Effects of water restriction on gene expression in mouse renal medulla: identification of 3betaHSD4 as a collecting duct protein.

To identify novel gene targets of vasopressin regulation in the renal medulla, we performed a cDNA microarray study on the inner medullary tissue of mice following a 48-h water restriction protocol. In this study, 4,625 genes of the possible approximately 12,000 genes on the array were included in the analysis, and of these 157 transcripts were increased and 63 transcripts were decreased by 1.5-fold or more. Quantitative, real-time PCR measurements confirmed the increases seen for 12 selected transcripts, and the decreases were confirmed for 7 transcripts. In addition, we measured transcript abundance for many renal collecting duct proteins that were not represented on the array; aquaporin-2 (AQP2), AQP3, Pax-8, and alpha- and beta-Na-K-ATPase subunits were all significantly increased in abundance; the beta- and gamma-subunits of ENaC and the vasopressin type 1A receptor were significantly decreased. To correlate changes in mRNA expression with changes in protein expression, we carried out quantitative immunoblotting. For most of the genes examined, changes in mRNA abundances were not associated with concomitant protein abundance changes; however, AQP2 transcript abundance and protein abundance did correlate. Surprisingly, aldolase B transcript abundance was increased but protein abundance was decreased following 48 h of water restriction. Several transcripts identified by microarray were novel with respect to their expression in mouse renal medullary tissues. The steroid hormone enzyme 3beta-hydroxysteroid dehydrogenase 4 (3betaHSD4) was identified as a novel target of vasopressin regulation, and via dual labeling immunofluorescence we colocalized the expression of this protein to AQP2-expressing collecting ducts of the kidney. These studies have identified several transcripts whose abundances are regulated in mouse inner medulla in response to an increase in endogenous vasopressin levels and could play roles in the regulation of salt and water excretion.

Effects of renal nerve stimulation on intrarenal blood flow in rats with intact or inactivated NO synthases.

AIM: We studied a possible action of nitric oxide (NO), an intrarenal vasodilator, to buffer a decrease in renal perfusion induced by electrical stimulation of renal nerves (RNS). METHODS: In anaesthetized rats RNS was performed (15 V, 2 ms pulse duration) for 10 s at the frequencies of 2, 3.5, 5 and 7.5 Hz. The total renal blood flow (RBF), an index of cortical perfusion, was measured using a Transonic probe on the renal artery. The outer and inner medullary blood flow (OMBF, IMBF) was measured by laser-Doppler flowmetry. The effect of RNS on RBF, OMBF and IMBF was determined in rats which were either untreated or pre-treated with L-NAME (0.6 or 1.8 mg kg(-1) i.v.), or S-methyl thiocitrulline (SMTC, 20 microg kg(-1) min(-1) i.v.), a selective inhibitor of neuronal NO synthase (nNOS). RESULTS: In untreated rats, RNS decreased IMBF significantly less than RBF and OMBF. High-dose L-NAME treatment significantly enhanced the RNS induced decrease of RBF but not of OMBF or IMBF. SMTC treatment significantly enhanced the decrease of IMBF, without affecting the response of RBF or OMBF. CONCLUSION: At intact NO synthesis the inner medullary circulation is not controlled by renal nerves to the extent observed for the outer medulla or cortex. NO generated by all NOS isoforms present in the kidney buffers partly the intrarenal vasoconstriction triggered by electrical RNS. The NO derived from nNOS seems of particular importance in the control of inner medullary perfusion, interacting with NO generated by endothelial NOS and renal nerves.

Tissue temperature oscillations in an isolated pig kidney during surface heating.

In the present study, an isolated pig kidney was used to study tissue temperature oscillations due to vascular thermoregulation, frequently observed during hyperthermia treatments. The kidney was perfused with the distilled water pumped through the renal artery to simulate blood flow. When the local perfusion rate was increased with a time delay, temperature oscillations were observed in the kidney as its surface temperature raised linearly with time in a water bath. The magnitude of tissue temperature decreased as the flow rate increased during the surface heating. A 3D transient model was developed to predict the temperature oscillations, which was validated by the measurements. Using the model, relationships of the changes in perfusion rate and heating rate with temperature oscillations were investigated. It was found that the heating rate, and the magnitude and time delay of the flow response to the temperature elevation, each significantly affected tissue temperature oscillations. The magnitude of oscillation was primarily determined by the spatial gradient of temperature, while the oscillation type depended on the change of flow rate and the time delay. In conclusion, to accurately predict and control the tissue temperature distribution during hyperthermia treatment, understanding of the local perfusion change with respect to tissue temperature is essential.

Hypoperfusion in the renal outer medulla after injection of contrast media in rats.

