Renomedullary antihypertensive function in accelerated (malignant) hypertension. Observations on renomedullary interstitial cells

The NF-κB/FXR/TonEBP pathway protects renal medullary interstitial cells against hypertonic stress

Farnesoid X receptor (FXR), a ligand-activated transcription factor, plays an important role in maintaining water homeostasis by up-regulating aquaporin 2 (AQP2) expression in renal medullary collecting ducts; however, its role in the survival of renal medullary interstitial cells (RMICs) under hypertonic conditions remains unclear. We cultured primary mouse RMICs and found that the FXR was expressed constitutively in RMICs, and that its expression was significantly up-regulated at both mRNA and protein levels by hypertonic stress. Using luciferase and ChIP assays, we found a potential binding site of nuclear factor kappa-B (NF-κB) located in the FXR gene promoter which can be bound and activated by NF-κB. Moreover, hypertonic stress-induced cell death in RMICs was significantly attenuated by FXR activation but worsened by FXR inhibition. Furthermore, FXR increased the expression and nuclear translocation of hypertonicity-induced tonicity-responsive enhance-binding protein (TonEBP), the expressions of its downstream target gene sodium myo-inositol transporter (SMIT), and heat shock protein 70 (HSP70). The present study demonstrates that the NF-κB/FXR/TonEBP pathway protects RMICs against hypertonic stress.

Role of medullary progenitor cells in epithelial cell migration and proliferation

This study is aimed at characterizing medullary interstitial progenitor cells and to examine their capacity to induce tubular epithelial cell migration and proliferation. We have isolated a progenitor cell side population from a primary medullary interstitial cell line. We show that the medullary progenitor cells (MPCs) express CD24, CD44, CXCR7, CXCR4, nestin, and PAX7. MPCs are CD34 negative, which indicates that they are not bone marrow-derived stem cells. MPCs survive >50 passages, and when grown in epithelial differentiation medium develop phenotypic characteristics of epithelial cells. Inner medulla collecting duct (IMCD3) cells treated with conditioned medium from MPCs show significantly accelerated cell proliferation and migration. Conditioned medium from PGE2-treated MPCs induce tubule formation in IMCD3 cells grown in 3D Matrigel. Moreover, most of the MPCs express the pericyte marker PDGFR-b. Our study shows that the medullary interstitium harbors a side population of progenitor cells that can differentiate to epithelial cells and can stimulate tubular epithelial cell migration and proliferation. The findings of this study suggest that medullary pericyte/progenitor cells may play a critical role in collecting duct cell injury repair.

AMPK potentiates hypertonicity-induced apoptosis by suppressing NFκB/COX-2 in medullary interstitial cells

Cells residing in the hypertonic, hypoxic renal medulla depend on dynamic adaptation mechanisms to respond to changes in energy supply and demand. The serine/threonine kinase 5'-AMP protein kinase (AMPK) is a sensor of cellular energy status, but whether it contributes to the survival of cells in the renal medulla is unknown. Here, hypertonic conditions induced a decrease in AMPK phosphorylation within 12 hours in renal medullary interstitial cells (RMIC), followed by a gradual return to baseline levels. Activation of AMPK markedly increased hypertonicity-induced apoptosis of RMICs and suppressed both hypertonicity-induced NFκB nuclear translocation and cyclooxygenase-2 (COX-2) activation; overexpression of COX-2 significantly attenuated these effects. AMPK activation also markedly reduced generation of reactive oxygen species and nuclear expression of tonicity-responsive enhancer-binding protein, which prevented upregulation of osmoprotective genes. In vivo, pharmacologic activation of AMPK led to massive apoptosis of RMICs and renal dysfunction in the setting of water deprivation in mice. Taken together, these results identify a critical role for AMPK in the maintenance of RMIC viability and suggest that AMPK modulates the NFκB-COX-2 survival pathway in the renal medulla. Furthermore, this study raises safety concerns for the development of AMPK activators as anti-diabetic drugs, especially for patients prone to dehydration.

