Absence of amino acid-induced glomerular hyperfiltration in dopamine D3 receptor knockout mice.

Pharmacological inhibition of receptors of the dopamine D2-like family has been shown to abolish the glomerular hyperfiltration in response to amino acids. To further discriminate between the receptor subtypes within the D2-like family, we investigated the effects of amino acid infusion on renal function in dopamine D3 receptor knockout (-/-) mice. In clearance experiments pentobarbital-anesthetized D3 receptor (-/-) and wild-type (+/+) mice were infused with Ringer solution at baseline, followed by a continuous infusion of mixed amino acids (10%). Baseline glomerular filtration rate (GFR), assessed by renal clearance of [3H]-inulin, was the same in D3 receptor (-/-) mice (0.56+/-0.08 ml/min per g kidney weight) and wild-type animals (0.56+/-0.04 ml/min per g kw). During infusion of amino acids, GFR was significantly elevated by 50% in D3 receptor (+/+) mice. In contrast, this amino acid-induced response of GFR was abolished in D3 receptor (-/-) mice. Baseline urinary water and sodium excretion was not significantly different in both groups of mice. As observed in GFR, these renal excretory parameters were significantly elevated during amino acid infusion in D3 receptor (+/+) but not in D3 receptor (-/-) mice. Time controls, constantly infused with Ringer solution, did not show significant changes in GFR, renal water or sodium excretion during the entire experiment, indicating stable experimental conditions. Taken together, the data underline the involvement of dopamine D2-like receptors in the renal response to amino acid infusion and, in addition, attribute this effect to the dopamine D3 receptor subtype.

Characterisation of cerivastatin as a P-glycoprotein substrate: studies in P-glycoprotein-expressing cell monolayers and mdr1a/b knock-out mice.

The aim of this study was to characterise the role of the efflux transporter P-glycoprotein in the disposition of cerivastatin. We investigated directional transport characteristics of [14C]cerivastatin across cell monolayers expressing P-glycoprotein (Caco-2 and L-MDR1) and disposition of cerivastatin in mice with disrupted mdr1a and mdr1b genes. The mice were given orally 1 mg/kg cerivastatin and plasma and tissue samples for analysis of cerivastatin were obtained 10, 20, or 30 min after drug administration. Four knock-out mice and four wild-type mice were studied at each time point. In addition, the hypothesis that gemfibrozil-mediated inhibition of P-glycoprotein contributes to the interaction between gemfibrozil and cerivastatin was tested in Caco-2 cells. The apparent permeability coefficient (P(app)) value for the basal-to-apical transport of cerivastatin in Caco-2 and L-MDR1 cell monolayers was 2.4 times (P<0.001) and 3.8 times (P<0.001) as high as the apical-to-basal P(app) value respectively. The P-glycoprotein inhibitor PSC-833 (1 microM) inhibited the net basal-to-apical transport of cerivastatin in Caco-2 monolayers by 35% (P<0.01) and the MRP inhibitor MK-571 (10 microM) by 50% (P<0.01). At concentrations up to 250 microM, gemfibrozil showed no significant effects on the net transport of cerivastatin in Caco-2 cells. The concentration of cerivastatin in the brain at 30 min was 3.1 times higher in the knock-out mice than in the wild-type mice (P<0.05). The brain-to-plasma cerivastatin concentration ratio at 20 min and 30 min was 2.1 (P<0.05) and 3.6 times (P<0.05) higher respectively in the knock-out animals compared with the wild-type animals. Collectively, these results indicate that cerivastatin is a P-glycoprotein substrate, although other transporters probably contribute to cerivastatin transport in humans. As several statins are P-glycoprotein substrates, beneficial as well as adverse effects of the statins might be affected by interindividual differences in P-glycoprotein expression or function caused by, e.g., the MDR1 polymorphism.

Blood glucose profiles in diabetic rodents using different insulin preparations.

The aim of the present study was to evaluate several long-acting insulin preparations for their ability to normalize the blood glucose profile of rats and mice with streptozocin-induced diabetes mellitus. The single injection of a long-acting zinc insulin (CAS 8049-62-5) suspension or insulin glargine (CAS 160337-95-1) in both species induced a steep to moderate fall in blood glucose concentration. Blood glucose was then normalized for 2-3 h, until 3 h after insulin injection blood glucose concentration tended towards levels before insulin application. In contrast, implants produced with a mixture of human insulin and palmitic acid micro-crystals normalized blood glucose profile over 24 h in both species at least 30 days after implantation. Therefore, these implants with a sustained release of insulin are suitable to control the blood glucose in diabetic rats and mice.

Age dependency of renal function in CD-1 mice.

Renal function was studied in mice of different ages. In metabolic cage experiments, the renal electrolyte excretion was similar in young (n = 8; 5- to 7-wk-old) and adult (n = 6; 20- to 22-wk-old) CD-1 (ICR) BR mice, whereas spontaneous drinking volume and urinary flow rate were significantly higher in the adult compared with the young mice. Subsequently, the renal functional reserve was investigated by amino acid (AA) infusion (10%) in anesthetized young (n = 8) and adult (n = 6) mice. Because the body weight of adult mice was significantly higher than that of young animals, one group of adult mice (n = 8) received 12.5% AA to ensure that the dose of AA related to body weight was similar in both groups. Young animals constantly infused with Ringer solution served as time controls (n = 8). Glomerular filtration rate (GFR) at baseline was similar in each group. Because of AA, GFR significantly increased in young mice but not in both groups of adult animals, whereas in time controls GFR remained constant. Urinary flow rate and sodium excretion were elevated by AA in young and adult mice. We conclude that in CD-1 mice the first signs of age-related changes in kidney function concern alterations in renal hemodynamics, whereas renal tubular function appears to be preserved.