Renomedullary and intestinal hyaluronan content during body water excess: a study in rats and gerbils

The role of hyaluronan in renal cell carcinoma

Renal cell carcinoma (RCC) is associated with high mortality rates worldwide and survival among RCC patients has not improved significantly in the past few years. A better understanding of the pathogenesis of RCC can enable the development of more effective therapeutic strategies against RCC. Hyaluronan (HA) is a glycosaminoglycan located in the extracellular matrix (ECM) that has several roles in biology, medicine, and physiological processes, such as tissue homeostasis and angiogenesis. Dysregulated HA and its receptors play important roles in fundamental cellular and molecular biology processes such as cell signaling, immune modulation, tumor progression and angiogenesis. There is emerging evidence that alterations in the production of HA regulate RCC development, thereby acting as important biomarkers as well as specific therapeutic targets. Therefore, targeting HA or combining it with other therapies are promising therapeutic strategies. In this Review, we summarize the available data on the role of abnormal regulation of HA and speculate on its potential as a therapeutic target against RCC.

Recent advances and prospects of hyaluronan as a multifunctional therapeutic system

Hyaluronan (HA) is a naturally occurring non-sulfated glycosaminoglycan (GAG), cell-surface-associated biopolymer and is the key component of tissue extracellular matrix (ECM). Along with remarkable physicochemical properties, HA also has multifaceted biological effects that include but not limited to ECM organization, immunomodulation, and various cellular processes. Environmental cues such as tissue injury, infection or cancer change downstream signaling functionalities of HA. Unlike native HA, the fragments of HA have diversified effects on inflammation, cancer, fibrosis, angiogenesis and autoimmune response. In this review, we aim to discuss HA as a therapeutic delivery system development process, source, biophysical-chemical properties, and associated biological pathways (especially via cell surface receptors) of native and fragmented HA. We also tried to address an overview of the potential role of HA (native HA vs fragments) in the modulation of inflammation, immune response and various cancer targeting delivery applications. This review will also highlight the HA based therapeutic systems, medical devices and future perspectives of various biomedical applications were discussed in detail.

Abundance and size of hyaluronan in naked mole-rat tissues and plasma

Large amounts of ultra-high molecular weight hyaluronan (HA) have been described as the main cause of cancer resistance in naked mole-rats (Heterocephalus glaber, NMR). Our work examined HA metabolism in these rodents more closely. HA was localized and quantified using HA binding proteins. Its molecular weight was determined using size exclusion chromatography and gel electrophoresis, HA family gene expression using RNAseq analysis, and hyaluronidase activity using zymography. Guinea pigs (Cavia porcellus) and mice (Mus musculus) were used as controls for some experiments. We found that HA localization was similar in NMR, guinea pig, and mouse tissues but NMR had larger amounts and higher molecular weight (maximum, around 2.5 MDa) of HA in serum and almost all tissues tested. We could not find ultra-high molecular weight HA (≥ 4 MDa) in NMR samples, in contrast to previous descriptions. Hyaluronidase-1 had lower expression and activity in NMR than mouse lymph nodes. RNAseq results showed that, among HA family genes, Tnfaip6 and hyaluronidase-3 (Hyal3) were systematically overexpressed in NMR tissues. In conclusion, NMR samples, contrary to expectations, do not harbor ultra-high molecular weight HA, although its amount and average molecular weight are higher in NMR than in guinea pig tissues and serum. Although hyaluronidase expression and activity are lower in NMR than mouse lymph nodes, this not sufficient to explain the presence of high molecular weight HA. A different activity of the NMR HA synthases remains possible. These characteristics, together with extremely high Hyal3 and Tnfaip6 expression, may provide the NMR with a bespoke, and perhaps protective, HA metabolism.

