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M L Johnson

Publications and source records attributed to M L Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1988

Acrylamide quenching of Yt-base fluorescence in aqueous solution.

Acrylamide was found to be an effective quencher of Yt-base (Y-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2a-purine) in water. In the absence of collisional quenching the decay of Yt-base in water is predominantly a single exponential. The intensity decays become increasingly heterogeneous when quenched by acrylamide. The frequency-domain data were analyzed using the radiation model, which provides estimates of molecular parameters characteristic of the system. The mutual diffusion coefficient at 20 degrees C was found to be 0.5 x 10(5) cm2/s, the Yt-base acrylamide interaction radius was 8 A, and the rate constant for quenching was 100 cm/s. These values indicate that quenching is diffusion-limited, i.e., the encounter complex is deactivated at least 2-fold faster than the rate of diffusive encounters.

Acrylamide↗
PubMed1988

Distribution of distances in thiopeptides by fluorescence energy transfer and frequency-domain fluorometry.

Frequency-domain fluorescence spectroscopy was employed to examine the decays of tryptophan in Boc-Trp-Met-Asp-Phe-NH2 (donor) and (Formula: see text) (donor-acceptor pair). The efficiency of energy transfer in the thiopeptide amounted to 60%. The measured dispersion of fluorescence decay times was used to recover the donor-acceptor distance distribution. The parameters of the Gaussian distance distribution obtained for this peptide (r, the mean distance (9 A); hw, the halfwidth (25 A)) indicate the lack of a distinct favorable conformation.

Energy Transfer↗
PubMed1988

Lifetime distributions and anisotropy decays of indole fluorescence in cyclohexane/ethanol mixtures by frequency-domain fluorometry.

We used frequency-domain fluorometry to measure intensity and anisotropy decay of indole fluorescence in cyclohexane/ethanol mixtures at 20 degrees C. In 100% cyclohexane or 100% ethanol the intensity decay of indole appears to be a single exponential with decay times of 7.66 and 4.10 ns, respectively. In cyclohexane containing a small percentage of ethanol (up to 10%), we observed increased heterogeneity in intensity decay, resulting in a 10-fold increase in chi 2R for the single-exponential fit, as compared with the double-exponential model. We obtained comparable or better fits using unimodal Lorentzian and Gaussian lifetime distributions (two floating parameters) than for the two-exponential model (three floating parameters). We believe that the distribution of decay times reflects a range of indole solvation states in the dominately nonpolar solutions. This result suggests that a variety of hydrogen-bonding configurations could be one origin of the distributions of decay times observed for tryptophan emission from proteins. We also measured rotational diffusion of indole in cyclohexane, ethanol and its mixtures at 20 degrees C. The picosecond correlation times required that the mean decay times be decreased by acrylamide quenching (in ethanol) or energy transfer (in cyclohexane). In ethanol we observed nearly isotropic rotation of indole; in cyclohexane we obtained two correlation times of 17 and 73 ps. The shorter correlation time in cyclohexane appears to be due to the slip boundary condition, which was found to be progressively eliminated by small percentages of ethanol. Hence, hydrogen-bonding interactions appear to have a substantial effect on the rotational dynamics of indole.

Cyclohexanes↗
PubMed1988

Equipment planning process. Organizing purchases.

Equipment planning for a new or renovated OR space is an essential part of the overall facility planning process. It can be accomplished by in-house staff or by outside equipment consultants. If outside consultants are hired to organize the process, it is important that the nursing and medical staff be involved because they use the equipment and will determine the ultimate success of the new facility.

Humans↗
PubMed1988

Resolution of end-to-end distance distributions of flexible molecules using quenching-induced variations of the Forster distance for fluorescence energy transfer.

