Evidence that inactive p42 mitogen-activated protein kinase and inactive Rsk exist as a heterodimer in vivo

Mitogen-activated protein kinases (MAP kinases) are active only when phosphorylated. Here we examine whether the activation of Xenopus p42 MAP kinase might involve changes in its association with other proteins as well as changes in its phosphorylation state. We find that when p42 MAP kinase is phosphorylated and active, it is monomeric, and that when p42 MAP kinase is nonphosphorylated and inactive, about half of it is monomeric and half is a component of a 110-kDa complex. We identify Rsk, an 82-kDa protein kinase that can be phosphorylated and partially activated by p42 MAP kinase, as being specifically associated with inactive p42 MAP kinase. It is possible that the complex of inactive p42 MAP kinase and inactive Rsk acts as a single signal reception particle and that the activation of the two kinases may be better described as a fork in a bifurcating signal transduction pathway than as successive levels in a kinase cascade.

Inflammatory fibroid polyp of the jejunum causing intussusception: a case report

Inflammatory fibroid polyp is a rare benign lesion of the gastrointestinal tract. This report concerns a 56-year-old female who presented with intermittent abdominal pain, vomiting and diarrhea; she had had partial intestinal obstruction over a period of two months. Plain abdomen showed dilatation of the small bowels. Abdominal echo revealed intussusception of the small intestine. During exploratory laparotomy a polypoid dumb-bell shaped polyp was noted as the leading point of the jejunojejunal intussusception, segmental resection of the jejunum was performed. Histological features of the polyp met the diagnosis of inflammatory fibroid polyp.

Hyperkalemia with high-dose trimethoprim-sulfamethoxazole therapy

In a patient with the acquired immunodeficiency syndrome, a progressive increase in the serum potassium concentration occurred with high-dose trimethoprim-sulfamethoxazole (TMP-SMX) therapy for Pneumocystis carinii pneumonia. In this patient, factors known to alter transcellular potassium shifts to induce hyperkalemia were not present. There was no evidence of glucocorticoid or mineralocorticoid insufficiency at the time of hyperkalemia, while the transtubular potassium gradient decreased. The hyperkalemia resolved spontaneously on discontinuation of TMP-SMX therapy, suggesting that this electrolyte abnormality is related to altered renal tubular secretion of potassium as a consequence of the high-dose TMP-SMX therapy.

Trimethoprim-sulfamethoxazole induces reversible hyperkalemia

OBJECTIVE

To determine the effect of trimethoprimsulfamethoxazole (Tmp-Smx) on serum potassium concentration.

DESIGN

Retrospective cohort study.

SETTING

An urban teaching hospital.

PATIENTS

Fifty-one persons hospitalized for symptomatic infection with human immunodeficiency virus (HIV). Twenty-five patients who were taking high-dose Tmp-Smx (trimethoprim 20 mg/kg per day; sulfamethoxazole, 100 mg/kg per day) for Pneumocystis carinii pneumonia were the study group. Twenty-six patients who had not received the drug were the control group. Patients who received potassium supplements, those taking medications known to alter potassium homeostasis or renal function, or those with a serum creatinine level more than 186 mumol/L were excluded.

MEASUREMENTS AND MAIN RESULTS

Serum potassium concentration in the study group was 4.1 +/- 0.1 mmol/L (mean +/- SE) and increased by 1.1 mmol/L (Cl, 0.8 to 1.5 mmol/L) (P < 0.0001) 9.8 +/- 0.5 days after starting Tmp-Smx therapy. Patients followed longitudinally showed a progressive increase in serum potassium levels during therapy and a progressive decline after discontinuing Tmp-Smx. Blood urea nitrogen and serum creatinine levels increased mildly from 4.3 +/- 0.5 mmol/L and 85 +/- 6 mumol/L to 6.4 +/- 0.7 mmol/L and 113 +/- 8 mumol/L, respectively. The serum potassium level in the control group was 4.3 +/- 0.1 mmol/L and remained unchanged during hospitalization.

CONCLUSIONS

High-dose Tmp-Smx therapy used for the treatment of P. carinii pneumonia in HIV-infected patients leads to an increase in the serum potassium concentration and may result in life-threatening hyperkalemia. Patients receiving high doses of Tmp-Smx require close monitoring of their serum potassium concentration, particularly 7 to 10 days after the start of therapy.

