IMMUNOASSAY OF PROTEIN AND PEPTIDE HORMONES

Anterior pituitary hormones: development of a bioassay leading to the discovery of prolactin

This essay looks at the historical significance of an APS classic paper that is freely available online:

Riddle O, Bates RW, and Dykshorn SW. The preparation, identification and assay of prolactin–a hormone of the anterior pituitary. Am J Physiol 105: 191—216, 1933 ( http://ajplegacy.physiology.org/cgi/reprint/105/1/191 ).

Changes in serum immunoreactive and bioactive growth hormone concentrations in boys with advancing puberty and in response to a 20-hour estradiol infusion

Acceleration of linear growth during puberty is associated with increased GH secretion, although the relationship between growth and GH is complex. As GH exists as a family of isoforms, some of which may not be identified by immunoassay, there may be alterations in isoform secretion during pubertal maturation that result in increased growth. The changes in serum immunoreactive and bioactive GH concentrations across pubertal maturation were determined in 30 boys, aged 6.5-19.3 yr, with idiopathic short stature or constitutional delay of adolescence. Data were grouped as follows: 1) 6 prepubertal boys with bone age 7 yr or less; 2) 5 prepubertal boys with bone age of more than 7 yr, 3) 10 boys in early puberty; 4) 9 boys with mid- to late puberty. Blood was obtained every 20 min from 2000-0800 h. An equal aliquot of each serum sample was pooled for determination of GH by bio- and immunoassays. The mean serum immunoreactive GH concentration increased from 2.1 +/- 0.3, 1.8 +/- 0.3, and 2.9 +/- 0.5 micrograms/L in groups 1, 2, and 3, respectively, to a peak of 4.6 +/- 0.7 micrograms/L in group 4 (P < 0.05 vs. groups 1-3). The mean serum GH bioactivity was 48 +/- 13 micrograms/L in group 1 and declined to 39 +/- 8 and 31 +/- 3 micrograms/L in groups 2 and 3, increasing to a maximum of 64 +/- 15 micrograms/L in group 4 (P < 0.05 vs. group 3). The ratio of bioactive to immunoreactive GH suggests that the biopotencies of secreted isoforms do not increase during pubertal maturation. The role of E2 in increasing GH secretion was characterized in 8 additional early pubertal boys. Each boy received a saline infusion from 1000-0800 h, followed 1 week later by an infusion of E2 at 4.6 nmol/m2.h. Blood was obtained every 15 min from 2200-0800 h for GH and LH and every 60 min for E2 and testosterone. An equal aliquot of each overnight serum sample was pooled for insulin-like growth factor I (IGF-I) and GH by immuno- and bioassays. The mean serum LH concentration decreased from 5.0 +/- 0.9 to 2.3 +/- 0.6 IU/L (P < 0.01), and the E2 concentration increased from 22 +/- 4 to 81 +/- 26 pmol/L (P < 0.01) during saline and E2 infusions, respectively. Mean serum GH concentrations as measured by immunoassay were similar during both infusions (6.6 +/- 1.4 vs. 9.7 +/- 2.1 micrograms/L; saline vs. E2 infusion, respectively). In contrast, the mean serum GH concentration, as measured by bioassay, decreased from 48 +/- 10 micrograms/L during saline infusion to 16 +/- 3 micrograms/L during E2 infusion (P < 0.05). The mean serum IGF-I concentration also decreased significantly from 116 +/- 17 to 93 +/- 15 micrograms/L (saline vs. E2 infusion, respectively; P < 0.05). Thus, although mean overnight serum GH concentrations increase in late puberty, whether measured by immuno- or bioassay, an acute increase in E2 produces an acute decline in serum GH bioactivity and a lesser decline in the serum IGF-I concentration. These unexpected changes indicate that E2 may affect pubertal growth and GH secretion in a complex or biphasic manner depending on the context in which it is administered.

