Effect of glucagon and glomerulopressin on the renal function of the dog.

Glucagon was infused through the porta or through the left renal artery in dogs. Another group of dogs were infused with glomerulopressin through the left renal artery. It was observed that glucagon when infused through the portal vein enhanced the glomerulopressin production and the glomerular filtration rate (GFR). When glucagon was infused intrarenally it did not alter GRF but it had a direct tubular action decreasing sodium reabsorption in the proximal tubule. Glomerulopressin infused intrarenally increased GRF and potassium excretion. The results suggest that the increase in GFR was due to increase in glomerulopressin activity. There are three reasons for this statement: a) GRF increased when glomerulopressin activity was high, but not when there was a low activity, 5) intrarenally infused glomerulopressin produced a very significant change in the GFR of the infused kidney, while the GRF of the contralateral kidney remained unchanged and c) intrarenally administered glucagon had no effect on GFR.     

Effect of glucagon on glomerulopressin production in diabetic dogs

Glucagon (21.5 +/- 0.23 ng/min/kg) was infused through the portal vein of normal or pancreatectomized dogs. It was observed that a dose of glucagon that produces no significant change in the glycemia of normal dogs has a very small activity in the production of glomerulopressin and does not alter glomerular filtration rate (GRF). In pancreatectomized dogs this same dose of glucagon also does not alter glycemia but it induces a large increase in the production of glomerulopressin and GFR. Our results suggest that in pancreatectomized dogs glomerulopressin production is more sensitive to glucagon infusion than in normal dogs.     

Induction of glomerulopressin production by cyclic AMP

Isolated rat livers were perfused with gassed Krebs-Ringer-Bicarbonate and different doses of theophylline and dibutyryl cyclic AMP were added to the perfusing solution. The perfusates were ultrafiltrated through Diaflo UM-05 membranes. The glomerulopressin activity of the ultrafiltrates were assayed in the tonic tension contraction (TTC) of isolated stomach fundus from rats. As glomerulopressin is known to be a glucuronide, it was inactivated with beta-glucuronidase to confirm that the effect on the stomach fundus was due to the glomerulopressin and not to another substance. It was observed that doses of theophylline between 2 x 10(-3) M and 2 x 10(-5) M enhanced glomerulopressin production. However, there was no relationship between dose of theophylline and the response, and a dose of theophylline 2 x 10(-6) M has no activity. The perfusion with dibutyryl cyclic AMP at 5 x 10(-8) M increased the amount of glomerulopressin produced by the liver. This was a log-dose response of glomerulopressin production to dibutyryl cyclic AMP between 5 x 10(-8) M and 5 x 10(-4) M. Theophylline (2 x 10(-6) M) potentiated the activity of cyclic AMP (5 x 10(-8) M). These results support the view that cyclic AMP is intracellular mediator of the hepatic production of glomerulopressin.     

Glomerulopressin production by isolated rat liver after amino acid infusion

The infusion of certain amino acids, such as serine, alanine, and proline (SAP), has been shown to increase the glomerular filtration rate, whereas branched chain amino acids (BCAA) leucine, isoleucine, and valine fail to modify the glomerular filtration rate. It has been suggested that this effect of amino acids on the glomerular filtration rate is mediated by the action of the hormone glomerulopressin. The purpose of this work was to study the action of SAP and BCAA on glomerulopressin production. Livers isolated from rats were perfused with (i) Krebs-Ringer-Bicarbonate, (ii) SAP, or (iii) BCAA. Results indicate that glomerulopressin production is stimulated by SAP, but inhibited by BCAA.     

Natriuretic effect of digoxin-like immunoreactive substance on dog kidney

We previously reported that digoxin-like immunoreactive substance (DLIS) was found only in the blood of those dialysis patients who were hypertensive and had high systemic vascular resistance. In order to determine whether the DLIS was a marker for the natriuretic hormone, renal infusion studies were carried out in anesthetized dogs. When ultrafiltrates from patients with high blood DLIS levels were infused into the renal artery of one kidney there was a significant increase in the fractional excretion of sodium (FE Na) from its baseline value. Further, the FE Na of these kidneys were significantly higher than the FE Na noted for the contralateral kidneys which were simultaneously infused with ultrafiltrates obtained from dialysis patients lacking DLIS activity in their blood. We conclude that the DLIS is or represents a marker for natriuretic hormone. Since the natriuresis noted was independent of renal plasma flow and glomerular filtration rate and since the fractional excretion of potassium was not influenced by the infusion, we believe that DLIS is different from atrial natriuretic factor.     

