Acute pressure-natriuresis relationship following withdrawal of chronic noradrenaline infusion.

1. Pathological changes to the kidney, such as vascular remodelling, have been found in several models of hypertension and may contribute to the maintenance of hypertension or confer susceptibility to redeveloping hypertension after the original prohypertensive stimulus is withdrawn. 2. To investigate whether noradrenaline-induced hypertension induces persistent, functionally important changes to the kidney, the acute pressure-natriuresis relationship was characterized in anaesthetized rats under controlled neural and hormonal conditions following chronic (14 days) intravenous infusion of noradrenaline (48 microg/kg per h) or vehicle (0.04 mg/mL ascorbic acid and 0.156 mg/mL NaH2PO4 2 H2O in 10 IU/mL heparinized saline). 3. Conscious mean arterial pressure was significantly elevated by infusion of noradrenaline at 48 microg/kg per h (+10 +/- 2 mmHg at Day 14; P < 0.01 vs vehicle group). The acute relationships between arterial pressure and renal blood flow, glomerular filtration rate, Na+ excretion and urine flow were not significantly different between the noradrenaline- and vehicle-infused rats immediately after termination of noradrenaline infusion. 4. In summary, chronic intravenous noradrenaline infusion did not cause persistent changes in renal function, indicating that, in contrast with many models of hypertension, this model does not induce underlying prohypertensive changes to the kidney.

Tumour-derived TGF-beta1 modulates myofibroblast differentiation and promotes HGF/SF-dependent invasion of squamous carcinoma cells.

The development of an altered stromal microenvironment is a common feature of many tumours including squamous cell carcinoma (SCC), and there is increasing evidence that these changes in the stroma, which include increased expression of proteases and cytokines, may actually promote tumour progression. A common finding is that stromal fibroblasts become 'activated' myofibroblasts, expressing smooth muscle actin and secreting cytokines, proteases and matrix proteins. We show that myofibroblasts are commonly found in the stroma of oral SCC and are often concentrated at the invasive margin of the tumour. Using oral SCC cells and primary oral fibroblasts, we demonstrate that tumour cells directly induce a myofibroblastic phenotype, and that this transdifferentiation is dependent on SCC-derived TGF-beta1. In turn, myofibroblasts secrete significantly higher levels of hepatocyte growth factor/scatter factor compared with fibroblast controls, and this cytokine promotes SCC invasion through Matrigel, a mixture of basement membrane proteins. This is the first time that this double paracrine mechanism has been demonstrated between squamous carcinoma cells and fibroblasts, and emphasises that cancer invasion can be promoted indirectly by the release of tumour-induced host factors from stroma.

Chronic angiotensin converting enzyme inhibition enhances renal vascular responsiveness to acetylcholine in anaesthetized rabbits.

OBJECTIVE: To determine whether 6 weeks continuous treatment with an angiotensin converting enzyme (ACE) inhibitor reduced renal vascular responsiveness in vivo, since this treatment results in extensive phenotypic conversion of afferent arteriolar cells from contractile to endocrine-like, renin secretory cells. METHODS: Enalapril (10 microg/kg per h s.c.) was delivered continuously for 6 weeks. In anaesthetized rabbits (treated or sham), arterial blood pressure and renal blood flow were measured and renal responsiveness tested by constructing dose-response curves to bolus doses of phenylephrine, angiotensin II and acetylcholine delivered directly into the renal artery. RESULTS: ACE inhibition resulted in a significant shift to the left in the renal vascular conductance responses to acetylcholine (P < 0.005) and angiotensin II (P < 0.05), indicating enhanced, not reduced, responsiveness to these agents. There were no significant effects of chronic ACE inhibition on the conductance responses to phenylephrine. CONCLUSIONS: Contrary to our hypothesis, 6 weeks ACE inhibition did not reduce renal vascular responsiveness to three vasoactive agents, suggesting that the phenotypic changes observed in the afferent arterioles and to a lesser extent the interlobular arteries, were either insignificant or compensated for by other changes in renal circulatory control.

Renal vascular resistance properties and glomerular protection in early established SHR hypertension.

