Biomedical subjects

M L Johnson

Publications and source records attributed to M L Johnson.

At least 127 records · Page 7Linked to original sources

PubMed1994

Sex influence on renal alpha 2-adrenergic receptor density in the spontaneously hypertensive rat.

Male spontaneously hypertensive rats (SHR) have higher blood pressure than females. We compared renal alpha 2-adrenergic receptor density among intact SHR and Wistar-Kyoto (WKY) rats of both sexes, male and female SHR gonadectomized at 4 weeks of age, and gonadectomized SHR supplemented with testosterone. Additional groups of SHR were treated with enalapril (30 mg/kg per day), an angiotensin-converting enzyme inhibitor, from 5 to 14 weeks of age. Renal alpha 2-adrenergic receptor density was higher in males than females in both SHR and WKY rats. Female SHR and WKY rats had identical low renal alpha 2-adrenergic receptor density. Castration of male SHR reduced the male-female differences in blood pressure and renal alpha 2-adrenergic receptor density by 60%. Treatment with testosterone raised blood pressure and renal alpha 2-adrenergic receptor density to the intact male levels in both gonadectomized males and females. Treatment with enalapril decreased blood pressure but not renal alpha 2-adrenergic receptor density in both male and female SHR. We conclude that (1) both renal alpha 2-adrenergic receptor density and blood pressure are influenced by sex in SHR and WKY, (2) renal alpha 2-adrenergic receptor density like blood pressure is regulated by androgens, and (3) increased renal alpha 2-adrenergic receptor density is not a consequence of high blood pressure in male SHR.

Animals↗

PubMed1994

Enhanced basal and disorderly growth hormone secretion distinguish acromegalic from normal pulsatile growth hormone release.

Pulses of growth hormone (GH) release in acromegaly may arise from hypothalamic regulation or from random events intrinsic to adenomatous tissue. To distinguish between these possibilities, serum GH concentrations were measured at 5-min intervals for 24 h in acromegalic men and women with active (n = 19) and inactive (n = 9) disease and in normal young adults in the fed (n = 20) and fasted (n = 16) states. Daily GH secretion rates, calculated by deconvolution analysis, were greater in patients with active acromegaly than in fed (P < 0.05) but not fasted normal subjects. Significant basal (nonpulsatile) GH secretion was present in virtually all active acromegalics but not those in remission or in fed and fasted normal subjects. A recently introduced scale- and model-independent statistic, approximate entropy (ApEn), was used to test for regularity (orderliness) in the GH data. All but one acromegalic had ApEn values greater than the absolute range in normal subjects, indicating reduced orderliness of GH release; ApEn distinguished acromegalic from normal GH secretion (fed, P < 10(-12); fasted, P < 10(-7)) with high sensitivity (95%) and specificity (100%). Acromegalics in remission had ApEn scores larger than those of normal subjects (P < 0.0001) but smaller than those of active acromegalics (P < 0.001). The coefficient of variation of successive incremental changes in GH concentrations was significantly lower in acromegalics than in normal subjects (P < 0.001). Fourier analysis in acromegalics revealed reduced fractional amplitudes compared to normal subjects (P < 0.05). We conclude that GH secretion in acromegaly is highly irregular with disorderly release accompanying significant basal secretion.

Acromegaly↗

PubMed1994

Enhanced sensitivity growth hormone (GH) chemiluminescence assay reveals lower postglucose nadir GH concentrations in men than women.