Pancreatectomy, amino acids and glucagon: effect on canine renal autoregulation

Using pancreactectomized (PX) dogs, we recently suggested the importance of glucagon in modulating amino acid-induced increases in renal blood flow (RBF) and glomerular filtration rate (GFR). We have now ascertained whether glucagon's modulatory effect is associated with an impairment in renal autoregulation. As renal arterial pressure (RAP) was reduced to 70 mmHg (the lower limit of the autoregulatory range) in both sham-operated control (C) and PX control dogs, RBF and GFR remained at values that were greater than 90% of their respective controls. In control dogs infused with amino acids (0.051 mmol/kg per min, i.v.), RBF and GFR rose by 26 and 27%, respectively, at baseline RAP. As RAP was reduced to 70 mmHg, RBF and GFR fell by 25 and 37%, respectively. In PX dogs infused with either amino acids or glucagon (0.86 pmol/kg per min, i.v.) alone, RBF and GFR did not increase appreciably at baseline RAP. As RAP was reduced to 70 mmHg in these dogs, RBF and GFR remained at values that were greater than 90% of their respective controls. Yet, in PX dogs infused simultaneously with amino acids and glucagon, RBF and GFR rose by 22 and 24%, respectively, at baseline RAP. Moreover, as RAP was reduced to 70 mmHg, RBF and GFR fell by 22 and 31%, respectively. These data suggest that the ability of glucagon to modulate the renal hemodynamic response to amino acid infusion involves an impairment in renal autoregulation.     

Effect of prostaglandin A1 infusion in hypertensive patients with renal artery stenosis

Clinical data, arteriographic findings, peripheral and renal vein plasma renin activity (PRA) studies and responses to prostaglandin A1 infusion are presented from observations in seven hypertensive patients with renal artery stenosis. PGA1 infusion caused an increase in PRA and urine sodium excretion but no significant change in blood pressure. Exaggerated increases in PRA were observed in five patients. With cessation of PGA1 infusion PRA returned toward pre-infusion levels. In two patients bilateral renal and peripheral vein PRA's were determined before and during PGA1 infusion. PGA1 caused a greater increase in renal vein PRA than in peripheral vein PRA indicating a direct enhancement of renin secretion. These studies indicate possible relationships between the vasoactive prostaglandins and the renin-angiotensin system in the pathogenesis of hypertension due to renal artery stenosis.     

Role of platelet-activating factor in renal function in normal rats and rats with bilateral ureteral obstruction

Platelet-activating factor (PAF) is a powerful vasodilator with important effects on kidney function. It has been suggested that the renal effects of PAF are mediated by thromboxane A2 (TxA2). We examined the effect of PAF on renal function in sham-operated rats and rats that had undergone unilateral release of bilateral ureteral obstruction (BUO) of 24-hr duration, a condition in which the synthesis of TxA2 is increased. To eliminate systemic hemodynamic changes, PAF was infused directly into the left renal artery using the lowest dose that affected renal function (2.3 x 10(-13) moles/min). Infusion of PAF significantly decreased the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in normal rats and rats with BUO. Normal (sham-operated) rats pretreated with an inhibitor of TxA2 synthesis also had a significant decrease in GFR after administration of PAF (ERPF also decreased, but not significantly). Rats with BUO pretreated with an inhibitor of TxA2 synthesis had significantly greater basal GFR and ERPF (increases of 72 and 171%, respectively) than untreated BUO rats. Administration of PAF to the former group further increased GFR and ERPF (by 37 and 39%, respectively; P less than 0.001). The role of endogenous PAF was evaluated by administering a specific PAF receptor antagonist. Sham-operated rats pretreated with high doses of the PAF receptor antagonist had significantly higher mean arterial pressure values than normal untreated rats, and had no decrease in GFR and ERPF during PAF infusion. Rats with BUO pretreated with the PAF antagonist had a significant, dose-dependent decrease in basal GFR and ERPF. These data suggest that endogenous PAF has a vasodilatory role in obstructive nephropathy. No significant differences in eicosanoid excretion in the urine corrected per GFR were observed during infusion of PAF in any of the groups examined. In BUO rats with intact TxA2 synthesis, exogenous administration of PAF decreased renal function, presumably through further increases in the production of TxA2. However, when TxA2 production was inhibited, PAF administration increased GFR and ERPF, presumably due to its unopposed vasodilatory properties. The data suggest an important role of PAF in the hemodynamic changes seen in obstructive nephropathy.     

