Formation of angiotensin III from [des-Asp1]angiotensin I in the mesentric vasculature

The effects of [des-Asp1]angiotensin I and angiotensin III on mesenteric blood flow were compared in 15 pentobarbital-anesthetized dogs. These agonists were administered as bolus injections directly into the vasculature supplied by the superior mesenteric artery. Both [des-Asp1]angiotensin I and angiotensin III produced dose-dependent decreases in mesenteric blood flow, with angiotensin III being more potent than [des-Asp1]angiotensin I at all doses tested. The constrictor responses to [des-Asp1]angiotensin I were markedly attenuated in the presence of an angiotensin-converting enzyme inhibitor (SQ20881); SQ20881 did not alter responses to angiotensin III or norepinephrine. The administration of [Ile7]angiotensin III (an angiotensin III antagonist) attenuated the responses to both [des-Asp1]angiotensin I and angiotensin III, without altering the responses to norepinephrine. These results suggest that the decrease in mesenteric blood flow produced by [des-Asp1]angiotensin I is largely caused by its local enzymatic conversion to angiotensin III. This conversion in one transit through the mesenteric vasculature is approximately 24%.

Role of vagal afferents in vasodepressor effects of PGE2 in spontaneously hypertensive rats

In anesthetized, spontaneously hypertensive rats (Okamoto-Aoki), injections of 0.75, 1.5, and 3.0 microgram/kg PGE2 into the jugular vein caused transient decreases (mean +/- SE) in arterial pressure of 21 +/- 2, 37 +/- 3, and 78 +/- 6 mmHg, respectively, before cervical vagotomy and of 1 +/- 1, 15 +/- 4, and 15 +/- 6 mmHg after cervical vagotomy. The vasodepressor effect of jugular vein injections of 3.0 microgram/kg PGE2, but not of lower doses, was depressed by vagotomy in normotensive Wistar-Kyoto and Sprague-Dawley rats. Vagotomy did not reduce the hypotensive response to intra-aortic injections of PGE2 in these hypertensive and normotensive rats. The depressor effect of PGE2 thus appears to have a significant reflex component mediated through cardiopulmonary receptors subserved by vagal afferents, with hypertensive rats exhibiting a lower threshold than normotensive rats. A vagally mediated reflex component to the depressor effect of PGE2 could not be demonstrated in normotensive rabbits or in rabbits and rats with chronic renovascular hypertension. Thus, a naturally occurring vasoactive substance can stimulate cardiopulmonary receptors subserved by vagal afferents in the rat, and spontaneously hypertensive rats appear to be especially sensitive to this effect.

Collection of urine from each kidney in the rabbit without ureteral cannulation

Collection of urine in rabbits by conventional methods such as catheterization of ureters or bladder with polyethylene tubing or Foley cannulas is hampered by the occurrence of hematuria or obstruction of urine flow, or both. These problems were solved by placing in the bladder a stainless steel device with a horizontal round disk attached to an eliptic vertical septum. The vertical septum divides the bladder into two compartments in such a way as to allow the collection of urine from each kidney. Studies show that this intrabladder devide can be satisfactorily used in acute experiments in anesthetized or conscious rabbits for periods up to 5-6 h.

Hypertension and the interrelated renal circulatory effects of prostaglandins and the renin-angiotensin system

Blockade of prostaglandin synthesis with indomethacin (1) did not induce significant changes in blood pressure or in renal circulation in renovascular hypertensive rabbits with normal renal blood flow; (2) induced renal insufficiency and aggravated hypertension in hypertensive rabbits whose renal blood flow was below normal levels; (3) did not alter the reversal of renovascular hypertension produced by the release of the renal arterial constriction; and (4) induced a decrease in plasma renin activity by decreasing renin release. These findings indicate that the vasodilator and natriuretic actions of prostaglandins may play an important role in protecting the kidney against ischemia; the facilitating role of renal prostaglandins on renin release raises the possibility that a primary hypersecretion of renal prostaglandins is responsible for Bartter's syndrome, whereas a primary deficiency may be responsible for "low-renin hypertension."