Modifications were made to a commercially available human (h) GH chemiluminescence assay (Nichols Luma Tag hGH assay), which improved its sensitivity to 0.002 micrograms/L. The results of this assay had a high correlation with those of the Nichols hGH immunoradiometric assay (IRMA; r = 0.91; P < 0.001). The addition of recombinant hGH-binding protein (0.1-10 nmol/L) to standards and serum samples caused a dose-responsive reduction in measured GH in both the chemiluminescence assay and the IRMA; at physiological concentrations of hGH-binding protein, a 10-20% reduction was observed. Fifteen normal young adults (nine men and six women) underwent a standard 100-g oral glucose tolerance test, and plasma GH was measured from 30 min before until 5 h after glucose ingestion. GH was measurable in all samples with the chemiluminescence assay, but fell below the sensitivity of the IRMA in 59% of the samples. There was no difference between baseline or peak glucose levels in male and female subjects, but serum GH concentrations (mean +/- SD) measured by the enhanced sensitivity chemiluminescence assay were lower in male than female subjects at both baseline (0.12 +/- 0.08 vs. 2.3 +/- 2.3 micrograms/L; P < 0.01) and the postglucose GH nadir (0.029 +/- 0.014 vs. 0.25 +/- 0.23 micrograms/L; P < 0.01). The high correlation between baseline and nadir GH (r = 0.82; P < 0.001) and the equivalent fractional decline in mean GH levels in men and women after glucose administration (67 +/- 17% vs. 84 +/- 8%; P = 0.06) suggest that the lower GH levels in men after glucose treatment are due to lower baseline values and not to a greater suppressive effect of glucose.

Adolescent↗

PubMed1994

On teaching dermatology to nondermatologists.

I am aware that the teaching of dermatology to nondermatologists is an issue of some controversy among dermatologists. In responding to the editor's invitation to write to this issue, I must first admit to a career-long practice of teaching dermatology to nondermatologists: to residents in primary care specialties, to generations of medical students, to nurses here in the United States and elsewhere, and to physician assistants and nurse practitioners.

Dermatology↗

PubMed1993

An acute form of T gamma lymphoproliferative disease presenting with massive splenomegaly--importance of immunophenotyping for diagnosis.

We describe a case of T gamma lymphoproliferative disease (T gamma LPD) which presented in an uncustomary acute onset in an adult with massive splenomegaly. Morphologically the cells represented monocytic leukemia. Karyotyping and equivocol special stain results suggested hairy cell leukemia. Gene rearrangement indicated a T lymphocytic malignancy. Immunocytochemistry stains were not definitive. Immunophenotyping by flow cytometry defined the cells as consistent with T gamma LPD (CD45+, CD56+, CD2+, CD3+, CD11b+, and CD38+; some cells CD8+; and CD57-). Although the cells did not have spontaneous activity, which is often the situation for most cases of T gamma LPD, the cells could be partially induced with exogenous interleukin 2 to exhibit in vitro cytotoxicity against a natural killer lymphocyte-susceptible target cell line (K562) but not a lymphocyte-activated killer target cell line (HEPG2). This report hopefully continues to increase the awareness of T gamma LPD as well as demonstrates an unusual acute form which could have been misdiagnosed unless a multidisciplinary approach, especially including flow cytometric immunophenotyping, was used to evaluate the patient.

Acute Disease↗

PubMed1993

End-to-end diffusion coefficients and distance distributions from fluorescence energy transfer measurements: enhanced resolution by using multiple acceptors with different Förster distances.

We measured distance distributions and end-to-end diffusion coefficients of donor-acceptor pairs linked by a flexible methylene chain using frequency-domain fluorescence energy transfer measurements. The donor was an indole group, and two acceptors with different Förster distances were used. The uncertainties in the recovered parameters describing the end-to-end distance distribution and diffusion coefficient were rather large when each donor-acceptor pair was analyzed separately. It was not possible to resolve distance distributions in the presence of intra-molecular diffusion when the Förster distance was comparable to the mean and half-width of the distribution. Global analysis using two acceptors dramatically improved the resolution. Surprisingly, the Förster distances need not be very different, and a 20% difference between the two R0 values resulted in substantial improvements in resolution. Both the simulations and the experiments suggest the benefit of using global analysis with different Förster distances to obtain reliable distance distribution parameters in the presence of diffusion.

Benzenesulfonates↗

PubMed1993

Reanalysis of the rat proestrous LH surge by deconvolution analysis.