Effect of free radicals in ischaemic renal failure in the dog

After a 30-minute control period ischaemia was evoked in dogs under Nembutal (30 mg/kg, i.v.) anesthesia, by clamping the left renal artery for 45 minutes. This was followed by a 90-minute reperfusion period when diuresis, GFR, PAH clearance, sodium and potassium excretion, malondialdehyde level in the plasma of the renal vein and SOD enzyme activity of the erythrocytes in renal venous blood were determined. Besides the control group (n = 6), the following treated groups were investigated: 1. Allopurinol (n = 7) in a dose of 100 mg/kg, given orally for two days, 2. Silibinin (n = 6) in a dose of 4 mg/kg/hour, given into the renal artery, 3. MTDQ-DS (n = 6) in a dose of 150 mg/kg/hour, given intravenously. 4. SOD (n = 4) 4 mg infusion (initiated 1 minute prior reperfusion). In the first 15-minute period following reperfusion GFR was 21%, cPAH 29% and sodium and potassium excretion 67 and 42% of the values of the contralateral kidney, respectively. Renal function improved gradually during the 90 minutes of reperfusion, and the above-mentioned parameters reached 59, 57, 65 and 76% of the corresponding control data. Increase of malondialdehyde level in the venous blood of the kidney during reperfusion might have been indicative of the production of free radicals; the difference, however, was not significant statistically. The administrations did not lead to considerable change in any of the parameters investigated. No difference could be demonstrated by histological methods between the kidneys of the treated and untreated animals. The compounds studied are thought to be free radical scavengers; in the present work, however, no protective effect could be demonstrated.     

Effect of prostaglandin A1 infusion in hypertensive patients with renal artery stenosis

Clinical data, arteriographic findings, peripheral and renal vein plasma renin activity (PRA) studies and responses to prostaglandin A₁ infusion are presented from observations in seven hypertensive patients with renal artery stenosis. PGA₁ infusion caused an increase in PRA and urine sodium excretion but no significant change in blood pressure. Exaggerated increases in PRA were observed in five patients. With cessation of PGA₁ infusion PRA returned toward pre-infusion levels. In two patients bilateral renal and peripheral vein PRA's were determined before and during PGA₁ infusion. PGA₁ caused a greater increase in renal vein PRA than in peripheral vein PRA indicating a direct enhancement of renin secretion. These studies indicate possible relationships between the vasoactive prostaglandins and the renin-angiotensin system in the pathogenesis of hypertension due to renal artery stenosis.     

Effect of intrarenal arterial infusion of magnesium on renin release in dogs.

Magnesium chloride was infused into the renal artery of anesthetized dogs in order to determine its effect on renal function. Natriuresis and diuresis were observed during MgCl2 infusion, but there appeared to be no effect on glomerular filtration rate (GFR), or plasma sodium or potassium concentrations. Although mean arterial blood pressure and renal plasma flow (RPF) decreased throughout the experiment, the fall was not significant until after stopping MgCl2 infusion. A significant stimulation of renin secretion occurred during magnesium administration.     

Alterations of the renal function and oxidative stress in renal tissue from rats chronically treated with aluminium during the initial phase of hepatic regeneration

Various indices of renal functions during the early stage of hepatic injury were studied in rats chronically treated with aluminum (Al) lactate. Tubular and hemodynamic parameters were analyzed four days after producing a 65% partial hepatectomy (PH). Water and sodium balances were also studied. Oxidative stress and the activity of Na-K-ATPase were determined in renal tissue. The rats were distributed in four groups: control, Al, PH, Al+PH. Al did not modify the hemodynamic renal functions and the PH-group reduced the glomerular filtrate rate (GFR). The Al + PH group presented a decrease in the renal blood flow and accentuated the GFR fall as compared with PH. The fractional excretion (FE) of water and sodium increased in the PH group. The rats chronically treated with Al and then submitted to the PH protocol developed a further increase in FE of water but a reduction in FE of sodium. Both PH and Al promoted an increase in the aldosterone. PH and Al induced a similar increase of the lipoperoxidation status with reduction of glutathione (GSH) and the activity of glutathione peroxidase (GSH-Px). The data indicated that Al is an inhibitor of catalase. The GSH and GSH-Px activity in the Al + PH group demonstrated a synergic effect of Al and PH. This work demonstrates that rats treated chronically with Al and submitted to another injury (such as hepatic damage) can aggravate renal functions, probably by increasing the oxidative state, at least in kidneys.     

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.     

