Evidence for an intrarenal renin-angiotensin system in the rainbow trout, Oncorhynchus mykiss

Physiological and molecular approaches were used to investigate the existence of an intrarenal renin-angiotensin system (RAS) in rainbow trout. Inhibition of angiotensin-converting enzyme by captopril (5 x 10(-4 )M) rapidly decreased vascular resistance of the trunk of the trout, perfused at 19 mmHg, resulting in an increased perfusate flow rate and a decreased intrarenal dorsal aortic pressure. A profound diuresis occurred in the in situ perfused kidney and reflected both increased glomerular filtration rates and decreased water reabsorption (osmolyte reabsorption was unchanged). Renal and vascular parameters recovered once captopril treatment was stopped. Diuretic and vascular effects of captopril on the in situ trout kidney concur with an inhibition of known vasoconstrictor and antidiuretic actions of angiotensin II. However, at a higher perfusion pressure (28 mmHg), captopril had no effect on intrarenal aortic pressure or perfusate and urine flow rates, suggesting that the trout intrarenal RAS is activated by low perfusion pressures/flows. Existence of the renal RAS in trout was further supported by evidence for angiotensinogen gene expression in kidney as well as liver.     

Evidence for an intrarenal renin‐angiotensin system in the European lesser‐spotted dogfish

The existence of an intrarenal renin‐angiotensin system (RAS) in a perfused European lesser‐spotted dogfish Scyliorhinus canicula trunk preparation was examined by the inhibition of angiotensin‐converting enzyme by captopril. This resulted in a glomerular diuresis, an increase in urea and chloride clearance and excretion, and an increase in transport maxima for glucose. It is proposed that these results suggest the presence of an intrarenal RAS.     

Osmoregulatory Functions of Neurohypophysial Hormones in Fishes and Amphibians

The renal effects of neurohypophysial hormones in fishes andamphibians are discussed. Injections of arginine vasotocin (AVT)elicit diuresis in fishes, but antidiuresis in amphibians. However,the physiological significance of these hormonal responses remainsto be demonstrated. Studies with bioassays and radio-immunoassayson circulating levels of AVT indicate that hypovolemia may bea very potent stimulus for the release of the hormone. Hyperosmoticstimuli may not be as important. In anurans, mesotocin has aglomerular diuretic effect. This neurohypophysial hormone appearsto dilate, while AVT constricts, the afferent glomerular circulationin bullfrogs, Rana catesbeiana.     

Arginine vasotocin and renal function in the conscious dog

The effects of arginine vasotocin (AVT), 4–6 ng/kg, on renal function and plasma prolactin (PRL) were determined in conscious American foxhounds undergoing a water diuresis. Intravenous AVT produced an antidiuresis, kaliuresis and inconsistent natriuresis, independently of changes in GFR, blood pressure, heart rate and plasma PRL.     

Effect of endothelin-3 (ET-3) on renal function in rat perfused kidney.

We examined the effect of endothelin-3 (ET-3) at a high dose (pressor dose) and a low dose (non-pressor dose) in rat perfused kidney (PK), since ET-3 has recently been reported to exert a vasodilator action especially at a low dose. Kidneys were perfused with Krebs-Henseleit buffer at a fixed flow rate (6 ml/min) in situ. After collection of the renal venous effluent and urine for 20 min, vehicle (saline; n = 6), 10(-13)M ET-3 (low dose; n = 6) or 10(-8) M ET-3 (high dose; n = 6) was added to the perfusate, and sample collection was performed for the same period with each. The high dose of ET-3 significantly increased the perfusion pressure, fractional sodium excretion and synthesis of prostaglandins (PGs) consistently with a significant reduction in the glomerular filtration rate (GFR). On the other hand, the low dose of ET-3 significantly increased the GFR, urine volume and free-water clearance with no change in the perfusion pressure or synthesis of PGs. These findings suggest that a low dose of ET-3 can increase the glomerular capillary ultrafiltration coefficient and that ET-3 exerts an influence on sodium and water handing in the rat PK.     