OBJECTIVE: To characterize the in vivo vascular properties of the spontaneously hypertensive rat (SHR) renal vascular bed by examining vascular conductance/resistance responsiveness to vasoactive agents in vivo and determining whether the filtration surface area of glomerular capillaries is reduced. DESIGN AND METHODS: in vivo renal blood flow responses to intrarenally administered angiotensin II, phenylephrine and acetylcholine were compared in 10-week-old SHR and Wistar-Kyoto (WKY) rats using a wide range of doses from near threshold to near maximal effect. Unbiased stereological techniques and high-resolution light microscopy were used to estimate the surface area and length of glomerular capillaries, and evidence of capillary damage. RESULTS: The SHR renal bed demonstrated significantly enhanced dose-vascular resistance responses to vasoconstrictors. For vascular conductance and calculated radius of resistance vessels, the SHR curves were significantly lower across the full dilator-constrictor range examined, but the dose-related changes were similar to those of WKY rats. There were only modest enhancements of the renal blood flow responses in the SHR, evident only when renal blood flow was reduced by more than 50% SHR and WKY rats did not differ in mean glomerular capillary surface area (0.13+/-0.02 mm2 and 0.14+/-0.02 mm2, respectively) or length (5.76+/-0.85 mm and 5.48+/-0.90 mm, respectively) nor was there evidence of glomerular capillary damage in either strain. CONCLUSIONS: The renal vascular bed of the SHR in vivo exhibits reduced vascular conductance across a wide vasomotor range, compatible with findings in other vascular beds. We have further shown no evidence of reduced glomerular capillary surface area or damage. These findings are compatible with the hypothesis that the reduced conductance of the SHR pre-glomerular vasculature increases the aorta-capillary pressure gradient thus protecting the glomerular capillaries from systemic hypertension at this age.

Renomedullary interstitial cell lipid droplet content is increased in spontaneously hypertensive rats and by low salt diet.

OBJECTIVE: To compare the volumes of renomedullary interstitial cell (RMIC) lipid droplets (putative source of vasodepressor substance) in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats on high and low salt diets as an indication of whether the renomedullary vasodepressor system of the SHR is defective. METHODS: Ten-week-old male SHR and WKY rats received a low (0.05% w/w) or high salt (5.0%) diet for 21 days. Conscious mean arterial pressure (MAP) was measured and the renal papilla perfusion fixed with a high osmolarity fixative. Using electron microscopic stereological techniques, the volume density of lipid in RMIC (VVLipid,RMIC) and the total volumes of lipid (VLipid) and RMIC (VRMIC) in papilla were measured. RESULTS: MAP of SHR (high 155 +/- 3 mmHg; low 151 +/- 3 mmHg) was significantly greater than WKY rats (high 126 +/- 2 mmHg; low 129 +/- 2 mmHg; P< 0.001), however salt diet had no significant effect on MAP. The VLipid of rats on the low salt diet was approximately 2.5 times greater than in rats on the high salt diet (P < 0.01). SHR had significantly greater VLipid than WKY rats irrespective of salt diet (P< 0.05; SHR-low 0.245 +/- 0.031 mm3, SHR-high 0.093 +/- 0.007 mm3; WKY-low 0.126 +/- 0.032 mm3, WKY-high 0.051 +/- 0.020 mm3). Similar differences were seen for VVLipid,RMIC, however VRMIC was not different between rat strains or salt diet groups. CONCLUSIONS: SHR and WKY rats responded similarly to the altered salt diets, and SHR demonstrated greater volumes of stored RMIC lipid droplets irrespective of the level of salt intake. These results indicate that SHR hypertension is not due to a deficiency in the amount of lipid droplets, the putative source of the renomedullary vasodepressor substance and that the renomedullary vasodepressor system of the SHR is capable of responding normally to the physiological stimulus of altered salt intake.

Glomerular hypertension and hyperfiltration in adrenocorticotrophin-induced hypertension in rats: the role of nitric oxide.

