Lymphocyte activation antigens permit early detection and discrimination between rejection and infection episodes.
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Antigens, CD↗
Biomedical subjects
M L Johnson
Publications and source records attributed to M L Johnson.
Consequences of neglecting the hemoglobin concentration on the determination of Adair binding constants.
It is commonly believed that the tetrameric Adair constants for oxygen binding to human hemoglobin can be evaluated from a single oxygenation experiment at 'high' hemoglobin concentration without considering the consequence of the presence of alpha beta dimers. We present examples which demonstrate that this is a very dangerous assumption. Without a knowledge of the complete oxygenation-linked dimer-tetramer association reaction (alpha beta Xi----(alpha beta)2Xj), it is impossible to predict a priori how high of a hemoglobin concentration would be required to make this assumption. Furthermore, without a knowledge of the complete oxygenation-linked dimer-tetramer association reaction, it is impossible to predict a priori the direction and magnitude of the systematic errors which are induced by making this assumption.
Calorimetry↗
Analysis of hemoglobin oxygenation from combined equilibrium and kinetic data. Is quaternary enhancement necessary?
An experimental approach based on four independent techniques, in which kinetic and equilibrium measurements of subunit assembly reactions are combined with concentration-dependent oxygen-binding curves, has previously been used to resolve parameters of the linkage system for human hemoglobin over a wide range of conditions [(G.K. Ackers and H.R. Halvorson, Proc. Natl. Acad. Sci. U.S.A. 71 (1974) 4312; F.C. Mills et al., Biochemistry 15 (1976) 1093; M.L. Johnson et al., Biochemistry 15 (1976) 5363). Throughout this extensive body of results it has been found that the affinity for binding oxygen to tetramers at the fourth step exceeds the mean affinity of dissociated dimers. The existence of this "quaternary enhancement" effect has recently been questioned by Gibson and Edelstein (J. Biol. Chem. 262 (1987) 516) and by Philo and Lary (J. Biol. Chem. 265 (1990) 139) on the basis of kinetically derived oxygen-binding constants that do not exhibit quaternary enhancement. These authors have also suggested that quaternary enhancement might not be necessary to explain the oxygen-binding data mentioned above. In this study, we have explored the effect of constraining the numerical analysis of oxygen-binding data against the new kinetically derived binding constants. It is found that the sets of linkage constants which are compatible with both the oxygen-binding data and the new kinetically derived dimer binding constant require both quaternary enhancement and substantial dimer cooperativity. Increasing the dimer cooperativity to compensate completely for quaternary enhancement requires both dimeric and tetrameric binding constants that disagree with the kinetically derived values. Thus, the quaternary enhancement effect cannot be eliminated by readjustment of the remaining constants of the linkage system. Possible sources of the discrepancy between the kinetically derived binding constants and the otherwise self-consistent data from the other four techniques are discussed.
Hemoglobins↗
Nature of gonadotropin-releasing hormone self-priming of luteinizing hormone secretion during the normal menstrual cycle.
To investigate further the nature of the gonadotropin-releasing hormone self-priming effect on luteinizing hormone release, we administered two submaximal doses of gonadotropin-releasing hormone 2 hours apart to women at three stages of the menstrual cycle and analyzed the resultant luteinizing hormone secretory episodes with deconvolution analysis. When the characteristics of the secretory episodes associated with the second gonadotropin-releasing hormone challenge were compared with those associated with the first, both an enhanced maximal secretory rate and mass of luteinizing hormone secreted was demonstrable at each phase of the cycle. No differences in the luteinizing hormone secretory event half-duration were detected when the responses to the first and second gonadotropin-releasing hormone doses were compared. These data confirm the gonadal hormone milieu-associated self-priming effect of gonadotropin-releasing hormone on luteinizing hormone release and indicate that it is the rate with which luteinizing hormone molecules are discharged from the pituitary gland, rather than the duration of the secretory episode itself, that provides for the self-priming effect.
Adolescent↗
Non-linear least squares analysis of phase diagrams for non-ideal binary mixtures of phospholipids.
