Effects of calcitonin gene-related peptide on renal blood flow in the rat

The effects of alpha-rat calcitonin gene-related peptide (alpha-rCGRP) on systemic and renal hemodynamics and on renal electrolyte excretion were examined in normal anesthetized rats. In one group of rats (n = 7), infusions of alpha-rCGRP at doses of 10, 50, 100, and 500 ng/kg/min for 15 min each produced dose-related and significant decreases in mean arterial pressure from a control of 130 +/- 3 mm Hg to a maximal depressor response of 91 +/- 2 mm Hg. During the first three doses of alpha-rCGRP, renal blood flow progressively and significantly increased from a control of 5.0 +/- 0.3 ml/min to a peak level of 6.3 +/- 0.3 ml/min achieved during the 100 ng/kg/min infusion. With the highest infusion rate of 500 ng/kg/min, renal blood flow fell below the control level to 4.5 +/- 0.2 ml/min (P less than 0.05). The responses in renal blood flow and mean arterial pressure were associated with reductions in renal vascular resistance. After cessation of alpha-rCGRP infusions, arterial pressure, renal blood flow, and renal vascular resistance gradually returned toward the baseline values. In another group of rats (n = 9), infusion of alpha-rCGRP for 30 min at 100 ng/kg/min produced a significant reduction in urinary sodium excretion from 0.28 +/- 0.06 to 0.14 +/- 0.5 muEq/min (P less than 0.05). Urine flow and urinary potassium excretion also appeared to decrease, but the changes were not significantly different (P greater than 0.05) from their respective baselines. These results demonstrate that alpha-rCGRP is a potent and reversible hypotensive and renal vasodilatory agent in the anesthetized rat. The data also suggest that alpha-rCGRP may have significant effects on the excretory function of the kidney.     

Activation of histamine H3 receptors inhibits renal noradrenergic neurotransmission in anesthetized dogs

To investigate the possible involvement of histamine H(3) receptors in renal noradrenergic neurotransmission, effects of (R)alpha-methylhistamine (R-HA), a selective H3-receptor agonist, and thioperamide (Thiop), a selective H3-receptor antagonist, on renal nerve stimulation (RNS)-induced changes in renal function and norepinephrine (NE) overflow in anesthetized dogs were examined. RNS (0.5-2.0 Hz) produced significant decreases in urine flow and urinary sodium excretion and increases in NE overflow rate (NEOR), without affecting renal hemodynamics. When R-HA (1 microg x kg(-1) x min(-1)) was infused intravenously, mean arterial pressure and heart rate were significantly decreased, and there was a tendency to reduce basal values of urine flow and urinary sodium excretion. During R-HA infusion, RNS-induced antidiuretic action and increases in NEOR were markedly attenuated. Thiop infusion (5 microg x kg(-1) x min(-1)) did not affect basal hemodynamic and excretory parameters. Thiop infusion caused RNS-induced antidiuretic action and increases in NEOR similar to the basal condition. When R-HA was administered concomitantly with Thiop infusion, R-HA failed to attenuate the RNS-induced antidiuretic action and increases in NEOR. However, in the presence of pyrilamine (a selective H1-receptor antagonist) or cimetidine (a selective H2-receptor antagonist) infusion, R-HA attenuated the RNS-induced actions, similarly to the case without these antagonists. Thus functional histamine H3 receptors, possibly located on renal noradrenergic nerve endings, may play the role of inhibitory modulators of renal noradrenergic neurotransmission.     

Renal effects of atrial natriuretic factor in domestic fowl

The renal hemodynamic and tubular effects of ANF were investigated using the Sperber technique in chickens. This technique takes advantage of the unique portal circulation of the avian kidney and permits direct access to the renal peritubular space independent of renal arterial blood flow and glomerular filtration. Infusion of ANF into the avian renal portal system increased urine flow rate and sodium excretion by as much as 300% and 100%, respectively. These changes occurred in the absence of significant alterations in glomerular filtration rate or renal plasma flow. There was no significant difference in urine flow, sodium excretion or glomerular filtration rate between the ANF-infused kidney and the contralateral, non-infused kidney. We conclude that the diuretic and natriuretic effects of ANF do not depend on changes in glomerular filtration rate and that the site of action of ANF is the renal medulla.     