The effect of high sodium intake and angiotensin antagonist in rabbits with severe and moderate hypertension induced by constriction of one renal artery

The role of renin was assessed in moderate and severe one-clip, two-kidney hypertension in rabbits during normal and high Na intake. Severe hypertension occurred with high levels of plasma renin and creatinine and with extracellular volume depletion. In this group, hypertension was significantly reduced by the 1-hour intravenous infusion of 1,000 ng/kg of an angiotensin II antagonist or by correcting the volume depletion with a high Na intake, which also decreased renin activity and creatinine. The infusion of the antagonist after a high salt diet failed to decrease blood pressure further. Moderate hypertension occurred with plasma levels of renin that were slightly below normal and with no significant abnormalities in extracellular volume depletion or creatinine. In this group, the administration of an angiotensin II antagonist or a high salt diet did not affect any of the three parameters. In normotensive controls, the blood pressure level was not affected by either the angiotensin II antagonist or the high salt diet, despite a reduction in plasma renin activity. Thus, high levels of renin are important in maintaining severe hypertension, and these increased levels probably are accompanied by a concomitant depletion of extracellular volume. Correction of the extracellular volume depletion by a high salt diet is followed by a decrease in renin activity and in blood pressure. In contrast, renin activity does not seem to be important in maintaining moderate hypertension, the pathogenetic mechanism of which remains to be elucidated.

Regulation of filtration rate in sodium-depleted and -expanded dogs

Sodium balance may affect the response of single-nephron filtration rate (SNFR) to changes in renal arterial pressure (deltaRAP) when the SNFR is measured in the absence of orthograde fluid delivery from the proximal tubule. This thesis was tested in sodium-depleted and -expanded dogs given furosemide, Doca, and low- or high-salt diets, respectively. After 7 days of treatment, renal renin content was significantly greater in the sodium-depleted group (delta = 23.5 +/- 7.4 DU [dog units]/g kidney). Glomerular filtration rate and renal plasma flow were similar in both groups following changes in RAP of 29 +/- 4 and 29 +/- 3 mmHg in the sodium-depleted and -expanded groups, respectively. SNFR at high RAP was not different from SNFR at low RAP in the sodium-depleted group (delta = -0.2 +/- 4.9 nl/min) and slightly, but significantly, greater in the sodium-expanded group (delta = 7.6 +/- 2;1 nl/min). However, the response of SNFR was similar to that of whole-kidney filtration rate. Furthermore, the autoregulatory response (deltaSNFR/deltaRAP) was not significantly different between the groups but was significantly greater than the response calculated for RAP below the range studied. It is concluded that an autoregulatory response of SNFR, in the absence of orthograde fluid delivery from the proximal tubule, is observed in both sodium-depleted and -expanded dogs.

The effect of indomethacin blockade of prostaglandin synthesis on blood pressure of normal rabbits and rabbits with renovascular hypertension

Indomethacin inhibits the synthesis of prostaglandin and the release of renin. These effects were studied in normal rabbits and rabbits with two-kidney Goldblatt hypertension (2KGH) and one-kidney Goldblatt hypertension (1KGH) by giving daily intravenous injections of indomethacin (3mg/kg after two initial doses of 9 mg/kg), and in appropriate control rabbits given diluent phosphate buffer without indomethacin. In normal rabbits, indomethacin significantly decreased immunoreactive plasma prostaglandin E-like substance (IPGE) and plasma renin activity (PRA). Indomethacin did not change plasma creatinine (PCr) or mean blood pressure but it decreased renal blood flow (RBF) and glomerular filtration rate (GFR). In 2KGH rabbits, responses depended on the level of renal function and, to a lesser extent, on the level of PRA. In six of10 2KGH rabbits in which hypertension developed without significant changes in PRA, IPGE, PCr, RBF, and GFR, indomethacin produced changes similar to those seen in normals. In the other four rabbits, development of 2KGH was accompanied by increased PRA, increased IPGE, and decreased RBF and GFR, and indomethacin produced renal failure, oliguria, malignant hypertension, and death within 5 days. In 1KGH rabbits, indomethacin decreased IPGE, PRA, and renal function but increased mean blood pressure. These observations suggest that prostaglandins exert a protective effect on renal function in renovascular hypertension.

