The biological assay of oxytocin in the presence of ergometrine

The oxytocin content of a solution of oxytocin and ergometrine can be assayed with great accuracy by the chicken blood pressure method provided the rooster preparation is highly sensitive to oxytocin. The hormone can also be assayed with reasonable accuracy by measuring the response of the milk-ejection pressure in the mammary gland of the lactating rabbit. However, the rat uterus in vitro method yields erroneously high results due to the additional uterotonic effect of the ergometrine.

Studies on the multiplication and the properties of the lactic dehydrogenase agent

The procedure used to determine the infective titer of the LDH agent, the reproducibility of this assay, and the relationship between virus dose and plasma enzyme activity were described. Multiplication of the LDH agent began within 6 hours after infection and reached 10^10.8 ID₅₀/ml of plasma within 24 hours. The titer rapidly decreased over the next 72 hours but viremia persisted for at least 16 months with titers as high as 10^5.2 ID₅₀/ml. The appearance of the LDH agent in the circulation preceded the first noticeable rise in plasma LDH activity by close to 24 hours. After 10 months, when the plasma titer of the LDH agent had decreased nearly one millionfold, the plasma enzyme LDH had decreased by less than 50 per cent. The LDH agent is inactivated by ether but withstands lyophilization, and freezing and thawing. It is stable at low temperatures. Ultracentrifugation at 105,000 G for 2 hours leaves less than 0.1 per cent of the LDH agent in the supernatant fluid and filtration through gradocol membranes suggesst that the upper size of the LDH agent is about 55 mµ. Spread of the LDH agent from infected to uninfected mice kept in the same cage and transmission from mothers (infected prior to mating) to their offspring was relatively low.

Observations on the use of a mouse bioassy method for investigating purgative activity

Some essentially practical observations have been made on the use of a simple purgative assay in mice. Modifications of the method have improved both the accuracy and precision of the assay. Senna extracts have been assayed in terms of a sennoside A standard.

On combining estimates of relative potency in bioassay

Biological assays based on a quantitative response in particular (e.g. hormone assays) typically involve the estimation of (log) relative potency (= M) with respect to some standard preparation on the basis of one or more symmetrical determinations usually at equally spaced (log) dose intervals. It is the purpose of this paper to consider further statistical aspects of estimates of M, and especially confidence limits for M based on a combination of separate assays. These are given as examples of tests of linear hypotheses. Two applications are given on the combining of quantitative bio-assay data.

Assay of oxytocin by rat mammary gland in vitro

A new method for quantitative assay of oxytocin using strips from rat mammary gland in vitro has been investigated. The method is very suitable for determination of small amounts of oxytocin. Doses down to 2 mu-u. oxytocin have been estimated. The dose-response curve is shown to be linear, and the precision of the method is good (lambda =0.10 to 0.14). The effect of adrenaline, noradrenaline, acetylcholine, histamine and 5-hydroxytryptamine on the rat mammary gland has also been tested.

Assay of substance P on goldfish intestine in a microbath

A technique is described for testing the effects of drugs on the intestine of goldfish in a microbath (0.05 ml.). This preparation may be used for the assay of substance P, which causes contractions of the muscle in doses as small as 1 m-u. Other substances in tissue extracts also act on this muscle, but the effects of most of these can be abolished by antagonists. Some tissues, however, contain an unknown substance which causes powerful contractions of the muscle and interferes with the assay of substance P. An attempt to demonstrate the release of substance P in the central nervous system was unsuccessful.

FOLIC ACID AND VITAMIN B12 LEVELS IN PREGNANCY AND THEIR RELATION TO MEGALOBLASTIC ANAEMIA

There is a significant fall in the serum folic acid level during pregnancy, reaching its lowest level at term. This is most pronounced in twin pregnancies. A similar but less spectacular fall occurs in the vitamin B(12) concentration. In megaloblastic anaemia both folic acid and vitamin B(12) levels are lower than in other pregnant women. The degree of megaloblastic change in the bone marrow, as measured by the type and number of megaloblasts, is reflected in the vitamin levels, cases with florid megaloblastosis showing the most marked depression of vitamin B(12) and folic acid activity. Although there is a significant difference in the mean folic acid levels between megaloblastic and normoblastic pregnant women, a considerable overlap exists between individual values in the two groups. When the labile folic-acid factor is determined separately the test becomes much more specific. In the present series, all cases of megaloblastic anaemia yielded labile-factor levels below 1.0 mmug. per ml., while a similar value was encountered in only one of 35 normal pregnancies. In five women with megaloblastic anaemia the vitamin B(12) concentration was less than 100 mumug. per ml. but rose to normal levels on folic acid therapy alone.