The stimulatory effect of insulin on diacylglycerol generation in adipocyte membranes from ob/ob mice is impaired by growth hormone

Physiologically, the action of insulin on carbohydrate and lipid metabolism is opposed by several hormones, including glucocorticoids, glucagon, catecholamines, and pituitary GH. Perhaps least is known about the mechanism(s) involved in the antiinsulin action of GH. Since the generation of diacylglycerol (DAG) appears to be an early event in the insulin-signaling cascade, it was of interest to determine whether GH would interfere with this effect of insulin. Experiments were conducted to determine whether insulin would stimulate the generation of DAG in adipocytes of the obese (ob/ob) mouse, and whether this response could be blocked by the diabetogenic GH derivative S-carboxymethylated human GH (RCM-hGH). Isolated adipocytes of the ob/ob mouse were used for these studies, because unlike normal rodents, the ob/ob mouse responds predictably to the antiinsulin action of GH. Insulin produced a rapid biphasic increase in the amount of DAG in a crude membrane fraction of the adipocytes. The first peak in DAG mass occurred within 5 min of exposure of the cells to insulin, and the second peak occurred after 30 min. The first peak in DAG mass did not occur in adipocytes that had been incubated with pertussis toxin before exposure to insulin. Also, adipocytes isolated from ob/ob mice that had been treated with RCM-hGH failed to respond to insulin with an increase in DAG mass. RCM-hGH blocked both the first and second insulin-induced peaks in DAG mass within 6 h of its administration. This is the time at which ob/ob mouse adipocytes exhibit increased insulin resistance in response to RCM-hGH. Neither exposure to insulin nor treatment with RCM-hGH had any appreciable effect on the fatty acid composition of the DAG present in the adipocyte membranes. These findings are compatible with the idea that GH produces some defect in the insulin-signaling cascade that is proximal to the events that result in the generation of DAG in the adipocyte.

The renal hemodynamic response to endothelin in chronic cyclosporine-treated dogs

Use of the immunosuppressive agent cyclosporine A (CyA) is limited by its associated nephrotoxicity, characterized by an increase in renal vascular resistance (RVR) and reductions in renal blood flow (RBF) and glomerular filtration rate (GFR). The vascular endothelium produces vasoactive substances including endothelium derived relaxation factor (EDRF) and endothelin (ET), which modulate vascular tone. Since CyA has been shown to damage the endothelium, we examined the renal hemodynamic response to intrarenal ET infusion (4 micrograms./kg./minute) in chronic cyclosporine-treated dogs. Prior to ET infusion, CyA-treated dogs had a lower RBF and a greater RVR than normal dogs. In normal dogs, after ET infusion RVR increased from 30.24 +/- 0.64 to 44.60 +/- 1.66 mmHg./ml./minute (p < 0.001), RBF decreased from 4.26 +/- 0.28 to 2.90 +/- 0.30 ml./min./g. (p < 0.001) and GFR decreased from 50.20 +/- 5.90 to 36.50 +/- 7.90 ml. per minute (p < 0.001). In contrast, there was no change in RBF, GFR and RVR after intrarenal ET infusion in CyA-treated dogs. Prior to ET infusion, arterial plasma ET concentration was 5.0 +/- 1.1 pg./ml. in CyA-treated dogs, similar to 7.5 +/- 1.4 pg./ml. in normal dogs, and was not significantly altered in either group after intrarenal ET infusion. We conclude that ET may not contribute to the increased RVR in chronic cyclosporine nephrotoxicity, and suggest a vascular toxicity of CyA, rendering renal vessels unresponsive to the vasoconstrictive effect of ET.

Inhibition of c-Jun DNA binding by mitogen-activated protein kinase

Here we demonstrate that partially purified Xenopus p42 mitogen-activated protein (MAP) kinase phosphorylates bacterially expressed human c-Jun at a single site, serine 243. Several lines of evidence argue that this phosphorylation is due to p42 MAP kinase itself rather than some contaminating species. Phosphorylation of serine 243 markedly decreases the binding of c-Jun to oligonucleotides containing the 12-O-tetradecanoylphorbol-13-acetate response element. These findings suggest that MAP kinase may play a role in the down-regulation of c-Jun or in the cycle of transcriptional initiation and elongation.

