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Biomedical subjects

G Johnson

Publications and source records attributed to G Johnson.

At least 505 records · Page 28Linked to original sources
PubMed1983

Age-dependent changes in electrophysiologic characteristics of fast and slow action potentials in rat papillary muscle.

Isolated papillary muscles from juvenile (about 2 months old, average weight of 250 g) and young adult rats (about 4 months old, average weight 485 g) were studied for age-dependent differences in the characteristics of fast and slow action potentials (APs). The fast and slow APs were recorded in 5.4 mM and 25 mM K+-Tyrode solutions, respectively (stimulation rate of 1 Hz). For the slow APs, the dose-response curves for isoproterenol versus Vmax (the maximum rate of rise of the APs), overshoot, and AP amplitude were linear between 10(-9) M and 10(-6) M (10(-5 M in some cases) in the juvenile and young adult rats. Isoproterenol pretreatment (1 mg/kg s.c., 1 h prior) decreased the slope of the dose-response curve, and saturation was achieved at a lower concentration. The Vmax, overshoot, and amplitude of both the fast and slow APs were somewhat smaller in the young adult rats than in the juvenile rats; there were no differences in the resting potential, AP duration, or threshold voltage. These results suggest that activation of a greater fraction of the beta-adrenergic receptors is coupled directly or indirectly to activation of a greater fraction of the slow channels. The pretreatment data suggest that down-regulation of the beta-adrenergic receptor may occur. The conductance per channel for the fast Na+ channels and slow channels, and (or) the number of both types of functional channels, may decrease with age.

Action Potentials↗
PubMed1983

Effects of water immersion on plasma catecholamines in normal humans.

Recent evidence indicates that stimulation of cardiopulmonary receptors in experimental animals results in a diminution of autonomic nervous system activity. Water immersion to the neck (NI) results in a preferential central hypervolemia (CV); thus it might be anticipated that NI would alter plasma catecholamine levels. Because two earlier studies have yielded divergent findings, we designed the present study utilizing more updated methodology to determine whether NI alters plasma catecholamines in normal humans. Eight normal subjects were studied on two occasions; during a seated control study (C) and during 4 h of NI. Norepinephrine (NE) and epinephrine (E) levels, determined by radioenzymatic assay, were measured hourly. Despite the induction of a marked natriuresis and diuresis indicating significant CV, NI failed to alter plasma NE or E levels compared with those of either C or the corresponding prestudy 1.5 h. Furthermore, the diuresis and natriuresis varied independently of NE. The current findings suggest that the response of the sympathetic nervous system to acute volume alteration may differ from the reported response to chronic volume expansion.

Adult↗
PubMed1983

Iron binding proteins of iron-absorbing rat intestinal mucosa.

The distribution and quantitation of the iron-binding proteins of rat small intestinal mucosa was studied, in iron-deficient and replete animals, to explore their role in the absorption of iron. Adsorption (mucosal uptake) of iron in in situ ligated loops of small intestinal mucosa was found to be uniform throughout the length of the small intestine whereas absorption (carcass uptake) showed a steep decreasing gradient from the duodenum to the ileum. The disrupted, in vivo labeled mucosal cells were fractionated by isopycnic centrifugation and transferrin and ferritin were quantitated by radioimmunoassay. Transferrin derived from mucosal cells was shown to have a higher affinity for the antibody than transferrin in serum. Of the transferrin present in the mucosal extract, only a portion could be accounted for by contamination from the serum; the proteolysis resistant and intrinsic transferrin may be mucosal cell specific. Transferrin was found in similar amounts in all regions of the small intestine, was not affected by iron loading but doubled in response to iron deficiency. Mucosal ferritin was found in greater amounts in the iron-absorbing areas of the intestine, increased in the duodenum of iron-loaded animals, and decreased in iron-deficient animals. The incorporation of newly absorbed radioiron into ferritin was only found in iron absorbing regions and was completely inhibited by colchicine and cytochalasin-B, suggesting that ferritin was loaded with iron at the point of iron absorption and that the process is associated with vesicle movement and not simple diffusion. Transferrin and ferritin-specific immunoabsorption and also gel filtration established that no other soluble iron binding proteins were involved in absorption.

