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Biomedical subjects

D C Johnson

Publications and source records attributed to D C Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1981

Fluorescence photobleaching recovery measurements reveal differences in envelopment of Sindbis and vesicular stomatitis viruses.

Fluorescence photobleaching recovery (FPR) measurements of virus glycoproteins on the surfaces of cells infected with vesicular stomatitis virus (VSV) and Sindbis virus showed that the VSV glycoprotein (G) remained mobile throughout the infectious cycle, whereas Sindbis virus glycoproteins (E1, E2) were partially mobile early after infection and immobile at later times when greater amounts of these proteins were on the cell surface. A highly mobile fraction of Sindbis virus glycoproteins was detected throughout the replication cycle of a temperature-sensitive mutant unable to form virus particles. This immobilization of E1 and E2 was the result of increasing surface glycoprotein concentrations and virus budding. Together with other data, which included the detection of E1 and E2 in particles as soon as these proteins were transported to the cell surface, the FPR results suggest that Sindbis virus assembly initiates on intracellular vesicles, where glycoproteins aggregate and bind nucleocapsids. In contrast, our FPR data on VSV support a model previously suggested by others, in which a small fraction of cell-surface G is immobilized into budding sites formed by interactions with virus matrix and nucleoproteins. FPR measurements also provide direct evidence for strong interactions between E1 and E2, as well as between E1 and PE2, the precursor form of E2.

Animals↗
PubMed1981

Production of 17-hydroxypregnenolone and 17-hydroxyprogesterone by the immature rat ovary.

The concentration of 17-hydroxyprogesterone (17-OH-prog), but not 17-hydroxypregnenolone (17-OH-preg), was detectable in the sera of 5 day old female rats. The level of 17-OH-preg increased dramatically between day 5 and 10, remained high for 5 days and then decreased to low levels by day 25; a second increase was found on day 35. 17-OH-prog began to increase in the serum after day 10, reached a peak by day 20 and then decreased by day 25 and remained the same through day 35. Stimulation of the ovaries of intact females with 20 IU of pregnant mare's serum gonadotropin resulted in a prompt increase in both progestins, but a much larger increase in 17-OH-preg than in 17-OH-prog. Increases were similar, but quantitatively less, in hypophysectomized females. The results demonstrate that the ovaries of immature rats contain an active 17-hydroxylase system.

17-alpha-Hydroxypregnenolone↗
PubMed1981

Peptidase regulation of gonadotropin-releasing hormone levels during in vitro incubations of the rat hypothalamus.

The fate of gonadotropin-releasing hormone (GnRH) was examined by a GnRH radioimmunoassay during in vitro incubations of the rat medial basal hypothalamus (MBH). There was a progressive disappearance of exogenous GnRH during MBH incubations. The GnRH degradation could be explained by the release of peptidases from the MBH into the incubation medium. The cytoplasmic marker lactic dehydrogenase (LDH) was also released into the incubation medium. The peptide antibiotic bacitracin produced a dose-dependent inhibition of GnRH degradation during MBH incubations; 1 mM-bacitracin completely inhibited exogenous GnRH degradation during 4-h incubations. Bacitracin also produced dose-dependent increases in the recovery of endogenous GnRH released from the MBH under basal conditions or when stimulated with the depolarizing agent veratrine. Veratrine also was found to decrease the GnRH peptidase activity significantly but not the LDH activity during MBH incubations. The present results indicate that peptidase activity can be an important regulator of endogenous GnRH released from the hypothalamus during in vitro incubations.

Animals↗
PubMed1981

Transthoracic right atrial cannulation for total parenteral nutrition- case report.

A man with severe peripheral vascular disease and requiring total parenteral nutrition because of short bowel syndrome was referred because a central venous catheter could not be inserted by conventional techniques. A right thoracotomy was performed and a Hickman catheter inserted via the right atrial appendage into the right atrium. This catheter was used for a total of seven months for total parenteral nutrition. For the last two months of this time, the patient was maintained at home on a Home Parenteral Nutrition Programme. After four months of total parenteral nutrition the patient developed recurrent fevers and the catheter was found to have migrated from the right atrium into the pulmonary artery. The catheter was resited under X-ray control and used for a further three months until the recurrence of fever and dyspnoea heralded the onset of septic pulmonary emboli resulting in his death.

Cardiac Catheterization↗
PubMed1981

Changes in follicle-stimulating hormone, luteinizing hormone, prolactin, oestradiol and progesterone concentrations in the sera of anovulatory androgenized female and castrated male parabiotic rats of the Fischer-344 strain.