We describe a new method to recover the distribution of donor-to-acceptor (D-A) distances in flexible molecules using steady-state measurements of the efficiency of fluorescence energy transfer. The method depends upon changes in the Forster distance (Ro) induced by collisional quenching of the donor emission. The Ro-dependent transfer efficiencies are analyzed using nonlinear least squares to recover the mean D-A distance and the width of the distribution. The method was developed and tested using three synthetic D-A pairs, in which the chromophores were separated by alkyl chains of varying lengths. As an example application we also recovered the distribution of distances from the single tryptophan residue in troponin I (trp 158) to acceptor-labeled cysteine 133. The half-width of the distribution increases from 12 A in the native state to 53 A when unfolded by guanidine hydrochloride. For both TnI and the three model compounds the distance distributions recovered from the steady-state transfer efficiencies were in excellent agreement with the distributions recovered using the more sophisticated frequency-domain method (Lakowicz, J.R., M.L. Johnson, W. Wiczk, A. Bhat, and R.F. Steiner. 1987. Chem. Phys. Lett. 138:587-593). The method was found to be reliable and should be generally useful for studies of conformational distributions of macromolecules.

Energy Transfer↗
PubMed1988

Massive renal hemorrhage owing to polyarteritis nodosa.

We report a case of massive renal hemorrhage owing to unsuspected polyarteritis nodosa. The bleeding was ultimately controlled by embolization of the renal artery. The findings on renal angiography and enhanced computerized tomography were characteristic of the disorder and they should be familiar to all urologists.

Adult↗
PubMed1988

Binding and internalization of rat colonic mucins by the galactose/N-acetyl-D-galactosamine adherence lectin of Entamoeba histolytica.

Purified rat colonic mucins inhibit Entamoeba histolytica in vitro adherence to and lysis of colonic epithelial cells by binding to the amoebic galactose/N-acetyl-D-galactosamine (Gal/GalNAc)-inhibitable adherence lectin. We found that 125I-labeled mucins demonstrated saturable Gal-specific binding to E. histolytica trophozoites (strain HM1:IMSS), with 2.8 x 10(3) binding sites per amoeba and a dissociation constant of 8.20 x 10(-11) M-1. Inhibition of parasite protein synthesis completely abrogated mucin binding; elevation of amoebic vesicle pH with ammonium chloride (10 mM) had no effect. Surface-bound 125I-labeled mucins were rapidly internalized and released from amoebae without evidence of proteolytic degradation. Three avirulent HM1 clones contained immunoreactive Gal/GalNAc lectin molecules with high-affinity binding of 125I-labeled mucins but exhibited markedly reduced rates of uptake and exocytosis of bound mucins. High-affinity binding by the Gal/GalNAc adherence lectin was followed by rapid internalization and eventual release of the colonic mucins. Additionally, defects in lectin surface expression and endocytosis were found in the avirulent clones.

Animals↗
PubMed1988

Comparative assessments of objective peak-detection algorithms. II. Studies in men.

The performances of eight currently available computerized pulse-detection algorithms were compared on signal-free noise and physiological luteinizing hormone (LH) time series. Signal-free noise was made to vary from 4 to 36% for Gaussian and empirical distributions. Physiological LH data were obtained by immunoassay of blood samples withdrawn every 5 min for 24 h in 8 healthy men, so that the data sets could be emended to simulate varying sampling intensities. Whenever possible, programs were tested at a presumptive 1% false-positive rate. In relation to signal-free noise, the Santen and Bardin program and its modification manifested elevated false-positive rates when the intraseries coefficients of variation increased. The Regional Dual-Threshold program yielded a 1% false-positive rate except on simulated series with high variance. The Cluster and Detect programs both approximated a 1% false-positive rate and the Ultra program approximated a 2.3% false-positive rate throughout the entire range of variance tested. In regard to physiological LH data, all algorithms disclosed a significant impact of sampling intensity on estimates of LH pulse frequency. Sampling-intensity dependent estimates of LH peak frequency by three of the eight programs (Ultra, Cluster, and Detect) were statistically indistinguishable from each other but distinct from the five other programs tested. Furthermore, when judged in relation to their ability to identify individual peaks, the three congruent programs were minimally distinguishable (McNemar's test). Rather, these programs identified the same particular peaks (as defined by concordance of peak maxima) at least 72% of the time.