Antihypertensive and bilateral renal responses to diuretics in 2-kidney, 1-clip Goldblatt hypertensive rats

Experiments were conducted to assess the effect of furosemide or amiloride alone and a combination of both agents on each kidney in anesthetized 2-kidney, 1 clip Goldblatt hypertensive rats (n = 25). Intravenous infusion of furosemide alone (1.02 mg/kg.hr) significantly reduced the blood pressure by 14 +/- 5 mmHg. There were 6- to 10-fold increases in water, absolute sodium and fractional sodium excretions and a 2-fold increase in potassium excretion in the nonclipped kidney. A smaller but significant increase in the excretory function was also observed in the clipped kidney. There was no significant change in GFR of both kidneys. Indomethacin pretreatment (2 mg/kg) failed to significantly alter the vasodepressor and renal responses to furosemide in both hypertensive and normal rats. Removal of the renal artery clip from the hypertensive rats reduced the blood pressure by 12 +/- 3 mmHg and enhanced the function of the ipsilateral, unclipped kidney. Subsequent administration of furosemide further increased the excretory response. Administration of amiloride alone (2.4 mg/kg.hr) or with furosemide into hypertensive rats reduced the arterial pressure and increased excretion rates of urine flow and urinary sodium. Potassium excretion rate decreased bilaterally in amiloride treated rats but did not alter significantly in rats which received a combination of amiloride and furosemide. These results indicate that diuretics ameliorate the excretory function of both the stenotic kidney and the nonstenotic kidney and that the improvement of the kidney function is independent of prostaglandin. Furthermore, removal of the stenosis accentuates the beneficial effect of diuretics on the kidney.     

Reflex responses to reductions in functioning renal mass

Both acute unilateral nephrectomy (AUN) and unilateral ureteral obstruction (UUO) result in an acute increase in cation excretion from the contralateral kidney. AUN results in reflex changes in systemic hemodynamics owing to an acute and transient increase in arterial pressure that activates carotid sinus baroreceptors and constitutes an afferent limb in the reflex; hemodynamic adjustments and increased cation excretion result. The reflex involves participation of the endogenous opioid system, with receptors located primarily in the central nervous system, and requires intact pituitary function because both hypophysectomy and pretreatment with large doses of dexamethasone prevent the postnephrectomy natriuresis. The natriuresis is closely correlated with an increase in the plasma concentration of the NH2-terminal fragment of the pituitary peptide precursor molecule proopiomelanocortin, which suggests that such a peptide could participate directly or indirectly in the postnephrectomy natriuresis. Surgical denervation of either the ipsilateral or the contralateral kidney markedly alters the response to AUN, which prevents the natriuresis and blunts the kaliuresis, and indicates a role for renal neural reflexes. Renorenal reflex pathways also mediate the response of the contralateral kidney to UUO, because denervation of either the ipsilateral (obstructed) or the contralateral kidney abolishes both the natriuresis and kaliuresis usually seen after UUO. This reflex also involves the endogenous opioid system, for it does not occur in rats receiving an i.v. infusion of the opiate receptor antagonist naloxone.     

Effect of somatostatin on renal water handling in the dog

When somatostatin was infused into the left renal artery of anaesthetized, hydropenic dogs in doses ranging from 1 to 10 micrograms/min, it produced an increased flow of a more dilute urine from the ipsilateral kidney. Similar infusions in dogs undergoing a maximal water diuresis had no effect. If aqueous antidiuretic hormone (ADH) was administered intravenously into water-loaded dogs prior to the intraarterial infusion of somatostatin, this latter peptide was able to produce an augmented flow of a more dilute urine from the ipsilateral kidney. If the left kidney was made to excrete a concentrated urine in the face of maximal water loading by restricting arterial perfusion, then the infusion of somatostatin had no effect on urinary dilution, though this peptide could increase water excretion in hydropenic dogs when the left kidney was similarly restricted as to arterial inflow. In dogs undergoing a water diuresis that were given cyclic AMP (4 mg/min) into the left renal artery, a decrease in ipsilateral water excretion was observed. The subsequent infusion of somatostatin produced no urinary dilution. We conclude that somatostatin increases renal water excretion by antagonizing the ADH effect on the renal tubule, and that this event probably occurs at a pre-cAMP site within the cell.     