A computer program for non-linear least squares minimization has been applied to construct temperature-composition phase diagrams for several binary systems of different phospholipids based on their calorimetric data. The calculated phase diagram is guided to fit the calorimetric data with two adjustable parameters that describe the non-ideal mixing of lipid components in the gel and liquid-crystalline phases. The parameter estimation procedure is presented to show that the computer program can be used not only to generate phase diagrams with characteristic shapes but also to numerically estimate the lipid-lipid pair interactions between the mixed and the like pairs in the two-dimensional plane of the bilayer in both the gel and liquid-crystalline states. The binary lipid systems examined include dimyristoylphosphatidylcholine/1-palmitoyl-2-stearoylphosphatidylchol ine, 1-capryl-2-behenoylphosphatidylcholine/1-behenoyl-2-lauro ylphosphatidylcholine, and 1-stearoyl-2-caprylphosphatidylcholine/dimyristoylphosphatidylchol ine.
Chemical Phenomena↗
Influence of end-to-end diffusion on intramolecular energy transfer as observed by frequency-domain fluorometry.
We investigated the influence of end-to-end diffusion on intramolecular energy transfer between a naphthalene donor and dansyl acceptor linked by polymethylene chain. A range of viscosities from 0.6 to 200 cP were obtained using propylene glycol at different temperatures (0-80 degrees C) and methanol at 20 degrees C. The intensity decays of naphthalene were measured in the frequency domain. Several theoretical models, including distance distributions, were used to fit the data. The results indicate that end-to-end diffusion of flexible donor-acceptor pairs can be detected and quantified using frequency-domain fluorometry, even in the presence of a distribution of donor-to-acceptor distances.
Diffusion↗
Evaluation of Adair binding constants from experimental data obtained with an Imai cell. Statistical weighting functions.
One group of laboratories uses an 'even-weighted', or unweighted, nonlinear least-squares method for the analysis of experimental oxygen binding data obtained with an Imai oxygenation apparatus. Another group uses an 'end-weighted' nonlinear least-squares analysis. With end weighting each observation is assigned a statistical weight which is proportional to Y(1-Y), where Y is the fractional saturation. In this work we discuss statistical weighting functions as applied to the Imai oxygenation apparatus and then determined what are the best weighting factors for an actual series of published experiments. Based on these calculations, it is concluded that the 'best' weighting for the Imai oxygenation apparatus is a very small amount of end weighting. Furthermore, the amount of end weighting is so small that even weighting, or no weighting at all, is also appropriate.
Least-Squares Analysis↗
Conformational distributions of melittin in water/methanol mixtures from frequency-domain measurements of nonradiative energy transfer.
We used fluorescence energy transfer to examine the effects of solvent composition on the distribution of distances between the single tryptophan residue of melittin (residue 19) to the N-terminal alpha-amino group, which was labeled with a dansyl residue. The tryptophan intensity decays, with and without the dansyl acceptor, were measured by the frequency-domain method. The data were analyzed by a least-squares algorithm which accounts for correlation between the parameters. A wide distribution of tryptophan to dansyl distances was found for the random-coil state, with a Gaussian half-width of 25 A. Increasing concentrations of methanol, which were shown to induce and alpha-helical conformation, resulted in a progressive decrease in the width of the distribution, reaching a limiting half-width of 3 A at 80% (v/v) methanol. The distance from the indole moiety of Trp-19 to the dansyl group in 80% (v/v) methanol/water was found to be 25 A, as assessed from the center of the distance distribution. A distance of 24-25 A was recovered from the X-ray crystal structure of the tetramer, which is largely alpha-helical. At low ionic strength (less than 0.01) the CD spectra revealed a small fraction or amount of alpha-helix for melittin in water, which implies a small fraction of residual structure. This residual structure is apparently lost in guanidine hydrochloride as demonstrated by a further broadening in the distribution of distances. These results demonstrate the usefulness of frequency-domain measurements of resonance transfer for resolution of conformational distributions of proteins.
Melitten↗
Operating behavior of dual or multiple endocrine pulse generators.
We describe an endocrine model of dual or multiple stochastic generators of episodic pulse signals, provide a sensitivity analysis of output responses, and illustrate the statistical effects of a plurality of independent pulse generators on peak detector performance (sensitivity, specificity, positive accuracy, and negative accuracy). We define the probability distribution of random summation or interference events and evaluate physiological implications of two or more interacting pulse-generator systems. Such observations offer a basis for quantitative examination of the operating characteristics of two or more interacting endocrine pulse generators in specified physiological contexts.
Animals↗
Temporal structure of in vivo adrenal secretory activity estimated by deconvolution analysis.