Adult↗
PubMed1988

A novel general biophysical model for simulating episodic endocrine gland signaling.

A multiple-parameter convolution integral is used to define and generate waveforms that quantitatively and qualitatively resemble the experimentally observed behavior of episodic endocrine signals. Our formulation of the convolution integral in terms of multiple distinct parameters with statistically bounded values allows investigators to quantitatively model variations in the duration, amplitude, frequency, and/or contour of the hormone secretory pulse, as well as alterations in rates of endogenous hormone clearance. Here we demonstrate the applicability of this new concept of endocrine gland signaling to experimentally observed (physiological) endocrine data, parameter sensitivity analysis, the evaluation of statistical errors in hormone peak detection, and the estimation of random-pulse coincidence rates between two independent endocrine series.

Animals↗
PubMed1988

Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.

Studies in man have shown that the episodic release of growth hormone (GH) is infrequent and erratic, and unlike that in the rat does not appear to have discernible ultradian periodicities. However, these observations in nonfasted subjects may be invalid since mixed nutrients have unpredictable effects on GH release. Moreover, in the fed state basal GH levels are frequently undetectable, thus rendering the identification of low amplitude pulses unreliable. Accordingly, the 24-h pulsatile pattern of GH secretion obtained from repetitive venous sampling in six normal adult male subjects was examined during a control fed day and during the first and fifth days of a 5-d fast. The GH data were analyzed using two distinct methods: a discrete pulse detection algorithm (Cluster analysis) and Fourier expansion time-series, which allows fixed periodicities of secretory activity to be resolved. The 5-d fast resulted in a significant increase in discrete GH pulse frequency (5.8 +/- 0.7 vs. 9.9 +/- 0.7 pulses/24 h, P = 0.028), 24 h integrated GH concentration (2.82 +/- 0.50 vs. 8.75 +/- 0.82 micrograms.min/ml; P = 0.0002), and maximal pulse amplitude (5.9 +/- 1.1 vs. 12.3 +/- 1.6 ng/ml, P less than 0.005). While multiple low-amplitude sinusoidal periodicities were present on the control fed day, time-series analysis revealed enhancement of circadian and ultradian cycles on the first and fifth days of fasting. Concomitantly, fasting resulted in a decline (day 1 vs. day 5) in serum concentrations of somatomedin C (1.31 +/- 0.22 vs. 0.77 +/- 0.18 U/ml) and glucose (4.9 +/- 0.2 vs. 3.2 +/- 0.2 mmol/liter), and a marked rise in free fatty acid (0.43 +/- 0.12 vs. 1.55 +/- 0.35 mmol/liter) and acetoacetate (35 +/- 6 vs. 507 +/- 80 nmol/liter). We conclude that the acute nutritional status is an important determinant of spontaneous pulsatile GH secretion in man. Fast-induced enhancement of GH release is achieved through combined frequency (discrete pulses) and amplitude (sinusoidal periodicities) modulation. Such alterations in somatotropic hormone release may play an important role in substrate homeostasis during starvation.

Acetoacetates↗
PubMed1988

Effects of gonadal steroids on somatotroph function in the rat: analysis by the reverse hemolytic plaque assay.