Persistent Hypotension Associated with Hypermedullipinemia: A New Syndrome

A new syndrome is described in a patient with advanced renal insufficiency. This consists of severe and persistent hypotension causing weakness but associated with a clear mental status. Also present is evidence for decreased vascular reactivity. The hypotension was not orthostatic. The hypotension was associated with a circulating vasodepressor substance having the characteristics of medullipin 1. The medullipin appears to have been derived from the remaining right kidney. Hypotension existed despite the presence of major prohypertensive mechanisms, including an endstage kidney, hyperreninemia and hyperaldosteronemia. It is likely that hypotension due to hypermedullipinemia is an entity occurring in the human being.

Transcriptional regulation of heme oxygenases by HIF-1alpha in renal medullary interstitial cells

The present study was designed to test the hypothesis that hypoxia-inducible factor-1alpha (HIF-1alpha)-mediated transcriptional activation contributes to increased expression of heme oxygenase (HO) genes in renal medullary interstitial cells (RMICs). By Northern blot analysis, HO-1 mRNA expression was found to significantly increase in response to reduction of PO(2) in culture medium. However, HO-2 mRNA was not altered by hypoxia. This hypoxia-induced upregulation of HO-1 mRNA was significantly blocked by HIF-1alpha inhibition with ferrous ammonium sulfate. To further determine the role of HIF-1alpha in the activation of HO-1, the inducers of HIF-1alpha were used to address whether induction of HIF-1alpha stimulates HO-1 mRNA expression. Both desferrioxamine and CoCl(2) markedly increased HIF-1alpha mRNA and protein levels and resulted in the upregulation of HO-1 mRNA but not HO-2. Furthermore, inhibition of HIF-1alpha degradation by CBZ-LLL, an inhibitor of ubiquitin-proteasome, significantly increased HIF-1alpha protein and HO-1 mRNA but not HO-2 in these cells. Using cis-element oligodeoxynucleotide transfection to specifically decoy HIF-1alpha and block HIF-1alpha binding, increased mRNA expression of HO-1 in response to hypoxia and CoCl(2) was attenuated. In vitro nuclear run-on assays further confirmed that hypoxia and alterations of HIF-1alpha mRNA or protein levels significantly affected the formation of HO-1 mRNA. Taken together, our results indicate that HO-1, but not HO-2, is transcriptionally activated by hypoxia through HIF-1alpha-mediated mechanism in RMICs. This hypoxia-induced transcriptional activation may be one of the important mechanisms mediating increased expression of HO-1 in the renal medulla.

Oxygen-dependent expression of hypoxia-inducible factor-1alpha in renal medullary cells of rats

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor that regulates the oxygen-dependent expression of a number of genes. This transcription factor may contribute to the abundant expression of many genes in renal medullary cells that function normally under hypoxic conditions. The present study was designed to determine the characteristics of HIF-1alpha cDNA cloned from the rat kidney and the expression profile of HIF-1alpha in different kidney regions and to explore the mechanism activating or regulating HIF-1alpha expression in renal medullary cells. A 3,718-bp HIF-1alpha cDNA from the rat kidney was first cloned and sequenced using RT-PCR and TA cloning technique. It was found that 823 amino acids deduced from this renal HIF-1alpha cDNA had 99%, 96%, and 90% identity with rat, mouse, or human HIF-1alpha deposited in GenBank, respectively. The 3'-untranslated region of HIF-1alpha mRNA from the rat kidney contained seven AUUUA instability elements, five of which were found to be conserved among rat, mouse, and human HIF-1alpha. Northern blot analyses demonstrated a corticomedullary gradient of HIF-1alpha mRNA expression in the kidney, with the greatest abundance in the renal inner medulla. Western blot analyses also detected a higher HIF-1alpha protein level in the nuclear extracts from the renal medulla than the renal cortex. A classic loop diuretic, furosemide (10 mg/kg ip), markedly increased renal medullary Po(2) levels from 22.5 to 52.2 mmHg, which was accompanied by a significant reduction of HIF-1alpha transcripts in renal medullary tissue. In in vitro experiments, low Po(2), but not elevated osmolarity, was found to significantly increase HIF-1alpha mRNA in renal medullary interstitial cells and inner medullary collecting duct cells. These results indicate that HIF-1alpha is more abundantly expressed in the renal medulla compared with the renal cortex. Increased abundance of HIF-1alpha mRNA in the renal medulla may represent an adaptive response of renal medullary cells to low Po(2).