Effect of prednisone on protein metabolism in Duchenne dystrophy

Prednisone improves strength in Duchenne dystrophy and changes the natural history of the disease. We studied the in vivo effects of prednisone (0.75 mg.kg-1.day-1) on muscle and whole body protein metabolism in six patients with Duchenne dystrophy and three patients with Becker dystrophy. Patients were admitted to the Clinical Research Center for study and consumed a constant flesh-free diet. Strength was measured by manual and quantitative muscle testing. Fractional muscle protein breakdown was estimated by the ratio of 3-methylhistidine to creatinine excretion determined in three consecutive 24-h urine collections. Whole body protein kinetics were studied in the postabsorptive state using a primed continuous infusion of L-[1-13C]leucine. Fractional muscle protein synthesis was determined from tracer incorporation into noncollagen muscle protein obtained by needle biopsy. After 6-8 wk of prednisone treatment, average muscle strength increased by 15% (P < 0.04), and 24-h creatinine excretion (an index of muscle mass) increased by 21% (P = 0.002). 3-Methylhistidine excretion decreased by 10%, but the change was not statistically significant. The ratio of 3-methylhistidine to creatinine excretion decreased by 26% (P < 0.04). Fractional muscle protein synthesis and whole body protein synthesis and breakdown did not change significantly. We conclude that the beneficial effect of prednisone on strength in Duchenne dystrophy appears to be associated with an increase in muscle mass, which may be mediated by inhibition of muscle proteolysis rather than stimulation of muscle protein synthesis.

Reduced short-term thermic effects of a meal in obese adolescent girls

Post-meal energy expenditure (TEM) was compared for 14 healthy obese (body fat = 45.3%, body mass index, BMI = 35.9 kg m-2) and 9 healthy nonobese (body fat = 20.7%, BMI = 17.8 kg m-2) adolescent girls. The test meal for both groups was a standard 3348.8-kJ, 0.473-1 chocolate milkshake of 15% protein (casein), 40% fat (polyunsaturated/saturated ratio = 0.05; 75 mg cholesterol) and 45% carbohydrate (lactose and sucrose). Glucose, insulin and resting energy expenditure (RMR) were measured at rest prior to meal consumption and 20, 40, 60, 90, and 120 min after the meal. Cumulative net TEM was calculated as the integrated area under the TEM curve with RMR as baseline. Reliability was assessed by retesting 4 subjects, and a placebo effect was tested by administering a flavored energy-free drink. Results indicated high reliability and no placebo effect. The meal resulted in a greater rise in insulin and glucose for the obese compared to the nonobese subjects (P < or = 0.05), and a significant TEM for both groups (P < or = 0.05). The cumulative TEM (W kg-1) was 61.9% greater for the nonobese (P < 0.01) when expressed relative to body mass, and 33.2% greater for the nonobese (P < or = 0.01) when expressed relative to the fat-free body mass. Expressed relative to the meal, the TEM was 25.5% less for the obese (P < 0.01). The data support an energy conservation hypothesis for obese female adolescents.

Angiotensin II receptors in the fowl aorta

In the domestic fowl, angiotensin II (ANG II) causes an in vivo depressor response and in vitro relaxation of aortic rings which appear to be a direct action of ANG II on the blood vessels. Thus, we determined whether binding sites specific to ANG II exist in the membrane fraction of the fowl aorta. The particulate fraction of aortas from adult female fowl, Gallus gallus, exhibits high specific binding to ANG II ligand. 125I-[Ile5]ANG II (0.5 nM) binding to the above fraction (30 micrograms protein) in 50 mM Tris (pH 7.2), 10 mM MgCl2, and 0.2% bovine serum albumin at 12 degrees (1) is rapid, saturable, and reversible; (2) increases as a function of ligand or membrane concentration, time, and temperature; and (3) optimally fits to a two-site (high and low affinity) model. The equilibrium dissociation constant (0.15 +/- 0.03 nM) and binding site concentration (28.7 +/- 8.1 fmol/mg protein) of the high affinity site as well as association (0.055 nM-1.min-1) and dissociation (0.0122 min-1) rate constants are similar to those of mammalian vascular ANG II receptors. Both 125I-[Ile5]ANG II and 125I-[Val5]ANG II are competitively displaced by unlabeled ANG II. These results suggest that specific ANG II receptors exist in the fowl aorta.

