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Biomedical subjects

J J Pratt

Publications and source records attributed to J J Pratt.

18 recordsLinked to original sources
PubMed1992

Second-trimester maternal serum immunoreactive inhibin as a marker for fetal Down's syndrome.

We measured immunoreactive inhibin in the maternal serum of 80 pregnancies with a chromosomally normal fetus and ten Down's syndrome pregnancies in the second trimester. The inhibin level in all Down's syndrome pregnancies was above the normal median; the multiple of the normal median (MoM) was 1.9. We found a statistically significant difference between the levels of inhibin in unaffected and affected pregnancies (Kolmogorov-Smirnov test: p < 0.002). Using an arbitrarily chosen cut-off of 2.4 MoM, 40 per cent of Down's syndrome and 5 per cent of the normal pregnancies were found. We conclude that immunoreactive inhibin may be useful as a marker for fetal Down's syndrome.

Biomarkers↗
PubMed1979

Brain sodium uptake after choroid plexectomy.

When in a (control) series of rats brain sodium uptake (BSU) -- as calculated from estimated radioactivities of brain and blood following the injection of [24Na]sodium chloride 30 min and [22Na]sodium chloride one minute before killing -- was plotted against average arterial blood pressure of the animals during the 30 min survival period, a linear dependence of BSU on blood pressure was observed. In another series of animals, in which the choroid plexuses of the fourth and both lateral ventricles had been removed, the regression line showed the same slope, but a significantly lower intercept. On the other hand, a series of rats which had been subjected to a sham operation without removal of the choroid plexuses, showed a regression line not different from the control series. The results indicate that probably the blood pressure independent component of brain sodium uptake, as represented by the intercept of the regression line, for the greater part constitutes cerebrospinal fluid secretion by the choroid plexus.

Animals↗
PubMed1979

Specificity of immunoassays. II. Heterogeneity of specificity of antibodies in antisera used for steroid immunoassay and the selective blocking of less specific antibodies, including a new method for the measurement of immunoassay specificity.

Practical aspects of the measurement of the specificity of immunoassay are reviewed. Antibody heterogeneity in an antiserum makes a pragmatic rather than a theoretical approach necessary. A new method for the measurement of immunoassay specificity is described. This method is based on the errors caused by the cross-reacting antigens and is directly relevant to the validity of results obtained by immunoassay methods. The effect of selectively blocking the least specific antibodies in antisera raised against steroid haptens is tested. The practical consequences of these considerations are tested using steroid radioimmunoassay and enzyme-immunoassay.

Androgens↗
PubMed1979

Specificity of immunoassays. III. Use of two antisera of differing specificities to improve the specificity of steroid immunoassay.

The specificity of immunoassays can be improved by using a second antiserum to bind substances that cross-react. Both theory and practice show that the effectiveness of the procedure is dependent of the complex interplay of the concentrations of the two antibodies, the concentrations of the three antigens involved (the labelled tracer, the antigen whose concentration is to be measured and the substance that cross reacts) and the affinities of the antibodies for these antigens. Measured cross-reactions can frequently be reduced to zero in the most important concentration ranges thereby enabling one to perform assays upon unpurified materials which other wise would not be possible. Limitations of the method are discussed.

Androstenedione↗
PubMed1979

The influence of sar1 ala8 angiotensin II (saralasin) on plasma aldosterone in hypertensive patients.

The effect of a 4-hour infusion of the angiotensin II analogue sar1 ala8 angiotensin II (saralasin) on plasma aldosterone concentration (PAC) was assessed in relation to plasma renin activity (PRA) in 12 patients, both on normal sodium intake and after marked sodium depletion. On normal sodium intake the response of PAC to saralasin was variable; following sodium depletion saralasin induced a marked decrease in PAC in 11 of 12 patients. The extent of the change in PAC induced by saralasin correlated closely with log PRA. The data indicate that saralasin is also a competitive antagonist of the effect of the endogenous renin-angiotensin system (RAS) on the adrenal cortex, with agonistic activity appearing at low levels of PRA. The effect of sodium depletion on AC appears to be mediated to a major degree by the RAS.

