Addition of colchicine--tubulin complex to microtubule ends: the mechanism of substoichiometric colchicine poisoning

Colchicine blocks microtubule polymerization by an unusual substoichiometric poisoning mechanism. We have investigated the mechanism by which this poisoning occurs with several experimental approaches, and have found that colchicine acts by addition to microtubule ends as a colchicine-tubulin complex.

A separation of clinical from epidermal thinning effect in the topical glucocorticoid clobetasone butyrate

Clobetasone butyrate ointment has been shown to be more effective in treating psoriasis and eczema than flurandrenolone ointment yet to cause less epidermal thinning in a human experimental model. This is an indication that the clinical activity of topical glucocorticoids may not necessarily be inseparable from their propensity to cause atrophy of the skin.

Properties of tubulin in unfertilized sea urchin eggs. Quantitation and characterization by the colchicine-binding reaction

The colchicine-binding assay was used to quantitate the tubulin concentration in unfertilized Strongylocentrotus purpuratus eggs and to characterize pharmacological properties of this tubulin. Specificity of colchicine binding to tubulin was demonstrated by apparent first-order decay colchicine-binding activity with stabilization by vinblastine sulfate, time and temperature dependence of the reaction, competitive inhibition by podophyllotoxin, and lack of effect of lumicolchicine. The results demonstrate that the minimum tubulin concentration in the unfertilized egg is 2.71 mg per milliliter or 5.0% of the total soluble cell protein. Binding constants and decay rates were determined at six different temperatures between 8 degrees C and 37 degrees C, and the thermodynamic parameters of the reaction were calculated. delta H0=6.6 kcal/mol, delta S0=46.5 eu, and, at 13 degrees C, delta G=-6.7 kcal/mol. The association constants obtained were similar to those of isolated sea urchin egg vinblastine paracrystals (Bryan, J. 1972. Biochemistry. 11:2611-2616) but approximately 10 times lower than that obtained for purified chick embryo brain tubulin at 37 degrees C (Wilson, L.J.R. Bamburg, S.B. Mizel, L. Grisham, and K. Creswell. 1974. Fed Proc. 33:158-166). Therefore, the lower binding constants for colchicine in tubulin-vinblastine paracrystals are not due to the paracrystalline organization of the tubulin, but are properties of the sea urchin egg tubulin itself.

The effect of clobetasone butyrate and other topical steroids on skin thickness of the domestic pig

A new glucocorticoid, clobetasone butyrate, has been shown in patients to have good topical anti-inflammatory activity and a minimal effect on hypothalamic-pituitary-adrenal function. Among a group of topically active corticosteroids, compared in a controlled study in the domestic pig, clobetasone butyrate is shown to cause less epidermal thinning than any of the others except only 1% hydrocortisone. This evidence of a lesser atrophogenic effect may indicate further dissociation of unwanted from wanted properties in clobetasone butyrate.

The clinical assessment of topical corticosteroid activity

Glucocorticoid-induced vasoconstriction of human skin has provided a useful guide to topical anti-inflammatory activity. The concentration and base in which a steroid is used influence this activity, and traditional greasy ointments are probably the most effective vehicles. Confirmation of clinical effectiveness should be by double-blind comparison in patients with bilateral skin lesions. Psoriasis provides a more discriminating test of steroidal activity than eczema; the use of occlusive dressings may mask differences between compounds. Short-term trials are informative but in patients with chronic diseases, longer studies should also be done.

Carcinoma of the urachus: its demonstration by pelvic pneumography

Carcinoma of the urachus is an uncommon neoplasm that usually presents a diagnostic problem. A case of urachal carcinoma visualized by pelvic pneumography is reported. The clinical and radiological features of this lesion are briefly discussed.

The membrane potential of rat diaphragm muscle fibres and the effect of denervation

1. Resting membrane potentials of rat diaphragm muscles were measured in vitro after previous denervation for 0-10 days. In some experiments denervated muscles were incubated in vitro for 3 hr while in others they were cultured for 15-24 hr to allow adequate exposure to drugs before recording. 2. It was found that resting membrane potentials, within 2-5 mm of the site of nerve section were significantly lower, within 3 hr, than resting membrane potentials measured more than 9 mm away from site of nerve section. This difference could be reduced or abolished by bathing preparations in solutions containing adrenaline (10 muM), noradrenaline (10 muM) or isoprenaline (10 muM) or dibutyryl cyclic AMP (10 muM-0-25 mM in the presence of 2 mM theophylline). Cyclic AMP (0-5 mM) was ineffective. 3. Application of solutions containing dibutyryl cyclic AMP for 3 hr also raised the resting membrane potential of muscles denervated 4-5 days previously. Culture studies showed that this effect was sustained when the time of incubation was 24 hr. 4. Incubating freshly denervated preparations with cycloheximide (22 mug/ml.) or actinomycin D (1 mug/ml.) did not prevent the development of the early (3 hr) fall in resting membrane potential despite a concomitant inhibition of RNA or protein synthesis. Culturing freshly denervated muscles in solutions containing cycloheximide (10 or 25 mug/ml.) which blocked 93% of protein synthesis, did not prevent the expected drop in resting membrane potential after 15 or 24 hr. 5. It was found that exposure to ouabain (1 or 5 mM) produced a rapid (15 min) fall in resting membrane potential in innervated and denervated preparations treated with dibutyryl cyclic AMP but not denervated preparations. After 5 days denervation cyclic AMP levels in muscle were increased by about 40%. 6. It is suggested that upon denervation an electrogenic action of a NA+-pump is blocked and that dibutyryl cyclic AMP and catecholamines are capable of stimulating this pump.