Effects of indomethacin in rabbit renovascular hypertension

1. Indomethacin inhibits prostaglandin synthesis and interferes with renin release; these effects were studied in rabbit renovascular hypertension. 2. Ten intravenous injections (3 mg day-1 kg-1 after two initial doses of 9 mg/kg) of indomethacin were given daily to ten normal rabbits, ten rabbits with two-kidney Goldblatt hypertension (2KH), tension (1KH). Twelve appropriate control rabbits received diluent phosphate buffer without indomethacin. Plasma renin activity and plasma prostaglandin E2 were measured by radioimmunoassay. 3. In the normal group, indomethacin significantly decreased plasma prostaglandin E2 (1-15 to 0-2 ng/ml, SEM 0-2; P less than 0-01) and plasma renin activity (20 to 3 ng h-1 ml-1, SEM 1, P less than 0-01). Plasma creatinine increased slightly but the mean blood pressure was not significantly changed by indomethacin. 4. Six of ten rabbits with 2KH showed results similar to those in the normal rabbits. In four of ten rabbits in which development of 2KH was accompanied by increments in plasma renin activity (18 to 31-5 ng h-1 ml-1, SEM 3 and 4 respectively; P less than 0-01) and plasma prostaglandin E2 (1-2 to 3-4 ng/ml, SEM 0-2 and 0-4 respectively; P less than 0-05), treatment with indomethacin produced renal failure (plasma creatinine increasing to 7-6 mg/100 ml), oliguria, malignant hypertension (mean blood pressure, 168 mmHg, SEM 7-7) and death within 5 days. 5. In 1KH, indomethacin decreased plasma renin activity and plasma prostaglandin E2, but caused increased mean blood pressure (102 to 121 mmHg, SEM 4 and 6 respectively; P less than 0-01) and decreased renal function (plasma creatinine 0-9 +/- 0-04 to 3-5 +/- 1 mg/100 ml, SEM 0-04 and 1 respectively; P less than 0-01). 6. Aggravation of hypertension was conditioned by pre-existing levels of renal function and, to a lesser extent, by plasma renin activities. 7. These results suggest that prostaglandins exert a protective effect on renal function in renovascular hypertension.

The effect of indomethacin and other anti-inflammatory drugs on the renin-angiotensin system

The administration of two different doses of indomethacin, 9 and 18 mg/kg, to two different groups of rabbits was followed 6 h later by a significant decrease in plasma renin activity, and these levels were not increased by hemorrhage. The administration of 2 mg/kg of indomethacin did not alter the basal levels of plasma renin activity, but it was effective in diminishing the peripheral increase of renin produced by hemorrhage. Similar effects were obtained in other groups of rabbits treated with 9 mg/kg of meclofenamate or 18 mg or aspirin. The lowering effect of indomethacin on plasma renin activity is not specifically related to hemorrhage because it also prevented the increase in plasma renin activity elicited by 5 mg/kg of furosemide. Further studies showed that indomethacin did not exert any significant effect in vivo on the plasma level of renin substrate or on the generation of angiotensin from normal plasma by exogenous renin. And indomethacin did not interfere with the binding capacity of anti-angiotensin I for angiotensin I in the radioimmunoassay reaction or with the in vitro formation of angiotensin from hog renin-nephrectomized rabbit plasma reaction. The results thus indicate that the lowering effect of indomethacin on plasma renin activity is due to the interference with renal renin release. That this effect may be related to the blockade of prostaglandin synthesis is suggested by the similar effect exhibited by other blockers of prostaglandin synthesis.

Influence of renin depletion on renal function after release of 24-hour ureteral obstruction

A marked increase in preglomerular resistance mediated through the renin-angiotensin system has been proposed as the mechanism for the sustained decrease in glomerular filtration rate seen following release of 24-hour ureteral obstruction. The importance of the renin-angiotensin system in mediating this response was evaluated by determining whole kidney and single nephron function following release of 24-hour ureteral obstruction in rats with normal renal renin content and in rats depleted of renal renin by desoxycorticosterone acetate acetate (DOCA) and saline treatment. The DOCA and saline treatment was effective in reducing renal renin content to less than 10% of the normal values. However, when compared to nonobstructed kidneys, both whole kidney filtration rate and single nephron filtration rate were similarly and significantly reduced in both groups following release of 24-hour ureteral obstruction. Single nephron stopflow techniques were used to determine the net hydrostatic force for filtration. The net hydrostatic force for filtration in control nonobstructed nephrons averaged 37.8 +/- 1.1 mm. Hg, but was significantly decreased to 22.5 +/- 2.2 mm. Hg in the normal renin obstructed kidney and to 18.8 +/- 1.0 mm. Hg in the renin-depleted obstructed kidney. It is concluded that the marked depression in glomerular filtration rate seen following release of 24-hour ureteral obstruction is due to increased afferent arteriole resistance and that the renin-angiotensin system is apparently not important in mediating the response.

Indirect blood pressure measurements in the rabbit: correlations with direct aortic and ear pressures

Blood pressures in the central artery of the ear were determined in rabbits by the use of a modified Grant-Rothschild pressure capsule using two end-points defined as the complete cessation (occlusion) or restoration (opening) of the arterial blood flow. In normal rabbits, the opening values measured by the capsule were closely related to diastolic pressures measured directly in the aorta or in the central artery of the ear, whereas the values obtained during arterial occlusion were higher, by a reproducible amount, than the direct systolic recordings in both the ear and the aorta. In rabbits rendered chronically hypertensive, systolic and diastolic blood pressures measured directly in the aorta and the ear were less (in a predictable manner) than their correspondent occlusion and opening values recorded with the capsule. The amount of this difference increased proportionally as blood pressure increased. Differences between direct and capsular recordings were less consistent in rabbits made acutely hypertensive with infusions of angiotensin. Through regression analysis, systolic and diastolic pressures in the aorta and in the central artery of the ear can be reliably predicted from capsular reading.