Evolution of Neurohypophyseal Hormone Actions in Vertebrates

Arginine vasotocin (AVT) is one neurohypophyseal principle thathas been found in all vertebrates including the cyclostomes.Although many effects have been seen with administered AVT inmany vertebrate species, the physiological role of endogenousAVT is largely unknown. In this review, the evolution of therenal and vascular actions of AVT are discussed. Injection ofAVT produces diuresis in teleosts and lungfishes, but antidiuresisin tetrapods. In fishes and all tetrapods except birds, AVTis hypertensive. We have proposed that the renal responses canin fact be explained by the vascular responses. In our hypothesis,there are four types of responses to AVT. In type I, the peripheralvasculature is more responsive to AVT than the renal preglomerulararteriole so that AVT will cause a significant rise in systemicblood pressure and a net increase in the glomerular perfusion.This will then result in diuretic and pressor responses. Teleostsand lungfishes belong to this type. Type 11 is exemplified bythe mudpuppy which responds to AVT with antidiuresis and bloodpressure increase. This can be explained by an increase in sensitivityto AVT by the preglomerular arteriole so that AVT will causea decrease in glomerular perfusion even when systemic bloodpressure is increased. In type III which can be seen in thebullfrog, the vascular response to AVT will produce glomerularantidiuresis and blood pressure increase. In addition, tubularreceptors for AVT are also present and these receptors are involvedin the tubular reabsorption of water, thus enhancing the antidiureticresponse. Type IV as seen in mammals is mainly a tubular antidiureticresponse to ADH. Evidence in support of this hypothesis is givenin the paper. The above discussion concerns the renal and vascularactions of exogenous AVT. Our studies so far indicate that endogenousAVT is not the major regulatory mechanism in renal and vascularfunctions of the lungfish or bullfrog, although it may havea modulatory role.     

Effects of hypothermic kidney preservation on the isolated perfused kidney: a comparison of reperfusion methods

Two isolated-perfused kidney methods were used to study the effects of hypothermic preservation on renal function in dog kidneys. The isolated-machine-perfused kidney (IMPK) used an in vitro perfusion technique--the perfusate was a Krebs-bicarbonate type delivered to the kidney at 37 degrees C by a mechanical pump at a constant pressure (100 mm Hg). The isolated-blood-perfused kidney (IBPK) utilized transplantation of the preserved kidney to the femoral vasculature. Renal function (urine analysis) was determined over a 1-hr reperfusion interval and included GFR (creatinine clearance), urine formation, and Na+ reabsorption. Kidneys preserved for only 24 hr by cold storage in either Collins'--C3 solution or in hypotonic citrate and kidneys hypothermically perfused for 24 hr demonstrated greater retention of renal function when reperfused by blood (IBPK) than with the in vitro perfusate (IMPK). The GFR was reduced by 38-58% when tested with the IBPK, but by 80-90% when tested with the IMPK. Na+ reabsorption was normal (97%) with blood reperfusion but was reduced to 36-50% in cold-stored kidneys and 82% in hypothermically perfused kidneys determined by machine reperfusion (IMPK). However, kidneys perfused for 72 hr demonstrated more similar renal functions when tested by either IMPK or IBPK. GFR was reduced to 20% (IBPK) and 11% (IMPK) and Na+ reabsorption averaged 76-85% (IBPK or IMPK). These results suggest that either reperfusion method is suitable for determining the effects of renal preservation on kidney function in kidneys preserved for 72 hr but, for short-term preserved kidneys (24 hr), the IBPK model may be preferred.     