Prostaglandin E2 induced changes in renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat

Prostaglandin E2, when infused into the renal artery of the dog, is a vasodilator and increases both renal interstitial hydrostatic pressure and sodium excretion. Similar studies in the rat, however, have been inconclusive. The present study examined the effect of prostaglandin E2 infusion into the renal interstitium, by means of a chronically implanted matrix, on renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat. Prostaglandin E2 was continuously infused directly into the kidney interstitium to mimic endogenous prostaglandin E2 production by renal cells. The maximum change in each of these parameters occurred when 10(-5) M PGE2 was infused. Renal blood flow increased from 4.70 +/- 0.91 to 5.45 +/- 0.35 ml/min (p less than 0.05) while renal interstitial hydrostatic pressure decreased from 3.9 +/- 0.4 to 2.6 +/- 0.5 mmHg (p less than 0.05) and fractional excretion of sodium decreased from 1.02 +/- 0.20 to 0.61 +/- 0.12% (p less than 0.05). Thus, the present study demonstrates that renal interstitial infusion of prostaglandin E2 increases total renal blood flow but decreases both renal interstitial hydrostatic pressure and urinary sodium excretion in the rat.     

Distinct effects on long-term function of injured and contralateral kidneys following unilateral renal ischemia-reperfusion

Salt-sensitive hypertension and chronic kidney disease (CKD) following recovery from acute kidney injury (AKI) may occur secondary to incomplete repair, or by activation of circulating factors stimulated by injury. We created two types of renal injury induced by unilateral ischemia-reperfusion (I/R); in a direct/ipsilateral AKI group, rats were subjected to unilateral I/R and the untouched contralateral kidney was removed by unilateral nephrectomy after 5 wk to isolate effects on the injured kidney. In the remote/contralateral AKI group, the injured kidney was removed after 5 wk to isolate effects on the untouched kidney. When these animals were subsequently challenged with elevated dietary sodium for an additional 4 wk (0.4 to 4%), both remote/contralateral and direct/ipsilateral AKI rats manifested a significant increase in blood pressure relative to sham-operated controls. Similarly, in acute studies, both ipsilateral and contralateral kidneys had impaired pressure natriuresis and hemodynamic responses. Reductions in vascular density were observed following direct/ipsilateral injury, but were not observed in the remote/contralateral kidney. However, both remote/contralateral and direct/ipsilateral kidneys contained interstitial cells, some of which were identified as activated (low CD62L/CD4+) T lymphocytes. In contrast, only the direct/ipsilateral AKI group demonstrated significant CKD following exposure to elevated salt. This was characterized by a significant reduction in creatinine clearance, an increase in albuminuria, and a dramatic expansion of interstitial inflammation. Taken together, these data suggest that the salt-sensitive features of AKI on hypertension and CKD are segregable such that effects on hemodynamics and hypertension occur independent of direct renal damage. However, prior direct injury to the kidney is required to elicit the full manifestation of CKD induced by elevated sodium intake.     

Renal effects of administered atrial natriuretic peptide in the conscious, aging rat

Studies were performed in conscious, chronically catheterized male Sprague-Dawley rats to investigate the effect of administered atrial natriuretic peptide (ANP) on blood pressure, renal hemodynamics and urinary electrolyte excretion. Studies were performed on young adult (3-4 month old) rats and on aging rats (18-24 months of age). Low dose ANP (80 ng/kg/min for 60 min) had no effects on renal hemodynamics in either young or old rats and produced only a slight blood pressure reduction in young animals. No effect on urinary electrolyte excretion was evident in young rats whereas in the old animals, low dose ANP produced large rises in the rate of sodium excretion, fractional excretion of sodium and urine flow rate. A four fold higher dose of ANP evoked a moderate natriuretic and a marked antihypertensive response in young rats. Time control studies indicated that time alone had no influence on urinary sodium excretion rate, the fractional excretion of sodium or urine flow rate. These studies indicate a much enhanced sensitivity to the natriuretic effects of administered ANP by the kidneys of old rats.     