Restricted Water Intake Adversely Affects Rat Vocal Fold Biology

OBJECTIVES

A holistic understanding of the many ways that systemic dehydration affects vocal fold biology is still evolving. There are also myriad physiologically relevant methodologies to induce systemic dehydration. To untangle the effects of systemic dehydration on vocal fold biology, we need to utilize realistic, clinically translatable paradigms of systemic dehydration in lab animals. Restricted access to water accommodates clinical translation. We investigated whether systemic dehydration via reduced water intake would negatively affect vocal fold biology.

STUDY DESIGN

Prospective, in vivo study design.

METHODS

Male Sprague Dawley rats (N = 13) were provided 4 mL/100 g of water/day for 5 days, whereas male control rats (N = 8) were given ad lib access to water. Following euthanasia, tissues were processed for histological staining, gene expression, and protein assays.

RESULTS

Renin gene expression level in kidneys increased significantly (P ≤ .05), validating dehydration. Dehydration induced by restricted water access downregulated the gene expression of interleukin-1α and desmoglein-1 (P ≤ .05). Hyaluronidase-2 gene expression increased after dehydration (P ≤ .05). The protein level of desmoglein-1 decreased after dehydration (P ≤ .05). Histological analyses suggested decreased hyaluronan (P ≤ .05) in the water-restricted rat vocal fold.

CONCLUSION

Reduced daily water intake for just 5 days impairs vocal fold biology by disrupting inflammatory cytokine release, reducing plasma membrane integrity, and disrupting the hyaluronan network. This is the first study investigating the dehydrating effects of restricted water intake on vocal fold tissue in an in vivo model.

LEVEL OF EVIDENCE

NA (prospective animal study). Laryngoscope, 131:839-845, 2021.

Dehydration and Estrous Staging in the Rat Larynx: an in vivo Prospective Investigation

OBJECTIVE

This novel study sought to untangle the association between hydration state and the estrous cycle in the vocal folds, since the voice is reported to negatively change in speakers during the estrous cycle and with dehydration. We hypothesized that there would be alterations in vocal fold tissue morphology depending on hydration state and that these changes would vary with the estrous cycle.

STUDY DESIGN

Prospective, in vivo study design.

METHODS

Female Sprague Dawley rats (n = 30) were used in this study. Sixteen rats were systemically dehydrated to an average of 10% reduction in body weight by withholding water (range of body weight loss: 8%-13%). Fourteen rats were assigned to euhydrated, control condition. Estrous stage of female Sprague Dawley rats (n = 30) was determined via cytological evaluation of vaginal smears. Following euthanization, larynges were prepared for histological staining with hematoxylin and eosin, Masson's trichrome and alcian blue (pH 2.5). To quantify hyaluronan, alcian blue staining was completed pre- and posthyaluronidase incubation. The change in staining percent was quantified with image analysis algorithms and reported as the hyaluronan quantity. Relative collagen distribution (index of dehydration), hyaluronan quantity, and tissue morphology were the outcome measures.

RESULTS

Systemic dehydration was associated with changes in hyaluronan quantity in the rat vocal fold lamina propria. Dehydration did not significantly affect the collagen distribution nor the tissue morphology. Estrous stage alone does not impact the quantity of vocal fold hyaluronan, alter tissue morphology, or change collagen distribution.

CONCLUSION

Decreases in hyaluronan quantity in the lamina propria of the rat vocal fold may play a role in tissue fluid balance during systemic dehydration. Future studies will expand this work to investigate additional components of the vocal fold extracellular matrix to fully elucidate the impact of hydration state on the vocal fold.

Hyaluronan Production by Renomedullary Interstitial Cells: Influence of Endothelin, Angiotensin II and Vasopressin