Prostaglandins modulate the renal actions of antidiuretic hormone in the Pekin duck

The present study was designed to determine whether the responses of the avian kidney to circulating arginine vasotocin (AVT), under different osmotic conditions, involve an interaction with prostaglandins (PGs). The renal effects of intravenously infused AVT at a dose of 0.1 ng.kg^–1.min^–1 for 45 min were compared in Pekin ducks given maintenance infusions of either 200 mosmol NaCl or glucose at 1 ml.min^–1, with and without PG inhibition by indomethacin. Birds infused with glucose responded with similar degrees of AVT-induced antidiuresis with and without indomethacin, however the urinary excretion of sodium was significantly reduced when PG production was prevented. In ducks receiving saline without indomethacin, the antidiuretic response to AVT was markedly less than that in the glucose-infused birds, however, indomethacin treatment increased the degree of antidiuresis to a level similar to that in the glucose-infused ducks. The results indicate that PGs have important renotropic actions in birds and in particular modulate the antidiuretic effect of AVT in salt- and volume-loaded animals.Abbreviations ANP atrial natriuretic peptide - AVT arginine vasotocin - PGs prostaglandinsCommunicated by I.D. Hume     

Transport and metabolism of N6- and C8-substituted analogs of adenosine 3',5'-cyclic monophosphate and adenosine 3'5'-cyclic phosphorothioate by the isolated perfused rat kidney

The clearance and metabolism of N6-substituted (N6-dimethyl-), C8-substituted (8-bromo-, 8-p-chlorophenylthio- (PCPT-)), and exocyclic oxygen substituted phosphorothioate diastereomers (cAMPS(Sp)) and cAMPS (Rp)) of adenosine 3':5'-monophosphate (cyclic AMP, cAMP) has been studied in an isolated perfused rat kidney. The N6- and C8-substituted analogs of cyclic AMP (10-100 microM) were not cleared as rapidly as exogenous cyclic AMP and were metabolized: N6- and C8-substituted analogs of adenosine accumulated in perfusate and urine. All analogs exhibited net transtubular secretion, i.e. their urinary excretion rate greater than glomerular filtration rate. Probenecid (0.9 mM) included in the perfusate abolished transtubular secretion and inhibited the metabolism of PCPT-cyclic AMP, suggesting that cyclic AMP analogs, like cyclic AMP itself, penetrate the renal cell at the peritubular membrane by an organic acid transport system. The phosphorothioate diastereomers of cyclic AMP: cAMPS(Sp) and cAMPS(Rp) were cleared as rapidly from the perfusate as cyclic AMP, were extensively secreted (urinary excretion/ glomerular filtration greater than or equal to 10) and exhibited no metabolism. The latter analog would seem most suitable as an intracellular agonist for cyclic AMP-mediated phenomena in the rat kidney.     

Evidence for direct renal injury as a consequence of glomerular complement activation

An isolated perfused kidney (IPK) preparation was used to study the functional consequences of antibody-initiated glomerular complement activation in an environment devoid of circulating inflammatory cells. Control IPK, with antibody bound to the glomerular basement membrane (GBM) (mean +/- SEM, 165.0 +/- 5.7 micrograms globulin/g renal cortex), were perfused with a 5% albumin solution. Control urinary protein excretion was 0.306 +/- 0.112 mg/min, renal vascular resistance (RVR) was 4.72 +/- 0.69 mgHg/ml/min, and the glomerular filtration rate (GFR) was 0.41 +/- 0.01 ml/min/g. To produce glomerular complement activation, IPK with equal quantities of bound antibody (167.0 +/- 6.1 micrograms/g) were perfused with fresh plasma. Glomerular complement activation was associated with linear deposition of C3 on the GBM, a significant increase in protein excretion (3.317 +/- 1.077 mg/min; p less than 0.001) and RVR (10.15 +/- 1.85 mmHg/ml/min; p less than 0.001), and a decline in GFR (0.38 +/- 0.01 ml/min/g; p less than 0.05). Equivalent IPK perfused with decomplemented plasma demonstrated neither glomerular complement deposition nor augmented renal injury. By using both complement repletion and depletion techniques, this study demonstrates that antibody-initiated glomerular complement activation produces direct, neutrophil-independent renal injury. Thus, activated complement components may directly contribute to antibody-induced immune renal injury, in addition to their well established role in the recruitment of circulating inflammatory cells.     