To evaluate the temporal mechanisms that give rise to the spontaneous proestrous surge of luteinizing hormone (LH) in the rat, we have applied deconvolution analysis to earlier immunoreactive LH concentration vs. time profiles obtained by sampling blood in proestrus at 2- to 3-min intervals in 10 animals over a span of 160-300 min. Six other animals were bled in 6-min intervals on day 1 of diestrus. Deconvolution analysis permitted us to calculate the number, duration, amplitude (maximal release rates), and mass of underlying LH secretory bursts and to simultaneously estimate basal secretion and the half-life of endogenous LH in each animal. Proestrus rats exhibited a significant increase in the number of computer-identified LH secretory bursts per hour (1.8 +/- 0.2 vs. 1.1 +/- 0.01 on diestrus, P < 0.01), with a corresponding reduction in the LH intersecretory burst interval from 61 +/- 6.4 min (diestrus) to 25 +/- 2.7 min (proestrus, P < 0.01). There was a remarkable 16-fold increase in the mass of LH secreted per burst, which rose from 72 +/- 5.2 to 1,230 +/- 200 ng/ml (P < 0.01). This resulted from a sixfold increase in LH secretory burst amplitude and a doubling of burst duration. The total amount of LH released in a burstlike fashion during the proestrous LH surge rose 20-fold, and calculated basal LH secretion increased to approximately 25% of this value. Of interest, the computed half-life of endogenous LH also increased from 10 +/- 1.1 to 19 +/- 3.7 min (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Inconsistent divergence of mitochondrial DNA in the spontaneously hypertensive rat.

We have recently shown that the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto (WKY) rat differ at a frequency of 1 per 62 bases in their nuclear DNA (Hypertension 1992; 19:425-427). Given the origin of these strains this level of divergence was unexpected. To investigate the origin of this nuclear divergence we have examined mitochondrial DNA. Mitochondrial DNA was isolated from SHR and WKY rats, digested with several restriction enzymes, electrophoresed in 1.0% agarose gels, and the fragments visualized with ethidium bromide staining. This approach allowed us to analyze 220 base pairs of mitochondrial DNA. No differences were detected between SHR and WKY rats. Comparison with the King-Holtzman rat strain produced differences at an average of 1 per 52 base pairs. We also examined several SHR and WKY rats from within our colonies and found no differences suggesting intrastrain homogeneity for mitochondrial DNA phenotypes. These data indicate that the SHR and WKY rat share a recent, common maternal ancestor. This result is consistent with the published origins of the SHR and WKY rat strains. Together with the nuclear divergence results, the data suggest that the original Wistar colony from which SHR and WKY rats were derived was probably highly polymorphic for nuclear genes.

Animals↗

PubMed1993

The hypertensive Y chromosome elevates blood pressure in F11 normotensive rats.

Our laboratory has shown that the Y chromosome has a significant effect on blood pressure in the spontaneously hypertensive rat (SHR) model of hypertension and that the testes and androgen receptor contribute to the blood pressure rise. As an extension of our research, we have developed two new rat strains, SHR/a and SHR/y (F11) to study the Y chromosome. The objectives of the following research were 1) to study the blood pressure of rats with an SHR Y chromosome in a normotensive genetic background (SHR/y) or a normotensive Y chromosome in an SHR genetic background (SHR/a), 2) to determine the effect of male sex phenotype on the blood pressure of these rats, 3) to determine if testosterone replacement in castrated rats would restore blood pressure, and 4) to determine whether the Y chromosome from the SHR/y strain when crossed with a normotensive female can induce hypertension in androgen receptor-deficient male offspring. Blood pressure of male SHR/y rats was significantly higher than that of normotensive Wistar-Kyoto males (p < 0.01), and SHR/a males had significantly lower blood pressure compared with that of the parent SHR strain (p = 0.05). Testosterone replacement in castrated rats of both strains (SHR/a and SHR/y) restored blood pressure to control levels. Normotensive female King-Holtzman rats heterozygous for the testicular feminization gene were crossed with F11 SHR/a and SHR/y males.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1993

Influence of the high-affinity growth hormone (GH)-binding protein on plasma profiles of free and bound GH and on the apparent half-life of GH. Modeling analysis and clinical applications.