OBJECTIVE: To determine the effects on pre- and post-glomerular vascular resistance of adrenocorticotrophin (ACTH)-induced hypertension in rats, before and after blockade of nitric oxide formation. DESIGN: Four groups of Sprague-Dawley rats were studied. Measurements were made in ACTH- (Synacthen Depot, 0.25 mg/kg twice daily for 8 days) and sham-treated anaesthetized rats, before and after either Nomega-nitro-L-arginine (L-NNA, 6 mg/kg) or vehicle. METHODS: Whole-kidney and single-nephron haemodynamics and function were measured. Glomerular capillary pressure was estimated from tubular stop-flow pressure measurements. RESULTS: Blood pressure (P < 0.001), renal blood flow (RBF, P < 0.05) and glomerular filtration rate (P < 0.01) were increased following ACTH treatment compared with sham. There were no differences in either total renal, or pre- or post-glomerular vascular resistances, but stop-flow-estimated glomerular capillary pressure was elevated (P < 0.001) as was single-nephron glomerular filtration rate (SNGFR) (P < 0.001) and single-nephron blood flow (P < 0.01 ) in the ACTH- compared to the sham-treated rats. L-NNA treatment increased blood pressure by a similar extent in both ACTH- and sham-treated rats, but reduced RBF (P < 0.05) and glomerular filtration rate (GFR) (P < 0.05) more in the ACTH group; similar changes were seen in single-nephron values. L-NNA increased pre- and post-glomerular resistances to a greater extent in the ACTH group. CONCLUSIONS: ACTH-induced hypertension produced glomerular hypertension and hyperfiltration, which may be due to nitric oxide-related vasodilatation of the renal vasculature.

Presence of a pet dog and human cardiovascular responses to mild mental stress.

The mechanisms underlying the possible cardiovascular benefits of pet ownership have not been established. Using a randomized design, the effect of a friendly dog on cardiovascular and autonomic responses to acute, mild mental stress was investigated. Seventy-two subjects (aged 40 +/- 14 y; mean +/- SD) participated. Rest was alternated with mental stress during four 10-minute periods. An unknown dog was randomly selected to be present during the first or the second half of the study. Blood pressure (BP) and heart rate (HR) were monitored continuously and cardiac autonomic function assessed using spectral analysis of heart period. Heart period variability data were expressed as the ratio of 0.1 Hz to respiratory or high frequency variation (LF/HF). Whereas mental stress significantly increased BP and HR in the absence of the dog (from 125/71 +/- 3/2 to 133/75 +/- 3/2 mm Hg; p <0.001), the presence of the dog had no effect on these variables. Heart period LF/HF ratio was lowest in dog owners in the presence of the dog (dog present 2.8 +/- 0.3 versus dog absent 3.4 +/- 0.4; p <0.001) and in non-dog owners in the absence of the dog (dog present 3.4 +/- 0.4 versus dog absent 2.8 +/- 0.3; p <0.001). In conclusion, a friendly but unfamiliar dog does not influence BP or HR either at rest or during mild mental stress. Cardiac autonomic profile was most favorable in the presence of the dog for dog owners and in the absence of the dog for non-owners.

Effects of renal arterial endothelin-1 and endogenous endothelins on regional kidney blood flow and renal antihypertensive mechanisms in anesthetized rabbits.

To determine how endothelins affect regional kidney blood flow and responses to increased renal artery pressure (RAP), an extracorporeal circuit was established to control RAP independent of the mean systemic arterial pressure (MAP). RAP was first set at approximately 65 mm Hg, and endothelin-1 (1 ng/kg/min for 30 min then 0.4 ng/kg/min) or vehicle was infused into the renal artery, or the ET(A)/ET(B) antagonist TAK-044 (3 mg/kg plus 3 mg/kg/h) or vehicle was administered intravenously. RAP was then progressively increased in steps from approximately 65 to approximately 160 mm Hg. When RAP was approximately 65 mm Hg, endothelin-1 increased renal vascular resistance (RVR, 72%), and reduced cortical (CBF, 26%) but not medullary blood flow (MBF). TAK-044 reduced MAP (12%) and RVR (15%) and increased CBF (21%) but not MBF. When RAP was increased, renal blood flow (RBF), glomerular filtration rate, and urine and sodium excretion increased, while MAP fell. These responses were unaffected by endothelin-1. TAK-044 potentiated the increases in RBF and reductions in MAP in response to increased RAP, but did not affect urine and sodium excretion. Plasma renin activity was reduced by endothelin-1 and increased by TAK-044. Thus, both exogenous and endogenous endothelins reduce CBF but not MBF, and reduce plasma renin activity, but neither affect pressure natriuresis.

Angiotensin II infused intrarenally causes preglomerular vascular changes and hypertension.