Failure of atrial natriuretic peptide to induce natriuresis in aortocaval fistula dogs

Creation of an aortocaval fistula (ACF) in dogs induces salt and water retention, activation of the renin-angiotensin and adrenergic nervous systems and renal papillary ischemia associated with high levels of circulating atrial natriuretic peptide (ANP). The effects of intrarenal ANP (1.2 micrograms/min) infusion on systemic and renal hemodynamics, renal excretory function, renal output of renin and norepinephrine (NE) and papillary plasma flow (PPF) were studied in both normal and ACF dogs. ANP did not alter systemic hemodynamics in either group, but led to a significant increase in renal blood flow (RBF), glomerular filtration rate (GFR), urine flow rate (V), sodium excretion (UNaV) and fractional excretion of sodium (FENa), and a significant decrease in renal vascular resistance (RVR) and urine osmolality (UOsm) in normal dogs. GFR, RBF, RVR, V, UNaV, FENa and UOsm remained unchanged, however, in ACF dogs. In ACF dogs, both renal renin and NE output were significantly greater during baseline and remained significantly greater following ANP infusion, associated with a significantly lower PPF compared with normal dogs. These data suggest that ACF dogs are resistant to the renal effects of ANP, which can neither mitigate the hormonal mediators of sodium retention nor reverse the papillary ischemia observed in this model.

Reversal of Na+ retention in chronic caval dogs by verapamil: contribution of medullary circulation

The effects of verapamil on papillary plasma flow (PPF) and Na+ excretion were studied in anesthetized chronic caval dogs with low cardiac output and Na+ retention. Infusion of verapamil into the left renal artery (5 and 10 micrograms.kg-1.min-1) caused a dose-dependent ipsilateral increase in renal blood flow and Na+ excretion (from 10 +/- 2 to 171 +/- 32 and 225 +/- 35 mu eq/min, respectively). PPF in the left kidney was 26.6 +/- 4.4 and was significantly greater than that measured in the contralateral kidney (13.3 +/- 2.4 ml.min-1.100 g-1) (P < 0.01). The natriuresis occurred independent of changes in cardiac output and peripheral vascular resistance. In a separate group of caval dogs in which stimulation of the renin-angiotensin and adrenergic systems was intensified with a tighter caval constriction, verapamil failed to induce renal vasodilation or natriuresis and PPF was not altered. Despite the disparate hemodynamic responses, verapamil stimulated renal production of both renin and prostaglandin E2 in both groups of caval dogs. We conclude that the ability of verapamil to induce papillary vasodilation may contribute to the natriuresis seen in the caval dog, in which the site of Na+ retention includes the loop of Henle.

The cellular and molecular regulation of 1,25(OH)2D3 production

The synthesis of 1,25(OH)2D3 is a critical control point in the regulation of calcium metabolism, and possibly in the growth and differentiation of a number of cell types. This paper reviews our current understanding of the regulation of this process at the cellular and molecular levels, with the emphasis on the mechanisms of feedback control 1,25(OH)2D3 itself, control of parathyroid hormone, the roles of cyclic AMP dependent protein kinase and protein kinase C, and the interaction between the various intracellular regulators of 1,25(OH)2D3 production.

Growth hormone inhibits activation of phosphatidylinositol phospholipase C in adipose plasma membranes: evidence for a growth hormone-induced change in G protein function