Actions of nicotine on renal function in dogs

Renal excretory and circulatory responses to nicotine were investigated in anesthetized dogs under three sets of conditions: (a) infusion of nicotine into the left renal artery (ia) at a dose of 0.5 microgram X min-1 X kg body wt-1 X 15 min; (b) ia nicotine after 1.0 mg/kg ia propranolol; and (c) ia nicotine after bilateral adrenalectomy. Measured and calculated left and right renal excretory variables included sodium, potassium, and chloride excretion rates (UNaV, UKV, and UClV, respectively), total solute excretion (UOsV), glomerular filtration rate (GFR), fractional sodium excretion (FENa), and urine flow rate. Systemic arterial pressure and left renal artery blood flow (RBF) were also measured. In seven intact dogs administered nicotine alone, there were significant increases in UNaV, UClV, UOsV, GFR, and urine flow rates from both kidneys. However, nicotine did not significantly affect UKV, FENa, arterial pressure, or RBF. The lack of circulatory effects of nicotine was also observed after either propranolol or adrenalectomy. However, when nicotine was administered after propranolol, the drug evoked significant decreases in UOsV, UNaV, UClV, and GFR, compared with prenicotine values. When nicotine was administered after bilateral adrenalectomy, the drug evoked decreases in the excretory parameters similar to those observed after propranolol. These findings seem to support several inferences: (a) nicotine stimulates renal excretory functions-the alkaloid is saluretic and diuretic; (b) the action of nicotine on the kidney is mediated mainly by the release of catecholamines from the adrenal medulla; (c) catecholamines released by nicotine act mainly on beta-adrenergic receptors; and (d) the saluresis prompted by the release of catecholamines in response to nicotine is due to a subsequent increase in GFR.     

Endothelin B receptor antagonism in the rat renal medulla reduces urine flow rate and sodium excretion

It is well established that activation of endothelin B (ETB) receptor induces natriuresis and diuresis and thus reduces blood pressure. However, the site of action of ETB receptor is debatable. The present study was undertaken to address the role of renal medullary ETB receptor in renal excretory function. In volume-expanded Sprague-Dawley rats, infusion of the ETB antagonist A192621 at 0.5 mg/kg/hr to the renal medulla induced an immediate and significant reduction of urine flow rate that was 87.5% +/- 7.1%, 68% +/- 20%, and 58.3% +/- 15.5% of the control value at 10, 30, and 60 mins, respectively (n=5, P < 0.05 at each time point). Following intramedullary infusion of A192621, urinary sodium excretion remained unchanged during the first 20 mins but started to decline thereafter with a maximal effect at 60 mins. Changes in urinary excretion of potassium and chloride followed the same pattern of changes as for urinary sodium. In contrast, urinary osmolality gradually and significantly increased (control: 419 +/- 66; A192621 at 60 mins: 637 +/- 204 mOsm/kg H2O, P < 0.05). Over a 60-min period of intramedullary infusion of A192621, none of the hemodynamic parameters examined, including mean arterial pressure, renal blood flow, or medullary blood flow, were affected. These data suggest that: (i) intramedullary blockade of ETB receptor produces antidiuresis and antinatriuresis independently of hemodynamic changes, and (ii) the immediate response to intramedullary blockade of ETB receptor is the reduction of water excretion followed by the reduction of sodium excretion.     