Renal amino acid excretion and aging

The urinary excretion and serum concentration of amino acids were studied in 62 healthy individuals aged 15 to 70 years. In elderly subjects (61-70 years), it was found that renal amino acid clearance per 100 ml GFR (fractional excretion, FE) rose significantly in the following amino acids: CYS, VAL, MET, ILE and LEU. Since the serum concentrations of these amino acids showed no significant changes, but the GFR was reduced, it can be concluded that the raised FE of these amino acids was due to a decrease in their effective tubular reabsorption. A significant correlation was found between FENa and FE of most amino acids including those mentioned above. The findings support the assumption that changes in tubular Na+ transport probably participate in the changes of tubular amino acid transport in elderly individuals.     

Intravenous epoprostenol sodium does not increase hepatic microsomal enzyme activity in rats

Previous studies have indicated that epoprostenol may increase hepatic microsomal enzyme activity both in animals and humans. However, interpretation of the results of these studies may be confounded by the route of epoprostenol administration or small sample sizes. The primary objective of the present investigation was to evaluate the effects of epoprostenol (given as a continuous intravenous infusion) on hepatic microsomal enzyme activity in rats. Male Sprague Dawley rats (220–290 g) received infusions of either vehicle (glycine buffer, 1 mL/hr) or 0.2 μg/kg/min epoprostenol through a jugular vein cannula for 24 hr or 7 days. At the end of the infusion, a 25 mg/kg ix. bolus of antipyrine was administered and blood samples were collected over 6 hr. Serum antipyrine concentrations were determined by HPLC. Twenty-four hr post-infusion, hepatic microsomes were prepared, and cytochrome P-450 content was determined by difference spectroscopy. Cytochrome P-450 content and antipyrine clearance values determined from serum antipyrine concentration-time profiles were not significantly different between treatment groups. Antipyrine clearance [mean (SD)] in the 24-hr vehicle-treated group was 3.68 (0.49) mL/min/kg versus 4.35 (1.1)mL/min/kg in the epoprostenol-treated group. In the 7-day vehicle-treated rats, antipyrine clearance was 5.43 (1.0) mL/min/kg compared to 4.68 (0.61)mL/min/kg in epoprostenol-treated rats. A statistically significant effect of infusion duration was observed in the control group, i.e., antipyrine clearance in rats treated with vehicle for 7 days was significantly greater than that observed in rats treated with vehicle for 24 hr. However, the increase was less than 50%. These data suggest that when epoprostenol is administered as an intravenous infusion to rats, no significant alterations in hepatic microsomal enzyme activity occur. Based on these data, long term changes in heparic metabolism in response to chronic epoprostenol administration are nor expected.     

Whole blood and plasma amino acid transfers across the portal drained viscera and liver of the pig.

Whole blood (WB) and plasma (P) amino acid transfers across the portal drained viscera and the liver were determined during 6 h of a constant p-aminohippuric acid infusion in three hourly-fed Landrace x Large-White pigs (30.5 kg, mean live weight) surgically prepared with chronically inserted catheters in a mesenteric vein (MV), the portal vein (PV), an hepatic vein (HV) and the carotid artery (CA). Plasma and WB amino acid concentrations were determined in the CA, PV and HV. The plasma/WB ratios showed no significant differences for vessels except for lysine and glutamate for which this ratio is significantly higher in the HV and in the PV for lysine. This suggests that the PV lysine and HV glutamate were preferentially transported in the plasma. In the PV, threonine, valine and alanine are transported by both plasma and red blood cells. These data show that the contribution of plasma and whole blood to amino acid transport can be different between amino acids and between individual tissues.     

Glucagon-like peptide-2 (GLP-2) increases net amino acid utilization by the portal-drained viscera of ruminating calves

Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in ruminant calves, but its impact on nutrient metabolism across the portal-drained viscera (PDV) and liver is unknown. Eight Holstein calves with catheters in the carotid artery, mesenteric vein, portal vein and hepatic vein were paired by age and randomly assigned to control (0.5% bovine serum albumin in saline; n = 4) or GLP-2 (100 μg/kg BW per day bovine GLP-2 in bovine serum albumin; n = 4). Treatments were administered subcutaneously every 12 h for 10 days. Blood flow was measured on days 0 and 10 and included 3 periods: baseline (saline infusion), treatment (infusion of bovine serum albumin or 3.76 μg/kg BW per h GLP-2) and recovery (saline infusion). Arterial concentrations and net PDV, hepatic and total splanchnic fluxes of glucose, lactate, glutamate, glutamine, β-hydroxybutyrate and urea-N were measured on days 0 and 10. Arterial concentrations and net fluxes of all amino acids and glucose metabolism using continuous intravenous infusion of [U¹³-C]glucose were measured on day 10 only. A 1-h infusion of GLP-2 increased blood flow in the portal and hepatic veins when administered to calves not previously exposed to exogenous GLP-2, but after a 10-day administration of GLP-2 the blood flow response to the 1-h GLP-2 infusion was substantially attenuated. The 1-h GLP-2 infusion also did not appreciably alter nutrient fluxes on either day 0 or 10. In contrast, long-term GLP-2 administration reduced arterial concentrations and net PDV flux of many essential and non-essential amino acids. Despite the significant alterations in amino acid metabolism, glucose irreversible loss and utilization by PDV and non-PDV tissues were not affected by GLP-2. Fluxes of amino acids across the PDV were generally reduced by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and amino acid requirements of this tissue. Increased PDV extraction of glutamine and alterations in PDV metabolism of arginine, ornithine and citrulline support the concept that GLP-2 influences intestine-specific amino acid metabolism. Alterations in amino acid metabolism but unchanged glucose metabolism suggests that the growth effects induced by GLP-2 in ruminants increase reliance on amino acids preferentially over glucose. Thus, GLP-2 increases PDV utilization of amino acids, but not glucose, concurrent with stimulated growth of the small intestinal epithelium in post-absorptive ruminant calves.     

Protein intake regulates the vasodilatory function of the kidney and NMDA receptor expression

Glycine infusion in normal rats causes an increase in renal plasma flow and glomerular filtration rate (GFR). Although the renal response to glycine infusion is well characterized, the mechanism initiating this vasodilation is unknown. We recently observed functionally active N-methyl-d-aspartate (NMDA) receptors in the kidney, located primarily in tubular structures. The mechanisms regulating activity of the NMDA receptor within the kidney are also unknown, as is its normal day-to-day functional role. Therefore, we hypothesize that dietary protein may impact the functional response to glycine infusion in both untreated rats and rats pretreated with angiotensin-converting enzyme (ACE) inhibitor and, furthermore, that renal NMDA receptors may be involved in the glycine response. Surprisingly, 2 wk of low-protein diet (8% protein vs. 21% protein in control diet) totally inhibited the glycine-induced vasodilation and GFR response. Associated with the absence of renal vasodilation, a significant reduction in proximal tubular reabsorption was observed during glycine infusion in low-protein-diet rats. In contrast to the disease models previously studied in our laboratory, administration of ACE inhibitors did not restore the glycine response in rats treated with low-protein diet. Western blots of normal- and low-protein-diet kidneys demonstrate that the newly described renal NMDA receptor is downregulated in rats fed a low-protein diet. Low-protein feeding results in loss of glycine-induced vasodilation and GFR responses associated with decreased renal NMDA receptor expression. Kidney NMDA receptor expression is conditioned by protein intake, and this receptor may play an important role in the kidney vasodilatory response to glycine infusion and protein feeding in rats.     

Induction of glutamate dehydrogenase in the ovine fetal liver by dexamethasone infusion during late gestation

Glucocorticoids near term are known to upregulate many important enzyme systems prior to birth. Glutamate dehydrogenase (GDH) is a mitochondrial enzyme that catalyzes both the reversible conversion of ammonium nitrogen into organic nitrogen (glutamate production) and the oxidative deamination of glutamate resulting in 2-oxoglutarate. The activity of this enzyme is considered to be of major importance in the development of catabolic conditions leading to gluconeogenesis prior to birth. Ovine hepatic GDH mRNA expression and activity were determined in near-term (130 days of gestation, term 147 +/- 4 days) control and acutely dexamethasone-treated (0.07 mg(-1) hr(-1) for 26 hr) fetuses. Dexamethasone infusion had no effect on placental or fetal liver weights. Dexamethasone infusion for 26 hr significantly increased hepatic GDH mRNA expression. This increased GDH mRNA expression was accompanied by an increase in hepatic mitochondrial GDH activity, from 30.0 +/- 7.4 to 58.2 +/- 8.1 U GDH/U CS (citrate synthase), and there was a significant correlation between GDH mRNA expression and GDH activity. The generated ovine GDH sequence displayed significant similarity with published human, rat, and murine GDH sequence. These data are consistent with the in vivo studies that have shown a redirection of glutamine carbon away from net hepatic glutamate release and into the citric acid cycle through the forward reaction catalyzed by GDH, i.e., glutamate to oxoglutarate.