Specific, high-affinity bradykinin binding by purified porcine kidney post-proline cleaving enzyme

Post-proline cleaving enzyme (PPCE) was purified from porcine kidney cytosol. The purified enzyme bound [125I-Tyr5]-bradykinin but neither [125I-Tyr1]-kallidin nor [125I-Tyr8]-bradykinin. Scatchard analysis of the data was consistent with a single class of binding sites with a Kassoc = 1.3 +/- 0.1 X 10(8) M-1. The optimal pH for [125I-Tyr5]-bradykinin binding was 6.8. The specificity of binding was evaluated with sixty-seven bradykinin analogs. The catalytic activity of the enzyme was measured with N-benzyloxycarbonyl-Gly-Pro-methylcoumarinyl-7-amide (Z-Gly-Pro-MCA). The optimal pH for hydrolysis of this substrate was broad and centered at 8.3. The apparent Km and Vmax were obtained from Lineweaver and Burk plots and were 4.8 +/- 0.4 X 10(-5) M and 42 +/- 5 mumoles X mg-1 X min-1 respectively. The IC50 values for bradykinin, diisopropylfluorophosphate (DFP), and N-benzyloxycarbonyl-Pro-Prolinal (Z-Pro-Prolinal) to inhibit Z-Gly-Pro-MCA hydrolysis by PPCE were 5.9 +/- 1.4 X 10(-7) M, 8.8 +/- 3.1 X 10(-7) and 7.9 +/- 0.3 X 10(-9) M respectively. Corresponding values for inhibition of [125I-Tyr5]-bradykinin binding by PPCE were 5.1 +/- 2.3 X 10(-9) M, 1.2 +/- 0.3 X 10(-6) M and 1.4 +/- 0.6 X 10(-8) M.

The effects of age on substrate depletion and hormonal responses during submaximal exercise in hamsters

Senescent hamsters display a marked reduction in volume of voluntary running. The purpose of this study was to determine whether age differences exist in the pattern of fuel utilization during submaximal exercise, which may account for the reduction in voluntary running. Further, we determined the effects of age on muscle oxidative capacity to assess its relationship to endurance performance in senescent hamsters. Depletion of carbohydrate and lipid content of skeletal muscle and liver, and changes in blood concentration of various hormones and substrates during one hour of exercise at 60 percent of VO2 max served to assess age effects on utilization of metabolic substrates. Exercise produced equivalent depletion of muscle glycogen and similar rise in plasma free fatty acids in young and old hamsters. No exercise effects on skeletal muscle triglyceride concentration or on plasma glycerol, glucagon or catecholamine concentrations were noted. With palmitoyl carnitine as substrate (but not with pyruvate) State 3 respiration of cardiac and skeletal muscle homogenates was lower in old compared to young hamsters. Although old hamsters have a reduced capacity to oxidize lipids in vitro, few age differences in fuel use are evident in vivo during submaximal exercise. Thus, these minor age differences in substrate utilization do not likely account for the substantial reduction in the levels of spontaneous running in senescent hamsters.

Interaction of thyrotrophin releasing hormone and the enkephalin analogue DAMME on pituitary hormone secretion

Because TRH counteracts the inhibitory effect of opiate peptides on LH secretion in cultured cells from normal pituitaries, six normal postmenopausal women were studied to determine whether TRH interacts in vivo with opioid peptides in the regulation of pituitary hormone secretion. At two different times a constant 3 h infusion of either saline or TRH (5 micrograms/min) was initiated. At 60 min a 250 micrograms bolus of the opiate agonist peptide D-Ala2-MePhe4-met-enkephalin-0-ol (DAMME) was injected in one of the two saline and TRH infusion tests. The four treatments, i.e. saline infusion alone, saline infusion with a DAMME bolus, TRH infusion alone; and TRH infusion with DAMME bolus were given at random with an interval of at least 7 d. Blood samples were taken every 15 min during the 3 h study. DAMME induced a significant fall (P less than 0.05) in serum LH (from 35 +/- 8.5 to 18.3 +/- 5.1 mIU/ml) (mean +/- SEM) without significantly affecting FSH levels (from 29 +/- 11.2 to 26.9 +/- 12.4 mIU/ml). These changes were not antagonized by the continuous infusion of TRH. PRL had a monophasic response pattern to continuous isolated TRH infusion; the basal levels increased from 4.2 +/- 1.2 to 24.5 +/- 6.8 ng/ml at 30 min and then slowly decreased with a plateau from 90 min until the end of the study. DAMME administration at 60 min induced a significant second peak of PRL secretion (44 +/- 6.5 ng/ml) 30 min later (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related dose response of selected reproductive parameters to acute cadmium chloride exposure in the male Long-Evans rat