Animals↗
PubMed1983

Operant control of auditory brainstem potentials in man.

Two studies are described which demonstrate operant conditioning of brainstem auditory evoked response (BAER) component V. Our results show that reinforcement of the cumulative summation of the wave V P8N11 component (20 dB HL stimulus clicks) hastens its summation leading to increased wave V amplitude not associated with trivial mediation factors. The results were interpreted as demonstrating operant control of very early neural events in the brainstem of man.

Acoustic Stimulation↗
PubMed1983

A passive system using rifampin to create an infection-resistant vascular prosthesis.

Vascular prosthesis infection is a devastating complication of vascular operations. The development of a simple process for imparting infection resistance to vascular prosthesis material would be invaluable. Rifampin was added to the blood that was used to preclot 8 mm Dacron vascular prostheses that were used to replace the infrarenal aorta in 10 mongrel dogs. Rings of the grafts were resected after blood had flowed through them for 0 minute, 15 minutes, 60 minutes, and 24 hours. The resected graft rings were placed on culture plates that had been inoculated heavily with Staphylococcus aureus. The rate of antibiotic dialysis from the graft was determined by comparison of the inhibition rings that were produced by the graft rings at each subsequent interval. At 60 minutes, inhibition was 94% of that at time 0. Inhibition at 24 hours was 91%, which demonstrated no significant decrease from 60 minutes. Other antibiotics were screened by this technique, but none of them demonstrated inhibition at 24 hours. In a pilot study in which two dogs were given parenteral rifampin before and after operation and grafts were preclotted with blood that contained rifampin, it was suggested that there was a slight increase in inhibition at 24 hours (93%). The data indicated that rifampin that is added to the blood that is used to preclot a porous Dacron prosthesis is so slowly dialyzed from the graft that inhibition remains at 24 hours. This passive system imparts potential resistance to the prosthesis.

Animals↗
PubMed1982

Graded compression stockings: custom vs noncustom.

Graded compression stockings of the leg (high pressure at the ankle and low pressure at the thigh) seem to help the return of venous blood to the heart and reduce the incidence deep-vein thrombosis and pulmonary emboli in supine patients. Recent advances allow noncustom stockings to be chosen for mesomorphic patients by leg length and calf circumference yet deliver the desired level of graded compression. To test the hypothesis that custom-tailored and noncustom, low-modulus. circular-knit stockings are equally efficient, a Doppler instrument and recorder were used to continually monitor femoral-vein velocity both when the patient had the stocking on and after it was removed. The changes in venous velocity after removal of custom and noncustom stockings were similar (-19% and -27%, respectively). In the five patients with whom both types of stocking were evaluated, the changes were -24% for custom and -22% for noncustom stockings. Using Laplace's law and measuring the tension created by a given stretch (circumference), low-modulus stockings were shown to deliver a more uniform pressure over a greater range of leg circumference than did high-modulus stockings. These results justify the use of noncustom, low-modulus, circular-knit elastic stockings to increase femoral-vein velocity in supine, mesomorphic patients.

Bandages↗
PubMed1982

Rifampin and cefazolin as prophylactic agents. A comparison in an animal model of vascular graft infection.

We investigated rifampin and cefazolin sodium as prophylactic agents in a dog model of vascular graft infection. A 1-cm segment of 3-mm-diameter polytetrafluoroethylene (Gore-tex) graft was sewn into the right carotid artery of each dog, and prior to closure, 10(3) Staphylococcus organisms sensitive to both cefazolin and rifampin were injected over the graft. The dogs were killed five days after surgery and the grafts cultured. Infection occurred in 100% of controls, 58% of cefazolin-pretreated dogs, and 17% of rifampin-pretreated dogs. Mean blood levels of antibiotics were assayed as follows: cefazolin, 50.1 micrograms/mL; rifampin, 2.9 micrograms/mL. Both were well above the minimal inhibitory concentration. Thus, rifampin proved to be more effective than cefazolin in this animal model.