The discovery of a specific high-affinity growth hormone (GH) binding protein (GH-BP) in plasma adds complexity to the dynamics of GH secretion and clearance. Intuitive predictions are that such a protein would damp sharp oscillations in GH concentrations otherwise caused by bursts of GH secretion into the blood volume, prolong the apparent half-life of circulating GH, and contribute a reservoir function. To test these implicit considerations, we formulated an explicit mathematical model of pulsatile GH secretion and clearance in the presence of absence of a specific high-affinity GH-BP. Simulation experiments revealed that the pulsatile mode of physiological GH secretion creates a highly dynamic (nonequilibrium) system, in which the half-life of free GH, its instantaneous secretion rate, and the GH-BP affinity and capacity all contribute to defining momentary levels of free, bound, and total GH, the percentage of GH bound to protein, and the percentage occupancy of GH-BP [corrected]. In contrast, the amount of free GH at equilibrium is specified only by the GH distribution volume and secretion rate and the half-life of free hormone. We conclude that the in vivo dynamics of GH secretion, trapping, and clearance from the circulation offer a variety of regulatory loci at which the time structure of free, bound, and total GH delivery to target tissues can be controlled physiologically.

Carrier Proteins↗

PubMed1993

A low dose euglycemic infusion of recombinant human insulin-like growth factor I rapidly suppresses fasting-enhanced pulsatile growth hormone secretion in humans.

To determine if insulin-like growth factor I (IGF-I) inhibits pulsatile growth hormone (GH) secretion in man, recombinant human IGF-I (rhIGF-I) was infused for 6 h at 10 micrograms.kg-1.h-1 during a euglycemic clamp in 10 normal men who were fasted for 32 h to enhance GH secretion. Saline alone was infused during an otherwise identical second admission as a control. As a result of rhIGF-I infusion, total and free IGF-I concentrations increased three- and fourfold, respectively. Mean GH concentrations fell from 6.3 +/- 1.6 to 0.59 +/- 0.07 micrograms/liter after 120 min. GH secretion rates, calculated by a deconvolution algorithm, decreased with a t 1/2 of 16.6 min and remained suppressed thereafter. Suppression of GH secretion rates occurred within 60 min when total and free IGF-I concentrations were 1.6-fold and 2-fold above baseline levels, respectively, and while glucose infusion rates were < 1 mumol.kg-1.min-1. During saline infusion, GH secretion rates remained elevated. Infusion of rhIGF-I decreased the mass of GH secreted per pulse by 84% (P < 0.01) and the number of detectable GH secretory pulses by 32% (P < 0.05). Plasma insulin and glucagon decreased to nearly undetectable levels after 60 min of rhIGF-I. Serum free fatty acids, beta-hydroxybutyrate, and acetoacetate were unaffected during the first 3 h of rhIGF-I but decreased thereafter to 52, 32, and 50% of levels observed during saline. We conclude that fasting-enhanced GH secretion is rapidly suppressed by a low-dose euglycemic infusion of rhIGF-I. This effect of rhIGF-I is likely mediated through IGF-I receptors independently of its insulin-like metabolic actions.

3-Hydroxybutyric Acid↗

PubMed1993

Alterations in luteinizing hormone secretory activity in women with insulin-dependent diabetes mellitus and secondary amenorrhea.