Groups of male Long-Evans rats 30, 50, or 70 d old were injected subcutaneously (sc) with a single dose of 0, 5.5, 11.5, or 24.6 mumol Cd/kg as cadmium chloride. All animals were killed 60 d after treatment. At 2 h prior to sacrifice, the rats were injected sc with 100 IU human chorionic gonadotrophin (hCG) to maximally stimulate serum testosterone concentrations. After sacrifice the testes, epididymides and seminal vesicles were removed and weighed. Cardiac blood was taken, and serum concentrations of testosterone (sT) and follicle-stimulating hormone (sFSH) were determined. Sperm concentration in luminal fluid collected from the vas deferens was determined. Significant (p less than 0.01) dose-dependent effects for all measured reproductive parameters were noted in the 70-d-old animals, while no effects were seen in the 30- or 50-d-old rats in either seminal vesicles weight or hCG-stimulated sT concentration. In the absence of significant (p greater than 0.05) changes in body weight gain, effects were seen in testes and epididymides weight, sperm concentration, and sFSH in the 70-d-old rats at Cd doses that were lower than those necessary to bring about similar changes in the 30- or 50-d-old animals. The sensitive indicators of Cd exposure in all age groups were testicular weight greater than epididymal weight greater than vas deferens sperm concentration greater than sFSH concentration. Seminal vesicle weight and sT concentration were found to be the least sensitive. Regression analyses indicated a significant interaction of age with dose; the 70-d-old rats required 30-61% less Cd/kg to cause a 50% change in a measured parameter than did the 30-d-old animals, while the 50-d-old rats required 15-47% less.

Assessment of the male reproductive system in the preweanling rat following Mn3O4 exposure

Long-Evans rat pups were dosed orally from birth to 21 d with particulate Mn3O4 to obtain a daily dose of 0, 71, or 214 micrograms Mn/body weight . d. Assessments of the hypothalamic, pituitary, or testicular functions were determined by measuring the endogenous or stimulated serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and/or testosterone (T) at 21 or 28 d of age. Body, testes, and seminal vesicles weight and tissue concentrations of Mn were also evaluated. Only slight Mn treatment effects were seen in body and testes weights. No effects were seen either on unstimulated or stimulated FSH or LH serum concentrations. Although no Mn treatment effects were seen on endogenous or 2 h human chorionic gonadotropin (hCG) stimulate serum T concentrations, there was a reduction in the serum T following 7 d of hCG stimulation. The hypothalamic Mn concentrations in animals with these reproductive effects were three times those where alterations in the dopaminergic pathway have been reported. However, no indication of hypothalamic or pituitary malfunction was found. These results suggest that the site of Mn damage that causes depression of sustained serum T concentration is in the testicular Leydig cell.

Effects of chronic manganese (Mn3O4) exposure on selected reproductive parameters in rats

Long-Evans rats were chronically exposed to dietary Mn3O4 beginning on d 1 of gestation and continuing through 224 d of age. Dietary concentrations of Mn, as Mn3O4, were 350, 1050, and 3500 ppm and were applied in either a normal Fe 240 ppm) or a low-Fe (20 ppm) basal diet. General toxic effects were apparent in young animals at a dietary dose of 3500 ppm Mn and were enhanced by concomitant Fe deficiency. Fertility was reduced in the group exposed to 3500 ppm Mn with a diet containing sufficient Fe. Male reproductive development was delayed by Mn treatment, as measured by testes weight, sperm count, and serum follicle-stimulating hormone and testosterone concentrations.

Measurement of urinary kallikrein activity. Species differences in kinin production

A sensitive, specific radioimmunoassay for kinins has been developed, which is able to detect 1.5 pg bradykinin or 3 pg lysyl-bradykinin (Lys-bradykinin). 50% displacement in the standard curve was obtained with 10 pg bradykinin or 15 pg Lys-bradykinin in 0.6-ml incubates. The antisera, raised against bradykinin, recognized well Lys-bradykinin and methionyl-lysyl-bradykinin (Met-lys-Bradykinin), but cross-reacted 0.4% or less with bradykinin fragments. Kininogen cross-reacted only 0.2%. The radioimmunoassay and kininogen from several species were used in the measurement of human and rat urinary kallikrein activity. The peptide generated by hydrolysis of the substrates by rat or human urines was characterized by radioimmunoassay in two different systems: polyacrylamide gel electrophoresis and carboxymethyl cellulose chromatography. Both urines did not produce the same kinin: the kinin produced by human urine migrated like Lys-bradykinin, whereas the kinin produced by rat urine migrated like bradykinin. This gives evidence of differences in the specificity between kinin-forming enzymes in rat and human urines.