The effects on the renal vasculature and on arterial blood pressure of chronic infusion of low doses of angiotensin II (Ang II) into the renal artery were studied. Sprague Dawley rats were infused continuously with Ang II (0.5, 1.5, or 4.5 ng. kg(-1). min(-1)) or vehicle into the right renal artery (contralateral nephrectomy). Intrarenal Ang II infusion for 25 days produced dose-dependent rises (P:<0.001) in awake mean arterial pressure (111+/-1, 119+/-5, and 130+/-3 mm Hg in rats receiving 0.5, 1.5, and 4.5 ng. kg(-1). min(-1) Ang II, respectively) compared with 105+/-1 mm Hg (vehicle). Renal vessel lumen characteristics were assessed with an established, maximally dilated, isosmotic perfused kidney preparation. This revealed a small dose-dependent right shift in the pressure-flow relation (P=0.05), as well as a dose-dependent right shift and a dose-dependent reduction in the slope of the pressure-glomerular filtration rate relation (P=0.04 and 0.03, respectively). The effects of Ang II infusion on arterial pressure were not affected by the timing of the contralateral nephrectomy but were reduced when the contralateral kidney remained in situ. Acute losartan administration (10 mg/kg IV bolus) produced similar effects on arterial pressure in rats infused with vehicle or Ang II (4.5 ng. kg(-1). min(-1)) for 14 days, P=0.89), indicating the lack of systemic spillover of Ang II. Intraperitoneal Ang II (0.5, 1.5, or 4.5 ng. kg(-1). min(-1) for 25 days) had no effect on arterial pressure. Thus, chronic intrarenal infusion of low doses of Ang II resulted in changes in the renal vasculature compatible with dose-related structural reductions in the lumen diameter of preglomerular vessels and produced dose-related increases in arterial pressure.

Renovascular hypertension: structural changes in the renal vasculature.

Experimental narrowing of the main renal artery to produce hypertension increases the aorta-glomerular capillary pressure difference and vascular resistance. This article examines the hypothesis that hypertension also may be caused by structural changes that narrow intrarenal blood vessels, similarly increasing preglomerular vascular resistance and the aortic-glomerular capillary pressure gradient. There is evidence of both wall hypertrophy and lumen narrowing of the preglomerular arteries in spontaneously hypertensive rats, with increased preglomerular resistance and aortic-glomerular capillary pressure difference. We have also attempted to induce structural changes in renal-preglomerular vessels experimentally by infusing angiotensin II at low doses (0.5 to 4.5 ng/kg per minute) into the renal artery of Sprague-Dawley rats and greyhound dogs for up to 4 weeks. This angiotensin II infusion produced apparent dose-related effects on preglomerular vessel structure and hypertension. The possibility that hypertension may be induced by structural changes in preglomerular resistance vessel walls, by simulation of the hemodynamic effects of main renal artery stenosis, deserves further investigation.

Sex differences in pressure diuresis/natriuresis in rabbits.

We tested for sex-related differences in the pressure diuresis/natriuresis relationships in anaesthetized, renally denervated rabbits, using an extracorporeal circuit to perfuse the left kidney with the rabbit's own blood, through a series of step-wise increases in renal artery pressure (RAP) (from 65 to 130 mmHg). Urine flow, sodium excretion, and the fractional excretions of sodium and urine increased with increasing RAP, and were greater in male than in female rabbits at all levels of RAP-tested. However, these apparent sex-related differences in the acute pressure diuresis/natriuresis relationships were not reflected in alterations in chronic regulation of mean arterial pressure (MAP). Thus, in rabbits on a normal salt diet (0.85 g day(-1)), resting conscious MAP was significantly greater in males (87 +/- 3 mmHg) compared with females (77+/-1 mmHg). Chronically increasing daily salt intake to 4.98 g day(-1) for 28 days had no significant effect on resting conscious MAP in either sex. Thus, although our observations indicate sex differences, at least under the present experimental conditions, in the factors regulating extracellular fluid volume, these do not appear to have a major impact in setting the level of MAP in the long term.

Effects of angiotensin II on regional afferent and efferent arteriole dimensions and the glomerular pole.

