Janet M. Ledingham

The use of p-phenylenediamine in the block to enhance osmium staining for electron microscopy.

Pieces of tissue 1 mm3 of rat renal medulla and cortex and rabbit myocardium were fixed in 2 or 4% glutaraldehyde, washed in buffer, postfixed in OsO4, rinsed in 70% alcohol, treated with 0.5–1% p-phenylenediamine in 70% alcohol 15–25 min, dehydrated, and embedded in Epon. Ultrathin sections were viewed in the electron microscope without further staining. Contrast was adequate except at very high magnification, when additional lead staining was required. In general, the appearances were similar to those seen after conventional lead staining. However, lipid droplets in myocardium and medullary interstitial cells were densely stained, and there was a tendency for extracellular material on the luminal surface of renal tubular epithelium and myocardial capillary endothelium also to stain densely. The main value of the method lies in the elimination of the need for section staining in both light and electron microscopy.

Intensification of Osmium Staining by p-Phenylenediamine: Paraffin and Epon Embedding; Lipid Granules in Renal Medulla

Tissue which had been fixed in 4% glutaraldehyde and postfixed in 2% OsO4 was subsequently treated with p-phenylenediamine, either in the block prior to embedding in paraffin or Epon or, in the case of Epon-embedded material, after sectioning for light microscopy. The p-phenylenediamine was best used as a 0.8-1% solution in 70% alcohol. The p-phenylenediamine caused a very considerable intensification of staining of any cell components; this intensification of staining was particularly marked in the case of the lipid granules of renal medulla.

REMODELLING OF RESISTANCE ARTERIES IN GENETICALLY HYPERTENSIVE RATS BY TREATMENT WITH VALSARTAN, AN ANGIOTENSIN II RECEPTOR ANTAGONIST

1. In the present study, New Zealand genetically hypertensive (GH) rats were treated with valsartan, a specific angiotensin II (AT1) receptor antagonist, to measure the effects on blood pressure (BP), cardiac hypertrophy and the structure of resistance arteries. Normotensive (N) rats were used as controls.

Endothelial Function In Mesenteric Resistance Arteries From The Genetically Hypertensive Rat

1. Endothelial function in mesenteric resistance arteries (MRA) from male 12‐week‐old New Zealand genetically hypertensive (GH) rats and their normotensive control strain (N) was compared in vessels mounted on a wire myograph and by the production of intracellular cGMP. In parallel experiments, MRA from the spontaneously hypertensive (SHR) rat strain, in which there is an endothelial defect, and from GH rats, in which an endothelial defect was induced by chronic nitric oxide synthase (NOS) inhibition with Nω‐nitro‐L‐arginine methyl ester (L‐NAME), were studied.

Renal afferent arteriolar structure in the genetically hypertensive (GH) rat and the ability of losartan and enalapril to cause structural remodelling.

Objective This study aimed to compare the structure of renal afferent arterioles in the genetically hypertensive (GH) rat strain with the normotensive (N) control strain in relation to pathogenesis, and to quantify structural remodelling in GH rats after treatment with losartan and enalapril and to relate this to blood pressure (BP) and left ventricular (LV) mass. Methods GH rats were given losartan 15 mg/kg/day, enalapril 10 mg/kg/day (enalapril 10) or 3 mg/kg/day (enalapril 3) from the age of 4 to 10 weeks. Untreated GH and N groups served as controls. Tail-cuff systolic BP was measured weekly from 4 weeks. At the age of 10 weeks, kidneys were perfused with microspheres to identify afferent arterioles, kidney pieces were fixed, embedded in Technovit and stained sections analysed. Lumen and media plus lumen diameters were measured; media width, media cross-sectional area (CSA) and media/lumen (M/L) ratio were derived. Results BP and LV mass were elevated in GH compared with N rats, and reduced by losartan and enalapril 10 and to a lesser degree by enalapril 3. In afferent arterioles, lumen diameter, media width and CSA were smaller in GH than N and M/L ratio was larger. Losartan and enalapril 10 reduced media width and increased lumen diameter, while enalapril 3 increased CSA (in distal arterioles) and lumen diameter. M/L ratio was reduced by losartan and enalapril. Conclusion Abnormal structure of the afferent arteriole, resulting in an increased M/L ratio, could explain abnormalities of renal blood flow and vascular resistance in GH and contribute to the hypertension. In GH, losartan and enalapril reduce BP and LV mass, cause remodelling of afferent arterioles, and lower the M/L ratio to below N levels.

