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Biomedical subjects

M Johnson

Publications and source records attributed to M Johnson.

At least 811 records · Page 45Linked to original sources
PubMed1978

Requirements of drug-induced endocytosis by intact human erythrocytes.

Study of drug-induced endocytosis in intact human erythrocytes continues to provide an opportunity for correlating membrane functions such as invagination and fusion with erythrocytic energetics and other determinants of plasma membrane function like Ca++. The studies reported indicate that high concentrations of vinblastine and chlorpromazine can produce endocytic vacuoles, albeit in reduced amounts, even in severely ATP depleted erythrocytes. In contrast, primaquine-induced endocytosis seems definitely dependent upon persistence of erythrocytic ATP stores. The ionophore mediated entry of Ca++ into erythrocytes potentiates primaquine endocytosis, inhibits vinblastine endocytosis, and has no regular effect on chlorpromazine endocytosis. Sodium lactate enhances primaquine endocytosis, probably by causing an increase in the entry of primaquine into erythrocytes. Cytochalasin B neither enhances nor inhibits erythrocytic endocytosis, thereby suggesting that microfibrils or analogues of microfibrils in erythrocytes are not involved in endocytosis. Cyclic nucleotide inhibition of endocytosis is confined to a very high concentration range of nucleotides in the medium. Primaquine and chlorpromazine endocytosis are inhibited by cyclic nucleotides as is vinblastine endocytosis.

Calcium↗
PubMed1977

Platelets and the vascular responses to arachidonic acid in dogs.

UNLABELLED: Platelets are rich in components of the prostaglandin synthetase system which converts arachidonic acid into vasoactive and platelet-active prostanoate and nonprostanoate compounds. Repeated injections of arachidonic acid in dogs cause hypotension of reproducible magnitude and lower circulating platelet counts with each injection. However, the circulatory response to injected arachidonic acid was unchanged when platelet-poor blood was exchanged in dogs. Moreover, in the hind limb preparation and the isolated lung lobe, the vasoactive responses to arachidonic acid were indistinguishable whether perfused with whole blood or an artificial perfusate. CONCLUSION: the vascular responses to arachidonic acid do not appear dependent on the presence of platelets.

Animals↗
PubMed1977

A dosimeter for long wave ultraviolet radiation.

A polymer film, which incorporates phenothiazine as the chromophore, has been developed as a personnel dosimeter for long wave ultraviolet radiation. It is stable, reproducible and is particularly suited to monitoring the doses received by patients undergoing photochemotherapy for psoriasis.

Dose-Response Relationship, Radiation↗
PubMed1977

Vasoconstrictor response to arachidonic acid in the isolated hind limb of the dog.

1 Arachidonic acid(AA) (25-200 mug/kg) produced a dose-related increase in perfusion pressure in dog isolated hind limbs perfused with either blood or a platelet-free perfusate. 2 Prostaglandin E2 produced vasodilation while prostaglandin F2 alpha produced no vascular change at these administered doses. 3 Phentolamine did not alter the arachidonic acid response, eliminating possible alpha-adrenoceptor mediation. 4 Aspirin and idomethacin blocked the vasoconstrictor response to AA. 5 This study indicates that a vasoactive intermediate in prostaglandin synthesis can be elaborated in the absence of platelets.

Animals↗
PubMed1977

Susceptibility of Propionibacterium acnes to seventeen antibiotics.

The in vitro susceptibility of 96 isolates of Propionibacterium acnes to 17 antibiotics was determined by utilizing an agar dilution technique. With the exception of the aminoglycosides, these organisms are susceptible to virtually all of the commonly used antimicrobial agents.

Aminoglycosides↗
PubMed1977

Androgen-mediated sensitivity in platelet aggregation.

Platelet responsiveness to an aggregating stimulus (ADP) was greater (X10) in male than in female rats. Castration reduced aggregability in males (X4) and increased it in females (X3). Pretreatment with testosterone (1 mg/kg, sc) enhanced platelet aggregability in both sexes and restored the diminished responsivity observed in castrated males. Incubation of platelets with testosterone (1-10 ng/ml) potentiated rat (18.0 +/- 1.5%) and guinea pig (40.0 +/- 5.0%) aggregability when compared with vehicle-treated platelets. Estradiol (1 mg/kg, sc) in vivo or estradiol, progesterone, and deoxycorticosterone (1 microng/ml) in vitro had the opposite effect and decreased aggregability. The rank order of effectiveness of androgens in vitro was dihydrotestosterone, testosterone, methyltestosterone, androstendione, and androsterone, which correlates with their androgenicity. The effect of androgens was antagonized in vitro by the antiandrogen (Flutamide) and by estradiol. These data suggest that gonadal steroids may play a role in regulating platelet function in the rat and guinea pig.