Pituitary growth hormone (GH) functions physiologically to oppose the actions of insulin on carbohydrate and lipid metabolism by interfering with metabolic events that occur after insulin binds to its receptor. Which postreceptor effects are involved is presently unknown. Recently, we found that insulin rapidly stimulates a phosphatidylinositol phospholipase C (PI-PLC) in adipose tissue of obese (ob/ob) mice and that this effect of insulin is blocked by treatment of the animals with S-carboxymethylated human GH (RCM-hGH), a derivative having mainly anti-insulin activity. The activation of this PI-PLC by insulin is also inhibited by pertussis toxin. Thus, this study was performed to examine whether the inhibitory effect of GH on the activation of this PI-PLC is exerted at the level of signal transmission by guanine nucleotide binding proteins (G proteins). We found that the nonhydrolyzable GTP analogue, guanosine 5'-[gamma-thio]triphosphate, stimulated basal PI-PLC activity in plasma membranes of adipose tissue of saline-treated ob/ob mice, but it did not stimulate the enzyme in adipose membranes from RCM-hGH-treated mice. Also, RCM-hGH treatment markedly inhibited pertussis toxin-catalyzed ADP ribosylation of G protein alpha subunits in the membranes, suggesting some modification of the G proteins by GH. Immunoblot analysis of adipose membranes from saline- and RCM-hGH-treated mice using antiserum AS/7 (anti-Gi1 alpha and anti-Gi2 alpha) or antiserum EC/2 (anti-Gi3 alpha) showed no difference in the amount of Gi alpha-like protein between the groups. These findings suggest that GH interferes with the ability of a putative Gi-like protein to mediate the activation of PI-PLC in adipose membranes without altering the expression of the G protein.

Renal actions of endothelin: interaction with prostacyclin

The renal actions of endothelin were examined by infusing it intrarenally in anesthetized dogs at 4 ng.min-1.kg-1 without affecting arterial blood pressure or cardiac output. Endothelin infusion caused a transient and significant increase in renal blood flow (RBF) by 13 +/- 2%, followed by large decreases in RBF and glomerular filtration rate (GFR; by 26 +/- 2 and 23 +/- 7%, respectively) but did not alter urine flow rate or absolute sodium excretion. After endothelin infusion, renal venous and arterial plasma 6-ketoprostaglandin F1 alpha increased from 250 +/- 58 and 117 +/- 31 to 1,044 +/- 249 and 617 +/- 211 pg/ml, respectively, and its renal output increased from 339 +/- 99 to 963 +/- 202 pg.min-1.g-1 (P less than 0.01 for all). The renal prostacyclin synthesis was augmented by endothelin without stimulating the renal renin release or norepinephrine output. Inhibition of prostaglandin synthesis with indomethacin partially prevented the early renal vasodilation induced by endothelin, which then caused a more pronounced decline in RBF and GFR (by 65 +/- 7 and 54 +/- 8%, respectively). With suppression of prostacyclin synthesis, inhibition of renin release by endothelin was observed. Thus the vasoconstrictive effects of endothelin on renal hemodynamics are significantly modified by its ability to enhance production of vasodilators, including prostacyclin.

The biosynthesis of cholesterol side-chain cleavage cytochrome P-450 in the rabbit corpus luteum depends upon estrogen

To gain a better understanding of the luteotropic action of estrogen, we have investigated the effect of estrogen on the synthesis of the enzyme, cholesterol side-chain cleavage cytochrome P-450 (P-450scc) in the rabbit corpus luteum. Using an established protocol, rabbits were treated with estradiol, and the estradiol was then withdrawn on day 9 of pseudopregnancy, which caused an 88% fall in serum progesterone within 48 h. In other rabbits, estradiol was replaced at 48 h which stimulated a 6.6-fold increase in serum progesterone concentration within the next 24 h. Luteal tissues were incubated with [35S]methionine and homogenized, and a mitochondrial fraction lysate was obtained. Equal trichloroacetic acid-precipitable radioactivity was taken for immunoprecipitation using a well-characterized polyclonal antiserum against bovine adrenal P-450scc. The immunoisolated proteins were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and radioactivity was visualized by autofluorography. The results indicate that the rate of synthesis of P-450scc in 48 h-estradiol withdrawn animals was markedly reduced, and by 72 h of withdrawal was barely detectable. When estradiol was reintroduced, the synthesis of P-450scc was increased. Despite the prominent changes in P-450scc synthesis, immunoblotting revealed only a minimal (approximately 30%) decrease in relative P-450scc content by 72 h after estradiol withdrawal. Analyses of DNA and protein contents of luteal tissues revealed an increase in DNA per mg luteal tissue, a decline in total tissue protein/DNA ratio, but no change in mitochondrial fraction protein/DNA ratio after estrogen withdrawal. The results indicate that de novo synthesis of P-450scc in the corpus luteum is sensitive to estrogen; however, the estrogen-sensitive rate-limiting step(s) for steroidogenesis are at other sites in the steroid biosynthetic pathway.