Prevention of increases in blood pressure and left ventricular mass and remodeling of resistance arteries in young New Zealand genetically hypertensive rats: the effects of chronic treatment with valsartan, enalapril and felodipine.

The relative efficacy of three antihypertensive drugs in the prevention of further elevation of blood pressure (BP) and cardiovascular structural remodeling in 4-week-old genetically hypertensive (GH) rats was studied by means of two complementary methods, stereology and myography. Four to 10-week-old GH rats were treated with valsartan (10 mg/kg/day), enalapril (10 mg/kg/day) or felodipine (30 mg/kg/day). Untreated GH and normotensive control rats of Wistar origin served as controls. Tail-cuff systolic SBP was measured weekly and left ventricular (LV) mass determined at the end of the experiment. Mesenteric resistance arteries (MRA) were either fixed by perfusion, embedded in Technovit and sections stained for stereological analysis, or mounted on a wire myograph for structural and functional measurements. BP and LV mass were significantly reduced by all drugs; decreases in BP and LV mass were smaller after felodipine treatment. Valsartan and enalapril caused a decrease in BP to normotensive control values. Felodipine kept BP at the 4-week level and prevented further rise with age. Valsartan caused hypotrophic outward remodeling of MRA, enalapril eutrophic outward remodeling and felodipine hypotrophic remodeling. Myograph measurements showed remodeling of the same order. While all drugs lowered the media/lumen ratio in GH to normal, the outward remodeling after valsartan and enalapril indicates that valsartan and enalapril might be more effective in reversing the inward remodeling of resistance arteries found in essential hypertension.

Fluvastatin remodels resistance arteries in genetically hypertensive rats, even in the absence of any effect on blood pressure.

1. The aims of the present study were, first, to determine whether, in the genetically hypertensive (GH) rat, fluvastatin would lower blood pressure and remodel mesenteric resistance arteries (MRA) and the basilar artery and, second, to see whether treatment with a combination of fluvastatin and the angiotensin receptor antagonist valsartan would have any extra beneficial effect on blood pressure and vascular remodelling.

NITRIC OXIDE SYNTHASE INHIBITION WITH Nω‐NITRO‐L‐ ARGININE METHYL ESTER AFFECTS BLOOD PRESSURE AND CARDIOVASCULAR STRUCTURE IN THE GENETICALLY HYPERTENSIVE RAT STRAIN

1. Inhibition of nitric oxide (NO) synthesis with the nitric oxide synthase (NOS) inhibitor Nω‐nitro‐L‐arginine methyl ester (L‐NAME) was used as a tool to investigate further a possible endothelial defect in the New Zealand genetically hypertensive (GH) rat strain compared with its normotensive (N) control strain.

Effect of simvastatin given alone and in combination with valsartan or enalapril on blood pressure and the structure of mesenteric resistance arteries and the basilar artery in the genetically hypertensive rat model

1. The aims of the present study were to investigate, in the New Zealand genetically hypertensive (GH) rat model, the effects of treatment with simvastatin, alone or in combination with valsartan or enalapril, on blood pressure (BP) and structural remodelling of mesenteric resistance arteries (MRA) and of the basilar artery, an artery that plays a major role in the regulation of cerebral resistance.

Effect of Captopril on Blood Pressure, Total Body Sodium and Fluid Consumption of Genetically Hypertensive (GH) and Normotensive (N) Rats

Captopril was administered in the drinking fluid to normotensive rats and rats of the New Zealand genetically hypertensive (GH) strain. It lowered BP in both strains of rat, particularly in rats deprived of sodium; in these rats BP rose again when the drug was stopped even though there was no access to sodium. Thus captopril appeared to lower blood pressure not by reduction in total exchangeable sodium but by some other mechanism, presumably inhibition of vasoconstriction. Total exchangeable sodium did not change significantly in rats treated with captopril and having access to salt in the drinking fluid, though it fell in rats deprived of sodium. Captopril caused an increase in fluid intake, particularly intake of 0.5% NaCl solution and this may have compensated for any loss of body sodium. It was not clear whether the thirst for water and the desire for salt were due to effects of captopril in the CNS or were secondary to increased excretion of salt and water.