To investigate hypothalamic and/or pituitary abnormalities in women with poorly controlled insulin-dependent diabetes mellitus (IDDM) and secondary amenorrhea, we measured serum LH every 10 min for 24 h and for 2 additional h after the administration of exogenous GnRH in 8 women with IDDM and amenorrhea and compared these to data from 15 eumenorrheic nondiabetic women. LH pulses were characterized by the pulse detection algorithm Cluster, and secretory episodes were evaluated using the multiple parameter deconvolution procedure Deconv. Cluster analysis revealed fewer LH pulses per 24 h (14.3 +/- 1.2 vs. 19.9 +/- 0.6; P < 0.001; mean +/- SEM), a greater peak width (63 +/- 4.9 vs. 44 +/- 2.2 min; P < 0.01), and greater peak area (136 +/- 17 vs. 89 +/- 13 IU/L.min; P < 0.01) in the diabetic women. Analysis with Deconv revealed fewer LH secretory episodes per 24 h in the diabetic women (14.4 +/- 0.9 vs. 20.4 +/- 0.5; P < 0.001) and no statistical difference in LH half-lives. The IDDM women responded to a 10-micrograms GnRH bolus with LH pulses of larger total (51 +/- 15.9 vs. 15 +/- 1.4 IU/L; P < 0.01) and incremental (29 +/- 7.6 vs. 9 +/- 1.2; P < 0.001) amplitude. In summary, we observed that amenorrheic diabetic women have fewer LH pulses/secretory episodes than normal women. However, they respond well to exogenous GnRH, suggesting that compromise of the GnRH pulse generator, rather than pituitary dysfunction, is responsible for their menstrual dysfunction.

Adult↗

PubMed1993

Slow baseline growth and a good response to growth hormone (GH) therapy are related to elevated spontaneous GH pulse frequency in girls with Turner's syndrome.

Spontaneous growth and growth responses to GH therapy vary considerably among girls with Turner's syndrome. In an attempt to clarify this variability, we assessed growth parameters, 24-h GH profiles, arginine-stimulated serum GH levels, and plasma insulin-like growth factor-I (IGF-I) concentrations in a group of 41 girls with Turner's syndrome with a mean (+/- SD) age of 13 +/- 3 yr (range, 6.7-18.9). We subsequently treated all girls with biosynthetic GH (24 IU/m2 x week) and documented the growth response after 1 yr of therapy. GH profiles were analyzed according to Pulsar and Cluster, and GH secretion rates were calculated by waveform-independent deconvolution (Pulse). Factor analysis selected the mean 24-h GH secretion rate and number of GH peaks according to Cluster and Pulse as the principal GH profile variables to be used for further analysis. The mean (+/- SD) daily pituitary GH secretion rate was 127 +/- 47 micrograms/L.24 h (range, 37-232). The GH secretion rate correlated inversely with body mass index (r = -0.45; P < 0.01; n = 41). There was no relationship between the GH secretion rate and the growth parameters before or after GH therapy. However, the number of GH peaks (Pulse) correlated negatively with baseline height velocity (r = -0.53; P = 0.03) and was a positive predictor for height velocity increment during the first year of GH therapy (r = 0.71, P = 0.001). The mean (+/- SD) IGF-I level was 217 +/- 91 ng/mL (range, 87-413). There was no relationship between GH secretion rate or growth parameters and IGF-I. However, the number of GH peaks correlated negatively with IGF-I (r = -0.49; P = 0.04; n = 17). We conclude that an elevated spontaneous GH pulse frequency pattern is associated with relatively low IGF-I levels and slow baseline growth in girls with Turner's syndrome and that girls with such a pulse pattern may benefit most from exogenous GH therapy.

Adolescent↗

PubMed1993

Comparison of antihypertensive and beta 1-adrenoceptor antagonist effect of nebivolol and atenolol in essential hypertension.

dl-nebivolol is a new, chemically unique, selective beta 1-adrenoceptor antagonist, without sympathomimetic activity. In the present study, the antihypertensive and negative chronotropic effects of 5 and 10 mg once-daily nebivolol were compared to those of 50 and 100 mg once-daily atenolol in 25 white, male subjects with essential hypertension, using a double-blind, crossover design, and a parallel placebo-treated group of subjects (N = 7). 24 hours after dosing, sitting and standing diastolic and systolic blood pressures and heart rates (at rest and during submaximal exercise) were reduced to the same extent by nebivolol and atenolol. On a weight-for-weight basis, nebivolol is ten times more potent than atenolol. Nebivolol and atenolol also reduced 1-hour ambulatory plasma renin activity. Once-daily nebivolol is an effective antihypertensive beta-adrenoceptor antagonist.