Circadian and ultradian rhythms of plasma cortisol concentrations have been documented under physiological conditions in diverse animal species. Using a novel, biophysical convolution model to remove subject-specific metabolic clearance rates, we have now estimated spontaneous adrenal secretory events in vivo. The latter were characterized by prominent ultradian rhythms of discrete secretory bursts with periodicities averaging 32, 46, 76, and 130 min. These ultradian cortisol secretory rhythms represented a 17- to 240-fold larger fraction of circadian secretory variations than did cortisol concentration rhythms. We conclude that deconvolution analysis can unmask underlying ultradian rhythms in adrenal secretory activity in vivo.
Activity Cycles↗
Returning to the roots of endocrinology: the challenge of evaluating in vivo glandular secretory activity.
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Animals↗
Dynamics of 24-hour endogenous cortisol secretion and clearance in primary hypothyroidism assessed before and after partial thyroid hormone replacement.
Although various abnormalities of hypothalamic pituitary adrenal function have been reported in primary hypothyroidism, neither 24-h patterns of pulsatile cortisol release nor estimation of its endogenous secretion and clearance rates have been fully investigated in this clinical setting. We studied pulsatile and circadian patterns of cortisol secretion in six hypothyroid men [mean free T4 index, 0.59 +/- 0.22 (+/- SE); mean TSH, greater than 50 mU/L] by sampling blood at 20-min intervals for 24 h before (unreplaced) and then after 5-7 months of partial replacement treatment with levo-T4. Compared to a normal group, hypothyroid men had significantly elevated 24-h mean serum concentrations of cortisol (419 vs. 254 nmol/L; P less than 0.001), with no change in serum cortisol-binding globulin concentrations. Cluster analysis of cortisol time series revealed a normal pulse frequency, with significant increases in mean peak amplitude (527 vs. 331 nmol/L; P = 0.001), mean interpulse valley concentrations (384 vs. 204 nmol/L; P less than 0.05), and mean prepeak nadir concentrations (298 vs. 166 nmol/L; P less than 0.05). Cosinor analysis showed preserved circadian rhythmicity (i.e. normal mean circadian amplitude of cortisol release) in hypothyroidism, with a significant delay in the timing of circadian acrophases and an increase in the mesor (mean). Analysis of data by a multiple parameter deconvolution method demonstrated a normal 24-h endogenous cortisol production rate in the presence of significantly prolonged subject-specific half-life of cortisol disappearance (155 vs. 73 min; P less than 0.05). Partial replacement therapy with levo-T4 caused significant decreases in 1) mean 24-h serum cortisol concentrations (419 vs. 323 nmol/L; P less than 0.05); 2) mean cortisol peak amplitudes (527 vs. 375 nmol/L; P less than 0.05); 3) mean prepeak nadir concentrations (298 vs. 221 nmol/L; P less than 0.05); and 4) mean half-life of cortisol disappearance (155 vs. 112 min; P less than 0.0019). In summary, the present study of cortisol secretory dynamics in hypothyroid men has shown elevated mean 24-h serum concentrations of cortisol with preserved circadian rhymicity and normal endogenous production rates, but prolonged half-lives of cortisol disappearance. In conjunction with normal serum cortisol-binding globulin concentrations, these largely reversible findings suggest that significant hypercortisolemia in primary hypothyroidism is primarily due to decreased metabolic clearance of cortisol and a presumptive decrease in the negative feedback effect of cortisol on the hypothalamo-pituitary axis.
Adult↗
Pulsatile cosecretion of estradiol and progesterone by the midluteal phase corpus luteum: temporal link to luteinizing hormone pulses.
Using recently defined analytical tools that permit quantitative and integrated assessments of pulsatile activities of two or more hormones, we have examined the coincidence of pulses of estradiol (E2), progesterone (P4), and LH determined in blood withdrawn at 15-min sampling intervals for a duration of 24 h in each of 15 women during the midluteal phase of the human menstrual cycle. The occurrence of E2 and P4 pulses is simultaneous, as their peaks were maximally correlated at zero time lag (P less than 10(-4], and there were comparable periodicities for E2 (13.5 +/- 0.7 pulses/24 h) and P4 (11.2 +/- 0.7 pulses/24 h). This coupling of E2 and P4 pulses suggests cosecretion by the mature corpus luteum. These E2 and P4 pulses are significantly coupled with LH pulses, with a lag time of about 30 min and/or 45 min for P4 (P = 0.029) and 0 min and/or 15 min for E2 (P = 0.032). Further, when considered together, LH, E2, and P4 are found to be triply copulsatile (P = 0.0066). However, significant numbers of discrete pulses of P4 and E2 are observed without antecedent LH pulses, suggesting some degree of corpus luteum autonomy. In conclusion, orchestrated synchrony of pulsatile pituitary and ovarian (corpus luteum) signaling can be demonstrated by the coordinated temporal release of LH, E2, and P4 in normal cycling women.