The content of hyaluronan (HA) in the interstitium of the renal medulla changes in relation to body hydration status. We investigated if hormones of central importance for body fluid homeostasis affect HA production by renomedullary interstitial cells in culture (RMICs). Simultaneous treatment with vasopressin and angiotensin II (Ang II) reduced HA by 69%. No change occurred in the mRNA expressions of hyaluronan synthase 2 (HAS2) or hyaluronidases (Hyals), while Hyal activity in the supernatant increased by 67% and CD44 expression reduced by 42%. The autocoid endothelin (ET-1) at low concentrations (10⁻¹⁰ and 10⁻⁸ M) increased HA 3-fold. On the contrary, at a high concentration (10⁻⁶ M) ET-1 reduced HA by 47%. The ET-A receptor antagonist BQ123 not only reversed the reducing effect of high ET-1 on HA, but elevated it to the same level as low concentration ET-1, suggesting separate regulating roles for ET-A and ET-B receptors. This was corroborated by the addition of ET-B receptor antagonist BQ788 to low concentration ET-1, which abolished the HA increase. HAS2 and Hyal2 mRNA did not alter, while Hyal1 mRNA was increased at all ET-1 concentrations tested. Hyal activity was elevated the most by high ET-1 concentration, and blockade of ET-A receptors by BQ123 prevented about 30% of this response. The present study demonstrates an important regulatory influence of hormones involved in body fluid balance on HA handling by RMICs, thereby supporting the concept of a dynamic involvement of interstitial HA in renal fluid handling.

Selective V₂-Agonist of Vasopressin Desmopressin Stimulates Activity of Serum Hyaluronidase

Effects of desmopressin (arginine vasopressin V2 receptor agonist) were studied for elucidation of the possible role of the kidneys in the regulation of blood hyaluronidase activity. Similar to vasopressin, intraperitoneal administration of desmopressin to Wistar rats increased blood hyaluronidase activity by 30%. Against the background of water load, nether desmopressin nor vasopressin increased blood hyaluronidase activity. The possibility of renal secretion of hyaluronidase into the blood as a mechanism of antidiuretic activity of vasopressin and its role in the regulation of water metabolism are discussed.

A role for the extracellular matrix component hyaluronan in kidney dysfunction during ACE-inhibitor fetopathy

Despite data showing that inhibitors of the renin-angiotensin system increase the risks of fetal morbidity and dysfunctionality later in life, their use during pregnancy has increased. The fetopathy induced by angiotensin converting enzyme (ACE) inhibitors is characterized by anuria, hypotension and growth restriction, but can also be associated with pulmonary hypoplasia. In the kidney, this fetopathy includes atrophy of the medulla, reduced number of glomeruli, developmental lesions of tubules and vessels, tubulointerstitial inflammation and extracellular matrix accumulation. Although angiotensin II (Ang II) inhibition during nephrogenesis interferes with normal growth and development, this review will focus on effects of the heavily accumulated matrix component hyaluronan (HA). An important mechanism of HA accumulation during nephrogenesis is disruption of its normal reduction as a consequence of lack of Ang II activation of hyaluronidase. Hyaluronan has very large water-attracting properties and is pro-inflammatory when fragmented. The ensuing inflammation and interstitial oedema affect kidney function. Hyaluronan is colocalized with CD44 overexpression and infiltrating immune cells. These properties make HA a plausible contributor to the observed structural and functional kidney defects associated with the fetopathy. Available data support an involvement of HA in kidney dysfunction of the foetus and during adulthood due to the physico-chemical characteristics of HA. No clinical treatment for HA accumulation exists. Treatment with the HA-degrading enzyme hyaluronidase and an HA synthesis inhibitor has been tested successfully in experimental models in the kidney, heart and pancreas. Reduced HA accumulation to reduce interstitial oedema and inflammation may improve organ function, but this concept needs to be tested in a controlled study before causal relationships can be established.

The role of hyaluronan in innate defense responses of the intestine

Hyaluronan is an abundant extracellular matrix component prevalent in the vertebrate intestinal tract. Here we discuss what is known about hyaluronan distribution during homeostasis and inflammatory diseases of the gut and discuss ways in which this glycosaminoglycan can participate in regulating innate host defense mechanisms. These natural responses include mechanisms promoting rapid leukocyte recruitment after bacterial challenge/colon tissue damage as well as promoting epithelial defense mechanisms in the intestine.