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.

Selective targeting of cyclooxygenase-2 reveals its role in renal medullary interstitial cell survival

Renal medullary interstitial cells (MICs) are a major site of cyclooxygenase (COX)-mediated PG synthesis. These studies examined the role of COX in MIC survival. Immunoblot and nuclease protection demonstrate that cultured MICs constitutively express COX2, with little constitutive COX1 expression. SC-58236, a COX2-selective inhibitor, but not SC-58560, a COX1 inhibitor, preferentially blocks PGE2 synthesis in MICs. Transduction with a COX2 antisense adenovirus reduced MIC COX2 protein expression and also decreased PGE2 production. Antisense downregulation of COX2 was associated with MIC death, whereas a control adenovirus was without effect. Similarly, the COX2-selective inhibitor SC-58236 (30 microM) and several nonselective COX-inhibiting nonsteroidal anti-inflammatory drugs (NSAIDs), including sulindac, ibuprofen, and indomethacin, all caused MIC death. In contrast, SC-58560, a COX1-selective inhibitor, was 100-fold less potent for inducing MIC death than its structural congener SC-58236. NSAID-induced MIC death was associated with DNA laddering and nuclear fragmentation, consistent with apoptosis. These results suggest that COX2 plays an important role in MIC survival. COX2 inhibition may contribute to NSAID-associated injury of the renal medulla.

Pathophysiology of renovascular hypertension

Renovascular hypertension has its experimental counterpart in the two-kidney, one clip model (Goldblatt hypertension). From the study of this model, a general pathophysiological scheme has evolved suggesting that temporal stages in the development and maintenance of hypertension are regulated by complicated hormonal and neural interrelations. The central roles played by the renin-angiotensin system and the renal nerves is discussed as they relate to other hormones. In addition, the possible contribution of converting enzyme inhibitors to understanding the pathophysiology of this condition is discussed.

Morphometric studies of the renomedullary interstitial cells

The renomedullary interstitial cell (RIC) is a unique cell found in the renal medullary interstitium among the collecting ducts, Henle's loop, and the vasa recta. A combination of morphologic and physiologic studies has defined some of the properties of this cell, which is the apparent source of the mediators of the antihypertensive function of the kidney. These may include prostaglandins (PGE2), APRL or platelet activating factor, and the incompletely defined neutral lipid, ANRL (or medullipin), the most likely candidate for this function. The lipid droplets in the RIC apparently are the precursors of the mediator(s). Degranulation of the RIC by an experimental maneuver usually indicates increased activity of these cells. The presence of abundant well-granulated RIC in a kidney indicates a resistance of that animal to the induction of salt-sensitive forms of experimental hypertension. There is definite evidence for an extrarenal antihypertensive function of the RIC mediators, but an intrarenal effect also is considered.

Regional hemodynamic effects of antihypertensive renomedullary lipids in conscious rats

Renomedullary tissue has been proposed to exert an antihypertensive endocrine-like action. The antihypertensive polar renomedullary lipids (APRL) and neutral renomedullary lipids (ANRL) are potential mediators of this action. We evaluated the blood pressure and regional hemodynamic responses to APRL administered peripherally (i.v.) and to the central nervous system (CNS) in normal rats and rats with sinoaortic deafferentation (SAD) to remove baroreflex buffering. Rats were chronically instrumented with Doppler flow probes for measurement of mesenteric, renal, and hind-quarter vascular resistance, with arterial pressure and intravenous catheters, and with lateral cerebroventricular cannuli for intracerebroventricular (i.c.v.) administration. Intravenous APRL (0.01 to 1.0 micrograms) produced a dose-dependent decrease in blood pressure, tachycardia, and dilation of all vascular beds studied. The dose-response relationships were shifted to the left in SAD animals. APRL administered i.c.v. had no effect on intact or SAD rats. Pressor and regional vasoconstrictor responses to norepinephrine, angiotensin, and vasopressin were markedly reduced in SAD animals during constant infusion of APRL. In a second group of conscious SAD animals instrumented for blood pressure and heart rate measurements, intravenous ANRL (500 micrograms) decreased both arterial pressure (-45 +/- 16 mm Hg) and heart rate (-50 +/- 16 bpm). When given i.c.v., however, ANRL (10-100 micrograms) had no significant effect on resting blood pressure or heart rate. These studies suggest that APRL and ANRL produce no significant cardiovascular effects that are mediated through the CNS. However, both lipids are potent depressor agents, and APRL exhibits a strong peripheral vasodilator action and nonspecifically reduces reactivity to vasoconstrictor agents.