Renal and systemic effects of synthetic atrial natriuretic factor

A synthetic peptide corresponding to a sequence of 26 amino acids contained in endogenous rat atrial natriuretic factor (ANF), was infused into one renal artery of anesthetized dogs for a comprehensive in vivo evaluation of the renal and systemic effects of pure ANF. The results proved conclusively that ANF acted directly on the kidney since urine volume and fractional excretion of sodium, potassium, chloride and calcium were elevated in a dose-related manner in the ANF-treated kidney, but were not significantly affected in the contralateral saline-infused organ. The maximum effects achieved with the synthetic ANF were higher than any reported following intravenous administration of crude extracts of rat atria and were similar to those produced by thiazide diuretics. In four of the five dogs studied, renal vascular resistance fell progressively as doses of ANF were increased. Glomerular filtration rate was not significantly elevated during ANF infusion, but was correlated with sodium excretion rates. Even though mean arterial pressure was progressively reduced, there was no significant change in heart rate and no stimulation of renin secretion. Arterial cyclic GMP concentration was higher in the basal state and rose more rapidly than did renal venous levels, indicating that increases in circulating concentrations of arterial cyclic GMP originated from an extrarenal source. Dose-related elevations in urinary cyclic GMP excretion could be explained by increased cyclic GMP filtration, by enhanced production in tubular cells, or by renal tubular secretion. Especially in the saline-infused kidney, there was a clear dissociation between excretion of cyclic GMP and fractional sodium excretion. We conclude that the synthetic ANF increased electrolyte excretion via a direct renal action which was not solely dependent upon changes in renal vasculature, renin secretion or cyclic GMP levels.     

Effect of lysophosphatidylcholine on renal hemodynamics and excretory function in anesthetized rats.

The effect of myristoyl-lysophosphatidylcholine (myristoyl-LPC) on renal hemodynamics, electrolyte and water excretion was examined over a 90 min period in sodium pentobarbital anesthetized male Sprague Dawley rats. Intravenous infusion of myristoyl-LPC at 13 +/- 3 pmol/min resulted in a small fall in systemic blood pressure, a 13% decrease in renal plasma flow without significantly altering glomerular filtration rate and produced a slightly greater excretion of sodium and water than vehicle controls. These results suggest that short term myristoyl-LPC administration can significantly alter renal function producing a weak natriuresis and diuresis which is not dependent on systemic blood pressure and renal hemodynamic changes.     

Systemic hemodynamics and renal function in hemorrhaged dogs resuscitated with cross-linked hemoglobin

Cross-linked hemoglobin (XL-Hb) infused into dogs increases mean arterial pressure (MAP) but decreases blood flow to the renal (RBF), mesenteric (MBF), and iliac (IBF) circulations. These actions differ markedly from dextran infusion (which increases RBF, MBF, and IBF without altering MAP) and may be due to scavenging of nitric oxide by XL-Hb. However, because the hormonal milieu regulating regional circulation is altered during hemorrhage (when XL-Hb may be used), we studied whether systemic hemodynamics, RBF, MBF, IBF, and renal excretory function in hemorrhaged dogs was altered when resuscitated with XL-Hb compared with dextran (n = 6 each). Hemorrhage decreased MAP by 25% due to a 75% decline in cardiac output. RBF, MBF, and IBF all fell by 33, 64, and 72%, respectively (P<0.05 each). There was also a fall in glomerular filtration rate (GFR), urinary flow, and sodium excretion (P<0.05 each). After resuscitation, MAP, cardiac output, RBF, MBF, IBF, and GFR all recovered to basal values with either XL-Hb or dextran. Urinary flow and sodium excretion increased to above basal levels with dextran (both by 3.5-fold; P<0.05) or XL-Hb (by 7.5- and 10-fold, respectively; P<0.05). We conclude that resuscitation with XL-Hb after hemorrhage not only increases MAP, but also restores RBF, MBF, IBF, GFR, and urinary sodium and volume excretion analogously to dextran. The results contrast with those in normal dogs and suggest that nitric oxide inhibition does not impair hemodynamic and renal function recovery during hemorrhage.     

Prostaglandin E2 induced changes in renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat

Prostaglandin E₂, when infused into the renal artery of the dog, is a vasodilator and increases both renal interstitial hydrostatic pressure and sodium excretion. Similar studies in the rat, however, have been inconclusive. The present study examined the effect of prostaglandin E₂ infusion into the renal interstitium, by means of a chronically implanted matrix, on renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat. Prostaglandin E₂ was continously infused directly into the kidney interstitium to minic endogenous prostaglandin E₂ production by renal cells. The maximum change in each of these parameters occured when 10⁻⁵ M PGE₂ was infused. Renal blood flow increased from 4.70±0.91 to 5.45±0.35 ml/min (p<0.05) while renal interstitial hydrostatic pressure decreased from 3.9±0.4 to 2.6±0.5 mmHg (p<0.05) and fractional excretion of sodium decreased from 1.02±0.20 to 0.61±0.12% (p<0.05. Thus, the present study demonstrates that renal interstitial infusion of prostaglandin E₂ increases total renal blood flow but decreases both renal interstitial hydrostatic pressure and urinary sodium excretion in the rat.     