The mechanism by which gonadal steroids modulate GH secretion is not known. We have used the reverse hemolytic plaque assay to examine whether gonadal steroid-induced modulation of GH secretion is effected by changes in the population of somatotrophs and/or alterations in their secretory properties. Two groups of Sprague-Dawley rats were studied: group 1 (n = 6) comprised male (M), castrate (Cx), and testosterone-replaced castrate male (Cx + T) rats and group 2 (n = 5) consisted of male (M), female (F), and 17 beta-estradiol-replaced castrate male (Cx + E) rats. The number of plaque-forming cells (expressed as both absolute number and a percentage of all cells) was determined, and secretory status was assessed by measuring plaque areas in response to 0, 0.01, 0.1, 1, 10, and 100 nM GHRH. While mean basal GH plaque areas were similar among the treatment groups of group 1, the maximal GH plaque area was significantly decreased in Cx [16.8 +/- 2.4 vs. 26.4 +/- 3.9 X 10(6) microns2 (mean +/- SEM); P less than 0.05], but not in Cx + T (27.5 +/- 4.1 microns2) rats. The GHRH EC50 was unaffected by castration or T replacement. The percentage and absolute population of somatotrophs were reduced in Cx, but not in Cx + T, rats, while the numbers of lactotrophs remained unchanged in these treatment groups. For group 2, the mean peak GH plaque area was reduced in Cx + E (16.5 +/- 2.9 microns2; P less than 0.001) compared to that in M rats (36.2 +/- 2.3 microns2), but was not significantly different from that in F (13.0 +/- 1.5 microns2) rats. The EC50 was significantly (P less than 0.025) greater in Cx + E (10.9 +/- 2.3 nM) and F (7.9 +/- 1.6 nM) compared to M rats (2.8 +/- 0.7 nM). The absolute somatotroph and lactotroph populations were increased in Cx + E compared to M and F rats, as were the populations of other pituitary cell types. Testosterone enhances GH secretion by increasing the secretory capacity, but not the sensitivity, of somatotrophs to GHRH and by recruiting the function of a subpopulation of somatotrophs. Estradiol reduces the secretory capacity and sensitivity of somatotrophs to GHRH, but increases the population of somatotrophs, lactotrophs, and non-GH- and non-PRL-secreting cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Physiological profiles of episodic progesterone release during the midluteal phase of the human menstrual cycle: analysis of circadian and ultradian rhythms, discrete pulse properties, and correlations with simultaneous luteinizing hormone release.

To define the physiological relationships between episodic progesterone and LH release, we measured serum progesterone and LH concentrations in blood sampled at 10-min intervals for 24 h in seven young women in the midluteal phase of the menstrual cycle. The resultant time series were assessed further by Fourier transformation, Cluster analysis, and cross-correlation analysis with autoregressive modeling. These techniques permitted an examination of circadian rhythms, discrete (ultradian) pulse properties, and simultaneous or lagged correlations between progesterone and LH release. We found the following. 1) Both serum LH and progesterone concentrations had significant circadian periodicities, with similar acrophases (times of maximal nyctohemeral values). LH and progesterone also manifested multiple ultradian rhythms of similar periodicities (range, 48-241 min). 2) Discrete serum progesterone peaks occurred at a mean interpulse interval of 118 +/- 12 (+/- SE) min, had durations of 92 +/- 12 min, and had incremental amplitudes of 4.3 +/- 0.9 ng/mL (14 +/- 3 nmol/L). The frequency and duration characteristics of the progesterone and LH peaks were not significantly different, but progesterone fractional peak amplitudes were one quarter those of LH pulses. 3) Fractional progesterone peak amplitudes in the seven women correlated inversely (r = -0.811) with 24-h mean LH concentrations, suggesting a negative feedback relationship between progesterone and LH release. 4) LH and progesterone interpulse intervals both exhibited significant nyctohemeral variations, with diurnal amplitudes of 73 +/- 12 min for LH and 43 +/- 8.9 min for progesterone (P less than 0.01). 5) Significant positive cross-correlations existed in all seven women between serum LH and progesterone concentrations considered simultaneously and at progesterone time lags of 10-50 min. By autoregressive modeling, the later (20-50 min) cross-correlations could be accounted for by sustained autocorrelations in the individual progesterone and LH time series and significant cross-correlations between LH and simultaneous progesterone concentrations and between LH and 10-min lagged progesterone concentrations. We conclude that progesterone release occurs in a periodic (circadian and ultradian) fashion as well as in a discrete (episodic or pulsatile) mode. Moreover, both positive and negative feedback relationships operate to coordinate LH and progesterone secretion in the midluteal phase of the human menstrual cycle.

