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Biomedical subjects

D G Johnson

Publications and source records attributed to D G Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Gag proteins of the highly replicative MN strain of human immunodeficiency virus type 1: posttranslational modifications, proteolytic processings, and complete amino acid sequences.

The MN strain of human immunodeficiency virus type 1 was grown in H9 cells, concentrated by centrifugation, and disrupted, and proteins were purified by reversed-phase high-pressure liquid chromatography. Complete amino acid sequences were determined for the mature Gag proteins, showing natural proteolytic cleavage sites and the order of proteins (p17-p24-p2-p7-p1-p6) in the Gag precursors. At least two sequence variants of p24 and eight sequence variants of p17 were detected. The two most abundant variants of p24 and p17 represented at least 50% +/- 5% and 20% +/- 5% of their totals, respectively. These data suggest heterogeneity in the virus population, with 50% of the total virus containing the most abundant forms of p17 and p24 and 20% of the virus containing the second most abundant forms. The Gag precursors of these suggested viruses differ from each other by only 3 amino acid residues but differ from the precursors predicted by the published MN proviral DNA sequence by 10 residues. Electrospray ionization mass spectrometry analysis of the purified p24 forms showed that the measured molecular weight of the protein was 200 +/- 50 atomic mass units greater than the calculated molecular weight. The source of additional mass for the p24 forms was not determined, but the observation is consistent with previous suggestions that the protein is phosphorylated. Greater than 98% of the total recovered p17 was myristylated at the N-terminal glycine residue, and the measured molecular weights (as determined by electrospray ionization mass spectrometry) of the most abundant forms were within 3 atomic mass units of the calculated molecular weights (15,266).

Amino Acid Sequence↗
PubMed1992

Sympathoadrenal-circulatory regulation of arterial pressure during orthostatic stress in young and older men.

Our purpose was to test the hypothesis that human aging alters sympathoadrenal-circulatory control of arterial blood pressure during orthostasis. Plasma catecholamine and hemodynamic adjustments to two different forms of orthostatic stress, lower body suction (-10 to -50 mmHg) and standing, were determined in 14 young (26 +/- 1 yr) and 13 older (64 +/- 1) healthy, normally active men. During quiet supine rest, cardiac output tended to be lower and systemic vascular resistance higher in the older men, but no other differences were observed. On average, arterial blood pressure was well maintained during both forms of orthostasis in the two groups; the older men actually demonstrated better maintenance of pressure (P < 0.05) and a lesser incidence of orthostatic hypotension than the young men during lower body suction. Despite a blunted reflex tachycardia during orthostatic stress (P < 0.05), cardiac output tended to decrease less in the older men because of a smaller decline in stroke volume (P < 0.05, suction only), whereas the reflex increases in systemic vascular resistance were not different in the two groups. The whole forearm vasoconstrictor response tended to be attenuated in the older men during lower body suction, but was identical in the two groups with standing. Forearm skin vascular resistance was unaltered during lower body suction in both groups. Orthostasis-evoked increases in antecubital venous plasma norepinephrine concentrations were similar in the young and older men, whereas little or no increases in plasma epinephrine concentrations were observed in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1992

Augmented forearm vasoconstriction during dynamic exercise in healthy older men.

BACKGROUND: We tested the hypothesis that the nonactive limb vasoconstriction evoked during large-muscle dynamic exercise becomes augmented with aging in humans. METHODS AND RESULTS: Sixteen young control subjects (age, 26 +/- 1 year) and twelve older (65 +/- 1 year) healthy men with similar chronic physical activity levels were studied during supine leg cycling exercise. Both peak work load (1,100 +/- 60 versus 1,400 +/- 40 kpm/min) and peak O2 uptake (1.85 +/- 0.10 versus 2.38 +/- 0.07 l/min) were lower in the older men (p < 0.05). There were no differences in the two groups under conditions of quiet supine (basal) rest. During cycling for 5 minutes each at mild, moderate, and heavy submaximal intensities (approximately 45%, 65%, and 85% of peak O2 uptake), the increases in arterial blood pressure generally were similar in the young and older subjects; however, heart rate rose less in the older men (p < 0.05). Whole forearm blood flow (venous occlusion plethysmography) was lower and vascular resistance was higher (approximately 55-90%) in the older men at all loads (p < 0.05), but the steady-state forearm skin blood flow responses (laser Doppler velocimetry) were not different in the two groups. The increases in antecubital venous norepinephrine concentrations were greater in the older men at each work load (p < 0.05), although the plasma epinephrine responses were similar in the two groups. In other studies, 1) peak whole forearm reactive hyperemia and vascular conductance after sustained circulatory arrest (ischemia) were slightly (approximately 20%) but not significantly lower in the older men and 2) the forearm vasoconstrictor and plasma norepinephrine responses to a nonexercise sympathoexcitatory stimulus (limb immersion in ice water) tended to be blunted in the older men. CONCLUSIONS: During brief, submaximal, large-muscle dynamic exercise, healthy older men demonstrate augmented forearm vasoconstriction that is probably caused by greater constriction of skeletal muscle resistance vessels; this appears to be mediated, at least in part, by increased sympathetic outflow. These altered sympathetic vasoconstrictor adjustments do not represent a nonspecific hyperresponsiveness to acute stress with human aging. Finally, the regulation of arterial blood pressure appears to be normal in these healthy older men.

