that enables target cardiac and hepatic cells to learn to desensitize their responses. Neonatal rats were sympathectomized with 6-OHDA on postnatal day 1 and were treated at various ages with a regimen of isoproterenol known to elicit desensitization in adults. In control rats, desensitization first appeared between days 6 and 15. Desensitization was heterologous, involving changes in the efficiency of G-protein coupling, as there were parallel decreases in isoproterenol-stimulated adenylyl cyclase activity, basal activity and fluoride-stimulated activity (maximal G-protein activation) without changes in forskolin-Mn2+-stimulated activity (total cyclase catalytic activity). The lesioned animals showed a delay in the onset of desensitization as isoproterenol did not evoke decreased responsiveness until day 25 in the heart; the liver did not display agonist-induced desensitization even at day 25. The effects of lesioning on development of desensitization were entirely separable from those on regulation of beta-receptors themselves: agonist-induced decreases in receptor binding appeared by day 15 in both control and lesioned animals. Uniquely in the youngest animals (6 days old), isoproterenol treatment produced heterologous sensitization of adenylyl cyclase responses rather than desensitization, with a parallel increase in basal, isoproterenol-, fluoride- and forskolin-Mn2+-stimulated activity; the latter indicates induction of total catalytic activity as the primary mechanism of sensitization. The lesioned neonates did not show sensitization, despite the fact that during this period, sympathetic pathways are not functionally competent. Our results indicate that innervation provides a timing signal for the onset of desensitization capabilities of sympathetic target cells, but is not absolutely required for the cells to learn how to desensitize. Prior to the onset of desensitization, agonists induce sensitization that may be important in preserving physiological responsiveness during ontogenetic surges of adrenergic activity. The absence of sensitization in lesioned animals implies that, before physiological function is completely established, early pioneer synapses provide a trophic signal that enables cells to increase their sensitivity to stimulation during the perinatal transition period.

Atypical regulation of hepatic adenylyl cyclase and adrenergic receptors during a critical developmental period: agonists evoke supersensitivity accompanied by failure of receptor down-regulation

Ordinarily, beta-adrenergic receptors and responses linked to the receptors increase with development but in the liver, beta-receptors are higher in the fetus and neonate than in adulthood. We examined how hepatic beta-receptor signaling mediated through adenylyl cyclase is regulated in rats of different ages. In each case, animals were pretreated with isoproterenol for 4 d, and on the 5th d, hepatic membrane preparations were examined for adenylyl cyclase activity and receptor binding capabilities. Uniquely in 6-d-old animals, the cyclase response to isoproterenol was enhanced by chronic pretreatment, caused by heterologous sensitization mediated through effects on total catalytic activity (increased response to forskolin-Mn2+) and on G-protein coupling (enhanced effect of fluoride and increased GTP dependence of basal activity). Isoproterenol pretreatment failed to cause beta-receptor down-regulation in 6-d-old animals, but by 15 d of age, down-regulation was detected along with slight desensitization of the cyclase response. However, at 25 d, neither effect was present. In adulthood, repeated isoproterenol administration failed to cause cyclase desensitization but did reduce beta-receptor numbers; the loss of receptors was still unusual in that beta-receptor down-regulation could be achieved with either isoproterenol or with methoxamine, an alpha-receptor agonist. The results indicate that, early in development, hepatic beta-receptor-mediated responses are enhanced, not desensitized, after chronic stimulation. These effects would foster responsiveness of hepatic gluconeogenesis in the face of the massive adrenergic stimulation associated with the transition from fetal to neonatal life. In adulthood, when receptor numbers are far lower than in the neonate, the inability to desensitize the signaling cascade despite receptor down-regulation would serve to maintain the response to catecholamines.

