The effect of vasopressin (Pitressin) administration and dehydration on the concentration of solutes in renal fluids of rats with and without hereditary hypothalamic diabetes insipidus

1. The method of sequential centrifugation has been used to obtain fluid samples from both the renal papilla and inner medulla of the rat.2. Experiments were carried out on Brattleboro rats with hereditary hypothalamic diabetes insipidus (DI; homozygous recessive), and on their (heterozygous) litter-mates with normal quantities of neurohypophysial vasopressin. Initial classification of the animals by measurement of urine volume and osmolality was confirmed by post-mortem bio-assay of the pituitary glands, in thirty-five out of forty-seven animals.3. In rats with DI, urine osmolalities comparable to those of heterozygous rats were obtained after four daily injections of 1 u. Pitressin Tannate in Oil (PTO). Under these conditions, when dehydration was superimposed for 72 hr, urine osmolality did not increase markedly. In heterozygous rats dehydrated for the same period of time, urine osmolality increased by some twofold.4. In rats with DI, the administration of PTO induced a rise of both sodium and urea concentrations in renal fluids and in urine. Dehydration during PTO administration caused a further rise of urea concentrations only. Dehydration per se significantly raised urinary and renal fluid urea concentrations, but sodium concentrations did not rise.5. In heterozygous rats dehydration per se increased both urea and sodium concentrations in renal fluids and urine.6. The evidence is discussed that the action of vasopressin involves factors apart from increasing the permeability of the distal nephron to water and urea.

Changes of sodium and urea concentrations in the renal papillary interstitial fluid on dehydration of rats

1. The isolated renal papillae of a rat were centrifuged in a two tube assembly which allowed fluid from the tissue to separate into the lower tube.2. The papillae were centrifuged for 15 min at 300 g and 1500 g consecutively.3. After intraperitoneal injection of Na (131)I-diatrizoate, the activities of urine, and fluid samples obtained from the papilla, were compared. It was found at 1500 g that the median value for papillary fluid activity was 1.52% of the activity of urine. This is evidence that the papillary fluid was virtually free from any contamination from the terminal collecting ducts.4. It is considered that the fluid sample obtained from the papillae by centrifugation at 1500 g is a representative and reproducible sample of interstitial fluid.5. The method was used to demonstrate changes in solute concentrations in the renal papillary fluid, following dehydration of rats.

QUANTITATIVE INHERITANCE IN DURUM WHEAT

Little or no heterosis was found for height, yield and yield components in the F1's resulting from the diallel crossing of six geographically diverse cultivars of durum wheat. General combining ability effects were more pronounced than specific combining ability effects and average parental performance gave a good prediction of hybrid performance. Heritability for yield was 0.61. For the cultivars studied, a conventional pedigree breeding program probably offers the most hope for genetic advancement. No easily measured character could substitute for yield per plant as a selection criterion for yield.

Antidiuretic activity of oxytocin preparations

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Enzymes involved in acetoacetate formation in various bovine tissues

1. The activities of acetoacetyl-CoA thiolase, hydroxymethylglutaryl-CoA synthase and lyase and acetoacetyl-CoA deacylase were measured in homogenates of samples of liver, rumen epithelium (long papillae), kidney and lactating mammary gland derived from slaughtered cows. 2. The activities of the four enzymes in bovine liver were similar to the activities previously reported for the corresponding enzymes in rat liver. 3. Acetoacetyl-CoA thiolase and hydroxymethylglutaryl-CoA synthase and lyase were present in rumen epithelium. The activities of the enzymes were all lower on a wet weight basis than in liver. Only very slight deacylase activity was detected. 4. Kidney contained acetoacetyl-CoA thiolase, hydroxymethylglutaryl-CoA lyase and acetoacetyl-CoA deacylase, but only trace amounts of hydroxymethylglutaryl-CoA synthase. 5. Mammary gland contained acetoacetyl-CoA thiolase and some hydroxymethylglutaryl-CoA lyase, but virtually no hydroxymethylglutaryl-CoA synthase or acetoacetyl-CoA deacylase. 6. Since physiologically significant ketogenesis probably occurs solely via the hydroxymethylglutaryl-CoA pathway, it is evident that, of the four tissues examined, such ketogenesis must be restricted to the liver and the rumen epithelium. 7. All the enzymes except hydroxymethylglutaryl-CoA lyase were also assayed in the four tissues derived from cows suffering from bovine lactational ketosis. Ketosis did not cause a statistically significant change in the activity of any of the enzymes measured. 8. Hepatic hydroxymethylglutaryl-CoA synthase and lyase were found to be associated mainly with the particulate fraction, as in the rat. A considerably greater proportion of these enzymes was found to be present in the cytoplasmic fraction from rumen epithelium, although it was not excluded that this was due to mitochondrial damage during homogenization. 9. Appreciable hydroxymethylglutaryl-CoA synthase was also present in epithelium from the dorsal region of the rumen, from the reticulum and from the omasum, but not from the abomasum.

