Fold Increase In Sensitivity Research Articles

Mineralocorticoid radioreceptor assay: Application to adrenal-regeneration hypertension

Identification of unknown hormones has traditionally involved utilizing a bioassay to initially detect the hormone and to follow its purification. However, radioreceptor assays may be more useful for this purpose by offering greater sensitivity and precision. A mineralocorticoid radioreceptor assay has been developed for use in conjunction with chromatographic separation of a urinary extract to detect the presence of unknown urinary mineralocorticoids. This assay utilizes competition of the unknown steroid and aldosterone for rat renal cytoplasmic mineralocorticoid receptors to enable mineralocorticoid quantitation in aldosterone equivalents. This assay provides 100 fold increase in sensitivity and a significant increase in precision over the commonly used adrenalectomized rat bioassay. The mineralocorticoid radioreceptor assay has been utilized to assay mineralocorticoid activity in chromatographic fractions of a urinary extract from rats with regenerating adrenals. A large area of mineralocorticoid radioreceptor activity has been identified which possibly represents an unknown mineralocorticoid contributing to the etiology of adrenal regeneration hypertension. This assay is applicable to other syndromes of postulated unknown mineralocorticoid excess, such as human low renin essential hypertension. In addition, similar radioreceptor assays are applicable for the initial detection of any type of hormone activity and for the subsequent purification and identification of this hormone.

Aspects of opiate dependence in the myenteric plexus of the guinea-pig

Myenteric plexus-longitudinal muscle strips prepared from tolerant/dependent guinea-pigs and continuously exposed to normorphine, display a contracture upon naloxone challenge. This phenomenon represents a sign of abstinence. Removal of the opiate by extensive washing resulted in the failure of naloxone to induce the abstinence sign, while the plexus still displayed considerable, although reduced, tolerance to morphine. Reexposure of withdrawn preparations to normorphine reinduced the ability to display the abstinence sign. Highly tolerant preparations exhibited a 30 fold increase in sensitivity to serotonin and prostaglandin E 1 when tested a few minutes after naloxone-precipitated withdrawal. Supersensitivity rapidly declined when normorphine was washed off the preparation, while reincubation of withdrawn tissues with the opiate resulted in reinduction of supersensitivity. The data confirms a close relationship between a state of tolerance and dependence (including display of the abstinence sign) and supersensitivity to putative neurotransmitters or neuromodulators, becoming evident following administration of naloxone.

Determination of Serum Iron and Iron Binding Capacity Using 4-(2-Pyridylazo) Resorcinol (Par)

Abstract Procedures are described for the determination of serum iron and iron binding capacity using the chromogenic reagent 4-(2-pyridylazo) resorcinol (PAR). The high molar absorptivity of the iron (II) PAR complex makes possible an approximate two fold increase in sensitivity over previous methods. The described procedures have few interferences, and give linear results for samples containing 0 – 750 μg/dl of iron.

The eye of Anoplognathus (Coleoptera, Scarabaeidae)