Chemical renal medullectomy. Effect on urinary prostaglandin E2 and plasma renin in response to variations in sodium intake and in relation to blood pressure

We have studied the possible vasodepressor role of the renal medulla by chemical medullectomy. Bromoethylamine hydrobromide (200 mg/kg) was injected to induce selective renal medullary necrosis in rats. The acute effects on sodium balance and long-term effects on blood pressure, plasma renin concentration (PRC) and urinary prostaglandin E2 (PGE2) were studied and compared with saline injected controls. There was an immediate and sustained increase in urine volume of low osmolality. Direct blood pressure in conscious free-moving animals was higher at 2 and 10 weeks after injection in medullary-damaged rats, although this was only significant at 10 weeks (136 +/- 3.3 vs 118 +/- 4.5 mm Hg, p less than 0.01). An initial negative sodium balance returned to normal by 7 days and rats with established medullary damage tolerated a wide range of sodium intakes. Although there was no evidence of sodium retention on the normal diet, with very high sodium loads some sodium retention was apparent since PRC was suppressed and body weight increased. Plasma creatinine and creatinine clearance were normal. PRC in rats with medullary damage was unchanged on normal diet and rose to similar levels as in control rats on low sodium intake. Urinary PGE2 was markedly reduced (148 +/- 54 vs 536 +/- 71 ng/day, p less than 0.01) in medullary damaged rats, consistent with the renal medulla being the major source of urinary PGE2. High salt intake increased urinary PGE2 in normal and proportionally in medullary damaged rats, whereas on a low sodium intake, urinary PGE2 was not different from that on the normal diet in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotensive and vasodilatory activity of (+/-) 1-o-octadecyl-2-acetyl glyceryl-3-phosphorylcholine in the normotensive rat

Synthetic (+/-) 1-O-octadecyl-2-acetyl-glyceryl-3-phosphorylcholine (octadecyl-AGPC) in microgram/kg doses given intravenously effectively and potently lowered mean arterial blood pressure in conscious and anesthetized normotensive rats. The hypotensive activity was much more pronounced in the anesthetized rat than in the conscious rat. The hypotension was associated with a significant elevation in plasma renin activity (PRA). In the rat in which the hindquarters were perfused, octadecyl-AGPC given intraarterially effectively decreased the perfusion and systemic pressures in a dose-dependent manner. Pharmacological blockade with specific cholinergic, histaminergic or beta-adrenergic receptor antagonists, did not block or attenuate the octadecyl-AGPC-induced reduction in perfusion or systemic pressure. These results suggest that the hypotensive activity of octadecyl-AGPC in the normotensive rat is the result of direct vasodilation and not the result of cholinergic, histaminergic or beta-adrenergic receptor interaction.

Morphometric studies of the renomedullary interstitial cells of Dahl hypertension-prone and hypertension-resistant rats

Two strains of rats, one genetically sensitive (the Dahl S rat) and the other resistant (the Dahl R rat) to the hypertensive effect of a high-salt diet were studied morphometrically for determination of whether any anatomic differences were present in the renomedullary interstitial cells (RICs) that might help explain these strain differences. The rats resistant to the hypertensive effects of sodium chloride had more RIC than those from the sensitive strain. In addition, they were more heavily granulated. These findings may be related to the known antihypertensive function of the RICs and may help explain observed differences in the prostaglandin metabolism of the Dahl S and R rats.