Inhibition of mTOR activity in diabetes mellitus reduces proteinuria but not renal accumulation of hyaluronan

OBJECTIVES

Accumulation of extracellular matrix (ECM) components is an early sign of diabetic nephropathy. Also the glycosaminoglycan hyaluronan (HA) is elevated in the renal interstitium during experimental diabetes. The mammalian target of rapamycin (mTOR) pathway participates in the signaling of hyperglycemia-induced ECM accumulation in the kidney, but this has not yet been investigated for HA. We hypothesized that interstitial HA accumulation during diabetes may involve mTOR activation.

METHODS

Diabetic rats (6 weeks post-streptozotocin (STZ)) were treated with rapamycin to inhibit mTOR or vehicle for 2 additional weeks. Kidney function (glomerular filtration rate, renal blood flow, urine output) and regional renal HA content were thereafter analyzed. The ability of the animals to respond to desmopressin was also tested.

RESULTS

Diabetic animals displayed hyperglycemia, proteinuria, hyperfiltration, renal hypertrophy, increased diuresis with reduced urine osmolality, and reduced weight gain. Cortical and outer medullary HA was elevated in diabetic rats. Urine hyaluronidase activity was almost doubled in diabetic rats compared with controls. The ability to respond to desmopressin was absent in diabetic rats. Renal blood flow and arterial blood pressure were unaffected by the diabetic state. In diabetic rats treated with rapamycin the proteinuria was reduced by 32%, while all other parameters were unaffected.

CONCLUSION

Regional renal accumulation of the ECM component HA is not sensitive to mTOR inhibition by rapamycin, while proteinuria is reduced in established STZ-induced diabetes. Whether the diabetes-induced renal accumulation of HA occurs through different pathways than other ECM components, or is irreversible after being established, remains to be shown.

Inhibition of hyaluronan synthesis in rats reduces renal ability to excrete fluid and electrolytes during acute hydration

BACKGROUND

Hyaluronan (HA) is the dominant glycosaminoglycan in the renomedullary interstitium. Renomedullary HA has been implicated in tubular fluid handling due to its water-attracting properties and the changes occurring in parallel to acute variations in the body hydration status.

METHODS

HA production was inhibited by 4-methylumbelliferone (4-MU in drinking water for 5 days, 1.45 ± 0.07 g/day/kg body weight) in rats prior to hydration.

RESULTS

Following hypotonic hydration for 135 min in control animals, diuresis and osmotic excretion increased while sodium excretion and glomerular filtration rate (GFR) remained unchanged. The medullary and cortical HA contents were 7.85 ± 1.29 ng/mg protein and 0.08 ± 0.01 ng/mg protein, respectively. Medullary HA content after 4-MU was 38% of that in controls (2.98 ± 0.95 ng/g protein, p < 0.05), while the low cortical levels were unaffected. Baseline urine flow was not different from that in controls. The diuretic response to hydration was, however, only 51% of that in controls (157 ± 36 versus 306 ± 54 µl/g kidney weight/135 min, p < 0.05) and the osmolar excretion only 47% of that in controls (174 ± 47 versus 374 ± 41 µOsm/g kidney weight/135 min, p < 0.05). Sodium excretion, GFR, and arterial blood pressure were similar to that in control rats and unaltered during hydration.

CONCLUSIONS

Reduction of renomedullary interstitial HA using 4-MU reduces the ability of the kidney to respond appropriately upon acute hydration. The results strengthen the concept of renomedullary HA as a modulator of tubular fluid handling by changing the physicochemical properties of the interstitial space.