Animals↗
PubMed1982

Aortoiliac operations and sexual dysfunction.

Male sexual dysfunction after aortoiliac operations can be a distressing complication. Since previous studies dealing with this problem have not excluded other causes of sexual dysfunction, the true incidence of this complication has been difficult to ascertain. We assessed preoperative and postoperative sexual function in a group of patients with no identifiable organic or functional etiology of sexual dysfunction other than aortoiliac operations or arterial occlusive disease. Seventy-six male patients had no evidence of sexual dysfunction of ambiguous etiology before or after operation. Preoperatively, 33% of patients with abdominal aortic aneurysm and 22% of those with aortoiliac occlusive disease were functionally impotent. Conventional dissection techniques rendered an additional 30% of each group functionally impotent. Postoperative impotence was twice as common in those with minor dysfunction preoperatively.

Adult↗
PubMed1982

Chemical nature of mouse antibodies homologous to the 3-pyridylazo group: the fine specificities of hybridoma and serum antibodies.

Rabbit antibodies which bind aromatic annular nitrogen-containing haptens exhibit a specificity wherein such nitrogens are distinguished from the closely related aromatic CH group. The mouse hybridoma system was used to extend this work producing hybridoma antibodies homologous to the 3-pyridylazo group. Fine specificity mapping by double antibody radioimmunoassay revealed differences among the individual hybridomas, as well as a greater resemblance of mouse serum antibodies to rabbit serum antibodies than to hybridoma antibodies. Quantitative structure-activity relationships applying the parameters of hapten molar refractivity had hydrophobicity were used to help elucidate the types of intermolecular forces involved in the interaction of pyridine derivatives with the antibodies. The results are consistent with the interpretation that pyridine binding to antibody does not involve desolvation.

Animals↗
PubMed1982

Synthesis and comparison of some cardiovascular properties of the stereoisomers of labetalol.

A useful method for the separation of labetalol into its two racemic diastereomers, as well as a stereoselective synthesis of its four stereoisomers, is described. The absolute stereochemistry of each isomer was determined by analysis of the DC spectra and confirmed by X-ray analysis. The alpha- and beta 1-adrenergic blocking properties, as well as the relative antihypertensive activities, have been measured in rats. The R,R isomer, 2a (SCH 19927), possesses virtually all of the beta 1-blocking activity elicited by labetalol and displays little alpha-blocking activity. In contrast, the S,R isomer, 3a, has most of the alpha-blocking activity. Of the four isomers, only 2a has antihypertensive potency comparable to that of labetalol. These findings, coupled with published data showing that labetalol possesses beta-adrenergic mediated peripheral vasodilating activity deriving essentially from its R,R isomer, lead to the following conclusion: The antihypertensive activity of labetalol can be ascribed to at least three identified complementary mechanisms, beta-adrenergic blockade, beta-adrenergic mediated vasodilatation, and alpha-adrenergic blockade, whereas the antihypertensive activity of 2a derives from the first two mechanisms only.

Adrenergic alpha-Antagonists↗
PubMed1982

The distribution of serum alanine aminotransferase levels in a blood donor population.

The authors studied the distribution of alanine aminotransferase (ALT) levels in 10,034 volunteer blood donors. The mean +/- SD ALT value was 21.4 +/- 19.3 IU/liter; 549 (5.5%) of the donors had a ALT value greater that 45 IU; 2.5 per cent had ALT values greater than 60 IU. In general, ALT levels were higher in males than in females, and were age related; peak values occurred in the third decade of life for males and between 50-60 years of age in females. ALT values greater than 45 IU were found significantly more often in males, in donors of both sexes 30-40 years of age, in married donors, in non-Caucasians, and in those whose education level was no higher than high school. Follow-up samples in donors with an initial ALT greater than 45 IU, revealed that 67% continued to have ALT values above 45 IU 2-8 weeks following initial sampling, and 40% had an ALT greater than 45 IU when tested again six months after entry into the study. ALT values greater than 60 IU were associated with a significantly increased prevalence of antibody of hepatitis B surface antigen (anti-HBs) and antibody to hepatitis B core antigen (anti-HBc) occurring together. No statistically significant association was found between transaminase activity and the prevalence of anti-HBs or anti-HBc alone, or with hepatitis A antibody. These findings demonstrate that there are defined sociodemographic and serologic features of donors with elevated ALT values.