Adenosine Diphosphate↗
PubMed1977

Plasma 20 alpha-dihydroprogesterone, progesterone and 17-hydroxyprogesterone in normal human pregnancy.

The peripheral plasma levels of 20alpha-dihydroprogesterone (20alpha-DHP), progesterone (P) and 17-hydroxyprogesterone (17-OHP) were measured by radioimmunoassay techniques in 440 samples during normal human pregnancy between weeks 4 and 41. The levels of 20alpha--DHP in plasma from the 4th to the 6th week were between 6.0 and 6.6 ng/ml. From then until the 21st week the average plasma 20alpha-DHP concentrations remained at the same level between 4.0 and 6.3 ng/ml; they then rose significantly to and beyond term, levels reaching over 40 ng/ml. The range of mean plasma concentration of P during the first trimester of pregnancy fell to a nadir in the 9th week (170 ng/ml) then rose with increased gestation until the 39th week (190.4 ng/ml) followed by a slight and not significant drop. Single measurements of plasma 17--OHP from the 4th to the 6th week of pregnancy gave value between 2.8 and 3.6 ng/ml, but from the 7th week the mean plasma 17--OHP levels gradually declined, then from week 30 the 17-OHP concentration increased to reach a mean level of 7.63 ng/ml in the 41st week. The ratio P/20alpha--DHP increased from the 4th (3.5:1) to the 24th week (15.6:1) and then decreased from 25th week (7.9:1) towards term (3.2:1).

20-alpha-Dihydroprogesterone↗
PubMed1977

The subarachnoid screw.

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Equipment and Supplies, Hospital↗
PubMed1976

Transport changes associated with growth control and malignant transformation.

We can distinguish two classes of membrane transport changes in cultured cells: (a) growth-rate contingent changes are those which occur in coordination with the onset of density-dependent inhibition of growth; (b) transformation-specific changes are those which occur when cells become transformed, and which can be detected even when normal and transformed cells are growing at the same rate. Growth-rate contingent changes include the density-dependent changes in phosphate, nucleoside, glucose, amino acid, and potassium transport. Only one transformation-specific transport change has been found in Rous-transformed chicken embryo fibroblasts: an increased rate of hexose transport. The variation in potassium transport are associated with variations in the number of ouabain binding sites in the membrane. The molecular basis for changes in the rate of hexose transport is unknown, although gross changes in membrane bilayer composition and "fluidity" seem not to be involved. In analyzing the regulation of hexose transport activity, we find that decreased cAMP may play a role in the transformation-specific increase in hexose transport, but that fibrinolytic activity is not necessary.

Aminobutyrates↗
PubMed1976

Perirenal lymphocyst formation in renal transplant recipients: diagnosis and pathogenesis.

Perirenal lymphocyst formation occurred in 7 of 46 consecutive renal allografts which had survived at least one month. This complication developed from one to four and one-half months post-transplantation, resulted in a specific spectrum of clinical signs and symptoms, and was best diagnosed by a combination of intravenous pyelography and ultrasonic examination of the transplanted kidney. The lymph fluid is of recipient origin and its collection appears to be related to use of a high-dose immunosuppressive regimen and to a conscious decision to avoid the use of postoperative surgical drains. Surgical intraperitoneal marsupialization of the lymphocyst emerges as the clear treatment of choice for peritransplant lymphocyst formation.

Adolescent↗
PubMed1976

Vascular responses to arachidonic acid in the perfused canine lung.

We compared the effects of arachidonic acid (AA), the bisenoic prostaglandin precursor, with those of prostaglandin F2a (PGF2a) and norepinephrine (NE) on pulmonary vascular resistance in the isolated (in situ), perfused canine lung lobe. The isolated lobe was perfused with autologous blood or an artificial perfusate under conditions of constant flow. Lobar artery and venous pressures were constantly monitored after bolus injections of AA, PGF2a, and NE into the inflow cannula. AA (100 mug/kg produced a significant increase in the pressure gradient (93.3 +/- 8.4%, SE) in the lobe. Similarly, PGF2a (1 mug/kg) significantly increased the pressure gradient (41.2 +/- 6.5%), as did NE (1 mug/kg, 41.6 +/- 3.2%). Aspirin (25 mg/kg) completely blocked the pulmonary vascular effect of AA, but did not affect the response to PGF2a, Linoleic acid, a control fatty acid, did not produce pulmonary vasoconstriction. The pressor effect of AA was not blocked by pretreatment with phentolamine, propranolol, cyproheptadine, or atropine. The use of an artificial perfusate free of cellular elements did not prevent the vasoconstrictor action of AA. The times to onset of action of the three agents were similar, and short. These results suggest that AA is converted into vasoactive intermediates or a prostaglandin, and the vasoactive intermediates or the prostaglandin act directly on precapillary pulmonary vascular smooth muscle rather than through platelet, plasma, adrenergic, or cholinergic mechanisms.

Animals↗