Hemodynamic effects of different preparations of stroma free hemolysates in the isolated perfused rat kidney

We have examined the effects of Stroma Free Hemolysate (SFH) solutions in the isolated perfused rat kidney. Three types of SFH, stored for 6 to 8 months at 4 degrees C, were tested: 1) unmodified, 2) glyoxalated and lightly cross linked and 3) pyridoxalated and polymerized. All three SFH solutions, added to the perfusate at a concentration of approximately 420 mg/100ml, increased renal vascular resistance (RVR) and reduced glomerular filtration rate (GFR). Unmodified, glyoxalated and lightly cross linked and pyridoxalated polymerized SFH resulted in a rise in RVR of 55%, 38% and 33% respectively and a fall in GFR of 42%, 57% and 83% respectively. In order to determine whether storage had altered the effect of SFH on renal function, one of the forms of SFH (glyoxalated and lightly cross linked) was studied only 4-6 weeks after preparation. While this preparation caused an increase in RVR of 41% it did not alter GFR; filtration fraction (FF) rose. However, after further storage of this preparation for 6-7 months, the solution resulted in a marked decrease in GFR of 47% as well as a rise in RVR of 23%. We conclude that three different SFH preparations resulted in marked vasoconstriction and reductions in GFR. These deleterious effects on renal hemodynamics were noted at a concentration of hemoglobin well below that necessary to effectively improve oxygen content. Storage of the SFH solutions may cause or contribute to their effects on renal function. SFH solutions intended for use as blood substitutes should be tested for vasoconstrictor activity.     

Decreased glucose production from maltose in perfused kidney of streptozotocin diabetic rats

To elucidate the role of renal maltase in the metabolism of circulating maltose, glucose production from maltose was investigated in perfused kidney of normal and streptozotocin (STZ) diabetic rats. The kidney was perfused with 150 mg/dl maltose for 30 min and perfusate maltose and glucose were measured. Perfusate glucose concentration in the kidney of control rats gradually increased during perfusion. That in the kidney of diabetic rats was significantly lower than that in controls. Perfusate maltose concentration in the kidney of diabetic rats was significantly higher than that in controls. These results suggest that circulating maltose may enter kidney cells and subsequently metabolized to glucose, and that maltose uptake and glucose production were decreased in the kidney of STZ diabetic rats.     

Regulation of renal and lower gastrointestinal function: role in fluid and electrolyte balance

For the majority of vertebrates, the kidneys are not the sole organs that function to maintain homeostasis of body fluid and electrolytes. Mammals are unusual in this respect, as the kidneys are the organs that fill this role. For non-mammalian vertebrates, other organs such as gills, skin, salt glands, urinary bladders and the gastrointestinal (GI) system function in concert with the kidneys in the control of fluid and ion balance. Birds are of particular interest and unique as they do not possess a urinary bladder and the renal output enters the lower GI tract. The physiology of the interaction of avian kidneys and lower GI tract is an excellent example of integrative physiology and several aspects of it have been examined, for example, the role of the avian antidiuretic hormone (arginine vasotocin, AVT) in controlling renal output. AVT produces both a tubular and glomerular antidiuresis. The glomerular antidiuresis is important, as the fluid from the kidneys that enters the GI should not be highly concentrated. Another hormone, aldosterone, has been shown to play an important role in regulating the transport of sodium by the GI epithelium. In addition, the lower GI tract plays a significant role in recycling a portion of the nitrogen that leaves the kidneys as uric acid. Furthermore, the output of avian kidneys contains large amount of protein that is conserved by the lower GI tract.     