Ca2+ antagonists and db-cAMP sustain a rise in renal blood flow induced by acetylcholine in indomethacin-treated dogs

Renal arterial infusion of acetylcholine (ACh) in the dog normally produces a sustained rise in sodium excretion (UNaV) and in renal plasma flow (RPF). When prostaglandin (PG) synthesis is inhibited, ACh induces only a transient increase in UNaV and RPF followed by a progressive decline in UNaV and RPF, and a rise in renin secretory rate (RSR). Renal arterial infusion of PGE2 but not a vasodilator such as bradykinin restored the response to ACh to normal in indomethacin (Indo)-treated dogs. During renal arterial infusion of dibutyryl cyclic AMP (6 mg/min), ACh also produced a sustained increase in UNaV and RPF despite an inhibition of PG synthesis by Indo. Renal arterial infusion of verapamil (60 micrograms/min) or diltiazem (60 micrograms/min) also prevented the subsequent fall in RPF when ACh was infused; RSR, however, did not show a rise. The results suggest that synthesis of PGE2 with stimulation of cAMP is required for sustained ACh action. When PGE synthesis is inhibited, ACh may produce renal vasoconstriction by increasing intracellular Ca2+ concentration. The partial effect of calcium channel blockers suggests that release of calcium from intracellular stores as well as calcium entry may mediate the response.     

Renal responses to acute reflex activation of renal sympathetic nerve activity and renal denervation in secondary hypertension

We tested whether the responsiveness of the kidney to basal renal sympathetic nerve activity (RSNA) or hypoxia-induced reflex increases in RSNA, is enhanced in angiotensin-dependent hypertension in rabbits. Mean arterial pressure, measured in conscious rabbits, was similarly increased (+16 +/- 3 mmHg) 4 wk after clipping the left (n = 6) or right (n = 5) renal artery or commencing a subcutaneous ANG II infusion (n = 9) but was not increased after sham surgery (n = 10). Under pentobarbital sodium anesthesia, reflex increases in RSNA (51 +/- 7%) and whole body norepinephrine spillover (90 +/- 17%), and the reductions in glomerular filtration rate (-27 +/- 5%), urine flow (-43 +/- 7%), sodium excretion (-40 +/- 7%), and renal cortical perfusion (-7 +/- 3%) produced by hypoxia were similar in normotensive and hypertensive groups. Hypoxia-induced increases in renal norepinephrine spillover tended to be less in hypertensive (1.1 +/- 0.5 ng/min) than normotensive (3.7 +/- 1.2 ng/min) rabbits, but basal overflow of endogenous and exogenous dihydroxyphenolglycol was greater. Renal plasma renin activity (PRA) overflow increased less in hypertensive (22 +/- 29 ng/min) than normotensive rabbits (253 +/- 88 ng/min) during hypoxia. Acute renal denervation did not alter renal hemodynamics or excretory function but reduced renal PRA overflow. Renal vascular and excretory responses to reflex increases in RSNA induced by hypoxia are relatively normal in angiotensin-dependent hypertension, possibly due to the combined effects of reduced neural norepinephrine release and increased postjunctional reactivity. In contrast, neurally mediated renin release is attenuated. These findings do not support the hypothesis that enhanced neural control of renal function contributes to maintenance of hypertension associated with activation of the renin-angiotensin system.     