PURPOSE: The effect on regional renal blood was studied after injection of nonionic iso-osmolar iotrolan or ionic high-osmolar iothalamate. MATERIAL AND METHODS: Laser-Doppler flowmetry was used to measure outer medullary (OMBF) and superficial cortical blood flow (CBF) simultaneously in anesthetized rats. Iotrolan (320 mOsm/kg H2O) was injected i.v. at a dose of 600 mg I/kg b.w. (normal dose) over 2 min or 1,600 (high dose) mg I/kg b.w. over 2 or 8 min. Iothalamate (2,580 mOsm/kg H2O) was injected i.v. at a dose of 1,600 (high dose) or 2,900 (extremely high dose) mg I/kg b.w. over 2 min. RESULTS: At the normal dose and 2-min injection of iotrolan, OMBF was reduced by 25+/-9% over 20 min. The high dose of iotrolan injected over 8 min resulted in a reduction in OMBF slightly smaller (17+/-9%) than that induced by the normal dose but lasting longer (30 min). Compared to the normal dose, the high dose and fast (2 min) injection of iotrolan resulted in a greater and more prolonged decrease in OMBF (32+/-6% lasting 50 min). After the high dose of iothalamate (1,600 mg I/kg) there was a decrease in OMBF by 21+/-6%, lasting 30 min. An extremely high dose (2,900 mg I/kg b.w.) gave a heterogeneous response with a mean increase in OMBF of 48+/-24% occurring 60 min after the injection. CONCLUSION: Iso-osmolar and high-osmolar contrast media (CM), at normal and high doses, decrease OMBF, while an extremely high dose of iothalamate may result in an increase. The depression of outer medullary perfusion may have implications for CM-induced acute renal failure in view of the vulnerability of this region to a decrease in oxygen tension.

Magnetic resonance elastography by direct visualization of propagating acoustic strain waves.

A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.

Effect of nitrendipine on autoregulation of perfusion in the cortex and papilla of kidneys from Wistar and stroke prone spontaneously hypertensive rats.

1. This investigation examined the autoregulatory efficiency of different vascular regions of the normotensive and stroke prone-spontaneously hypertensive rat (SP-SHR) kidney and determined how these myogenic responses were dependent upon extracellular calcium. In acute studies, renal autoregulatory blood perfusion curves for cortex and papilla were generated, autoregulatory indices (AI's) calculated as a ratio of the perfusion change divided by the ratio of the pressure difference where zero represents perfect and 1 equates to no autoregulation. The influence of a calcium channel antagonist on this AI was measured at both cortex and papilla. 2. Rats were anaesthetized with sodium pentobarbitone, the kidney exposed and cortical and papillary perfusion measured by Laser-Doppler flowmetry. Groups of rats either received no drug or nitrendipine at either 0.125 or 0.25 micrograms kg-1 min-1. 3. In the Wistar normotensive rats there was efficient autoregulation in the cortex (AI = 0.21 +/- 0.17), from 127 to 90 mmHg, but not in the papilla (AI = 0.89 +/- 0.08), while below 90 mmHg perfusion in both regions decreased with renal perfusion pressure. Nitrendipine attenuated cortical autoregulation at the higher pressure range (AI = 0.62 +/- 0.13 and 0.92 +/- 0.10 at the low and high dose, respectively) while having no effect on the papillary pressure perfusion pattern. 4. In the SP-SHR, reduction in renal perfusion pressure, from 150 to 100 mmHg, gave a cortical AI of 0.49 +/- 0.10, indicating impaired autoregulation, whereas the papilla demonstrated little myogenic response. Over the high pressure range in the presence of both doses of nitrendipine there was neither cortical (AI of 0.75 +/- 0.11 and 0.94 +/- 0.12, respectively) nor papillary autoregulation. 5. Autoregulation in the renal cortex but not papilla of the young Wistar rats is well developed. The myogenic responses are attenuated by the calcium channel antagonists suggesting that they are dependent upon the availability of extracellular calcium. Cortical autoregulation in the SP-SHR is deficient compared to the normotensive rats and is further impaired by the calcium channel antagonists.

Cloning and expression of an inwardly rectifying ATP-regulated potassium channel.

A complementary DNA encoding an ATP-regulated potassium channel has been isolated by expression cloning from rat kidney. The predicted 45K protein, which features two potential membrane-spanning helices and a proposed ATP-binding domain, represents a major departure from the basic structural design characteristic of voltage-gated and second messenger-gated ion channels. But the presence of an H5 region, which is likely to form the ion conduction pathway, indicates that the protein may share a common origin with voltage-gated potassium channel proteins.

Acute regulation of the predominant organic solutes of the rabbit renal inner medulla.

High concentrations of organic solutes are present in the medulla of the antidiuretic kidney. However, their role in and response to acute changes in the diuretic state are unknown. In this study the organic solute content of the renal medulla was determined from extracts with the use of high-performance liquid chromatography following the acute dilution of the medullary interstitium during various forms of diuresis. After acute infusion of saline and furosemide, inner medullary urea, sodium, inositol, sorbitol, and betaine decrease significantly with no change in glycerophosphorylcholine (GPC) content. After diuresis, inner medullary urea and sodium contents eventually returned to control levels, although inositol, sorbitol, and betaine contents still remained low. Addition of antidiuretic hormone to the saline/furosemide infusion gave similar results. In contrast, induction of diuresis from mannitol infusion caused an acute decrease in all 4 organic solutes, whereas glucose infusion caused an acute decrease in all organic solutes except sorbitol. These data demonstrate that a decrease in all four organic solutes can accompany medullary dilution. However, GPC and sorbitol do not decrease when diuresis is induced by furosemide or glucose, respectively. In addition, the recovery of these compounds in a normally functioning kidney after diuresis is much slower than the regeneration of the sodium chloride and urea gradients.

Cortisol secretion after hemorrhage: multiple mechanisms.

Multiple mechanisms appear to be involved in mediation of increased secretion of cortisol after hemorrhage. Signals from cardiovascular receptors are transmitted to the hypothalamus through ascending neural pathways to release ACTH. Angiotensin II stimulates release of ACTH by an action on the median eminence, but does not stimulate adrenal secretion of cortisol directly. However, secretion of cortisol can increase rapidly after hemorrhage without changes in ACTH. Common afferent pathways probably mediate all these mechanisms.