Beta-adrenoceptor control of cardiac adenylyl cyclase during development: agonist pretreatment in the neonate uniquely causes heterologous sensitization, not desensitization

In the adult, increased stimulation of postsynaptic receptor sites produces compensatory desensitization that reduces tissue responsiveness. During development, however, responses in most systems increase with age and with the maturation of neuronal inputs. In the current study, we examined whether agonist-induced desensitization of cardiac beta-adrenergic receptor signaling mediated through adenylyl cyclase could be elicited in 6-, 15- and 25-day-old rats, and in adults. In each case, animals were pretreated with isoproterenol daily for four days preceding the experiment, and on the fifth day, cardiac membrane preparations were examined. Fifteen and 25-day-old animals and adults all exhibited desensitization, as demonstrated by a diminished cyclase response to isoproterenol in vitro. However, in 6-day-old animals, the enzymatic response to isoproterenol was enhanced by chronic pretreatment. Measurements of the G-protein-sensitive component of cyclase (decrement in activity obtained with deletion of GTP from the reaction mixture, stimulatory response to fluoride) indicated heterologous desensitization in the older animals, evidenced by diminished dependence on GTP and reduced response to fluoride; the 6-day-old animals showed enhanced GTP dependence and augmentation of the fluoride response. Uniquely in 6-day-old animals, the total catalytic activity of adenylyl cyclase, measured with forskolin-Mn2+, was markedly elevated by chronic isoproterenol pretreatment, whereas it was unaffected in older animals. These data suggest that regulation of receptor signaling is completely different early in neonatal life. Instead of producing desensitization of responses, agonist exposure promotes receptor signaling by enhancing expression and/or catalytic efficiency of adenylyl cyclase. In older animals, the predominant effect is heterologous desensitization mediated at the level of G-proteins. These developmental differences are likely to be important in the maintenance of tissue responsiveness during the period in which innervation develops, as well as in the ability of neurotrophic input to 'program' the responsiveness of target tissues.

Neural input and the development of adrenergic intracellular signaling: neonatal denervation evokes neither receptor upregulation nor persistent supersensitivity of adenylate cyclase

In the adult, denervation of adrenergic target tissues leads to compensatory upregulation of receptor sites and to supersensitive responses. When 6-hydroxydopamine (6-OHDA) was given to neonatal rats, cardiac beta-receptors failed to show significant upregulation throughout the first five postnatal weeks and alpha 1-receptors were unchanged except at 35 days of age, despite 70-95% depletion of norepinephrine. The failure to upregulate could not be attributed to the high background level of receptor expression commensurate with ontogenetic increases in receptor numbers, since the same deficiency was seen in the liver, a tissue in which beta-receptors decline with development; liver alpha 1-receptors also failed to upregulate after neonatal denervation. Examination of the linkage of beta-receptors to adenylate cyclase indicated major differences from mature regulatory mechanisms, as denervation supersensitivity was completely absent (liver) or emerged only transiently several weeks after 6-OHDA treatment (heart). In the heart, there was evidence for a defect in the G-protein-dependent component of the receptor/cyclase linkage that could contribute to the delayed appearance of supersensitivity. Because the fundamental patterns of receptor ontogeny and of adenylate cyclase responsiveness are still present after neonatal denervation, it is unlikely that neural input provides the major impetus for basal development. However, adult-type regulation of receptors and responses did not emerge even after a prolonged period; thus, neural input during a critical developmental stage may be required for the cell to learn how to adjust receptor expression and the receptor/cyclase link in response to stimulation.

Effect of chemical sympathectomy on (-)-isoprenaline-induced changes in cardiac beta-adrenoceptor subtypes in the guinea-pig and rat