Adult↗
PubMed1991

Hypoxia potentiates exercise-induced sympathetic neural activation in humans.

Our purpose was to test the hypothesis that hypoxia potentiates exercise-induced sympathetic neural activation in humans. In 15 young (20-30 yr) healthy subjects, lower leg muscle sympathetic nerve activity (MSNA, peroneal nerve; microneurography), venous plasma norepinephrine (PNE) concentrations, heart rate, and arterial blood pressure were measured at rest and in response to rhythmic handgrip exercise performed during normoxia or isocapnic hypoxia (inspired O2 concn of 10%). Study I (n = 7): Brief (3-4 min) hypoxia at rest did not alter MSNA, PNE, or arterial pressure but did induce tachycardia [17 +/- 3 (SE) beats/min; P less than 0.05]. During exercise at 50% of maximum, the increases in MSNA (346 +/- 81 vs. 207 +/- 14% of control), PNE (175 +/- 25 vs. 120 +/- 11% of control), and heart rate (36 +/- 2 vs. 20 +/- 2 beats/min) were greater during hypoxia than during normoxia (P less than 0.05), whereas the arterial pressure response was not different (26 +/- 4 vs. 25 +/- 4 mmHg). The increase in MSNA during hypoxic exercise also was greater than the simple sum of the separate responses to hypoxia and normoxic exercise (P less than 0.05). Study II (n = 8): In contrast to study I, during 2 min of exercise (30% max) performed under conditions of circulatory arrest and 2 min of postexercise circulatory arrest (local ischemia), the MSNA and PNE responses were similar during systemic hypoxia and normoxia. Arm ischemia without exercise had no influence on any variable during hypoxia or normoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Responses of dairy cows to supplemental rumen-protected forms of methionine and lysine.

Multiparous Holstein cows at six universities were utilized to examine effects of ruminally protected methionine and lysine on lactational performance. Three hundred and four cows began the study; 259 cows were included in the production analysis. Following a 21-d standardization period, cows received a basal diet of corn silage and ground corn supplemented with one of five dietary treatments, which were supplements of soybean meal or corn gluten meal, the latter with zero and three combinations of protected methionine and lysine (methionine; methionine and lysine; methionine and double (2x) lysine). Treatment effects were evaluated during early, mid, late, and total lactation (22 to 112, 113 to 224, 225 to 280, and 22 to 280 d postpartum, respectively). On a DM basis, ratios of forage to concentrate (50:50, 60:40, and 70:30) increased, and dietary CP (16.0, 14.5, and 13.0%) decreased during the three periods of lactation. Amount of amino acid supplementation also decreased (15, 12, and 9 g/d methionine; 20, 16, and 12 g/d lysine; and 40, 32, and 24 g/d 2x lysine) with period of lactation. Actual and least squares means for milk, FCM, and milk protein yields were greater for soybean than for corn gluten meal during early, mid, and total lactation. In addition, these variables responded linearly to lysine in early lactation. Response to lysine was quadratic during mid and total lactation for these variables. Differences in nutrient intake explained production responses to protein sources but not to lysine. Serum amino acid responses primarily reflected differences in dietary protein source and rumen-protected amino acid.

Amino Acids↗
PubMed1979

Patterns of postcibal gastroesophageal reflux in symptomatic infants.

Symptomatic infants displayed three patterns of gastroesophageal reflux after drinking apple juice (20 ml/kg or 300 ml/m2 of body surface area). The type I pattern occurred in patients who had continuous postcibal gastroesophageal reflux, large hiatal hernias and frequently required an antireflux operation. A functional motility disorder suggesting delayed gastric emptying appeared to be important in infants with discontinuous reflux (type II pattern). These infants had frequent gastroesophageal reflux for only 2 3/4 hours postcibally, antral-pylorospasm, increased low esophageal sphincter pressures, and a high incidence of pulmonary symptoms and non-specific watery diarrhea. The mixed (type III) pattern of gastroesophageal reflux occurred in a small number of infants and exhibited features of both type I and II patterns.

Child, Preschool↗
PubMed1979

Reduction of plasma triglyceride concentration by acute stress in man.