The night flying scarabaeid beetle Anoplognathus provides an example of a dark-adapted clear-zone compound eye in which rays from a distant point source, entering by a large patch of facets, are imperfectly focused upon the receptor layer. The optical system of the eye was investigated by six methods, all of which give similar results: (1) ray tracing through structures of known refractive index, (2) measurement of visual fields of single receptors, (3) measurement of the divergence of eyeshine, and (4) of the optomotor response to stripes of decreasing width, and (5) by direct observation of distribution of light within the eye. Finally (6) anatomically there is no single plane upon which an image could be focused. In each ommatidium, beneath the thick cornea, with its short corneal cone, lies a non-homogeneous crystalline cone (range of r. i. 1.442-1.365) that is significant in partially focusing rays across the wide clear zone (340 μm) in the dark-adapted eye. On the proximal side of the clear zone the rhabdoms form 7-lobed columns, isolated from each other over half their length by a tracheal tapetum. In the light-adapted eye the cone cells extend to form a crystalline tract (70-90 μm long) which is sur­rounded by dense pigment, and the optical path across the clear zone is completed by retinula cell columns that are of higher density than the surrounding cells. Pigment movement upon adaptation takes about 10 min to complete. Dark adaptation can be induced only at night on account of a strong diurnal rhythm. Eyeshine can be seen in the dark-adapted eye so long as the distal pig­ment leaves free the tips of the crystalline cones. Eyeshine falls to 50% at an angle of 12° from the direction of a parallel beam shining on the eye, as is consistent with a partial focus in which the distribution of light on the receptor layer is 18°-24° wide at the 50% contour. This distribution was confirmed by direct examination of the inside of the eye and by measure­ment of receptor fields as follows. The mean acceptance angle for 13 light-adapted units was 12.57° ± 1.97° s. d. and that of 10 dark-adapted ones 20.3° ± 3.36° s. d. The sensi­tivity to a point source on axis is increased at least 1000 fold by dark adaptation. Rays traced through a scale drawing of the eye, with refractive index measured for each component, show how the eye as a whole comes to be partially focused, and predicts an acceptance angle of 12° in the light-adapted and 20°-24° in the dark-adapted eye. In optomotor experiments dark-adapted Anoplognathus does not respond to stripes narrower than 18° repeat period, but light-adapted beetles respond down to 10°. The optomotor experiments also show a 1000 fold increase in sensitivity when dark-adapted at night. The eye has poor acuity that goes with wide visual fields of its recep­tors, and this is surprising when other excellently focused clear zone eyes are known. A possible compensation for the poor acuity is that the aperture of the eye can be larger, so that sensitivity although only to large objects, is that much increased.

Acetone as solvent in flame-photometric determination of lithium in serum

The effect of some water miscible organic solvents on the flame photometric emission of Li is discussed. A simple procedure is described with acetone as diluting solution giving a ten to twenty fold increase in sensitivity.

A bio-assay for parathyroid hormone in mice.

A bio-assay for parathyroid hormone based on the prevention of fall of plasma calcium in thyroparathyrocauterized mice has been developed. The assay is similar to the Munson procedure in rats with the advantage that it is cheaper, simpler, and has an approximate 10- fold increase in sensitivity over the rat assay. The routine log dose response to standard injections of parathyroid hormone is linear from 0.5 to 20 U and an average lambda of 0.27 is obtained. It has been in routine use in our laboratory for over 2 yr for the measurement of biologic extracts and for the monitoring of column and chromatographic procedures. (Endocrinology 81: 67, 1967)

Studies on the spectrophotometric determination of phosphorus using hydriodic acid as a reducing agent, and a proposed new method applicable to serum and urine

1. 1. The determination of phosphorus as molybdenum blue using HI as the reducing agent of phosphomolybdic acid has been investigated. 2. 2. The reaction is found to be dependent on temperature and also on the concentrations of molybdate, potassium iodide, and acid employed. Optimal conditions for each of these variables have been evaluated and described. 3. 3. The use of HI as reductant results in a 2 1 2 fold increase in sensitivity when compared with amino-naphthol-sulphonic acid. In addition, very stable colours are produced which conform to Beer's law. 4. 4. A method of estimation of serum and urine phosphorus which take advantage of these features is presented which requires 0.5 ml serum to perform. This volume may be still further reduced if necessary. 5. 5. The described method was found to be highly reproducible, and recoveries of P added to serum fell between 97–104%. The range of serum phosphorus concentration in 52 healthy adults was found to be 3.3 mg% ± S.D. 0.51 mg%.

Use of I-131-labeled antigens in gel diffusion precipitate reactions.

Abstract I 131 -trace labeled proteins have found a variety of uses in immunologic studies. The present study describes the use of I 131 -trace labeled antigens in gel double diffusion precipitin reactions. With low concentrations of antigen and antibody, the immune aggregates in gel may not be grossly visible, yet they become evident by autoradiography of the gel medium when I 131 -trace labeled antigens are used. This resulted in a hundred fold increase in sensitivity of the technique.