Renal vascular responsiveness to angiotensin II at an early stage of diabetes: interaction between intrarenal noradrenergic and renin-angiotensin systems.

The renin-angiotensin system (RAS) has been implicated in haemodynamic maladaptations of diabetic kidney. Its effects may be modulated by endogenous substances like noradrenaline. Our aim was to study renal vascular response to angiotensin II and the interaction between intrarenal RAS and noradrenergic system at an early diabetic stage. Seven days after alloxan induction of diabetes, concentration-response curves to noradrenaline and angiotensin were generated in isolated, perfused rat kidneys. Percent changes in renal vascular resistance were considered as contractile responses. Diabetic kidneys showed enhanced noradrenaline sensitivity compared to controls. Enalapril and losartan elicited increments in ED(50) of noradrenaline in diabetics (diabetic, 3.4+/-0.2 nmol; diabetic + enalapril, 5.1+/-0.5 nmol, p<0.01 vs. diabetic; diabetic + losartan, 5.5+/-0.7 nmol, p<0.05 vs. diabetic). Maximum response (MR) and sensitivity to angiotensin were augmented in diabetics compared to controls. Prazosin decreased MR and sensitivity in diabetics (MR: control, 156.4%+/-5.1%; diabetic, 262.2%+/-21.1%, p<0.001 vs. control; diabetic + prazosin, 178.8%+/-11.2%, p<0.01 vs. diabetic). Enalapril, losartan and prazosin did not change control responses. At this diabetic stage, renal vasculature presented increased response to angiotensin, and an interaction between renal RAS and noradrenergic system was evidenced. Vascular response to noradrenaline requires the integrity of intrarenal RAS and the participation of AT(1) receptors; alpha(1)-adrenoceptors contribute to vascular response to angiotensin.

Probenecid protects against In vivo acetaminophen-induced nephrotoxicity in male Wistar rats.

Renal effects of acetaminophen (APAP) were studied in rats pretreated with probenecid to analyze whether acute APAP-induced nephrotoxicity could be related to a probenecid-sensitive transport system for APAP or its S-derived conjugates. The administration of probenecid (200 mg/kg b.wt. i.p.) 30 min before APAP administration (1000 mg/kg b.wt. i.p.) improved urine flow rate and protected against the alterations on glomerular filtration rate and urea and creatinine plasma levels induced by APAP. Fewer epithelial cells and granular casts and a decrease in the urinary excretion of protein and glucose were observed in rats pretreated with probenecid. Probenecid pretreatment promoted an elevation in the urinary 16-hr excretion of APAP and a diminution in the plasma levels attained by APAP. These results suggest that protection afforded by probenecid in vivo could be a consequence of the inhibition of APAP S-conjugate renal uptake and/or an increase in APAP renal clearance. The effects of APAP in presence of probenecid were studied with the isolated perfused kidney model. Perfusion with probenecid (0.1 mM) before APAP (10 mM) did not change APAP direct renal effects, APAP urinary excretion, or APAP renal clearance relative to glomerular filtration rate. Our results suggest that protection afforded by probenecid in vivo could be the result of the inhibition of the uptake of nephrotoxic APAP metabolites and/or a diuresis-induced enhanced APAP renal excretion.

Nephrotoxicity of acetaminophen in male Wistar rats: role of hepatically derived metabolites.

The role of hepatically derived metabolites was studied in rats treated with a nephrotoxic dose of acetaminophen (APAP, 1000 mg/kg b.wt. i.p.). Hepatic glutathione (GSH) content 16 h after APAP dosing was significantly decreased (control = 3.83 +/- 0.1, APAP = 2.51 +/- 0.3 mumol/g wet tissue), whereas renal GSH levels were not changed. The role of hepatically derived GSH conjugates was investigated by administering the gamma-glutamyl-transpeptidase inhibitor, acivicin (20 mg/kg b.wt. i.p.). Treatment with acivicin led to a significant decrease in hepatic and renal gamma-glutamyltranspeptidase activity. Administration of acivicin 1 h before APAP administration protected against the alterations of glomerular filtration rate and urea and creatinine plasma levels induced by APAP. The appearance of epithelial cells and granular casts as well as the urinary excretion of protein and glucose were decreased compared with rats not pretreated with acivicin. Hepatocellular damage (evaluated by glutamic pyruvic transaminase levels) induced by APAP was not altered by acivicin pretreatment. APAP plasma levels and its urinary excretion were the same whether the rats were pretreated with acivicin or not. A group of rats was fitted with an exteriorized biliary cannula before APAP administration to study the contribution of the biliary excretion route of APAP metabolites in the APAP-induced renal damage. No differences were observed on APAP-induced renal effects between rats cannulated or not. Our results suggest that hepatically derived APAP metabolites are partially responsible for APAP renal effects. The sinusoidal efflux of these metabolites is also suggested.

Effects of gamma-aminobutyric acid agonists on the isolated perfused rat kidney.

The effects of gamma-aminobutyric acid (GABA) agonists were studied in the isolated perfused rat kidney. Perfusions were performed at constant flow with modified Ringer-Krebs solution. The GABAA agonist muscimol (0.1-75 microM) induced an increase in fractional excretion of water and sodium without promoting hemodynamic changes. These tubular changes were inhibited by atropine pretreatment. Thus, a possible modulation of tubular transport mechanisms via GABAA receptors acting on cholinergic system could be suggested. Muscimol was unable to modify the renal vascular resistance either at basal conditions or in noradrenaline-pretreated preparations. However, the GABAA antagonist bicuculline (50 microM) evoked an increased perfusion pressure. Despite the speculation that endogenous GABA could result in a maximal activation of these GABAergic processes, nonspecific binding sites for bicuculline should be considered. The GABAB agonist baclofen (0.05-500 microM) elicited a raised perfusion pressure and diminished glomerular filtration rate, accompanied by an increment in fractional excretion of water, sodium and glucose. These findings suggest a major GABAB receptor-mediated vasoconstriction at the afferent arteriole level. Proximal tubular structures seem to be a biological target for baclofen. GABA (0.05-1000 microM) evoked changes similar to those described for baclofen, although the glomerular filtration rate was not diminished. Data from this study indicate that the GABA system may be involved in the modulation of rat renal function.