Steroids as potential modulators of angiotensin receptors in bovine adrenal glomerulosa and kidney

To test the hypothesis that there is feedback inhibition of adrenal angiotensin receptors by substances released in response to the peptides, we measured binding of labeled angiotensins in the presence of various steroids. Approximately half of the 70 steroids tested inhibited binding of labeled angiotensin II and III to intact and broken cells from bovine adrenal glomerulosa and kidney, but the concentrations required for inhibition were relatively high. The most potent inhibitors were 3 alpha, 5 beta tetrahydroaldosterone and tetrahydrodeoxycorticosterone (ID50 = 8 x 10-5 M). Kinetic analysis showed that inhibition was mostly competitive. among steroids whose reduced congeners were tested, potency increased in the sequence: parent steroid less than 5 alpha dihydroderivative less than 5 beta dihydro derivative less than 3 alpha, 5 beta tetrahydro-derivative. Tetrahydrodeoxycorticosterone inhibited aldosteronogenesis by intact cells at concentrations that inhibited angiotensin binding. Steroids differentially inhibited binding of labeled angiotensins in II and III, and discriminated between receptors in adrenal glomerulosa and kidney. The results provide additional evidence for heterogeneity of angiotensin receptors, and lead to the prediction that any normal or pathological inhibition of angiotensin receptors by steroids will be mediated by reduced derivatives.

Radioiodination of human growth hormone with characterization and minimization of the commonly defined "damaged products"

The radioiodination and chromatographic purification of human growth hormone (hGH) has been studied in order to better define and control the so-called "preparation damage", which is often a cause of interferences, loss in specific activity and sensitivity, misclassification errors in radioligand assays, and a source of misinterpretation when the tracer is used in receptors or in vivo studies. A series of labelings and false labelings, with and without protein carrier in the buffer used for Sephadex purification, indicate that the "preparation damage" peak is made up of two components: aggregated 125I-hGH and BSA-carried radioactivity. The former can be minimized by the use of recently extracted non-lyophilized hGH, and the latter by enzymatic labeling. Both components can be better resolved, and thus eliminated, when Sephadex G-100 is employed rather than G-75.

Angiotensin receptors in bovine umbilical artery and their inhibition by nonsteroidal anti-inflammatory drugs

1 The contractile effect of angiotensin II on bovine isolated umbilical arteries was compared to [125I]-angiotensin II binding by a subcellular fraction of that tissue. The ED50 of angiotensin was 3.1 +/- 2.8 x 10(-8) M, while the apparent dissociation constant was 4.9 +/- 1.6 x 10(-9) M. 2 Indomethacin, meclofenamate, and eicosatetraynoic acid inhibited angiotensin-induced contraction of the isolated artery and binding to a particulate fraction at comparable doses. Phenylbutazone inhibited [125I]-angiotensin binding more potently than the response. Inhibition by the first three agents was noncompetitive, whereas phenylbutazone inhibited competitively. 3 Inhibition of angiotensin activity by the nonsteroidal anti-inflammatory agents was not specific. These agents also inhibited 5-hydroxytryptamine-induced contraction, but not the contraction induced by KCl. 4 The data suggest that the angiotensin binding sites studied include receptors that mediate contraction of the isolated umbilical artery. Our data also indicate that indomethacin, meclofenamate, eicosatetraynoic acid and phenylbutazone are capable of direct inhibitory effects on receptors, as well as their well-known synthetase actions. The net effect of these activities will determine the change these agents cause in tissue responses to hormones.

Aspects of bradykinin radioimmunoassay

125I-derivatives of Tyr1-kallidin, Tyr5-bradykinin, and Tyr8-bradykinin were prepared. A technique for purification of the monoiodinated derivative is described. Bradykinin antisera were tested for their ability to bind the mono-iodinated analogues. Each antiserum had a characteristic preference for one of the three labeled peptides. The sensitivity of each antiserum was greatest when it was used with the label bound most avidly by that antiserum. The specificity of an antiserum was not changed by varying the labeled analogue. Some common enzyme inhibitors had significant effects on the antigen-antibody reactions. Lecithin interfered with the reaction between antiserum and Tyr1-kallidin. The data suggest that antisera for bradykinin radioimmunoassay be tested with several radioactive iodobradykinins to maximize their usefulness. In addition, enzyme inhibitors used to stabilize levels of kinins in biological fluids should be tested for their effects on the assay. Biologic samples rich in lipid may give spurious radioimmunoassay results unless they are freed of those phospholipids that can bind labeled and unlabeled peptides.

