F. O. Simpson

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.

Salt appetite, body sodium, handling of a NaCl load, renin, and aldosterone in genetically and spontaneously hypertensive rats.

Salt appetite, body sodium, handling of a NaCl load, plasma renin activity (PRA), and plasma aldosterone concentration (PAC) were compared in New Zealand genetically hypertensive (GH) and Japanese spontaneously hypertensive rats (SHRs) and their respective normotensive controls [normal Wistar (N) and Wistar-Kyoto (WKY) rats]. Salt appetite was increased in SHRs compared with GH, N, and WKY rats when rats were on salt-free chow and given a choice of distilled water and NaCl solution. Body sodium, measured by whole body counting, was higher in SHRs than in the other strains but did not differ among GH, N, and WKY rats. The rate of excretion of a NaCl load was not increased in GH rats and was slightly increased in SHRs only when on a very low NaCl intake. PRA and PAC (radioimmunoassay) were lower in SHRs than in GH, N, and WKY rats. PAC had a significant negative correlation with body sodium across the four strains. There is no evidence of any abnormality in sodium regulation in GH rats. However, the SHRs have an increased salt appetite and an increased body sodium even when sodium intake is limited; PRA and PAC appear to have responded appropriately to the increased body sodium.

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.

Long-Term Measurement of Total Exchangeable Sodium in One- and Two-Kidney Goldblatt Rats

Total exchangeable sodium (Nae) was measured by wholebody counting of 22Na in 1- and 2-kidney Goldblatt rats before, and for 12 weeks after, renal artery clipping. In 1-kidney Goldblatt rats, Nae relative to body weight increased immediately after the clipping procedure and then fell though not to normal levels; from the 10th to the 12th week it again rose rapidly, probably secondary to vascular damage. In 2-kidney Goldblatt rats, Nae relative to body weight increased immediately after the clipping procedure but by the 5th day it was back to normal and remained normal thereafter. Consideration of the values for absolute Nae (i.e. expressed in mmol per rat) casts some doubt on the reality of the sodium retention, except in the 1-kidney Goldblatt rats in the later stages of their hypertension. Immediately after surgery temporary loss of weight (presumably mainly affecting fat stores and muscle) probably accounts for much of the rise in Nae relative to body weight.

EFFECT OF FELODIPINE ON BLOOD PRESSURE, BODY SODIUM, PLASMA RENIN ACTIVITY AND PLASMA ALDOSTERONE IN HYPERTENSIVE AND NORMO-TENSIVE RATS

1. To explore its effect on blood pressure (BP) in relation to body sodium (Na), felodipine was given to New Zealand genetically hypertensive (GH) and normotensive (N) rats and to Japanese SHR and WKY rats, prepared for repeated measurements of body sodium (Na) by a whole body counting technique (22Na) using an Na‐free pelleted diet and 22Na‐NaCl fluid as the sole source of Na, with water also available. The drug was added to the food before pelleting pellets, 0.5 mg/g food.

Handling of a sodium load by rats on a low sodium intake and frusemide

1. Groups of rats (n= 9–10 per group) were given a medium sodium (Na) diet or a low Na diet or a low Na diet plus low or high dose frusemide in order to have their body Na in a state of surplus or deficit or neither.

Body Sodium Level in Hypertensive and Normotensive Rats: Effects of Dietary Sodium Levels and Sodium Loads

Rats of the genetically hypertensive (GH) strain do not have an increased body sodium content or increased natriuresis of hypertension. Spontaneously hypertensive rats (SHR), on the other hand, have an increased body sodium content and an increased rate of excretion of a sodium load. They also have an increased appetite for salt. In a study on three groups of normotensive rats with high normal, low normal, and very low sodium intakes, respectively, body sodium content was highest with the highest intake and lowest with the lowest intake. At the age of 22 weeks, after being on these intakes for 6 weeks, all three groups were put on a low sodium intake. Body sodium content of the two groups with the previous higher intakes failed to fall to the level of the group with the previous lowest intake. Thus there may be a prolonged carryover effect of salt intake in rats. The results are discussed in terms of the set point theory for sodium homeostasis.

Surfeit and deficit of sodium: evidence from studies of body sodium in rats.

The concept of a basal level of body sodium (Strauss state between surfeit and deficit) was studied by means of body sodium measurements in rats on different sodium intakes, in some cases after diuretic pretreatment. At a certain level of body sodium, when sodium intake was just enough to allow for body growth, a sodium chloride load (followed by a zero sodium intake) was excreted more or less quantitatively in 24-48 h. In rats pretreated with an ample sodium intake, the load was excreted more quickly and some additional sodium was also excreted. In rats pretreated with diuretic and a zero sodium diet, body sodium was very low and a sodium chloride load was retained to an extent that was more or less appropriate to the deficit. In a subsidiary part of the study, rats pretreated with a low sodium intake and frusemide and continuing on frusemide during and after the load, excreted a sodium chloride load at much the same rate as rats given a load following pretreatment with a very low sodium diet alone (i.e. not given a diuretic); after excreting the load they were able to maintain a stable (though reduced) level of body sodium in spite of cessation of sodium intake. Rats pretreated with hydrochlorothiazide, and continuing on this drug during and after the load, had a continued loss of sodium after cessation of sodium intake. The results are discussed in the light of the Strauss concept and appear to confirm it. Basal body sodium is, by inference, identified as the level at which delivery of sodium to the distal tubule exactly equals distal sodium reabsorption.