Adult↗
PubMed1988

In vivo dynamics of luteinizing hormone secretion and clearance in man: assessment by deconvolution mechanics.

The dynamics of LH secretion and clearance were studied in vivo in eight healthy young men using a novel multiple parameter deconvolution procedure to resolve underlying secretion and clearance rates simultaneously from serial serum immunoactive LH concentrations. This deconvolution analysis disclosed random LH secretory bursts occurring at a mean (+/- SEM) interpulse interval of 72 +/- 5 min. The frequency of these secretory bursts was 6.9 +/- 0.6 episodes/8 h. Each resolved LH secretory event had an average half-duration of only 7.8 +/- 0.5 min, which was remarkably shorter than the LH concentration peak duration of 60 +/- 6 min. The maximal LH secretory rate achieved within a secretory burst averaged 0.40 +/- 0.05 mIU/min.mL (0.14 IU/min.L), which corresponded to a mass of LH released of 3.2 +/- 0.3 mIU/mL distribution vol (IU/L). By linear regression analysis, both the maximal rate and mass of LH released per secretory burst were positively correlated with the duration of the subsequent interpulse interval (P less than 0.001). In physiological experiments, the mass of LH released per secretory burst was increased by iv GnRH injections or primary gonadal failure, and decreased by sc administration of a selective GnRH antagonist (Nal,Glu-GnRH). The mean endogenous LH production rate calculated by deconvolution [180 +/- 40 mIU/min (0.18 IU/min)] was not different from a nominal value of 228 +/- 80 mIU/min (0.228 IU/min) extrapolated from earlier steady state LH infusions. Deconvolution estimated single phase half-times of endogenous LH disappearance of 87 +/- 8 min, were in general harmony with values of 44-106 min obtained previously in four LH-deficient men injected with purified LH. Moreover, creation of synthetic LH series using our deconvolution estimates yielded 24-h LH pulse profiles similar quantitatively and qualitatively to those in normal men. In summary, we applied a new multiple parameter deconvolution procedure to immunoactive LH pulse profiles to discern the nature of physiological LH secretory events and estimate endogenous LH disappearance rates. These studies in normal men have revealed that 1) LH secretory bursts occur every 72 min; their mean half-duration is 7.8 min; and 3.2 mIU/mL (3.2 IU/L) are released per secretory peak; 2) amplitudes of in vivo LH secretory bursts are augmented in primary gonadal failure and/or by exogenous GnRH injections and attenuated by a GnRH antagonist; 3) the duration of a postsecretory pause is proportional to the amplitude of the preceding LH secretory burst; and (4) 95% of total daily LH release occurs in only 5 h/day.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

Operating characteristics of the hypothalamo-pituitary-gonadal axis in men: circadian, ultradian, and pulsatile release of prolactin and its temporal coupling with luteinizing hormone.