PRODUCTION OF ANTIRENIN TO HOMOLOGOUS RENIN AND ITS EFFECT OF EXPERIMENTAL RENAL HYPERTENSION

1. Procedures are described for the extraction and partial purification of dog renin, on a large scale, as well as for the acetylation of rat, rabbit, and dog renin. 2. Untreated homologous renin was not antigenic in rat, rabbit, or dog, but the acetylation of homologous renin made it antigenic. 3. Immunization of rats, rabbits, and dogs, with acetylated rat, rabbit, and dog renin, respectively, resulted in each case in the development of anti-renin to the homologous, untreated, as well as to the acetylated renin. 4. The progressive development of antirenin as a result of repeated, subcutaneous injections of acetylated dog renin, in a dog with experimental renal hypertension for more than 6 years, was accompanied by a correspondingly progressive fall of the mean arterial blood pressure to the prehypertensive level. This points up the important part played by the renin-angiotensin mechanism in the maintenance of the hypertension, even in the chronic phase of experimental renal hypertension.

STUDIES ON BACTERIAL PYROGENICITY. 3. SPECIFICITY OF THE UNITED STATES PHARMACOPEIA RABBIT PYROGEN TEST

The specificity of the first or "presumptive" portion of the USP rabbit pyrogen test was investigated by use of a new absolute standard of reference. The reference standard was a 0.9% sodium chloride solution prepared to be pyrogen-free. Details of the preparation were described. The hypothesis was explored that the temperature response of rabbits after intravenous injection of the standard solution was independent of exogenous pyrogen. Reactions observed among the rabbits in our colony allowed a classification of these animals ranging from "consistently reliable" to "consistently unreliable." Details of the experimental results and implications for pyrogen testing are discussed. The recommendation was made that all rabbit test animals be "screened" in sham and actual tests before being used for pyrogen testing.

LIQUID NITROGEN FREEZING IN MICROBIOLOGICAL ASSAY SYSTEMS. I. PRESERVATION OF LACTOBACILLUS LEICHMANNII FOR DIRECT USE IN THE VITAMIN B12 ASSAY

Suspensions of Lactobacillus leichmannii were stored in liquid nitrogen and were used as direct inocula in vitamin B(12) assays. Complete recovery of viable cells was obtained when the suspensions in basal B(12) medium were rapidly frozen by direct immersion into liquid nitrogen and rapidly thawed by agitating the suspensions in a water bath at 40 C. Greater than 90% destruction occurred when the suspensions were in saline. However, both suspensions were usable in the B(12) assay system. Assay results on a number of test materials indicated good correlation between freshly prepared suspensions and frozen suspensions in basal medium stored 3 months. Suspensions in saline stored for 1 year in liquid nitrogen showed no detectable difference from the first day after freezing. Suspensions frozen slowly at the rate of 1 degree per min from 4 to -40 C and subsequently immersed in liquid nitrogen had a longer lag period of growth and were not usable in the 18-hr assay incubation system. A major advantage of a stored inoculum for direct use in a microbiological assay is the reduced day-to-day variation in the inoculum.

QUANTITATIVE COMPARISON BETWEEN OXYTOCIN AND FOUR RELATED NEUROHYPOPSIAL PEPTIDES ON THE HUMAN UTERUS IN SITU

Quantitative assays of four synthetic peptides related to oxytocin were carried out on the post partum human uterus in vivo by means of external tocography. The following activities (U/mg, means and standard errors) were found: isoleucine(8)-oxytocin 365+/-70, asparagine(4)-oxytocin 150+/-40, desamino(1)-oxytocin 1,030+/-300, serine(4)-isoleucine(8)-oxytocin 335+/-95. None of the conventional bioassay procedures proved to be fully reliable for predicting the oxytocic activity in man of peptides related to oxytocin. If the tocographically recorded effects of equipotent doses of the compounds are compared with those of oxytocin no qualitative differences can be observed.