The diversity of renal arteriole diameters in different cortical regions has important consequences for control of glomerular capillary pressure. We examined whether intrarenal angiotensin II (ANG II; 0.1, 1, or 5 ng. kg(-1). min(-1)) in anesthetized rabbits acts preferentially on pre- or postglomerular vessels using vascular casting. ANG II produced dose-related reductions in afferent and efferent diameters in the outer, mid, and inner cortex, without effecting arterial pressure. Afferent diameter decreased more than efferent in the outer and mid cortex (P < 0.05) but by a similar extent in juxtamedullary nephrons (P = 0.58). Calculated efferent resistance increased more than afferent, especially in the outer cortex (127 vs. 24 units; 5 ng. kg(-1). min(-1) ANG II). ANG II produced significant dose-related increases in the distance between the arterioles at the entrance to the glomerular pole in all regions. Thus afferent diameter decreased more in response to ANG II, but efferent resistance rose more due to smaller resting luminal dimensions. The results also indicate that glomerular pole dimensions change in response to ANG II.

Extended angiotensin converting enzyme inhibition changes the innervation of renal glomerular afferent arterioles.

Chronic inhibition of the angiotensin I converting enzyme (ACE) with enalapril, results in a phenotypic change of the medial cells of renal afferent arterioles from contractile smooth muscle cells to renin containing epithelioid cells. In normal animals, the density of the innervation of the juxtaglomerular renin containing epithelioid cells is much lower compared to the contractile cells. The effector tissues are known to play an important role in determining the pattern and density of their innervation. In this study, we tested the hypothesis that the density of the innervation of the afferent arteriole smooth muscle cells decreases when they change their phenotype from contractile to renin containing epithelioid cells. The results show that the density of the innervation had significantly increased and the association of the terminals with the smooth muscle cells had changed. There were significantly more varicosities around renal afferent arterioles from rabbits treated with enalapril (10 microg/kg/h) for 6 weeks (mean +/- SEM = 634 +/- 175 x 10(3)/mm2 vessel surface, cf. 329 +/- 69 x 10(3)/mm2 vessel surface in untreated rabbits, P = 0.05), with the number of neuroeffector junctions remaining the same (124 +/- 14 and 164 +/- 32 x 10(3)/mm2 vessel surface) and significantly more non-contacting varicosities (i.e. lying > 100 nm from the medial cells) (74 +/- 5% and 25 +/- 7%, respectively; P = 0.003). Thus, there was no reduction in the innervation of afferent arterioles in which the smooth muscle cells had changed phenotype in response to enalapril treatment as hypothesised. Instead, it would appear that proliferation of the innervation had occurred, with the formation of additional varicosities but these varicosities failed to form neuromuscular junctions. This study has identified a form of neural plasticity in the kidney that has not previously been described.

Renal hemodynamic responses to intrarenal infusion of ligands for the putative angiotensin IV receptor in anesthetized rats.

Angiotensin IV, a hexapeptide fragment (3-8) of angiotensin II metabolism, has been reported to produce vasodilatation within the renal vasculature by activation of the putative AT4 receptor. However, there are conflicting findings, with previous in vivo studies providing evidence for and against a renal vasodilator action of angiotensin IV. In this study, the renal hemodynamic responses to activation of the putative AT4 receptor were studied in anesthetized rats by left renal arterial infusion of two endogenous ligands, angiotensin IV and LVV-hemorphin-7. Angiotensin IV (10, 100, and 1,000 pmol/min) infusion caused dose-dependent reductions in blood flow to the infused kidney, which were abolished by pretreatment with losartan. In respect to this effect, angiotensin IV was approximately 300-fold less potent than angiotensin II. There were no significant effects of angiotensin IV on mean arterial pressure, heart rate, or blood flow to the noninfused kidney. Intrarenal infusion of LVV-hemorphin-7 (10, 100, and 1,000 pmol/min) had no significant effect on renal blood flow in the infused and noninfused kidneys, or on mean arterial pressure or heart rate. These results provide no evidence for a renal vasodilatory action of angiotensin IV or LVV-hemorphin-7. On the contrary, intrarenal angiotensin IV infusion produced vasoconstriction of the renal vasculature, mediated by activation of AT1 receptors. These observations provide evidence against a vasodilatory role of putative AT4 receptors in the rat kidney.