To investigate the circadian, ultradian, and pulsatile nature of PRL release in the human, we sampled blood at 10-min intervals for 24 h in each of 12 normal young men. The subsequent serum PRL time series were subjected to contemporary techniques of rhythmic and episodic peak detection. Fourier analysis revealed a significant circadian rhythm in serum PRL concentrations in all 12 men. The mean circadian amplitude was 2.1 +/- 0.3 ng/mL (micrograms/L), which accounted for an average of 30 +/- 4% of the 24-h mean PRL concentration. In addition, multiple ultradian PRL rhythms were found with periodicities ranging from 22-242 min. Spectral analysis disclosed ultradian cycles with periodicities of 30-32, 51-59, 90-98, and 234 min. Assessment of episodic PRL pulsatility by Cluster analysis revealed 14 +/- 1 PRL peaks/24 h (P less than 0.01 vs. signal-free noise), which occurred at an interpulse interval of 95 +/- 6 min. The average duration of a serum PRL peak was 67 +/- 5 min, and its incremental amplitude was 4.0 +/- 0.3 ng/ml (micrograms/L), which represented a 58 +/- 6% increase above the preceding nadir. Discrete PRL peaks were separated by nonpulsatile valleys, with a mean duration of 27 +/- 1 min. Analysis of the temporal coupling between LH and PRL release by bivariate autoregressive modeling in six men revealed significant cross-correlations between LH and simultaneous PRL concentrations as well as between LH and PRL concentrations that lagged LH by 10 or 20 min. Cross-spectral analysis demonstrated significantly correlated PRL and LH cycles with periodicities of 33-37, 47-52, and 84-106 min. In summary, PRL release in normal young men is characterized by significant circadian and ultradian periodicities, by discrete episodic pulsations that occur approximately every 95 min, and by a close temporal coupling with LH (temporal lag between LH and PRL of 0-20 min).

Activity Cycles↗
PubMed1988

Acute androgen receptor blockade increases luteinizing hormone secretory activity in men.

To investigate the nature of androgen feedback mechanisms in normal men, we studied the hypothalamo-pituitary responses to administration of a potent, highly selective nonsteroidal androgen receptor antagonist, flutamide HCl (1 g/day, orally, for 3 days). The impact of reversible blockade of endogenous androgen action was assessed in 11 normal men by analyzing quantitative alterations in specific pulsatile properties of LH secretion basally (hypothalamic regulation) and after 2 (n = 6) consecutive iv pulses of exogenous GnRH (pituitary responsiveness). Androgen blockade resulted in significant increases in 1) 12-h mean and integrated serum immunoactive LH concentrations (P = 0.01), 2) LH pulse frequency (P = 0.01), and 3) mean interpulse (valley) serum LH concentrations (P = 0.02) and maximal LH peak heights (P = 0.01). Additionally, there were significant decreases in LH interpulse interval (P = 0.02), LH peak duration (P = 0.02), and interpeak valley duration (P = 0.02). The augmented LH pulsatility reflected enhanced hypothalamic activity, since 1) pituitary secretory responses to exogenous GnRH pulses were not altered, and 2) multiple parameter deconvolution disclosed an increased number of computer-resolved LH secretory bursts generated per 12 h, with no changes in the apparent half-duration of LH secretory impulses or the calculated mass of LH released per secretory burst. We conclude that endogenous androgens act selectively to modulate the number of spontaneous LH secretory bursts in man.

Adult↗
PubMed1988

Contemporary tools for the analysis of episodic growth hormone secretion and clearance in vivo.

The evaluation of episodic GH release is made difficult by the apparently random nature of GH secretory bursts, the frequent occurrence of minimally detectable plasma GH concentrations, the relatively rapid plasma disappearance rate of endogenous GH, and the large number of metabolic and environmental cues that alter GH dynamics. Nonetheless, the development of objective, statistically based, and reproducible computerized algorithms to quantify episodic GH release has offered new insights into the pathophysiological regulation of GH secretion in health and disease. Moreover, the recent formulation of algebraically explicit biophysical models of GH secretion and clearance has made possible a complete quantitative description of GH secretory and clearance dynamics over a full 24 hours of observation. Such analytical tools allow investigators to enumerate with statistically bounded confidence limits the number, amplitude, durations, and temporal locations of all significant underlying secretory bursts and simultaneously calculate the half-life of endogenous GH disappearance from all GH concentrations and their variances considered together. Accordingly, in conjunction with contemporary refinements in GH assay techniques, such novel approaches to dissecting the temporal structure of GH secretion and clearance in vivo should result in significantly enhanced understanding of GH dynamics in health and disease.

Child↗