Hormonal regulation of salt and water excretion: a mathematical model of whole kidney function and pressure natriuresis

We present a lumped-nephron model that explicitly represents the main features of the underlying physiology, incorporating the major hormonal regulatory effects on both tubular and vascular function, and that accurately simulates hormonal regulation of renal salt and water excretion. This is the first model to explicitly couple glomerulovascular and medullary dynamics, and it is much more detailed in structure than existing whole organ models and renal portions of multiorgan models. In contrast to previous medullary models, which have only considered the antidiuretic state, our model is able to regulate water and sodium excretion over a variety of experimental conditions in good agreement with data from experimental studies of the rat. Since the properties of the vasculature and epithelia are explicitly represented, they can be altered to simulate pathophysiological conditions and pharmacological interventions. The model serves as an appropriate starting point for simulations of physiological, pathophysiological, and pharmacological renal conditions and for exploring the relationship between the extrarenal environment and renal excretory function in physiological and pathophysiological contexts.

Virtual patients and sensitivity analysis of the Guyton model of blood pressure regulation: towards individualized models of whole-body physiology

Mathematical models that integrate multi-scale physiological data can offer insight into physiological and pathophysiological function, and may eventually assist in individualized predictive medicine. We present a methodology for performing systematic analyses of multi-parameter interactions in such complex, multi-scale models. Human physiology models are often based on or inspired by Arthur Guyton's whole-body circulatory regulation model. Despite the significance of this model, it has not been the subject of a systematic and comprehensive sensitivity study. Therefore, we use this model as a case study for our methodology. Our analysis of the Guyton model reveals how the multitude of model parameters combine to affect the model dynamics, and how interesting combinations of parameters may be identified. It also includes a "virtual population" from which "virtual individuals" can be chosen, on the basis of exhibiting conditions similar to those of a real-world patient. This lays the groundwork for using the Guyton model for in silico exploration of pathophysiological states and treatment strategies. The results presented here illustrate several potential uses for the entire dataset of sensitivity results and the "virtual individuals" that we have generated, which are included in the supplementary material. More generally, the presented methodology is applicable to modern, more complex multi-scale physiological models.

Renal interstitial hyaluronan: functional aspects during normal and pathological conditions

The glycosaminoglycan (GAG) hyaluronan (HA) is recognized as an important structural component of the extracellular matrix, but it also interacts with cells during embryonic development, wound healing, inflammation, and cancer; i.e., important features in normal and pathological conditions. The specific physicochemical properties of HA enable a unique hydration capacity, and in the last decade it was revealed that in the interstitium of the renal medulla, where the HA content is very high, it changes rapidly depending on the body hydration status while the HA content of the cortex remains unchanged at very low amounts. The kidney, which regulates fluid balance, uses HA dynamically for the regulation of whole body fluid homeostasis. Renomedullary HA elevation occurs in response to hydration and during dehydration the opposite occurs. The HA-induced alterations in the physicochemical characteristics of the interstitial space affects fluid flux; i.e., reabsorption. Antidiuretic hormone, nitric oxide, angiotensin II, and prostaglandins are classical hormones/compounds involved in renal fluid handling and are important regulators of HA turnover during variations in hydration status. One major producer of HA in the kidney is the renomedullary interstitial cell, which displays receptors and/or synthesis enzymes for the hormones mentioned above. During several kidney disease states, such as ischemia-reperfusion injury, tubulointerstitial inflammation, renal transplant rejection, diabetes, and kidney stone formation, HA is upregulated, which contributes to an abnormal phenotype. In these situations, cytokines and other growth factors are important stimulators. The immunosuppressant agent cyclosporine A is nephrotoxic and induces HA accumulation, which could be involved in graft rejection and edema formation. The use of hyaluronidase to reduce pathologically overexpressed levels of tissue HA is a potential therapeutic tool since diuretics are less efficient in removing water bound to HA in the interstitium. Although the majority of data describing the role of HA originate from animal and cell studies, the available data from humans demonstrate that an upregulation of HA also occurs in diabetic kidneys, in transplant-rejected kidneys, and during acute tubular necrosis. This review summarizes the current knowledge regarding interstitial HA in the role of regulating kidney function during normal and pathological conditions. It encompasses mechanistic insights into the background of the heterogeneous intrarenal distribution of HA; i.e., late nephrogenesis, its regulation during variations in hydration status, and its involvement during several pathological conditions. Changes in hyaluronan synthases, hyaluronidases, and binding receptor expression are discussed in parallel.