Auricular chondritis in rats. An experimental model of relapsing polychondritis induced with type II collagen

Outbred Wistar rats immunized with native type II collagen developed ear lesions resembling those of human relapsing chondritis. As in human disease, these lesions were characterized by intense chondritis, positive immunofluorescence reactions to IgG and C3, and circulating IgG reactive with native type II collagen. Furthermore, electron-dense deposits were seen near the surface of chondrocytes and corresponded with deposits of IgG and C3. These observations suggest a causal relation between humoral immunity to type II collagen and auricular chondritis in the rat and support the hypothesis than human relapsing polychondritis is an autoimmune disease mediated by immunity to type II collagen.

Renomedullary deficiency in partial nephrectomy-salt hypertension

Partial nephrectomy-salt hypertension (PN-SH) of the rat is associated with Na volume loading. As the hypertensive state evolves, the renomedullary interstitial cells (RIC) of the renal nubbin undergo major changes, decreasing significantly in number while the remaining ones exhibit degenerative changes. The antihypertensive action of the RIC in the renal nubbin, as measured by transplants of fragmented papillae into hypertensive recipients, virtually disappears as the hypertension develops. The changes in the RIC occur whether vascular disease of the kidney is or is not overtly present. It is suggested that deficiency of the antihypertensive action of the RIC allows the prohypertensive effects of Na volume loading to operate without proper control. Thus, the sustained hypertensive state of this model does not appear to be due solely to volume expansion. Rather, it appears due to a combination of the effects of Na and volume and a renomedullary deficiency of hormonal type. The specific cause(s) of the changes in the RIC was not determined. It seems evident that it is related to the high salt intake since the partial nephrectomy procedure without the added salt load did not alter the appearance of the RIC.

Alterations in responses to bradykinin, angiotensin I, and angiotensin II during the induction phase of one-kidney, one-wrapped hypertension and associated arterial disease in rabbits

During the induction phase of low-renin, one-kidney, one-wrapped hypertension in rabbits,serum angiotensin converting enzyme (ACE) activity is depressed and correlates inversely with the degree of necrotic arterial disease that develops. Responses to the vasoactive polypeptides, bradykinin (BK), angiotensin I (AI), angiotensin II (AII), the ACE blocker teprotide, and the AII antagonist 1-sar-8-ile AII were studied. Responses to BK, AII, and AI showed significant changes in both magnitude and duration (recovery time). Recovery time for depressor responses to BK in hypertensive rabbits was approximately three times that in the control period. One-wrapped, two-kidney control rabbits without hypertension-associated arterial disease showed no change in BK recovery time, although serum ACE activity was significantly depressed. In the experimental period BK recovery time correlated directly with the degree of arterial disease and indirectly with the final serum ACE activity. Duration of the pressor responses after AII correlated directly with the degree of arterial disease and indirectly with final serum ACE activity. In untreated hypertensive rabbits the percentage of increases in blood pressure after AI relative to control animals were decreased, and for all hypertensive rabbits' the increase in blood pressure correlated directly with the final serum ACE activity. Long-term treatment with teprotide moderated the hypertension but had little effect on serum ACE activity or the responses to BK, AII, and AI. Short-term infusions of 1-sar-8-ile AII and teprotide caused significant decreases in blood pressure in both the control and experimental periods, although no change in response to either polypeptide occurred. These studies support other evidence that pressor components of the renin-angiotensin system do not sustain the elevation of blood pressure in this form of experimental hypertension. Alterations in response patterns following AII and AI suggest that a vasodepressor system may be altered. In addition, part of the altered response to BK, and possibly AII, appears related to the development of the hypertension-associated arterial disease.

On the lipid granularity of renomedullary interstitial cells in benign and malignant courses of renal hypertension

The number of lipid droplets of the renal medullary interstitial cells was registered in 40 rats with "two-kidney Goldblatt hypertension" and in 27 sham operated normotensive controls. A strong degranulation in the unclaimed kidneys was always associated with the malignant course of hypertension, characterized by a disturbance in the sodium and water balance. Giving 2 per cent saline in addition to demineralized water as a drinking fluid the decrease in the number of granules was prevented in most of the malignant cases. Significant changes in the granule count were never registered at a benign course of hypertension. Degranulation of the medullary interstitial cells in the unclamped kidneys does not unequivocally represent the loss of medullary antihypertensive function. It seems to be directly determined by the disturbance of sodium and water balance and indirectly by the hypertension.