1. Quantitative autoradiography was used to determine beta-adrenoceptor densities in cardiac regions of guinea-pigs and rats after chemical sympathectomy with 6-hydroxydopamine, and to examine how chemical sympathectomy affected beta-adrenoceptor changes following infusion of (-)-isoprenaline (400 micrograms kg-1 hr-1, 7 days). 2. Seven days after 6-hydroxydopamine (100 mg kg-1, i.v.), cardiac tissue levels of noradrenaline were reduced by 94.0 +/- 3.5% (guinea-pig) and 86.0 +/- 7.0% (rat). The blood pressure increase in rats to tyramine (0.5 mg, i.v.) was reduced from 118 mmHg in controls to 4.4 mmHg in 6-hydroxydopamine-treated animals. 3. There were no changes 7 and 14 days after 6-hydroxydopamine treatment in total, beta 1-and beta 2-adrenoceptor density in the atrioventricular conducting system and atrial and ventricular myocardium in both species. 4. In control animals, (-)-isoprenaline infusion produced selective reductions in beta 2-adrenoceptor density, whilst beta 1-adrenoceptor density remained unchanged. 5. In 6-hydroxydopamine treated guinea-pigs or rats, (-)-isoprenaline infusion caused no change in beta 1-adrenoceptors except in the right bundle branch whilst beta 2-adrenoceptors were reduced in the atrioventricular conducting system (atrioventricular node, bundle of His, right and left bundle branches) and myocardium (interventricular septum and atria). 6. The differential effect of (-)-isoprenaline on beta 1- and beta 2-adrenoceptors is not therefore due to the occupation of beta 1-adrenoceptors by noradrenaline or to prior down-regulation of beta 1-adrenoceptors by noradrenaline, since it persists after depletion of noradrenaline.

Characterization of muscarinic receptors mediating vasodilation in rat perfused kidney

The muscarinic receptor mediating vasodilation of resistance vessels in the rat isolated, constant-pressure perfused kidney (preconstriction by 10(-7) M cirazoline) was characterized by subtype-preferring agonists and selective antagonists. The agonists produced vasodilation with the following rank order of potency: arecaidine propargyl ester (APE) > 5-methylfurtrethonium = methacholine = oxotremorine > (S)-aceclidine > arecaidine 2-butyne-1,4-diyl bisester > 4-Cl-McN-A-343 = (R)-nipecotic acid ethyl ester = N-ethyl-guvacine propargyl ester approximately (R)-aceclidine = (S)-nipecotic acid ethyl ester > McN-A-343. Agonist-induced vasodilation disappeared after destruction of the endothelium with detergent. Highly significant correlations of agonist potencies for vasodilation were found between rat kidney and guinea-pig ileum submucosal arterioles as well as agonist potencies at smooth muscle muscarinic M3 receptors of the guinea-pig ileum. The rank order of antagonist potencies (4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > (R)-hexahydro-difenidol approximately hexahydro-sila-difenidol > pirenzepine approximately p-fluoro-hexahydro-sila-difenidol approximately himbacine approximately AF-DX 384 approximately AQ-RA 741 > (S)-hexahydro-difenidol) to attenuate vasodilation to APE in rat kidney, correlated significantly with affinities at M3 receptors in submucosal arterioles and in smooth muscle of the guinea-pig ileum, but differed from those at M1 and M2 receptors in rabbit vas deferens. The agonist and antagonist potencies suggest that vasodilation elicited by muscarinic stimuli in endothelium-intact rat renal vasculature is mediated by functional muscarinic M3 receptors.

Characterization of muscarinic receptors in rat kidney

Muscarinic receptors in mammalian kidney seem to be involved in diuresis. In this study we give a detailed characterization of receptors in rat kidney. Specific binding of [3H](-)-quinuclidinylbenzilate ([3H]QNB) to membranes of rat kidney cortex was saturable and of high affinity. A dissociation constant of 0.063 +/- 0.003 nM and a receptor density of 1.46 +/- 0.07 pmol/g wet weight were obtained. The dissociation kinetics could be best described by assuming a mono-exponential function (k-1 = (0.52 +/- 0.1) x 10(-4) s-1). The binding of [3H]QNB reached a maximum in 60 min at 0.6 nM at 37 degrees C. Competition experiments with the enantiomers of benzetimide confirmed the muscarinic nature of the [3H]QNB binding sites. The inhibition constants of pirenzepine (0.23 +/- 0.02 microM), (+-)-hexahydrosiladifenidol (0.040 +/- 0.002 microM), AF-DX 116 (1.45 +/- 0.07 microM), methoctramine (1.67 +/- 0.02 microM) and gallamine (78 +/- 3 microM) classified this receptor as an M3 receptor. Inhibition of [3H]QNB binding by the agonists methylfurtrethonium, arecoline, isoarecoline methiodide, arecaidine propargyl ester and McN-A-343 displayed monophasic inhibition curves. With (+/-)-cis-2-methyl-4-dimethylaminomethyl-1,3- dioxolane methiodide in two out of four experiments a small (11%) population of high affinity agonist sites could be detected. The potassium sparing diuretic amiloride inhibited [3H]QNB binding (36 +/- 3 microM). Although in a way related to the amiloride binding site, the muscarinic receptors in rat kidney are unlikely to be the primary target of diuretic action of this drug.