Adult↗
Amplitude, but not frequency, modulation of adrenocorticotropin secretory bursts gives rise to the nyctohemeral rhythm of the corticotropic axis in man.
The ACTH-adrenal axis is a critical stress-responsive system with prominent circadian rhythmicity. To test the basis for the circadian ACTH physiology, we have used 1) a sensitive and specific two-site immunoradiometric assay to estimate plasma ACTH-(1-39) concentrations during intensive (every 10 min) and extended (24-h) blood sampling to capture complete diurnal ACTH profiles in eight normal men, and 2) a novel deconvolution model designed to resolve the number, amplitude, and duration of ACTH secretory bursts and simultaneously estimate subject-specific ACTH half-lives under physiological conditions in vivo. Deconvolution revealed 40 +/- 1.5 significant ACTH secretory bursts/24 h, with a mean interburst interval of 39 +/- 2.3 min. ACTH secretory bursts were discrete punctuated events arising without tonic interpulse secretion and had a half-duration (duration at half-maximal amplitude) of 19 +/- 2 min. The estimated half-life of endogenous ACTH was 15 +/- 1.2 min, and its daily production rate was 0.96 +/- 0.16 ng/mL (0.21 +/- 0.035 nmol/L) distribution volume. Cosinor analysis revealed a significant (3.8-fold) 24-h rhythm in the mass (or rate) of ACTH secreted per burst (maximal at 0818 h), but no nyctohemeral variation in ACTH secretory pulse frequency. The validity of ACTH pulse analysis was supported by the significantly nonrandom associations among ACTH, beta-endorphin, and cortisol peaks in the same subjects. Specifically, we found that ACTH and beta-endorphin bursts occurred simultaneously (P less than 10(-4)) and were both followed in 10 min by a cortisol pulse (P less than 10(-4)). We conclude that 1) selective amplitude control of a punctuated burst-like mode of ACTH secretion can give rise to the nyctohemeral corticotropic rhythm without the need to postulate any tonic (or interpulse basal) component of ACTH release; and 2) there is exquisite 3-fold temporal synchrony among bursts of ACTH, beta-endorphin, and cortisol release in normal men.
Adrenocorticotropic Hormone↗
Testosterone and oxandrolone, a nonaromatizable androgen, specifically amplify the mass and rate of growth hormone (GH) secreted per burst without altering GH secretory burst duration or frequency or the GH half-life.
We investigated the mechanisms by which androgens increase mean circulating GH concentrations in boys. We tested two hypotheses: 1) testosterone increases serum GH concentrations at least in part via an androgen receptor-mediated mechanism, rather than exclusively by way of aromatization to estrogen; 2) androgen augments one or more specific features to GH secretion (secretory burst number, amplitude, and/or duration) and/or prolongs the half-life of GH removal. To examine these hypotheses, prepubertal boys with constitutionally delayed development and/or growth were given injections of testosterone (100 mg monthly; n = 7) or treated with oral oxandrolone, a nonaromatizable androgen (1.25 mg twice daily; n = 5). Pulsatile GH release was studied before and during androgen administration by sampling blood at 20-min intervals for 24 h. The immunoreactive GH time series were subjected to a novel deconvolution technique, which revealed that 1) testosterone and oxandrolone each increased mean (24-h) serum GH concentrations significantly; 2) both androgens augmented the daily endogenous GH secretory rate significantly; 3) increased GH production resulted from a higher mass of GH secreted per burst and a higher maximal rate of GH secretion within each burst; and 4) androgens amplified the magnitude of the nyctohemeral rhythm in the mass (but not frequency) of GH secretory pulses. The observed effects of androgen were specific, since the number and duration of GH secretory bursts and the subject-specific GH half-life were unaltered by androgen treatment. We conclude that androgen acting apart from conversion to estrogen is capable of specifically activating the somatotropic axis via distinct neuroendocrine secretory mechanisms.