An accurate determination of human growth hormone content in different pituitary extracts, using a radioimmunoassay with polyacrylamide gel electrophoresis as a bound-free separation system

Human growth hormone was extrated and purified according to the method of Roos et al. (Roos, P., Fevold, H.R. and Gemzell, C.A. (1963) Biochim. Biophys. Acta 74, 525). A first control of its purification and integrity was performed through molecular weight determination by gel filtration on Sephadex G-100 and on polyacrylamide gel electrophoresis (PAGE). Its biological activity was confirmed by the growth promoted in non-hypophysectomized rats at plateau. The main object, however, was the setting up of accurate, reproducible method tha could furnish the more absolute and comparable values of radioimmunoassayable HGH content in perfect agreement with the results obtained by other laboratories. This was accomplished through a radioimmunoassay system that uses HGH labelled with 125I, where separation of the bound from the free antigen is achieved on polyacrylamide gel electrophoresis, by a modification introduced in the original method of Davis. The resulting values, extremely close to that stated by the KABI-Laboratories (Stockolm), though obtained in quite different conditions of incubation, antibody concentration and with no use of second antibody, represent a confident approach to a comparable measure of this hormone in extracts, which can also be applied to plasma determinations.

Attachment of thioglycosides to proteins: enhancement of liver membrane binding

Thioglycosides of D-galactose, D-glucose, N-acetyl-D-glucosamine, and D-mannose were covalently attached to Aspergillus oryzae alpha-amylase, hen's eggs lysozyme, and bovine serum albumin by amidination, diazo coupling, and amide formation. The binding of the newly formed glycoproteins (neoglycoproteins) to rabbit liver membranes was measured, using asialoorosomucoid as a reference. Attachment of D-galactosides by any of the three methods enhanced binding by several orders of magnitude. Coupling of a comparable number of D-mannosides or N-acetyl-D-glucosaminides had little or no effect. Attachment of D-glucosides also enhanced binding but to a variable extent depending on the method of attachment. Thus, the behavior of neoglycoproteins toward rabbit liver membranes closely paralleled that of serum glycoproteins (Ashwell and Morell, 1974) with respect to sugar specificity.

Parathyroid function tests with EDTA infusions in infancy and childhood

To determine the functional capabilities of the parathyroid glands, 17 EDTA infusions were given to 11 children (ages 1 month to 12 years) and to two mothers of four of the children. Serum ionized Ca fell from 4.1 mg/dl to 3.4 mg/dl. Excessive parathyroid hormone responses were elicited during seven of nine EDTA infusions in five children and in one adult with hypophosphatemic rickets, during the active phase of rickets. In four of five subjects with problems related to hypercalcemia, borderline low or undetectable PTH responses were elicited. Three relatively normal PTH responses were obtained, two in an infant after phosphate-induced hypocalcemic tetany was corrected, and one in a child with a malabsorption syndrome. The renal tubular reabsorption of phosphate was inversely related and the urinary cyclic AMP excretion was positively related to the PTH response. Thus EDTA infusions in infants and children might be useful in the identification of hyper-, normo-, or hypoparathyroid states and would be of value in defining the functional condition of the parathyroid glands in children with deranged Ca or P metabolism.

Immunological and biophysical properties of hepatitis B antigen labeled by the chloramine-T and by the lactoperoxidase methods