Hemodynamic function in dogs with chronic obstructive jaundice: effects of radiocontrast medium

Chronic obstruction of the biliary tract alters circulatory function. The effects of radiocontrast medium (iothalamate meglumine) on systemic and renal hemodynamics were studied in normal dogs and dogs with chronic common bile duct ligation (CBDL). After intravenous injection of radiocontrast, cardiac output and stroke volume were not altered in normal and CBDL dogs; arterial pressure was stable in normal dogs but decreased significantly in CBDL dogs and was accompanied by reduced systemic vascular resistance. In normal and CBDL dogs the renal hemodynamic responses to radiocontrast medium were characterized by initial vasoconstriction (independent of renal renin release) and later vasodilation. This vasodilatation in CBDL dogs was particularly striking as it occurred despite reduced renal perfusion pressure and the augmented renin-angiotensin system. Inhibition of prostaglandin synthesis with indomethacin in CBDL dogs abolished both the hypotensive and the renal vasodilator responses to radiocontrast medium. We conclude that enhanced prostaglandin activity contributes to the labile hemodynamic function noted in obstructive jaundice.

Renal medullary circulation: hormonal control

It is now becoming apparent that the medullary circulation in the kidney can be regulated separately from overall renal blood flow. This characteristic of the medullary circulation plays an important role in the kidney's ability to excrete a dilute or concentrated urine in concert with changes in water and sodium transport in the distal nephron secondary to the action of vasopressin, prostaglandins, the renal nerves, and other hormones without significant other renal hemodynamic changes. There is strong evidence that renal autocoids such as angiotensin II and prostaglandins uniquely affect regional blood flow in the inner medulla because of the special structure and organization of the microvasculature in this region. There is also evidence that this regional blood flow is in part regulated by circulating hormones, such as vasopressin and atrial natriuretic peptide, which are released in response to changes in extracellular fluid volume or osmolality. In addition, data are emerging to suggest that the kallikrein-kinin system, acetylcholine, the renal nerves and adenosine participate in this regulation. In addition to the role of the medullary circulation in the urinary concentrating operation, there are data to suggest that the medullary circulation either directly (by changes in physical forces) or indirectly (by regulating medullary toxicity) may influence sodium excretion in a variety of conditions. In this regard, activation of the renin-angiotensin system locally reduces blood flow in the papilla which may be necessary before sodium retention is fully expressed in salt retaining states. Future research looking at the microvasculature of the medulla and papilla and those factors that control the contractility of these vessels are necessary before a clearer picture emerges. Nevertheless, from the data already available it seems reasonable to suggest that the medullary circulation may be as important to kidney function during physiological and pathophysiological states as is the cortical circulation.

Growth hormone inhibits activation of phosphatidylinositol phospholipase C by insulin in ob/ob mouse adipose tissue

The cellular mechanism(s) by which GH produces insulin resistance in peripheral tissues is poorly understood. Recent evidence suggests that insulin exerts certain of its intracellular actions by rapidly activating phosphatidylinositol-specific phospholipase C(s) (PI-PLC) in the plasma membranes of target cells. Therefore, the present study was conducted to determine whether insulin can activate PI-PLC in adipose tissue of the genetically obese (ob/ob) mouse, an animal that responds markedly to GH with enhanced peripheral insulin resistance. Also, experiments were performed to determine whether the activation of PI-PLC by insulin could be blocked by S-carboxymethylated human GH (RCM-hGH), a GH derivative possessing mainly diabetogenic activity. Isolated adipose segments were incubated for various periods with insulin (10 mU/ml), homogenized and centrifuged to obtain a 150,000 x g pellet, and the latter was assayed for the ability to produce [3H]inositol phosphate from phosphatidyl[3H]inositol. PI-PLC activity was significantly stimulated 5 min after exposure of the segments to insulin. By 10 min, the insulin effect was no longer apparent, and after 30 min, insulin reduced the activity of the enzyme. One hour after exposure to insulin, PI-PLC activity returned to the control level. When adipose segments of RCM-hGH-treated mice (200 micrograms/day for 3 days sc) were incubated for 5 min with insulin, the ability of insulin to activate PI-PLC was abolished. However, RCM-hGH did not alter basal PI-PLC, indicating that its action involves the mechanism by which the enzyme is activated by insulin. Also, studies utilizing acute RCM-hGH treatment showed that its inhibitory effect on insulin activation of PI-PLC occurs within the same time frame as the onset of enhanced insulin resistance in the adipose tissue. Thus, the ability of GH to inhibit the activation of PI-PLC by insulin in adipocytes may account, at least in part, for its ability to induce insulin resistance in these cells.