Three different forms of stress all resulted in acute reduction of plasma triglyceride concentrations. Pyrogen reactions in two hypertriglyceridemic men resulted in the lowering of very-low-density lipoprotein (VLDL) triglyceride levels by 93% and 73% due to decreased secretion of this lipoprotein into plasma. More modest reductions in plasma triglycerides were observed after 2-deoxyglucose-induced intracellular glucopenia and insulin-induced hypoglycemia. With hypoglycemia, the lowering of plasma triglyceride concentration correlated significantly with the stimulation of urinary epinephrine output (r = 0.86) but with neither the urinary norepinephrine response nor with the increase in plasma immunoreactive glucagon levels. To further test whether these changes in plasma triglyceride levels were mediated via the sympathetic nervous system, hypoglycemia was evoked by insulin in subjects with traumatic spinal cord transactions. Two such subjects, who demonstrated sympathetic stimulation in response to hypoglycemia, had evidence of reduced VLDL secretion into plasma, while in two who had no evidence of an adrenergic response. VLDL secretion was not inhibited. Thus, acute lowering of plasma triglyceride concentrations by certain forms of stress appears to be mediated via the sympathetic nervous system.

Acute Disease↗
PubMed1979

The lower esophageal sphincter in gastroesophageal reflux in children.

Esophageal function was evaluated in 51 children less than 2 years of age with radiologic evidence of gastroesophageal reflux. Detection of an acid esophageal pH was a sensitive measure of gastroesophageal reflux. Lower esophageal sphincter pressures were greater in reflux patients with respiratory symptoms (18.0 +/- 1.4 mm Hg) than in reflux patients without respiratory symptoms (9.5 +/- 1.0 mm Hg). The intra-abdominal segment of the lower esophageal sphincter was shorter in patients with reflux than in controls (0.51 +/- 0.05 cm vs. 0.75 +/- 0.08 cm). It was also shorter in patients requiring surgical therapy (0.34 +/- 0.05 cm) than in those responding to medical therapy (0.63 +/- 0.07 cm).

Age Factors↗
PubMed1979

Catecholamine elevation in iron deficiency.

Iron-deficient rats have increased blood and urinary catecholamines regardless of whether anemia is or is not present. The catecholamine response in both iron-deficient and control animals is largely temperature dependent, showing little difference at the isothermic temperature of 30 degrees C but a two- to threefold increase in iron-deficient animals over controls at lower temperatures. The iron-deficient rat is unable to maintain body temperature at 4 degrees C and this is independent of anemia or of food intake. When animals are run on the treadmill for 4 h, body temperatures increase but the difference observed at 4 degrees C between iron-deficient and control animals persists. The underlying abnormality in temperature regulation and in catecholamine response disappeared after 6 days of iron therapy.

Animals↗
PubMed1979

Parathyroid hormone release is not associated with acute sympathetic arousal in goats.

Physiological activation of the sympathetic adrenomedullary (SAM) axis following both thermal and non thermal stress was assessed by changes in serum norepinephrine, glucose and/or protein as well as indices of peripheral blood flow. The occurrence of elevated serum parathyroid hormone (PTH) did not reliably reflect SAM activation as might be predicted from pharmacological studies that document a beta adrenergic receptor mechanism in the parathyroid gland that mediates catecholamine stimulated release of PTH into the circulation. The beta agonist isoproterenol at 1 microgram/min for 60 min did produce a transient increase in serum PTH at 20 min. Overall, the data raise doubts about the physiological significance of the adrenergic receptor in the parathyroid gland. Significant increases in serum PTH of 67% and 109% above basal respectively were seen following ruminal loading with cold and thermoneutral water. Associated with the PTH change were increased serum phosphorus and elevated or constant serum protein and serum total calcium.

Animals↗
PubMed1978

Infant tracheostomy. A new look with a solution to the difficult cannulation problem.

Although most infant airway and ventilatory problems will be best solved by the use of endotracheal tubes, clear-cut indications for tracheostomy exist. Past reticence to use tracheostomy for infants has been due mainly to the fear of decannulation problems. Recognition of obstructive airway lesions, particularly the lumen-narrowing tracheal stomal granuloma, has been facilitated by the routine use of the newer infant bronchoscopes with optical telescopes. Successful decannulation begins with proper tracheostomy technique, and continues through tracheostomy management and a well-conceived decannulation program. Decannulation should include evaluation of the structure and function of the airway endoscopically and it may include translaryngeal endoscopic resection or formal surgical removal of any obstructing lesions. Experienced nursing personnel are essential to the entire program.

Airway Obstruction↗
PubMed1978

Survey of graduates of a traditionally black college of medicine.

Over 700 Howard University medical alumni of seven representative classes graduating from 1955 to 1975 were surveyed by questionnaire in 1975-76. Replies of the 311 respondents confirm that this college of medicine has trained a substantial number of physicians who are providing care to blacks, the economically disadvantaged, and residents of inner city areas. Survey findings may also be useful in reaffirming the necessity for training more minority physicians, assessing the impact which the increasing number of minority physicians will have on health care delivery in this country, and suggesting the probable practice patterns of future minority graduates of U.S. medical schools.

Adult↗