Vascular and tubular actions of diazepam in isolated and perfused rat kidney.

The effects of diazepam were studied in the isolated rat kidney under conditions of constant flow. Kidneys were perfused with modified Ringer-Krebs solution. Diazepam produced a raised fractional excretion of water and sodium without hemodynamic changes, suggesting a direct effect on tubular transport mechanisms. Diazepam decreased renal perfusion pressure in a concentration-dependent fashion when kidneys were pretreated with either noradrenaline or potassium chloride. Similar responses were observed when 7-chloro-5-[4-chloro-phenyl]-1, 3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one (Ro 5-4864) or clonazepam was used. These data provide evidence for a relaxant effect of benzodiazepines on preconstricted renal vasculature.

Tubular effects of acetaminophen in the isolated perfused rat kidney.

The effects of different acetaminophen (APAP) concentrations (1, 5 or 10 mM) on renal function were investigated in the isolated perfused rat kidney (IPK). APAP was added to the perfusion media as a single dose after a equilibration time and control periods. Changes in fractional excretion of sodium (FENa), water (FEH2O), glucose (FEglu) and in glomerular filtration rate (GFR) were measured. The lower concentration used only modified the FEH2O. APAP 10 mM induced an increment in FEH2O (72% higher than control preparation), FENa (79% higher than control preparation) and an elevation in glucose excretion (55% higher than control preparation), associated with a decrease in GFR (23% lower than control preparation). The influence of PGE2 on the effects of APAP was also investigated. PGE2 prevented the APAP-induced decrease in GFR and in glucose reabsorption, but did not change the pattern of sodium and water handling. The effects of another vasodilator, verapamil, on APAP-induced renal effects were also tested. Verapamil prevented the glomerular but not the tubular effects of APAP. Urinary APAP excretion data showed a similar availability of APAP to the tubular cells in all the groups. Our data suggest that APAP exerts a direct action in the IPK, affecting hemodynamic and tubular functions, and that the latter are not a consequence of hemodynamic alterations.

Evidence that diazepam elicits alterations on rat renal function.

The effects of diazepam on rat renal function were investigated by means of clearance techniques in conscious animals. Different intravenous doses of diazepam were tested: 0.1, 0.3 and 10 mg/Kg body weight A marked increase in fractional water, sodium and potassium excretion was found in every group studied. This alteration was associated with a urine-to-plasma osmolality ratio diminution. On the other hand, no modifications in glomerular filtration rate or p-aminohippuric acid clearance were observed. The reabsorption of water in collecting tubule in diazepam treated rats was decreased as compared with control rats. To assess diazepam-effects on collecting tubule response to vasopressin, the effects of desmopressin on concentrating ability in control and diazepam-treated rats were tested. Desmopressin-treatment promoted a significantly lower free water reabsorption in diazepam-treated group as referred to control rats. This results indicate that diazepam may promote impairments on renal tubular ions reabsorption and that it modifies the collecting tubule response to desmopressin.

Rat renal functions during the first days post-bile duct ligation.

Renal functions during the early stage of hepatic damage before ascites formation were studied in adult female rats. Tubular and hemodynamic parameters were analyzed for 12 days after common bile duct ligation. The fractional excretion of water, sodium, and potassium increased from control values at every day studied. Glomerular filtration rate and renal plasma flow were found to be diminished on the fourth day. Renal plasma flow remained decreased while glomerular filtration rate was recovered on the sixth day after common bile duct ligation. Filtration fraction in both experimental groups (4 and 6 days) was higher than in control animals. These observations suggested a preferential efferent arteriole vasoconstriction that could be responsible for a blood flow redistribution to the medulla. This fact might cause the sodium diuresis with diminished urine-to-plasma osmolalities ratio. The onset of cortical vasoconstriction was confirmed by dopamine infusion to bile duct-ligated rats 4 days postsurgery. Hemodynamic and tubular parameters recovered to control values during dopamine administration. All the data point out diuresis and natriuresis as the earliest renal abnormalities in bile duct-ligated rats. This phenomenon could be associated not only to the cortical vasoconstriction proposed but also to another systemic modification associated to liver damage.

Acetylcholine modulates the effect of ovarian steroids on glutamic acid decarboxylase activity in the rat fallopian tube.

Glutamic acid decarboxylase (GAD) activity was measured in the oviduct of normal rats in diestrous and in rats ovariectomized (OVX) seven days before. OVX induced a significant decrease of GAD activity in the Fallopian tube. This effect was completely reversed by coadministration of estradiol benzoate + progesterone (E + P). Simultaneous injection of atropine, but not of alpha-methyl-para-tyrosine or labetalol, completely prevented the activation of GAD induced by ovarian sterois. Moreover, prostigmin significantly potentiated the action of E + P on GAD activity in the rat oviduct. These data clearly suggest the participation of acetylcholine in the mechanisms whereby ovarian steroids regulate GAD activity in the rat Fallopian tube.

[Surveillance of congenital malformations. Experiences in 1986-1987]. / Sorveglianza delle malformazioni congenite. Esperienza relativa al biennio 1986-1987.

Epidemiological data on the congenital malformations detected in 8,723 newborns over a two year period are presented.