Effects of naloxone on the haemodynamic and renal functional responses to plasma volume expansion in conscious rabbits.

We tested whether the opioid antagonist naloxone affects responses to plasma volume expansion (PVE) in conscious rabbits. Under basal conditions, naloxone (6 mg x kg-(1) plus 0.3 mg x kg(-1) x min(-1) i.v.) had no observable effect, except to slightly reduce heart rate. During vehicle treatment, PVE (Haemaccel; 1 ml x kg(-1) min(-1) for 30 min plus 0.2 ml x kg(-1) x min(-1) for 60 min i.v.) reduced haematocrit by 7.1+/-0.8% (from 34.8+/-1.1%), and increased central venous pressure by 3.0+/-0.9 mmHg (from -2.8+/-1.5 mmHg), cardiac output by 42+/-9 ml min(-1) x kg(-1) (from 152+/-17 ml x min(-1) x kg(-1)), systemic vascular conductance by 0.49+/-0.11 ml x min(-1) x mmHg(-1) kg(-1) (from 1.58+/-0.23 ml x min(-1) x mmHg(-1) x kg(-1)), urine flow by 0.13+/-0.04 ml x kg(-)x min(-1) (from 0.12+/-0.02 ml kg(-1) x min(-1)) and sodium excretion by 21+/-5 micromol x kg(-1) min(-1) (from 5+/-2 micromol x kg(-1) x min(-1)). During naloxone treatment, the PVE-induced changes in haematocrit and central venous pressure were similar to those during vehicle treatment, but the increases in cardiac output (24+/-7 ml kg(-1) min(-1)), systemic vascular conductance (0.25+/-0.05 ml min(-1) x kg(-1) x mmHg(-1)), urine flow (0.09+/-0.03 ml x kg(-1) min(-1)) and sodium excretion (11+/-4 micromol x kg(-1) x min(-1)) were 31-49% less. These observations indicate that endogenous opioids mediate some of the circulatory and renal excretory responses to PVE in conscious rabbits.

Effects of long-term intrarenal angiotensin II infusion on renal vascular responsiveness to vasoactive agents.

1. We tested whether chronic intrarenal angiotensin II (AngII) infusion altered renal vascular responsiveness to vasoactive agents, which would provide evidence of vascular structural changes. 2. The renal blood flow (RBF) responses to renal arterial administration of bolus doses of acetylcholine, glyceryl trinitrate, AngII and noradrenaline were measured before commencement of and 1 day after cessation of 28 days intrarenal AngII infusion (0.5 ng/kg per min) in chronically instrumented conscious dogs. 3. The RBF responses to these vasoactive agents were unaltered by chronic intrarenal AngII infusion in conscious dogs. 4. These functional studies provide no evidence for renal vascular hypertrophy in response to chronic intrarenal AngII infusion in conscious dogs.

Effects of intrarenal infusion of 17-octadecynoic acid on renal antihypertensive mechanisms in anesthetized rabbits.

To characterize the role of cytochrome P450 metabolism of fatty acids in the renal response to increased renal perfusion pressure, we tested the effects of renal arterial infusion of 17-octadecynoic acid (17-ODYA, 450 nmol/min) on renal and systemic hemodynamic, and renal excretory responses to step-wise increases in renal perfusion pressure (RPP) in anesthetized rabbits, using an extracorporeal circuit for renal autoperfusion. Inhibition of cytochrome P450-dependent fatty acid metabolism was estimated by comparing the metabolism of arachidonic acid in microsomes prepared from the kidneys of control and 17-ODYA-treated animals. Step-wise increases in RPP decreased mean arterial pressure, which previous studies have indicated is attributable to the release of a depressor hormone from the renal medulla. Elevations in RPP also increased renal blood flow and glomerular filtration rate, and the absolute and fractional excretions of urine and sodium. Intrarenal infusion of 17-ODYA reduced the metabolism of arachidonic acid to 20-hydroxyeicosatetraenoic acid by 41%, but it did not significantly influence the responses to increased renal perfusion pressure. We conclude that either the responses elicited by increased renal perfusion pressure in anesthetized rabbits do not depend on cytochrome P450-dependent fatty acid metabolism, or that cytochrome P450 activity must be inhibited by more than was achieved in the present study (41%), before functional effects on the response to increased renal perfusion pressure are observed.