The mechanism of action of vinblastine. Binding of [acetyl-3H]vinblastine to embryonic chick brain tubulin and tubulin from sea urchin sperm tail outer doublet microtubules

Tritium-labeled viblastine, specific activity 107 Ci/mol, was prepared by acetylation of desacetylvinblastine with [3H]acetic anhydride, and has been employed in a study of vinblastine binding to tubulin. There are two high affinity vinblastine-binding sites per mole of embryonic chick brain tubulin (KA = 3-5 X 10(5) l./mol). Binding to these sites was rapid, and relatively independent of temperature between 37 and 0degreeC. Vincristin sulfate and desacetylvinblastine sulfate, two other active vinca alkaloid derivatives, competitively inhibited the binding of vinblastine. The inhibition constant for vincristine was 1.7 X 10(-5) M; and for desacetylvinblastine, 2 X 10(-5) M. The vinblastine binding activity of tubulin decayed upon aging, but this property was not studied in detail. Vinblastine did not depolymerize stable sea urchin sperm tail outer doublet microtubules, nor did it bind to these microtubules. However, tubulin solubilized from the B subfiber of the outer doublet microtubules possessed the two high affinity binding sites (KA = 1-3 X 105 l./mol). These data suggest that vinblastine destroys microtubules in cells primarily by inhibition of microtubule polymerization, and does not directly destroy preformed microtubules.

Clobetasone butyrate, a new topical corticosteroid: clinical activity and effects on pituitary-adrenal axis function and model of epidermal atrophy

Clobetasone butyrate is a new corticosteroid, selected for study because of its combination of good activity in the vasoconstriction test and low systemic activity in animals. Formulated as an 0.05% ointment and cream (Molivate) it was clinically effective in patients with eczema, its activity being significantly greater than that of hydrocortisone 1% or fluocortolone 0.2% (Ultradil). Under conditions that predispose to maximal percutaneous absorption clobetasone butyrate ointment had minimal effect on hypothalamic-pituitary-adrenal function. In an animal model of cutaneous atrophy it caused less thinning of the epidermis than steroids other than hydrocortisone. Clobetasone butyrate 0.05% ointment and cream gave every indication of offering clinically effective topical anti-inflammatory activity with a wide margin of safety.

B and T cells in a cat with thymic lymphosarcoma

The mixed antiglobulin reaction and the formation of nonimmune rosettes with guinea-pig red blood cells (RBC) distinguished feline B and T cells, respectively. In a cat with thymic lymphosarcoma, the cells reacting in these tests formed separate, nonoverlapping populations. The malignant cells were large lymphoblasts replacing the normal thymus and infiltrating local lymph nodes, where they localized only in the paracortical, i.e., thymus-dependent areas. Cells from the nodes could therefore be identified as malignant or normal by their size. The mixed antiglobulin reaction showed that the malignant cells did not carry the surface Ig characteristic of B cells, whereas these malignant cells formed nonimmune rosettes with guinea-pig RBC. Among lymph node cells, most surviving normal and small lymphocytes, from outside the thymus-dependent areas, reacted as B cells. The morphologic evidence therefore corroborated the test results, which indicated that the formation of rosettes with guinea-pig RBC seems a reliable means for the demonstration of T cells in the cat.

A mixed-immunoglobulin rosette technique for detection of antibody to feline oncornavirus-associated cell membrane antigen

A mixed-immunoglobulin rosette technique has been developed for the detection of antibodies to feline oncornavirus-associated cell membrane antigens. Lymphoblastoid cells infected with feline leukemia virus were incubated with test sera and then fixed in paraformaldehyde. They were then exposed to a rabbit anti-cat immunoglobulin G serum. Antigen-antibody reactions were detected by mixing the cells with sheep erythrocytes sensitized with cat anti-sheep red blood cell serum; the presence of cat antibody on the lymphoid cells was registered by the formation of sheep red blood cell rosettes around them. The method was shown to be at least 10 times more sensitive than indirect immunofluorescence. A high degree of correlation was shown between the mixed-immunoglobulin rosette and indirect immunofluorescence tests, using both feline leukemia virus-infected cat and dog cells as targets. The results indicate that the tests are likely to be measuring similar reactions. Using the indirect immunofluorescence test we found that 75% of cats with lymphoid neoplasia had no demonstrable antibodies. Twenty-four of such indirect immunofluorescence-negative sera were tested by the mixed-immunoglobulin rosette technique; antibody was shown in at least seven of these sera.

Intravascular hemolysis: a complication of midtrimester abortion: a report of two cases

Intravascular hemolysis occurred twice in a series of 1582 consecutive intraamniotic midtrimester saline abortions. The hemolysis was associated with consumption coagulopathy and acute renal failure. Both patients made a complete recovery after a prolonged hospital stay; one required peritoneal dialysis. The pathogenesis of this serious complication of saline abortion is discussed but no satisfactory explanation has been reached.