Age Factors↗
PubMed1982

Femoral venous trauma in a university referral center.

Therapeutic results from extremity vascular injuries have been improved by early definitive care by surgeons trained in peripheral vascular techniques. Serious venous injuries are uncommonly seen other than in large urban referral centers or military installations. Seventeen patients with major femoral venous injuries were evaluated over the past 25 years at the North Carolina Memorial Hospital. The records from these patients were analyzed regarding mechanisms of injury, time delay for definitive care, clinical presentation, significant associated injuries, operative management of the venous injury, early and long-term morbidity, and mortality. Major femoral venous injury was associated with simultaneous arterial injury in 59% of cases. Primary venous repair was performed in seven cases with a satisfactory functional result in all instances. Chronic venous insufficiency developed in five patients (29%), all of whom had arterial injuries and venous ligation. Postoperative complications were commonly related to associated injuries. No patient in this series developed thrombophlebitis or a pulmonary embolus. Isolated femoral vein injuries are usually associated with both early and late favorable results. Femoral vein ligation in the presence of arterial injuries usually leads to serious long-term venous disability. When technically feasible, operative repair of major femoral vein injuries is advocated.

Femoral Vein↗
PubMed1982

Performance of a level II nursery in a neonatal regional program: part I. Patient population and role of the general pediatrician.

We examined the performance of a level II nursery in a regional neonatal program during a 30-month period. Of 3,851 live-born infants, 527 (13.7%) were admitted to the special care nursery and 70 (1.8%) were transferred to a level III nursery. There were 23 neonatal deaths, ten of them in the level II facility; the other 13 infants had been transferred to a level III center and died there. Three hundred eleven (59%) of the admissions to the special care nursery were infants whose birth weights exceeded 2,500 gm, and 241 (46%) were of more than 37 weeks' gestation. There were 262 infants admitted with respiratory distress. In an additional 55 infants, respiratory distress was part of their clinical presentation. Procedures done by the professional staff reflected these needs. A total of 3,476 days of care were provided in the special care nursery, with a mean duration of 6.6 +/- 5.91 days (+/- 1 SD). Physician time required in the special care unit was 2,317.3 hours, an average of 4.4 hours per admission. These data support the contention that general pediatricians operating level II nurseries within a regionalized program can provide care of the majority of newborns, including care of the majority of ill neonates.

Georgia↗
PubMed1982

Cirrhosis, variceal bleeding, and distal splenorenal shunt in hemophilia A.

Chronic liver disease has become a significant complication of the therapy of hemophilia disorders. We describe two patients with hemophilia A and hepatitis B virus hepatitis who progressed to cirrhosis with bleeding esophageal varices. Each underwent distal splenorenal shunt under plasma concentrate therapy without difficulty. One patient died 19 months after operation and unsuspected hepatocellular carcinoma was found at autopsy. These cases illustrate the potential severity of liver disease in hemophilia and the ability to safely perform surgery for portal hypertension if required.

Adult↗
PubMed1982

Diagnosis of mycotic abdominal aortic aneurysm using 67-gallium citrate.

Mycotic aneurysms of the abdominal aorta are uncommon, but potentially lethal problems. Clinical subtleties may suggest their presence, but in the past, definitive diagnosis has been dependent on surgical exploration or autopsy findings. A case is presented in which 67-gallium citrate abdominal scanning localized the site of sepsis in an abdominal aortic aneurysm and allowed for prompt and successful surgical therapy. This noninvasive technique is recommended as a adjunct in the diagnosis of mycotic abdominal aortic aneurysms.

Aged↗