Adrenergic beta-Antagonists↗

PubMed1992

Why, when, and how biochemists should use least squares.

One of the most commonly used methods for the analysis of experimental data in the biochemical literature is nonlinear least squares (regression). This group of methods are also commonly misused. The purpose of this article is to review the assumptions inherent in the use of least-squares techniques and how these assumptions govern the ways that least-squares techniques can and should be used. Since these assumptions pertain to the nature of the experimental data to be analyzed they also dictate many aspects of the data collection protocol. The examination of these assumptions includes a discussion of questions like: Why would a biochemist want to use nonlinear least-squares techniques? When is it appropriate for a biochemist to use nonlinear least-squares techniques? What confidence can be assigned to the results of a nonlinear least-squares analysis?

Biochemistry↗

PubMed1992

Frequency domain imaging of absorbers obscured by scattering.

Multiple pixel, frequency domain measurements of phase shift, theta, and modulation, m, in a phantom containing an absorber obscured by a relatively non-absorbing scattering solution are presented in combination with a theory of photon migration imaging. Results employing a single point source show that two dimensional theta measurements made in the presence (theta presence) and in the absence (theta absence) of an absorber can be used to create delta theta images. delta theta (theta absence-theta presence) images can be used to detect as well as locate the three dimensional position of the absorber. Images of mpresence measured in the presence of the absorber normalized by mabsence also provided detection and two dimensional location of its position. Images of % mpresence/mabsence at higher modulation frequencies provided greater resolution as predicted by photon migration theory. Neither theta nor m images alone could be used to detect or locate the presence of the absorber.

Light↗

PubMed1992

Saltation and stasis: a model of human growth.

Human growth has been viewed as a continuous process characterized by changing velocity with age. Serial length measurements of normal infants were assessed weekly (n = 10), semiweekly (n = 18), and daily (n = 3) (19 females and 12 males) during their first 21 months. Data show that growth in length occurs by discontinuous, aperiodic saltatory spurts. These bursts were 0.5 to 2.5 centimeters in amplitude during intervals separated by no measurable growth (2 to 63 days duration). These data suggest that 90 to 95 percent of normal development during infancy is growth-free and length accretion is a distinctly saltatory process of incremental bursts punctuating background stasis.

Aging↗

PubMed1992

Fluorescence lifetime imaging of free and protein-bound NADH.

We introduce a methodology, fluorescence lifetime imaging (FLIM), in which the contrast depends on the fluorescence lifetime at each point in a two-dimensional image and not on the local concentration and/or intensity of the fluorophore. We used FLIM to create lifetime images of NADH when free in solution and when bound to malate dehydrogenase. This represents a challenging case for lifetime imaging because the NADH decay times are just 0.4 and 1.0 ns in the free and bound states, respectively. In the present apparatus, lifetime images are created from a series of phase-sensitive images obtained with a gain-modulated image intensifier and recorded with a charge-coupled device (CCD) camera. The intensifier gain is modulated at the light-modulation frequency or a harmonic thereof. A series of stationary phase-sensitive images each obtained with various phase shifts of the gain-modulation signal, is used to determine the phase angle or modulation of the emission at each pixel, which is in essence the lifetime image. We also describe am imaging procedure that allows specific decay times to be suppressed, allowing in this case suppression of the emission from either free or bound NADH. Since the fluorescence lifetimes of probes are known to be sensitive to numerous chemical and physical factors such as pH, oxygen, temperature, cations, polarity, and binding to macromolecules, this method allows imaging of the chemical or property of interest in macroscopic and microscopic samples. The concept of FLIM appears to have numerous potential applications in the biosciences.

In Vitro Techniques↗