Adolescent↗
Twenty-four-hour rhythms in plasma concentrations of adenohypophyseal hormones are generated by distinct amplitude and/or frequency modulation of underlying pituitary secretory bursts.
To evaluate the nature of anterior pituitary secretory events in vivo, we have applied a novel waveform-independent deconvolution technique that dissects the underlying secretory behavior of endocrine glands quantitatively from available serial plasma hormone concentration measurements assuming one- or two-compartment elimination kinetics. We used this new tool to ask the following physiological questions. 1) Does the pituitary gland secrete exclusively in randomly dispersed bursts, and/or does a tonic (constitutive) mode of interburst hormone secretion exist? 2) What secretory mechanisms generate the nyctohemeral rhythms in plasma hormone concentrations? Analysis of 24-h plasma concentration profiles of GH, LH, FSH, PRL, TSH, ACTH, and beta-endorphin (n = 6-8 men/group) revealed that 1) pituitary secretion in vivo occurs in an exclusively burst-like mode for all hormones except TSH and PRL (for the latter two, a mixed burst and constitutive mode pertained); 2) significant nyctohemeral regulation of secretory burst frequency alone was not demonstrated for any hormone; 3) prominent 24-h variations in secretory burst amplitude alone were delineated for ACTH and LH; 4) TSH, GH, and beta-endorphin were both frequency and amplitude controlled; 5) no significant diurnal variations in FSH secretory parameters occurred; and 6) a fixed hormone half-life yielded fits of the 24-h data series with a normalized residual variance of less than 8%. We conclude that the normal human anterior pituitary gland releases its multiple (glyco)protein hormones via punctuated secretory episodes unassociated with tonic basal (constitutive) hormone secretion, except in the case of TSH and PRL. Hormone-specific amplitude and/or frequency control of secretory burst activity over 24 h provides the mechanistic basis for the classically recognized 24-h rhythms in plasma concentrations of adenohypophyseal hormones in men.
Adrenocorticotropic Hormone↗
An overview of computer algorithms for deconvolution-based assessment of in vivo neuroendocrine secretory events.
The availability of increasingly efficient computational systems has made feasible the otherwise burdensome analysis of complex neurobiological data, such as in vivo neuroendocrine glandular secretory activity. Neuroendocrine data sets are typically sparse, noisy and generated by combined processes (such as secretion and metabolic clearance) operating simultaneously over both short and long time spans. The concept of a convolution integral to describe the impact of two or more processes acting jointly has offered an informative mathematical construct with which to dissect (deconvolve) specific quantitative features of in vivo neuroendocrine phenomena. Appropriate computer-based deconvolution algorithms are capable of solving families of 100-300 simultaneous integral equations for a large number of secretion and/or clearance parameters of interest. For example, one application of computer technology allows investigators to deconvolve the number, amplitude and duration of statistically significant underlying secretory episodes of algebraically specifiable waveform and simultaneously estimate subject- and condition-specific neurohormone metabolic clearance rates using all observed data and their experimental variances considered simultaneously. Here, we will provide a definition of selected deconvolution techniques, review their conceptual basis, illustrate their applicability to biological data and discuss new perspectives in the arena of computer-based deconvolution methodologies for evaluating complex biological events.
Algorithms↗
Myelination of axons within cytosine arabinoside treated mouse cerebellar explants by cultured rat oligodendrocytes.
Cell suspensions of cultured purified rat oligodendrocytes prepared by the differential substrate adhesion method were applied to neonatal mouse cerebellar explant cultures in which myelination and oligodendrocyte maturation had been irreversibly inhibited by exposure to cytosine arabinoside. Myelination of Purkinje cell axons within 92% of the host explants was observed 2-5 days after oligodendrocyte application. Ultrastructurally, mature oligodendrocytes and axons surrounded by compact myelin, as well as spherules of compact myelin membranes without axons, were present within the cerebellar explants. It is evident that cultured dissociated purified oligodendrocytes retain the ability to myelinate appropriate axons. Such oligodendrocytes may be hyperreactive with regard to myelin membrane formation, as suggested by the presence of spheres of compact myelin without axons.
Animals↗