Alanine transport by the isolated perfused rat kidney

L-alanine transport kinetics were examined in the isolated perfused rat kidney (1) using different perfusate concentrations of alanine (PAla) to obtain different filtered loads and (2) under conditions of osmotic diuresis. The transport maximum for alanine (TmAla) was found to be very high relative to $\text{in}$$\text{vivo}$ filtered loads of alanine. The apparent TmAla was dependent on glomerular filtration rate (GFR) and it could be modified by osmotic diuresis. It is suggested that the variation of TmAla with changes in GFR may be the consequence of variations in fractional volume flow through the proximal tubule.     

Effect of crude extract of Stevia rebaudiana on renal water and electrolytes excretion.

To evaluate the effect of crude extract of Stevia rebaudiana on renal water, Na+ and K+ excretion, male Wistar rats (250-350 g each) under antidiuresis or water diuresis conditions, were evaluated. During intravenous infusion of the extract (0.05 mg/min/100 g) no significant differences were detected in mean arterial pressure or renal hemodynamics parameters. In contrast, fractional water and sodium excretion and solute clearance increased significantly, in both groups of animals. In antidiuresis rats the extract significantly increased reabsorption of water by the collecting duct and in water diuresis animals the extract significantly increased free water clearance. The data suggest preferential action of the extract in the proximal tubular cells involved with salt transport mechanism.     

Effects of changes in intravascular oncotic pressure on renal responses to volume loading in the saltwater-acclimated Pekin duck (Anas platyrhynchos)

Summary The relative contributions of the intra-and extravascular compartments of the extracellular fluid (ECF) to the control of osmoregulatory renal functions were examined in saltwater-acclimated Pekin ducks. Having established steady-state diuresis and salt gland secretion by continuous infusion of 1 ml·min^-1 isotonic Krebs-Ringer-Bicarbonate (KRB) solution, 5% dextran-70 was added to the infusate for 30 min thereby confining volume expansion to the intravascular compartment. General volume expansion by isotonic KRB caused a drop in plasma osmolality by 23 mOsm·kg^-1, due to NaCl elimination by the salt glands, and decreases in hematocrit (het) and radioimmunologically measured plasma levels of Arg⁸-vasotocin (AVT) and Val⁵-angiotensin II (ANG II), whereas immunoreactivity associated with atrial natriuretic factor (ir-ANF) was increased. Adding 5% dextran-70 to the infusate left plasma osmolality and electrolytes unchanged but was followed by a further decrease in hct and a 36% increase in the plasma colloidosmotic pressure (COP) facilitating fluid shifts from the extra-to the intravascular compartment of the ECF. Plasma levels of AVT and ANG II remained unchanged, but ir-ANF rose three-fold, its increase being three times as great relative to the decrease in hct, as during general volume expansion by isotonic KRB solution. Arterial and central venous pressure measurements did not indicate changes in cardiovascular function. Hyperoncotic infusion initially induced marked antidiuresis with decreased osmolal excretion, despite a slightly elevated urine osmolality. This effects, however, was trasient and not proportional to the rise in COP, but rather seemed to be related to fluid shifts resulting from hyperoncotic loading. With tracer dilution techniques, reductions in both renal plasma flow and glomerular filtration rate were found to contribute to antidiuresis which was associated with reduced fractional water excretion. Salt gland secretion rate did not increase during hyperoncotic intravascular volume expansion but rather tended to decrease. The results of this study are in line with the idea that contributions of the interstitial fluid compartment (IFC) to volume-dependent control of osmoregulatory functions have to be considered. In the present study on saltwater-acclimated ducks, AVT, ANG II, and ir-ANF could be excluded as mediators of the adjustments in renal water and salt handling following fluid shifts due to hyperoncotic intravascular volume expansion.Abbreviations ANF atrial natriuretic factor - ir-ANF ANF-like immunoreactivity - ANG II angiotensin II - AVT arginine vasotocin - BF breathing frequency - b. w. body weight - COP colloid osmotic pressure - CVP central venous pressure - ECF extracellular fluid - ERPF effective renal plasma flow - FF filtration fraction - GFR glomerular filtration rate - IFC interstitial fluid compartment - i.v. intravenous(ly) - hct hematocrit - HR heart rate - KRB Krebs-Ringer Bicarbonate solution - MABP mean arterial blood pressure - PAH paraaminohippuric acid - SEM standard error of mean     

The metabolism of 3-H-cortisone and 3-H-cortisol by the isolated perfused rat and guinea pig lungs.