Optimal conditions were sought for the radiolabeling of microgram quantities of hepatitis B surface antigen (HBs Ag) employing the chloramine-T or lactoperoxidase iodination procedures. Preparations of HBsAg labeled by these procedures are referred to as chloramine-T preparations and lactoperoxidase preparations, respectively. Labeled HBsAg having specific activities between 10-20 muCi/mug were found to display the greatest degree of sensitivity for unlabeled HBsAg and for anti-HBs using a double-antibody radioimmunoassay (RIA-DA). Increasing the specific activity above this level redulted in a decreased affinity of labeled 1251-HBs Ag for anti-HBs, indicating that soluble antigenic alterations had developed. At equivalent specific activities, chloramine-T preparations competed less effectively for unlabeled HBs Ag than lactoperoxidase preparations, and anti-HBs endpoint titers were slightly reduced, especially among preparations of high specific activity (greater than or equal to 65 muCi/mug). Chloramine-T preparations of HBs Ag (sp. act. 15--30 muCi/mug) showed essentially no antigenic deterioration over a 2-month period at minus 196 degrees C or minus 70 degrees C. Utilization of optimally labeled 1251-HBs Ag has increased the sensitivity of the RIA-DA for unlabeled HBs Ag 30-fold to a level below 1 ng/ml and enhanced antiamine-T method revealed that only the most acidic population was labeled (pH 3.75+/-0.5). In contrast, six antigenic components with distinct pI values ranging from 3.7 to 5.2 were detected by RIA-DA in both unlabeled HBs ag and in the chloramine-T preparation. This indicated that the chloramine-T method did not radically change the relative number or charge of each of the pI populations present in purified preparations of HBs Ag. Analysis of HBs Ag iodinated by the lactoperoxidase procedure revealed the presence of three of four populations of particles with pI values ranging from 3.9 to 4.5, suggesting that this procedure labels HBs Ag more uniformly.

Radioimmunoassay: review of basic principles

The development of radioimmunoassay by the late Solomon A. Berson and Rosalyn S. Yalow during the late 1950s represents a milestone in the history of the application of radionuclide methodology to biology and to medical investigation and practice. The method offers a technique to assay materials otherwise unmeasureable or detectable only with difficulty. Radioimmunoassay is based upon the competition between labeled and unlabeled antigen for specific antibody sites, forming antigen-antibody complexes. This reaction is described by the expression see journal for formula. At equilibirum, the radioactive complex (bound) is separated from the radioactive antigen (free). The B/F ratio is dependent upon the amount of nonradioactive antigen. Antigen concentration in unknown samples is determined by comparing the B/F ratio to the B/F ratios obtained by incubating varying amounts of known nonradioactive antigen with the same amount of antibody as in the unknown sample under similar assay conditions. Sensitivity of the order of 10-12 moles/liter may be achieved through the preparation and use of a labeled antigen of high specific activity and the production and selection of antisera with appropriately high affinity constants. Specificity is dependent upon the ability of the antiserum to recognize subtle structural features of the antigen molecule. The ability to conveniently assay large numbers of samples with good precision has led to the application of this technique to quantitate substances (such as steroids) already measurable but by more cumbersome methods. Since the initial description of competitive binding radioassay techniques, there have been numerous contributions to its further development, refinement, and application. This article reviews the conception and development of this invaluable contribution to our understanding of health and disease.

Mutations affecting the structure of hypoxanthine: guanine phosphoribosyltransferase in cultured Chinese hamster cells

14 Clones resistant to 8-azaguanine, isolated from mutagenically treated cultured cells from Chinese hamsters, were tested for loss of enzymic and immunological activities of hypoxanthine: guanine phosphoribosyltransferase. Three of the clones had no enzymic activity but reacted strongly with antiserum prepared against the enzyme (CRM(+)), indicating the presence of a defective enzyme protein, probably caused by a mutation in its structural gene. The other 11 mutants had little or no enzymic or immunologic activity. Revertant clones with positive enzymic and crossreacting immunologic activities were derived from both classes of mutants. The antiserum has been used for rapid purification of the phosphoribosyltransferase from Chinese hamster cells by immunoadsorbant affinity chromatography.

Stimulation of adenosine 3':5'-cyclic monophosphate accumulation in anterior pituitary gland in vitro by synthetic luteinizing hormone-releasing hormone

A near-maximal dose (20 ng/ml) of synthetic luteinizing hormone(LH)-releasing hormone/follicle-stimulating hormone(FSH)-releasing hormone added to incubated anterior pituitary tissue of male rats leads to concomitant increases of intracellular concentrations of adenosine 3':5'-monophosphate and of release of both LH and FSH. The stimulatory effect of LH-releasing hormone/FSH-releasing hormone is observed after a lag period of about 90 min and is progressive at later time intervals; a 3-fold stimulation of cAMP accumulation over control is seen after 210 min of incubation. Half-maximal stimulation of cAMP accumulation is observed between 0.1 and 1.0 ng/ml (0.1-1 nM) of LH-releasing hormone/FSH-releasing hormone. In the presence of 10 mM theophylline, the stimulatory effect of LH-releasing hormone/FSH-releasing hormone on cAMP accumulation is similar to that observed in the absence of the inhibitor of cyclic nucleotide phosphodiesterase, indicating that the releasing hormone exerts its effect by specific activation of adenylate cyclase in LH- and FSH-secreting cells rather than by inhibition of cyclic nucleotide phosphodiesterase. Since the release of growth hormone, thyrotropin, prolactin, and adrenocorticotropic hormone is not affected by LH-releasing hormone/FSH-releasing hormone, and since cAMP stimulates the release of all six adenohypophyseal hormones. the observed changes of cAMP concentrations indicate specific stimulation of adenylate cyclase activity in LH-and FSH-secreting cells of the adenohypophysis.