The serum concentrations of FSH, LH and prolactin, as well as oestradiol and progesterone, were measured by immunoassays at various intervals up to 35 weeks after parabiotic union of an anovulatory androgenized female and a castrated male rat of the Fischer-344 strain. Modest increases in FSH (28%) and larger increases in LH (128%), compared to levels found in single adult animals, produced large increases in follicular growth, ovarian weight and oestrogen production in the female partners; thecal and interstitial elements of the ovaries were not heavily stimulated. Prolactin concentrations in the sera increased to exceedingly high levels and massive pituitary tumours were produced in all of the female partners. Development of cystic follicles with loss of granulosa-cell layers and the formation of early stages of granulosa-cell tumours progressed with time in union. Serum LH levels were as high in parabiotic as in single castrated male rats within 2 weeks, but concentrations of FSH remained much below those of the single animals until 27 weeks after castration. The results are consistent with the view that the ovaries of androgenized female rats of the Fischer strain produce some factor which prevents the post-castration rise in FSH of parabiotic male partners.

Animals↗
PubMed1981

Examination of a lognormal distribution equation for describing distributions of diameters of bovine adipocytes.

Samples of subcutaneous, intermuscular and mesenteric adipose tissues from beef steers were fixed with osmium tetroxide, and freed adipocytes were counted with an automatic particle counter to determine whether a lognormal distribution function would describe adipocyte size distributions more accurately than a normal distribution function. Modes and medians of size distributions generally were larger than means for adipocyte size distributions modeled with a lognormal distribution function. Normalized third and fourth moments of predicted lognormal distributions often were close to 0 and 3, respectively, which are expected values for a normally distributed population. Considerable variation was observed in the skewness of adipocyte size distributions. Both normal and lognormal models for adipocyte size distribution yielded similar means. The lognormal model yielded a greater standard deviation than the normal model for adipocyte size distributions. Smaller chi-square values were found for size distributions modeled with a lognormal than with a normal distribution function. Results suggest that a lognormal distribution function more accurately models the size distributions of bovine adipocytes.

Adipose Tissue↗
PubMed1981

Guinea worm control: testing the efficacy of health education in primary care.

Health education has been advocated as a major foundation for primary health care. However, the value of this approach is yet to be fully proven. An experimental PHC programme in ten Nigerian farm hamlets using methods such as community organization, participatory training and village meetings, put health education to the test. Significant short term improvements in community health knowledge resulted after training of a village health worker from each hamlet. Positive intermediate results in water sanitation behaviours were later observed. Three years after initial intervention, long term health outcomes included the reduction in prevalence of guinea worm, a locally endemic water borne disease. The programme also encountered certain organizational and technological issues. For example, integration with existing health care systems and local well construction capabilities surfaced as problems. Consequently efforts are currently underway to expand research into these areas.

Dracunculiasis↗
PubMed1981

Gastric lipomas: a rare cause of massive upper gastrointestinal bleeding.

Gastric lipomas are rare and most frequently present as upper gastrointestinal bleeding. Wide excision is advocated for small lesions and incisional biopsy followed by excision or shelling out of the tumor for large lesions. Histologic confirmation is essential so that a cancer operation, should it be necessary, will not be compromised. Concomitant lesions must be sought and treated appropriately.

Endoscopy↗
PubMed1980

Release of gonadotropin-releasing hormone by veratrine in a hypothalamic-pituitary coincubation.

The effects of veratrine and veratridine on the release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) from incubations of pituitary alone, hypothalamus alone, and coincubations of hypothalamus and pituitary were examined. Veratrine produced only small increases in LH secretion from pituitaries alone relative to that produced by exogenous GnRH. Veratrine caused a calcium-dependent release of GnRH from the hypothalamus. When a pituitary and hypothalamus were coincubated veratrine produced increases in LH secretion that were much larger than its direct pituitary effects. Veratridine also produced large increases in the release of GnRH and LH from hypothalamic-pituitary coincubations. The direct effect of veratridine on pituitary LH release, however, was greater than that of veratrine. The results indicate that veratrine is capable of releasing hypothalamic GnRH with relatively small direct effects on pituitary LH secretion. Hypothalamic-pituitary coincubations coupled with veratrine depolarization may be quite useful for studying hypothalamus factors controlling pituitary hormone release.

Animals↗
PubMed1980

Acute lymphocytic leukemia developing in a male with germ cell carcinoma: a case report.