Renal hemodynamic response to intrarenal infusion of calcitonin gene-related peptide in dogs

The renal hemodynamic and excretory effects of intrarenal infusions of synthetic β-human calcitonin gene-related peptide (β-hCGRP) were examined in normal sodium replete dogs (Group 1, n=6), in sodium replete dogs pretreated with indomethacin (Group 2, n=6), and in sodium deplete dogs (Group 3, n=5). In all groups of anesthetized dogs β-hCGRP was infused at 5 and 10 ng·kg⁻¹·min⁻¹ for 50 min periods each. In the sodium replete group, β-hCGRP infusions strikingly increased renal blood flow, but this response was markedly attenuated in the other 2 groups. During β-hCGRP infusions, the clearance of creatinine also increased significantly in the sodium replete and deplete groups, but not in the indomethacin pretreated animals. No consistent changes in urinary sodium excretion or plasma renin activity were observed with β-hCGRP infusions in any of the 3 groups of dogs. These results indicate that β-hCGRP is a potent renal vasodilator and can increase renal blood flow and glomerular filtration. The data also suggest that the renal hemodynamic actions of β-hCGRP are partially mediated by renal prostaglandins, and that the vasodilatory effects of β-hCGRP may be antagonized by high circulating levels of endogenous angiotensin II in sodium-volume depletion. Finally, β-hCGRP does not appear to have significant actions on urinary sodium excretion or plasma renin activity under the experimental conditions of the present study.     

The effects of clonidine on the kidney function in the anesthetized dog

Studies were performed to determine the mechanism by which the antihypertensive agent clonidine increased urine flow. The response of the kidney has been examined in four combinations. The parameters of renal function have been compared during volume expansion by 1.5-2.0% body weight Ringer solution. In the control animals, volume expansion by 2% body weight, resulted in a slight increase in sodium excretion and urine flow. In 10 anesthetized dogs 1.0 microgram/kg/min of clonidine infused i.v. during 30 minutes (the total amount of clonidine infused was 30 micrograms/kg) decreased the arterial blood pressure from 136 +/- 13 mmHg to 127 +/- 12 mmHg and elevated urine flow from 2.95 +/- 1.65 ml/min to 4.34 +/- 1.77 ml/min while the urine osmolality diminished from 399 +/- 107 mosm/l to 265 +/- 90 mosm/l and the glomerular filtration remained constant. In 5 animals 0.1 microgram/kg/min of clonidine was infused into the left renal artery (this dose is corresponding to the renal fraction of the cardiac output) without any effects in the left kidney. 1.0 microgram/kg/min of clonidine infused directly into the left renal artery produced vasoconstriction in the ipsilateral kidney, decreased the glomerular filtration rate and the urine flow. By contrast in the right kidney the urine flow rose without hemodynamic changes, and the urine osmolality became hypoosmotic compared to the plasma. In ten dogs 1.0 microgram/kg/min of clonidine and 1 mU/kg/min of arginine-vasopressin were infused intravenously. The vasopressin infusion superimposed on the clonidine could not inhibit the increase of the urine excretion, and the fall of the urine osmolality. The results suggest that the clonidine increases the renal medullary blood flow possibly via a direct mechanism, decreases the sympathetic outflow to the kidney and via an indirect pathway, mediated by the renin-angiotensin system. The renal medullary flow increase produces a washout of the medullary osmotic gradient, and the water reabsorption diminishes.     

A role for the angiotensin IV/AT4 system in mediating natriuresis in the rat

Angiotensin II (AngII) or Angiotensin IV (AngIV) was infused into the renal artery of anesthetized rats while renal cortical blood flow was measured via laser Doppler flowmetry. The infusion of AngII produced a significant elevation in mean arterial pressure (MAP) with an accompanying decrease in cortical blood flow, glomerular filtration rate (GFR), urine volume, and urine sodium excretion. The infusion of AngIV induced significant increases in renal cortical blood flow and urine sodium excretion, without altering MAP, GFR, and urine volume. Pretreatment infusion with a specific AT1 receptor antagonist, DuP 753, blocked or attenuated the subsequent AngII effects, while pretreatment infusion with the specific AT4 receptor antagonist, Divalinal-AngIV, blocked the AngIV effects. These results support distinct and opposite roles for AngII and AngIV, i.e. AngII acts as an anti-natriuretic agent, while AngIV acts as a natriuretic agent.