Intra-renal oxygenation in rat kidneys during water loading: effects of cyclooxygenase (COX) inhibition and nitric oxide (NO) donation

PURPOSE

To evaluate intra-renal oxygenation by blood oxygenation level dependent (BOLD) MRI in rat kidneys during water loading and to investigate if the NO donating moiety in naproxcinod could compensate for the effect of cyclooxygenase (COX) inhibition of naproxen.

MATERIALS AND METHODS

Nineteen male Sprague Dawley rats were divided into three groups and dosed with vehicle, naproxen or naproxcinod by gavage for two weeks. On the day of the experiment, hypotonic saline with glucose was infused intravenously to induce water diuresis. BOLD MRI data to monitor renal oxygenation and timed urine samples for estimation of prostaglandins (PGs) and urine flow were obtained.

RESULTS

The data in this study is consistent with previous experience in humans in that pre-treatment with naproxen abolished the improvement in medullary oxygenation during water loading. In addition, the inhibition of PGs by naproxcinod reached similar levels as naproxen but maintained the improvement in oxygenation in renal medulla during water loading.

CONCLUSION

This suggests that naproxcinod may have less nephrotoxicity and that the NO donating moiety partially compensates for the hemodynamic effects of prostaglandin inhibition by naproxen.

Sodium sensing in the interstitium and relationship to hypertension

PURPOSE OF REVIEW

Internal environment regulation, particularly volume and osmoregulation, has been a fundamental concept important to physiologists and clinicians for almost two centuries. Na balance, intracellular K homeostasis, the crucial role of the Na,K-ATPase pump, osmotic forces, and the overriding effect of the kidney on maintaining homeostasis are notions that have been taught by many and accepted by most for over 50 years. Nevertheless, contradictory findings, problems with simplistic balance explanations, and the notion of salt-sensitive and salt-resistant hypertension have been nagging headaches in the straightforward, two-compartment model of electrolyte balance.

RECENT FINDINGS

Na can be accumulated without commensurate water retention in the interstitium of the skin, and this skin Na storage is paralleled by increased polymerization and sulfation of glycosaminoglycans in the Na reservoir. Subcutaneous tissue macrophages express the transcription factor tonicity enhancer binding protein in response to Na-mediated interstitial osmotic stress and thereby secrete vascular endothelial growth factor C, which stimulates lymphatic formation and endothelial nitric oxide synthase expression, suggesting that the immune system is a regulator of volume and blood pressure homeostasis.

SUMMARY

Our findings do not abrogate the notion of pressure natriuresis and renal regulatory function. However, we do suggest that extracellular Na, volume and blood pressure homeostasis cannot be maintained without extrarenal regulatory mechanisms.

Angiotensin converting enzyme inhibition blocks interstitial hyaluronan dissipation in the neonatal rat kidney via hyaluronan synthase 2 and hyaluronidase 1

A functional renin-angiotensin system (RAS) is required for normal kidney development. Neonatal inhibition of the RAS in rats results in long-term pathological renal phenotype and causes hyaluronan (HA), which is involved in morphogenesis and inflammation, to accumulate. To elucidate the mechanisms, intrarenal HA content was followed during neonatal completion of nephrogenesis with or without angiotensin converting enzyme inhibition (ACEI) together with mRNA expression of hyaluronan synthases (HAS), hyaluronidases (Hyal), urinary hyaluronidase activity and cortical lymphatic vessels, which facilitate the drainage of HA from the tissue. In 6-8days old control rats cortical HA content was high and reduced by 93% on days 10-21, reaching adult low levels. Medullary HA content was high on days 6-8 and then reduced by 85% to 12-fold above cortical levels at day 21. In neonatally ACEI-treated rats the reduction in HA was abolished. Temporal expression of HAS2 corresponded with the reduction in HA content in the normal kidney. In ACEI-treated animals cortical HAS2 remained twice the expression of controls. Medullary Hyal1 increased in controls but decreased in ACEI-treated animals. Urine hyaluronidase activity decreased with time in control animals while in ACEI-treated animals it was initially 50% lower and did not change over time. Cells expressing the lymphatic endothelial mucoprotein podoplanin in ACEI-treated animals were increased 18-fold compared to controls suggesting compensation. In conclusion, the high renal HA content is rapidly reduced due to reduced HAS2 and increased Hyal1 mRNA expressions. Normal angiotensin II function is crucial for inducing these changes. Due to the extreme water-attracting and pro-inflammatory properties of HA, accumulation in the neonatally ACEI-treated kidneys may partly explain the pathological renal phenotype of the adult kidney, which include reduced urinary concentration ability and tubulointerstitial inflammation.