Autoradiographic localization of muscarinic receptors within the rat kidney

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [3H]quinuclidinyl benzylate (QNB) in kidney sections of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). [3H]QNB was bound by sections of rat kidney in a manner consistent with the labeling of muscarinic acetylcholine receptors. Anatomically, these receptor sites were located primarily within the smooth muscle of the renal vascular tree and to a lesser extent within cortical and medullary tubules. The density of renal muscarinic acetylcholine receptors (both vascular and tubular) was decreased in hypertension but the affinity of the ligand for muscarinic receptors was unchanged. A possible role of muscarinic acetylcholine receptors in renal function is suggested.

High NaCl diets increase alpha 2-adrenoceptors in renal cortex and medulla of NaCl-sensitive spontaneously hypertensive rats

Diets high in NaCl simultaneously elevate renal alpha 2-adrenoceptor binding and exacerbate hypertension in young NaCl-sensitive spontaneously hypertensive rats (SHR-S). The present study tests the hypothesis that in SHR-S on a high NaCl diet, an upregulation of renal alpha 2-adrenoceptors is present in densely innervated areas of the kidney, and this precedes the increase in blood pressure. Seven week old SHR-S fed on a high (8%) compared to basal (1%) NaCl diet for 2 weeks displayed significantly exacerbated hypertension and elevated renal alpha 2-adrenoceptor binding in both cortex and medulla. In contrast one week on the high NaCl diet did not alter renal alpha 2-adrenoceptor number or blood pressure in SHR-S. Autoradiographic experiments demonstrated that the NaCl-induced upregulation of alpha 2-adrenoceptors occurs in all areas of the renal cortex and medulla. None of these differences were observed in NaCl-resistant, Wistar-Kyoto rats (WKY). Further, the high NaCl diet did not alter renal alpha 1-adrenoceptor binding in SHR-S or WKY. Together with previous findings, these data suggest that the NaCl-induced upregulation of renal alpha 2-adrenoceptors is not specific to densely innervated regions of the kidney.

Renal nerve contribution to NaCl-exacerbated hypertension in spontaneously hypertensive rats

Previous studies demonstrate that bilateral renal denervation enhances urinary sodium excretion and delays the onset of hypertension in young (7-week-old) spontaneously hypertensive rats (SHR) maintained on ordinary laboratory chow. We interpret these data as suggesting that increased renal nerve activity in this model contributes to hypertension by causing excess sodium retention. More recent studies show that dietary NaCl supplementation increases blood pressure and peripheral sympathetic nervous system activity in NaCl-sensitive SHR (SHR-S). The present study tests the hypothesis that the renal nerves contribute to the rise in arterial pressure caused by dietary NaCl supplementation in this model. SHR-S were fed a high (8%) or basal (1%) NaCl diet beginning at age 7 weeks. Bilateral renal denervation was carried out 2 weeks after the initiation of the diets, at which time systolic blood pressure was significantly higher in the high (compared with the basal) NaCl group. Systolic blood pressure was reduced slightly less in denervated SHR-S on the high (compared with basal) NaCl diet during the following 5 weeks. Renal denervation performed 1 week before initiation of the diets attenuated the subsequent development of hypertension equally in both groups. Both renal denervation and the high NaCl diet increased alpha 2-adrenergic receptor numbers in the kidney; renal denervation caused an approximately equal increase in alpha 2-adrenergic receptor binding in SHR-S on high and basal NaCl diets. The high NaCl diet increased plasma noradrenaline concentration, and renal denervation lowered mean arterial pressure but did not decrease circulating catecholamines in either diet group.(ABSTRACT TRUNCATED AT 250 WORDS)