Adrenal Cortex↗
PubMed1978

Chemiluminescence-linked immunoassay.

Covalent complexes of a chemiluminescent compound (a luminol derivative), protein and a steroidal hapten have been used as a labelled antigen in a way analogous to the radioactive label in radioimmunoassay. The antibody-bound complex emits light when treated with hydrogen peroxide and copper acetate at high pH. The chemiluminescent complex bound to antibody can be displaced by free steroid to produce a standard curve in a way analogous to radioimmunoassay.

Animals↗
PubMed1977

Reevaluation of triethers as markers for triglycerides during gastric emptying.

The validity of using triethers as markers for triglycerides during gastric emptying was investigated. Rats were given a lipid mixture containing [75Se]triether plus [131I]triolein or [3H]triether plus [14C]triolein intragastrically. Similar studies were performed on humans using a homogenized test meal to which was added [75Se]triether plus corn oil. Analysis of gastric contents at various time intervals after administration of the test meal did not show evidence of separation of triglyceride and triether in the stomach. It is discussed that the disappointing results of other workers using [3H]triether may be due to an artifact associated with instability of the tritium-to-triether bond in the preparation used.

Animals↗
PubMed1976

Specificity of immunoassays. I. Effect of plasma proteins on the specificity of steroid immunoassay.

The theory of the measurement of the specificity of antigen binding by antibodies is reviewed. The specificity of steroid immunoassay has been investigated using a new solid phase radioimmunoassay system. The effects of plasma proteins on the specificity of the immunoassays have been tested. The methods used and the conclusions reached have been tested with homogeneous antibodies in order to simplify the interpretation of the results obtained. A new criterium of antibody homogeneity is proposed. The importance of correcting all results accurately for "non-specific binding" is emphasised. A new method for plotting radioimmunoassay standard curves is presented.

Aldosterone↗
PubMed1975

The dependence of the blood to brain passage of radioactive sodium on blood pressure and temperature.

Brain sodium uptake (BSU) was calculated from estimated radioactivities of brain and blood, collected from rats which were given [24Na]sodium chloride 30 min and [22Na]sodium chloride 1 min before killing. The calculated BSU values, when plotted against the average blood pressure of the animal during the survival time of 30 min, showed a linear dependence of BSU on blood pressure. In another series of animals, in which in addition to variation of the blood pressure as in the former series, the brain was cooled to 15 degrees C, the resulting regression line showed the same slope, but a significantly lower intercept than at normal temperature. The results indicate the existence of a blood pressure-dependent component of sodium passage, reflecting the exchange of fluid at the blood-brain interface as governed by the Starling hypothesis, and an additional component which being temperature dependent, presumably constitutes an active transport mechanism.

Animals↗
PubMed1975

Estimation of plasma testosterone without extraction and chromatography.

A new radioimmunoassay for plasma testosterone in human blood plasma is described. The assay is performed directly upon the plasma without extraction and purification of the testosterone. Antibodies to testosterone-7alpha-carboxyethyl thioether-bovine serum albumin are used and data concerning the specificity of these antibodies are given.

Animals↗
PubMed1975

A new cocktail for liquid scintillation counting of aqueous radioimmunoassay-samples.

The aim of this investigation was to find a scintillation mixture for counting up to 1 ml of plasma. We succeeded in obtaining a mixture of xylene/Triton X-100/mono- and di-butylphosphate, and called it Plasmasol. The properties were ideal for radioimmunoassays of steroids. Good dissolving properties, high counting efficiency, absence of chemiluminescence and a good stability and reproducibility with respect to the disintegrations per minute were achieved. The cost was only 25% of the commercially available ready-to-use liquid scintillation mixtures, with which a comparison was made.

Blood↗