Structure and concentration capacity of the kidneys in brattleboro rats under conditions of long-term vasopressin treatment

The function and histochemistry of the kidney were studied in homozygous Brattleboro rats after 28-day treatment with exogenous arginine-vasopressin. The long-lasting effect of the hormone includes normalization of osmotic concentration, decrease in the number of b-glucuronidase granules in the medulla, and increasing content of hyaluronan in the interstitium. These changes promote physiological optimization of the antidiuretic reaction to vasopressin.

Hormonal regulation of renomedullary hyaluronan

AIM

Hyaluronan (HA) is involved in renomedullary water handling through its water-binding capacity. This study addressed the effect of hormones involved in regulating fluid-electrolyte homeostasis on renomedullary HA content in vivo and in vitro.

METHODS

The kidneys from rats treated with L-NAME, indomethacin, vasopressin (AVP) or methylprednisolone (MP) during euvolaemia or water loading were analysed for HA by RIA, ELISA and histochemical staining. HA was measured in renomedullary interstitial cells treated with AVP, angiotensin II (Ang II) or a combination of AVP and Ang II.

RESULTS

Baseline renal cortical and medullary HA content was unaffected by 2 h of intravenous treatment with L-NAME (NOS inhibitor) or indomethacin (cyclo-oxygenase inhibitor), whereas AVP reduced medullary HA by 33%. During 2 h of acute water loading, diuresis was accompanied by an increase in renomedullary HA (+45%), but cortical HA was unaffected. In both L-NAME- and indomethacin-treated animals, the water loading-induced increase in renomedullary HA was absent, indicating involvement of NO and prostaglandins. After 7 days of MP treatment, medullary HA was reduced by 40%, but the water loading-induced elevation in HA remained. In cultured renomedullary interstitial cells, AVP reduced the HA content in the supernatant by 63%, and simultaneous treatment with Ang II reduced the HA content even further (95%).

CONCLUSION

AVP reduces HA content, and NO and prostaglandins are needed for the increase in HA during water loading.

The distribution of renal hyaluronan and the expression of hyaluronan synthases during water deprivation in the Spinifex hopping mouse, Notomys alexis

Hyaluronan (HA) is a glycosaminoglycan that is synthesized by a family of enzymes called hyaluronan synthases (HASs), of which there are three isoforms (HAS1, 2 and 3) in mammals. The HASs have different tissue expression patterns and function, indicating that synthesis of HA and formation of the HA matrix may be regulated by various factors. The HA matrix has an important role in renal water handling and the production of a concentrated urine. We investigated the distribution of HA and the expression of HAS1, HAS2 and HAS3 mRNAs in the kidney of the Spinifex hopping mouse, Notomys alexis, a native Australian desert rodent that is reported to produce the most concentrated urine of any mammal. After periods of three, seven and fourteen days of water deprivation, the distribution of renal HA changed considerably, and there was a general down-regulation of HAS mRNA expression. It is proposed that the regulation of HA synthesis by the different HAS isoforms during water deprivation in N. alexis, could be influenced by the molecular mass of the HA chains produced by each isoform, followed by the rate at which the individual HAS produces HA.