Isolated perfused rat lungs removed more than 35% of 3-H-cortisone (1 times 10-9M) from the perfusate during one passage through the pulmonary circulation. The cortisone in the lungs was then rapidly converted to cortisol, which was returned to the perfusate. The tritiated steroid taken up was so rapidly washed from the lung, that only 10% remained after a 12 minute perfusion with steroid-free medium. In recirculating experiments, nearly 60% conversion to cortisol occurred over 32 cycles; in addition, there was a slow increase in the percentage of polar compounds in the medium. Similarly, the perfused hindlimbs preparation from the rat converted cortisone to cortisol and returned the cortisol to the perfusate. In contrast, guinea pig isolated perfused lungs had neglible effect on cortisone. Rat lungs demonstrated only a limited ability to convert 3-H-cortisol to cortisone. The results suggest that the lungs may play an important role in maintaining cortisone/cortisol levels in the plasma.     

Antidiuretic action of prolactin in the rat with diabetes insipidus.

Rats with hereditary hypothalamic diabetes insipidus, devoid of endogenous ADH, exhibited a prompt antidiuresis when injected subcutaneously or intraarterially with ovine prolactin. The antidiuresis was accompanied by a decrease in free water clearance and an increase in urine osmolality without a change in osmolal clearance or creatinine excretion. Measurement of PAH and insulin clearances indicated that prolactin had no effect on renal plasma flow or glomerular filtration rate. Prolactin injection caused a transient decrease in urinary sodium excretion, but proximal tubular sodium reabsorption, estimated by lissamine green transit time, was unaffected. The antidiuretic effect of prolactin could not be attributed to ADH contamination of the ovine prolactin preparation. Kidney cyclic AMP content was increased significantly 5 min after injection of prolactin. Thus, prolactin has an antidiuretic effect similar to that which occurs as a result of ADH action on the kidney and does not require either the release or the presence of ADH in order to cause the antidiuresis. Further, the impaired water excretion cannot be attributed to an increase in proximal tubular sodium reabsorption or to alteration of renal hemodynamics. It is suggested that prolactin has a direct ADH-like action on the kidney resulting in antidiuresis.     

Lack of effect on human lipoprotein-triacylglycerol on the function of perfused rat kidney

We determined whether addition of human lipoprotein-TG to the perfusate for the isolated rat kidney would increase net Na+ reabsorption or maintain renal tissue K+ content. Rat kidneys (n = 6) were perfused for 75 min with a perfusate containing 6 g% of substrate-free albumin in Krebs-Ringer bicarbonate and a mixture of human chylomicrons and very low density lipoproteins (human lipoprotein-triacylglycerol (HL-TG]. Control kidneys (n = 6) were perfused in the substrate-limited state, i.e., without any exogenous substrates added to the perfusate. Means (n = 6) for function of control kidneys were GFR = 808 +/- 50 microliter g-1 X min-1; %T-Na+ = 63.3 +/- 1.3%. A significant loss of tissue K+ occurred: tissue K+ remaining after 75 min of perfusion = 79.1 +/- 1.9%. Although kidney tissue contains lipoprotein lipase, HL-TG (n = 6) did not increase %Na+ reabsorption (64.3 +/- 2.6%) or maintain tissue K+ content (80.6 +/- 2.0%). Therefore, the TG might have been hydrolyzed and taken up for biosynthesis, the rat kidney lipoprotein lipase might have been inactive, or the rat kidney might not use lipoprotein-TG for biosynthesis or oxidation.