Acute non-Q wave cocaine-related myocardial infarction

Since our initial report in 1984 of six patients with AMI temporally related to cocaine use, we have observed 19 additional patients in whom ischemic chest pain syndromes occurred shortly after intranasal or IV use of cocaine or after smoking the drug. Seventeen patients (89 percent) developed non-Q wave infarction and two had Q-wave infarction. One patient manifested angina with striking ST-segment elevation. None of the patients had diabetes or hypertension, and all but one were cigarette smokers. The serum cholesterol level was 162 +/- 7 mg/dl. Four of the five patients who consented to coronary angiographic studies displayed normal coronary arteries, and one showed proximal stenosis of the right coronary artery. The cold pressor test was performed in seven patients; none had angina or ECG changes induced by cold stimulation. We conclude that T-wave infarction is a common form of an acute cardiac event related to cocaine abuse, and its pathogenesis may involve that of the cocaine-induced coronary vasospasm.

Pancreatic vasoactive intestinal polypeptide-secreting tumor: report of a case

A 58-year-old Taiwanese woman was admitted to Mackay Memorial Hospital for evaluation profuse watery diarrhea. She presented with watery diarrhea, hypokalemia, and hypochlorhydria, and had experienced these problems for 2 years prior to admission. A pancreatic tumor with liver metastasis was noted by the ultrasound, abdominal CT scanning, and angiography studies. Surgical exploration disclosed an ill-defined ovoid tumor in the body and tail of the pancreas measuring 8 x 3 x 3 cm. The immunohistochemistry study of the tumor for VIP-immunoreactivity (VIP: vasoactive intestinal polypeptide) was markedly positive, and also stained slightly positive for other peptides, including pancreatic polypeptide (PP), calcitonin, glucagon, and neuron-specific enolase (NSE). Postoperatively, the patient recovered immediately from her symptoms and there has been no evidence of recurrence during the past 8 months of follow-up.

[Mucocele of appendix-report of three cases]

Mucocele of appendix comprises 0.07%-0.3% of the resection of appendix. Three such cases were encountered over the past four years at MMH. Tumor mass could be palpated before operation in two of our cases. The third case was found incidentally during sigmoid cancer resection. Mucocele of the appendix should be differentiated from submucosal lesion such as leiomyoma, lipoma, lymphoma in the cecum or appendiceal abscess. Recent advances of ultrasound, CAT scan as well as angiography have made correct preoperative diagnosis possible, yet literature still shows diverse opinion about its etiology (neoplastic vs. obstructive). Although most authors favor simple appendectomy for the management of this disease, some surgeons still think it should be managed aggressively with colectomy. Rupture of mucocele might result in pseudomyxoma peritonei and possibly a fetal outcome. Avoidance of iatrogenic rupture of appendix is essential. Aggressive removal of accessible masses and implants was suggested in the literature.

Regulation of papillary plasma flow by angiotensin II

We examined in anesthetized dogs the effects of left (L) intrarenal artery infusion of angiotensin II (AII) on renal hemodynamics, urinary concentration and Na excretion, and papillary plasma flow (PPF) (measured by the albumin accumulation technique) in both kidneys. Following AII infusion (0.5 ng/kg/min) into the L renal artery, urinary Na excretion decreased and osmolality increased slightly ipsilaterally, whereas Na excretion did not change significantly and osmolality decreased in the right (R) kidney. PPF was significantly lower in the L compared to the R kidney. When saline loading was superimposed on L intrarenal AII infusion, there was a blunted natriuretic response ipsilaterally with a significantly smaller decrease in urine osmolality compared with the R kidney. PPF increased significantly in the R, but not in the L kidney. Finally, AII blockade with saralasin prior to AII infusion and saline loading prevented the differences between the two kidneys, including PPF. In all groups GFR and renal blood flow did not differ between the two kidneys before or after AII. These data suggest that AII regulates regional blood flow in the medulla, and that the exogenously administered AII induces papillary ischemia, which serves to preserve medullary hypertonicity, preventing an increase in PPF during saline loading, and possibly contributing to the diminished natriuretic response.