Prostaglandins and hypertension

Evidence is presented demonstrating the role of prostaglandins in salt metabolism and on peripheral vasodilation. A number of animal studies and observations in human hypertensive subjects suggest that the prostaglandin system plays a role in the pathogenesis of hypertension. The most striking and consistent finding over many decades of investigation is the relationship between dietary salt intake and the development of hypertension. Only a small percentage of any population develops hypertension. It is suggested that those people whose kidneys have an abnormal salt-handling capacity develop hypertension when challenged by a chronic high-salt intake. The salutary effects of diuretics or low-salt diet support this concept. Hypertension then is an expression of a renal abnormality. Prostaglandins, one of the renal salt regulating factors of the kidney, amy be involved in this abnormality. Whether there is a defect in the matabolic pathways or an unresponsiveness to normal stimuli of prostaglandins has not been determined. The use of prostaglandins in the treatment of hypertension is being explored. The demonstration that PGA1 can effectively lower blood pressure and reverse hypertensive emergencies indicates that prostaglandins probably have a broader, still unidentified role in the overall management of essential hypertension.

The effects of prostaglandin E1 and sodium meclofenamate on blood pressure in renal hypertensive rats

Conflicting evidence exists regarding the ability of PGE1 to normalize blood pressure in renal hypertensive rats. We performed experiments to determine the effect of PGE1 (15 mug/kg i.p. daily for 3 weeks) in renal hypertensive Wistars and found no significant change in systolic pressure. A higher dose (150 mug/kg i.p.) lowered pressure after 14 days of treatment, but not back to control levels. Further investigations are required to establish the mechanism whereby PGE1 evokes this fall. To test the hypothesis that endogenous prostaglandins have a hypotensive function in renal hypertension, experiments were performed using sodium meclofenamate to inhibit prostaglandin biosynthesis. In chronic hypertensive rats the drug had no significant effect, while in the acute phase of renal hypertension there was a dose-dependent inhibition of the pressure rise. The possibility is suggested that prostaglandins may initiate or sustain the acute phase of renal hypertension in rats.

Renomedullary interstitial cell lesions and hypertension

The notion that renomedullary nodules of the kidney arise as a response to hypertension was tested. Heart weight, ratio of heart weight to body weight, and blood pressure in 160 patients in whom such nodules were found at autopsy were compared with similar measurements in 160 patients without nodules. There were no significant differences between the two groups, and it was concluded that there was no evidence to support the idea that the renomedullary nodule represents a response to hypertension.

Peripheral circulation in arterial hypertension

The underlying causes of hypertensive disease remain unclear. This article has attempted to highlight potential dysfunctions in arterial pressure regulation which could either initiate or sustain the hypertensive process. As has been suggested innumerable times hypertension must certainly be a multifactorial abnormality. The current state of knowledge about control of the peripheral circulation in high arterial pressure reinforces the view that interactions between neurogenic, myogenic, humoral, and structural factors are probably disrupted when hypertension appears.

Analyses of renal medullary lipid droplets from normal, hydronephrotic, and indomethacin treated rabbits

Lipid droplets isolated from rabbit renal medullary tissue were analyzed and found to be composed of triglyceride and free fatty acids in a ratio of 2.9:1. These triglycerides were unique when compared to triglycerides of other rabbit tissues examined, in that they contained high percentages of octadecanoic acid (stearic acid, 9.8%), 5,8,11,14-eicosatetraenoic acid (arachidonic acid, 6.8%), and 7,10,13,16-docosatetraenoic acid (adrenic acid, 10%). Lipid droplet triglycerides were found to increase during experimental hydronephrosis and after administration of indomethacin, a prostaglandin synthetase and phosphodiesterase inhibitor. From gas liquid chromatography of fatty acid methyl esters of these triglycerides, it was determined that they were enriched further in their percent composition of 9,12-octadecadienoic acid (linoleic acid) and arachidonic acid, a prostaglandin precursor. The inverse relationship between lipid droplets and prostaglandin content in the inner medulla suggested a significant role of lipid droplet triglycerides as storage pools for prostaglandin precursors.