Role of prostaglandins in the reversal of one-kidney hypertension in the rabbit

Hypertensive rabbits with a clip on the renal artery of their solitary remaining kidney show an abrupt decrease in blood pressure after the arterial constriction is released. Although the mechanism underlying this phenomenon remains controversial, some experimental evidence suggests that it could be humorally mediated. The involvement of prostaglandins was investigated by examining the effect of the release of the arterial constriction on blood pressure, renal blood flow, glomerular filtration rate, and urinary output in five conscious single-kidney hypertensive rabbits in which prostaglandin synthesis was blocked with indomethacin (priming intravenous injection of 9 mg/kg followed by a constant infusion of 1 mg/kg hour-1). The results were compared with those obtained in another group of five single-kidney hypertensive rabbits submitted to the same protocol but not treated with indomethacin. The blockade of prostaglandin synthesis with indomethacin prevented the increments in renal blood flow and glomerular filtration rate seen in the control rabbits after unclipping a significantly retarded the appearance of diuresis and the fall in blood pressure. Despite these observations, the results do not indicate a major participation of prostaglandins in the reversal of single-kidney hypertension, because the decrease in blood pressure 9 hours after the removal of the arterial constriction was similar in both groups.

Continuous inhibition of renin release in dogs by vagally innervated receptors in the cardiopulmonary region

Inhibition of the release of renin by vagal afferents from the heart and lungs was studied in 14 dogs with their aortic nerves cut and their carotid sinuses vascularly isolated. The release of renin from one kidney was calculated from the venous-arterial difference in plasma renin activity (radioimmunoassay) and the renal blood flow (electromagnetic flowmeter). Renin release was determined before and during temporary interruption of afferent vagal nerve traffic (bilateral cooling of the cervical vagi). With carotid sinus pressure maintained at 40 mm Hg, vagal cooling increased mean aortic blood pressure (24%), decreased renal blood flow (19%), and increased renin release (241%). With sinus pressure maintained at the mean aortic blood pressure existing during the control period, vagal cooling caused a lesser increase in mean aortic blood pressure (12%), little decrease in renal blood flow (7%), and a marked increase in renin release (522%). The changes in renal blood flow and renin release with vagal cooling were prevented by renal denervation. Thus, vagal afferents from the cardiopulmonary region exert a tonic restraint on the release of renin; this restraint occurs in circumstances in which these afferents cause little change in total renal blood flow.

Indomethacin enhancement of glycerol-induced acute renal failure in rabbits

Seventy-three rabbits (2 to 3 kg in weight) were studied during a control period and after receiving 50% glycerol (G) or mercuric chloride (M) with or without indomethacin (I) (controls received the diluent used for I). Plasma creatinine, plasma renin activity, blood pressure, sodium and potassium concentrations, hematocrit value, urinary output, body wt and histologic appearance of the kidney were determined. I enhanced the incidence and severity of the acute renal failure produced by G but failed to aggravate that produced by M. Because the dose of I used in this study blocked the synthesis of renal prostaglandins in the rabbit, we suggest that renal prostaglandins protect against the development of G-induced acute renal failure (a circulatory type of renal failure) in this animal model. Furthermore, the failure of I to aggravate M-induced acute renal failure indicates that it is unlikely that I aggravates G-induced acute renal failure by a direct nephrotoxic effect. No evidence was found for other possible side actions of I being responsible for the observed aggravation.

Changes in plasma renin substrate, plasma and renal renin, and plasma osmolarity during glycerol-induced acute renal failure in rabbits

Seven groups of rabbits were studied before or at various intervals after the subcutaneous administration of 50 percent glycerol in isotonic saline (14 ml/kg). A sharp increase in plasma crystalloid osmolarity, due to glycerol reabsorption from the subcutaneous tissue, was detected at 1.5 and 6 hours and was maximal between 12 and 20 hours. Plasma renin activity did not change at 1.5 hours, but it was significantly elevated at 6 hours and maximally increased between 12 and 20 hours. The increase of plasma crystalloid osmolarity might contribute to renin release in this experimental model. Changes in renal renin levels after the administration of glycerol were not significant, although lower renal renin values were consistently found in rabbits with more severe impairment of renal function. Plasma renin substrate increased later than plasma renin activity (20 hours) and remained high after plasma renin activity had returned to normal (48 hours). The increase of plasma renin substrate was interpreted as mainly due to the impairment of renal function, since a positive correlation was found between plasma creatinine and plasma renin substrate.