A case of germ cell carcinoma (of presumed testicular origin) is described in which acute lymphocytic leukemia developed within nine months of the diagnosis. Possible relationships between the two neoplasms are discussed, as well as the need for continued observation of patients with germ cell tumors as they are living longer and may be at higher risk for developing a second cancer.

Adult↗
PubMed1980

Twenty-four hour pattern of prolactin levels in female rats subjected to transection of the mesencephalic raphe or ablation of the suprachiasmatic nuclei.

The present study was undertaken to evaluate the 24-hour periodicity in serum prolactin levels subsequent to transecting the ascending serotonergic system or ablating the suprachiasmatic nuclei (SCN) of adult (185 g) female rats. The ascending serotonergic system was transected at the level of the rostral mesencephalon using a 1.5 mm wide knife and the SCN was ablated with a modified Halász-Pupp knife. The effect of raphe transection (RT) or SCN ablation on the circadian rhythm in nonstress serum prolactin levels was assessed 45 days after surgery by measuring with radioimmunoassay the serum prolactin concentration in serial blood samples obtained from the tail vein of lightly restrained rats. Serum prolactin concentration in control and RT animals showed circadian periodicity; peak levels occurred during the midafternoon, 4 h prior to the dark phase of the lighting regime (lights on at 4 a.m., off at 6 p.m.). The amplitude of the fluctuations of both groups varied markedly and were related to the estrous cycle. However, RT animals showed a reduced amplitude in the rhythm. In controls peak prolactin levels on days of proestrus and estrus were 15-20 times higher than on days of diestrus. In contrast, serum prolactin levels in SCN-ablated rats did not vary with a circadian periodicity but rather showed random, low amplitude fluctuations. Reproductive cyclicity was also abolished by SCN ablation, i.e., SCN-ablated rats presented persistent vaginal cornification. These data indicate that circadian periodicity in serum prolactin levels is not compromised by sectioning the ascending serotonergic fibers but is abolished after ablating the SCN.

Animals↗
PubMed1980

Histamine formation by mouse preimplantation embryos.

Mouse embryos recovered on the 4th day of pregnancy produced histamine, as evidenced by the 14CO2 produced from carboxy labelled L-histidine, at the rate of 1.5 +/- 0.3 (s.e.m.) pmol/embryo per hour. Most (83.2 +/- 4.6%) of the embryos flushed from the oviducts on Day 3 of pregnancy (4--8-cell stage) developed into blastocysts within 48 h after being placed in culture. Inclusion of L-histidine hydrochloride (4.7 x 10(-4) M) in the culture medium did not alter this development but DL-alpha-methylhistidine (3.8 x 10(-4) M), an inhibitor of histidine decarboxylase, reduced the number of embryos developing into blastocysts to only 10.8 +/- 6.8%. A combination of L-histidine and DL-alpha-methylhistidine in the medium prevented the growth-retarding effect of the latter compound. The results indicate that mouse embryos can produce histamine and suggest that this is necessary for normal development.

Animals↗
PubMed1980

Trans--pulmonary arterial repair of supracristal ventricular septal defects in infancy.

Five patients aged 2 months to 2 years with isolated large supracristal ventricular septal defect (VDS) and severe pulmonary hypertension had corrective operation between April, 1978, and November, 1979, performed via a trans--pulmonary arterial approach. This technique provided excellent exposure for accurate placement of sutures, especially between the two semilunar valves. All patients are well, with no residual defects, and their postoperative electrocardiograms (ECGs) do not show any intraventricular conduction abnormality. The technique is especially useful in the presence of severe pulmonary hypertension, wherein ventriculotomy is best avoided and the dilated main pulmonary artery offers excellent access.

Body Weight↗
PubMed1979

Anatomical accuracy of echocardiographically assessed left ventricular wall thickness.

1. A comparison of direct measurement and M-mode echocardiography in the determination of posterior left ventricular wall thickness was performed in 26 subjects, of whom 21 underwent cardiac bypass surgery; the remainder came to necropsy. 2. In the surgical group a close correlation was demonstrated between direct measurement of posterior wall thickness and the echocardiographic end-diastolic dimension (r = 0.76, P less than 0.001). 3. The necropsy measurement of posterior wall thickness correlated with the echocardiographic end-systolic dimension (r = 0.99, P less than 0.001). 4. These findings confirm that the echocardiographic measurement of posterior wall thickness accurately reflects the anatomical dimension.

Blood Pressure↗