THE EFFECTS OF GUANETHIDINE ON THE NORADRENALINE CONTENT OF THE HYPOTHALAMUS IN THE CAT AND RAT

Single injections of guanethidine 15 mg./kg. i.p. did not lower the hypothalamic noradrenaline in cats, but, daily injections of 15 mg./kg. s.c. over a 7 day period consistently produced a decrease in the hypothalamic noradrenaline. Attempts to lower the hypothalamic noradrenaline in rats after single injections or daily injections of guanethidine were unsuccessful.

THE ASSAY OF FOLIC-ACID ACTIVITY OF LIVER

Methods of preparing liver for the microbiological assay of folic-acid activity have been compared. Maximum values were obtained by incubating an alkaline homogenate of liver in the presence of ascorbic acid for five hours at 37 degrees C. Most other procedures resulted in significant loss of folic-acid activity.

NATURE OF THE ENDOTOXIN-INACTIVATING PRINCIPLE IN GUINEA-PIG LIVER

Corwin, L. M. (Walter Reed Army Medical Center, Washington, D.C.), and W. E. Farrar, Jr. Nature of the endotoxin-inactivating principle in guinea-pig liver. J. Bacteriol. 87:832-837. 1964.-Guinea-pig liver preparations inactivate Serratia marcescens endotoxin as assayed in chick embryo. The activity is optimal at pH 6.5 to 7.0 and 8.5 to 9.0. Mitochondria and the supernatant fraction containing microsomes possess activity. Mitochondria are only active at the acid pH optimum. The activity of acetone powder extracts of mitochondria is enhanced by adenosine triphosphate and nicotinamide adenine dinucleotide, whereas the mitochondria themselves are also activated by malate. It was concluded that the enzymes which inactivate endotoxin involve fatty acid activation and oxidation. Such a finding suggests that the lipid moiety of endotoxin is required for toxicity.

THIN-LAYER CHROMATOGRAPHY AND BIOASSAY OF PROSTAGLANDINS IN EXTRACTS OF SEMEN AND TISSUES OF THE MALE REPRODUCTIVE TRACT

By acid ether extraction and thin-layer chromatography, prostaglandins have been separated from biologically active compounds of other chemical groups. The technique does not, however, separate different prostaglandins from each other. The biological activity of the eluates was estimated on the rabbit isolated jejunum and the hamster isolated colon preparations in terms of prostaglandin E(1); the concentrations (thus expressed) of prostaglandin in human semen ranged from 24 to 783 mug/ml. with a mean of 226 mug/ml. No prostaglandins (minimal detectable concentration, 0.5 mug/g) could be detected in the male reproductive organs of several species of laboratory animal.

QUANTITATIVE ASSAY FOR CRUDE ANTHRAX TOXINS

Haines, Bertram W. (U.S. Army Biological Laboratories, Frederick, Md.), Frederick Klein, and Ralph E. Lincoln. Quantitative assay for crude anthrax toxins. J. Bacteriol. 89:74-83. 1965.-The whole crude toxins of Bacillus anthracis, although apparently responsible for the death of animals with anthrax, had never been quantitated. A total of 14 lots of the toxic culture filtrate of B. anthracis were pooled into one large lot of crude anthrax toxins. An extensive assay of this reference material was conducted in four laboratories by use of the time-to-death of the intravenously challenged Fischer 344 rat as the response variable. Doses of the material were varied factorially by concentration, dilution, and volume. The data from this study were used to define a potency unit of the crude anthrax toxins. Procedures were developed and illustrated for the assay of unknown lots of the toxins by comparing the rat time-to-death response to the unknown with either (i) the responses reported in this study, or (ii) directly with the rat responses to a new sample of the reference toxins. The possibilities and limitations of this standardization and of the statistical procedure through which it was developed are discussed.