Mitotic and nonmitotic multiple-layered perfusion cultures

Cell types in addition to those previously described (Kruse et al. 1963. J. Nat. Cancer Inst. 31:109; Kruse and Miedema. 1965. J. Cell Biol. 27:273) were found to form multiple-layered cultures by perfusion-culture technique. Dense populations containing 43 x 10(6) embryonic rat muscle (NF-ER) cells, 23 x 10(6) diploid human tonsillar (NF-JAM) cells, 77 x 10(6) human pleural effusion isolate (RPMI 2650) cells, 35 x 10(6) embryonic diploid human lung (Flow 2000) cells, 21 x 10(6) bovine lung (FB4BM) cells, 108 x 10(6) bat lung (Tb1Lu) cells, and 81 x 10(6) SV-40 virus-transformed embryonic diploid human lung (WI-38VA13A) cells were obtained in 6-14 days from dilute inocula in T-60 or T-75 flasks; these were equivalent to about 4, 3, 3, 4, 2, 4, and eight monolayers, respectively. Perfusion of an NF-ER culture for 6 wk with medium plus 10% whole calf serum yielded a cell density equivalent to 12 monolayers (140 x 10(6) cells per T-75 flask). This culture exhibited random labeling of nuclei from bottom to top after pulsing for 90 min with thymidine-(3)H. Medium plus 0.1% serum maintained NF-JAM cultures at constant viable cell numbers with virtual absence of thymidine-(3)H labeling. Similar results were obtained with WI-38 cultures, but WI-38VA13A cells continued active DNA synthesis and mitosis in medium with 0.1% serum to form 16-20 layers of cells (191-239 x 10(6) cells per T-75 flask) in 27 days. WI-38VA13A cells ceased proliferation and became nonviable rapidly in serumless medium.

Radioimmunoassay of ACTH in plasma

Techniques are described in detail for a radioimmunoassay of plasma adrenocorticotropin (ACTH) that is capable of detecting hormone in unextracted normal human plasma at 1:5 dilution under the conditions described. The sensitivity of the assay is at the level of 1 mumug/ml (equivalent to 0.014 mU/100 ml). In normal subjects ACTH concentrations averaged 22 mumug/ml (equivalent to 0.308 mU/100 ml) plasma at 8-10 a.m. In a smaller group the concentrations averaged 9.6 mumug/ml (equivalent to 0.134 mU/100 ml) at 10-11 p.m. Although a circadian rhythm in normal subjects was not always well marked throughout the daytime hours, plasma ACTH usually fell to its lowest value in the late evening. In hospital patients who were not acutely ill, concentrations were infrequently above 100 mumug/ml in the morning and usually fell to significantly lower levels in the late evening. Severely ill hospital patients occasionally exhibited a.m. concentrations above 200 mumug/ml. In a group of subjects showing frequent spiking of plasma 17-OHCS concentrations throughout the day parallel spiking of plasma ACTH as well was generally observed.Metyrapone produced marked increases in plasma ACTH within 24 hr in all cases and generally within 3-6 hr except when started late in the day. Dexamethasone brought about a persistent reduction in plasma ACTH in a patient under continued treatment with metyrapone.Hypoglycemia, electroshock, surgery under general anesthesia, histalog and vasopressin administration were usually followed by significant increases in plasma ACTH concentration. Prior administration of dexamethasone blocked the response to hypoglycemia. Marked elevations in plasma ACTH were observed in patients with adrenal insufficiency off steroid therapy, in Cushing's disease after adrenalectomy even in the presence of persistent hypercortisolemia, and in some untreated patients with Cushing's disease. Umbilical cord blood contained higher plasma ACTH concentrations than maternal blood at delivery in seven of eight cases. After suppression of ACTH secretion by dexamethasone or cortisol. ACTH disappeared from plasma with half-times ranging from 22 min to 30 min in three cases studied.