Inner medullary hemodynamics in dogs with aortocaval fistula

To investigate the role of medullary hemodynamics and vasoactive hormones in sodium retention in dogs with aortocaval fistula, we examined papillary plasma flow (PPF), solute content, and renal output of renin, norepinephrine, and prostaglandin E2 (PGE2) in anesthetized normal and fistula dogs. During hydropenia, cardiac output was elevated and systemic vascular resistance reduced in fistula dogs, accompanied by markedly increased renal output of renin, norepinephrine, and PGE2. In fistula dogs the blunted diuretic and natriuretic response to saline loading was not due to impaired myocardial contractility. During hydropenia and after saline loading, glomerular filtration rate (GFR) and renal blood flow were similar in normal and in fistula dogs; however, PPF was significantly lower in fistula dogs, accompanied by significantly greater papillary tissue osmolality and sodium content. These findings indicate that in fistula dogs enhanced medullary sodium reabsorption is associated with decreased PPF and stimulation of the renin-angiotensin and adrenergic nervous system. Furthermore, the reduced PPF obviates medullary solute washout during saline loading, and may contribute to the blunted diuretic and natriuretic response.

Contribution of angiotensin to the control of medullary hemodynamics

The unique architecture and organization of medullary vasculature permit regional regulation of medullary hemodynamics by vasoactive hormones and are conducive to the operation of the countercurrent multiplication system. Recent studies suggest that an increase in inner medullary blood flow causes medullary solute washout, which in turn decreases passive sodium transport in the thin ascending limb of Henle's loop. In canine models of chronic sodium retention accompanied by activation of the renin-angiotensin system, glomerular filtration rate (GFR), renal blood flow (RBF), and intracortical blood flow distribution were similar to those in normal dogs; however, papillary plasma flow (PPF) was markedly reduced and papillary tissue solute content was increased significantly both during hydropenia and after saline loading. During euvolemic diuresis with loop diuretics, there was an increased renin release associated with a marked reduction in PPF, despite an increase in total RBF. Direct intrarenal infusion of angiotensin II (AngII) (at a dose not affecting GFR and RBF) induced ipsilateral sodium retention, conservation of urinary concentration, and papillary ischemia. These studies provide evidence for regional regulation of medullary hemodynamics by AngII, possibly contributing to sodium retention in chronic salt-retaining states.

Effects of chlorpromazine on ischemic rat kidney: a functional and ultrastructural study

The effects of chlorpromazine, an agent with inhibitory effects of calcium influx, phospholipase activation, and Na-K-ATPase, on preserving renal function and proximal tubular ultrastructure were evaluated in renal ischemia. After right nephrectomy chlorpromazine (0.025 mg) or 1 ml of 0.9 per cent saline was selectively administered to the rat kidney immediately prior to a sixty-minute occlusion of the remaining renal artery. Pretreatment with chlorpromazine resulted in a significant attenuation in the rise in postischemic serum creatinine. Hypothermia of the kidney during ischemia provided an additional protective effect. Electron microscopic study of the proximal convoluted tubule demonstrated that the structural damage was less severe in chlorpromazine-treated rats and virtually complete preservation of a normal ultrastructure was observed when hypothermia was added.

Effects of verapamil on preservation of renal function after ischemia: functional and ultrastructural study

The effects of hypothermia and verapamil, a calcium antagonist, on preventing renal damage after 60 minutes of ischemia were studied in rats. Hypothermia alone provided the best protection, and pretreatment with verapamil failed to afford protective effects in normothermic and hypothermic ischemia, findings further supported by electron microscopic studies.