Primary role of renal homografts in setting chronic blood pressure levels in rats

The genotype of homograft kidneys plays the primary role in determining chronic blood pressure levels in two strains of rats with opposite genetically controlled propensities for hyptertension. In hypertensive rats from the hypertension-prone (S) strain, a renal homograft from the same strain resulted in a slight rise in blood pressure to a level that was equivalent to that in appropriate uninephrectomized S controls. In contrast, a renal homograft from the hypertension-resistant (R) strain led to a sharp fall in blood pressure in hypertensive S recipients. Opposite results were found when the host came from the R strain: R homografts maintained the same low pressure as that seen in controls, whereas S homografts resulted in hypertension. We concluded that genetically controlled factors operating through the kidney can chronically modify the blood pressure up or down. The central role of the kidney in hypertension is thus further documented.

Experimental hypertension. The effects of chemical ablation of the renal papilla on the blood pressure of rats with and without silver-clip hypertension

Because of the ease with which ablation of the renal papilla of the rat can be effected by chemical means, a study was carried out to determine the effects of this ablation on the blood pressure. Significant elevation was found, lennding support to the idea of the antihypertensive role of the renal medulla. Constriction of one renal artery of rats with their papillae removed resulted in a more rapid and greater elevation of pressure than the same procedure in rats ith their papillae intact. The rise in pressure approximated the sum of the rises caused by removal of the papilla alone and by renal artery constriction alone, consistent with the idea of two mechanisms being at work in this model.

Experimental oliguric acute renal failure: protective effects of renomedullary autotransplants

An acute circulatory renal failure (ARF) was induced in 18 rabbits by temporary ischemia of the remaining kidney 8 days after unilateral nephrectomy and subcuteaneous autotransplantation of renomedullary tissue.--Mortality in the postischemic course was 50% in treated animals but 100% in the control group (n = 18) without autotransplantation. In the postischemic period plasma urea concentration was significantly lower (p smaller than 0.005) in the surviving transplanted animals and excretion of sodium and water significantly higher (p smaller than 0.005) as compared with the control group. Plasma renin values which were significantly lower than thos of the control(p smaller than 0.005) had decreased significantly even as compared with the initial values. These results indicate that hormonal substances are produced in interstitial cells of renomedullary autotransplants exerting a distinct protective effect against experimental acute renal failure. Decreased plasma renin activity may point to an inhibition of circulating and/or intrarenal renin by lipids originating from the transplants. Changes in sodium and water excretion indicate effects of circulating prostaglandins

Genetic Influence of the Kidneys on Blood Pressure

In two strains of rats with opposite genetic propensities for hypertension, interstrain renal transplants chronically modified the blood pressure of the recipients. The blood pressure of rats with these renal homografts was largely determined by the genotype of the donor kidney rather than by the genotype of the recipient. Kidneys from the hypertension-resistant (R) rats generally had an antihypertensive effect, and kidneys from the hypertension-prone (S) rats had a prohypertensive effect. These effects on blood pressure were most clear-cut in rats maintained on a low-sodium diet, but they were still evident in a modified form in rats on a high-sodium diet. Results from this study and from earlier studies suggest that kidneys from S rats have a greater hypertensinogenic and a smaller antihypertensive capacity than do kidneys from R rats. Therefore the influence of the kidney on blood pressure appears to have genetic determinants. If this finding is applicable to man, it would help to explain the well-established but anomalous observation that one of two individuals who apparently have similar renal disorders can have hypertension when the other does not.

Output of prostaglandins from the rabbit kidney, its increase on renal nerve stimulation and its inhibition by indomethacin

1. In each of six experiments, prostaglandins were identified in the renal venous blood of the rabbit. The concentrations in renal venous blood were up to 45 times higher than in aortic blood, suggesting that most of the prostaglandins originate from the kidney.2. Prostaglandins E(2), F(2a) and a prostaglandin of the A, C or B series were estimated by biological assay after solvent partition and column or thin-layer chromatography.3. Prostaglandins E(2) and F(2a) were identified conclusively by combined gas chromatography-mass spectrometry.4. Electrical stimulation of the renal nerve increased the output of prostaglandins.5. Indomethacin (10 mg/kg) injected intravenously, reduced the output of prostaglandins into renal venous blood and prevented the increase in output on renal nerve stimulation.