The release, clearance and plasma protein binding of oxytocin in the anaesthetized rat

At 4°, the activity of exogenous 8-arginine vasopressin in rat plasma decreased to 50% in 2 days, whereas there was no loss of oxytocin under the same conditions after 3 days. At 37°, oxytocin was not inactivated in 9 hr., whereas 50% of 8-arginine vasopressin was lost in 2 hr.

Forty per cent of exogenous oxytocin in rat plasma was unable to pass through a cellophane (Visking 8/32 in.) membrane, when subjected to a pressure of 100 torr for 18 hr.

In rats under pentobarbitone anaesthesia, progressive haemorrhage of more than 2·0 ml./100 g. induced a secretion of both oxytocin and 8-arginine vasopressin, to produce maximum concentrations of 450 and 700 μ-u./ml., respectively, in the carotid plasma.

In the intact rat (weighing 200–250 g.) anaesthetized with pentobarbitone, 50% of oxytocin in the circulation disappeared within 2 min. after stopping an i.v. infusion of 250–6000 μ-u./100 g./min. The half-time was increased to 4 min. by sham operation, and to 6 or 7 min. by occluding either the renal, or the portal, coeliac and mesenteric vessels. In non-lactating animals, the half-time was 8 min. after clamping both the renal and splanchnic vessels, whereas it was 6 min. in the lactating rat, under the same conditions.

The apparent volume of distribution of oxytocin was 7·3 ml./100 g. in intact rats, and 10–13 ml./100 g. after operation.

The plasma clearance of oxytocin was unaltered in the sham-operated rat, but it decreased after the operative procedures.

INFLUENCE OF SEVERAL FACTORS ON EGG SHELL STRENGTH AND ITS PREDICTION

Experiments were conducted to determine the effect of genotype, (reciprocal crosses), age of pullet (three consecutive 42-day periods) and egg storage treatment on the relationship of crushing strength to shell elasticity (the ability to recover from deformation and expressed as deformation per unit load), and to study the influence of storage treatment on crushing strength.Small but occasionally significant differences were noted among crosses and ages in the relationship of crushing strength to elasticity. Storage treatment exerted a much more marked effect on this relationship. The average increase in standard error of estimate incurred by pooling the raw data from all storage treatments was 15.0%, as compared with a maximum increase of 2.1% when the raw data for crosses or ages were pooled.Eggs stored in water, either intact or with the albumen and yolk removed, became progressively weaker throughout the 60-day storage period, as judged by a significant linear increase in elasticity. The strength of eggs stored at 21 °C in a normal or CO2 atmosphere and of those stored at 4 °C, with or without spray-oiling, underwent no significant change during storage.

Factors influencing the sensitivity of the rat to vasopressin

1. Indirect evidence suggests that the concentration of arginine vasopressin in the plasma of normally hydrated man is about 1 mu-u./ml., but this is usually considered to be below the limit of sensitivity of the standard assay preparation, the water-loaded Wistar rat under ethanol anaesthesia.2. It was found that there was a surprising variation in sensitivity to vasopressin between batches of Wistar rats, and that other varieties of rat (including those with diabetes insipidus) were no more sensitive.3. Three modifications of the standard assay procedure produced an increase in sensitivity:(a) using Wistar rats weighing 100-150 g, rather than larger animals;(b) commencing the assay shortly after surgery, i.e. as soon as the urine flow reached 25 mul./min;(c) infusing vasopressin intravenously (0.5-3 mu-u./min). By using modification (a) with either (b) or (c) it was possible to detect as little as 0.5 mu-u.4. With these modifications antidiuretic activity equivalent to 0.5-2.0 mu-u./ml. of arginine vasopressin was measured in nine samples of plasma from a normally hydrated subject.5. It is suggested that the frequent reports of enhanced sensitivity may have been due to the fortuitous use of a particularly sensitive batch of rats, or to a high endogenous secretion of vasopressin due to operative trauma.