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Biomedical subjects

R R Almon

Publications and source records attributed to R R Almon.

At least 37 records · Page 2Linked to original sources
PubMed1984

Comparison of filtration and equilibrium dialysis methods for [3H]imipramine binding to human platelets.

Receptor binding of imipramine in human platelets was assessed by filtration through glass-fiber filters and by equilibrium dialysis. Both methods yield drug-receptor dissociation constants of similar magnitude (10(-9) M) to literature values. However, the density of binding sites (Bmax) was fivefold lower by filtration (473 +/- 92 fmol/mg protein) compared to equilibrium dialysis (2652 +/- 765 fmol/mg protein). Dialysis allows direct assessment of free imipramine and avoids drug loss during the separation step of the filtration assay. Additional advantages were found for computer nonlinear regression analysis of untransformed data to eliminate errors owing to linear transformation in the Scatchard analysis and for simultaneous quantitation of nonspecific and total drug binding.

Blood Platelets↗
PubMed1984

Increased content of glucocorticoid receptors in mouse muscular dystrophy.

An analysis of the glucocorticoid receptor population of skeletal muscle and liver from dystrophic and control mice was performed. These data demonstrate that the cytosol of muscles from dystrophic animals contain a significantly higher concentration of glucocorticoid receptors (approximately 100%) relative to the cytosols of muscles from control mice. No differences in the glucocorticoid receptor population was noted in the livers removed from these animals. These data are consistent with previous observations on the chicken dystrophic model, and may suggest a general phenomenon associated with dystrophy regardless of species or type.

Animals↗
PubMed1984

Glucocorticoid sites in skeletal muscle: adrenalectomy, maturation, fiber type, and sex.

The glucocorticoid receptor population in skeletal muscle of the rat was examined. Data are included that address the following: tissue preparation, receptor stabilization, method of assay and analysis, cross-reactivity of a large variety of steroids, time to equilibrium, and the effect of adrenalectomy on the number of sites as well as the apparent binding affinity. In addition, we have observed the following: 1) an exponential decline in the concentration of sites from 27 to 160 days after birth; 2) a significantly higher concentration of sites in muscle from male animals as compared with female animals; and 3) a significantly higher concentration of sites in the slow-fiber soleus muscle as compared with the fast-fiber extensor digitorum longus muscle.

Adrenal Glands↗
PubMed1984

Perineal muscles: possible androgen regulation of glucocorticoid receptor sites in the rat.

The glucocorticoid receptor population of the androgen-dependent levator ani-bulbo cavernosus muscle complex in response to both androgen withdrawal and androgen replacement was examined in rats. After castration the concentration of receptor sites more than doubled. The increase in the sites began within the first 24 h after castration and reached a plateau level within 7 days. Parallel dry weight studies demonstrated that no loss in muscle mass is observed until 48 h after castration. In a second series of experiments, both the regrowth of the muscle and the number of receptor sites in response to androgen injections were examined. By day 11 of injection, the muscle had increased in dry weight to a point where it was equal to the size of this muscle in normal intact male controls. During this process, the concentration of receptor sites began to decline 5 days after the beginning of injections and reached control or below control values by 11 days.

Androgens↗
PubMed1983

Effect of castration on the metabolism of androgens in rat skeletal muscle.

The metabolic conversion of testosterone and 17 beta-hydroxy-5 alpha-andro-stan-3-one by cell fractions from skeletal muscle was examined. Little or no conversion of testosterone to 17 beta-hydroxy-5 alpha-androstan-3-one is observed with any skeletal muscle fraction studied. The cytosol from all muscles examined contained substantial levels of the enzyme 3 alpha-hydroxysteroid oxidoreductase, which converts 17 beta-hydroxy-5 alpha-androstan-3-one to 5 alpha-androstane-3,17 beta-diol. The Km of the reaction in the three muscles (extensor digitorum longus, soleus and levator ani) is in the order of 3-6 X 10(-6) M. Following castration, there is no significant change in the Km value of this reaction in any of the muscles. The Vmax of the conversion in the extensor digitorum longus and soleus are similar (in the order of 2.0 X 10(-11) mol/mg per min) and castration has no significant effect on Vmax in either of these muscles. Vmax is significantly lower for the levator ani (3.4 X 10(-12) mol/mg per min) than for the extensor digitorum longus and soleus. Following castration the Vmax for the levator ani undergoes a significant rise which peaks at 3 days.

Animals↗
PubMed1980

Disuse atrophy of skeletal muscle is associated with an increase in number of glucocorticoid receptors.

Atrophy of muscles due to disuse is similar in form to glucocorticoid atrophy of the general body musculature. Because of this similarity, a hypothesis was formed which attributed the selective muscle atrophy resulting from immobilization to an increase in glucocorticoid sensitivity. As an initial test of this hypothesis, the thermodynamic characteristics of 3H-dexamethasone binding were examined in cytosol prepared from immobilized and contralateral control gastrocnemius muscles. We report here an increase in numbers of glucocorticoid receptors in immobilized muscles relative to contralateral controls, with no change in binding affinity. These findings support the hypothesis that selective muscle atrophy is a result of changes in glucocorticoid sensitivity.

Animals↗
PubMed1980

Fiber-type effects of castration on the cholinergic receptor population in skeletal muscle.

The effects of castration on the extensor digitorum longus, soleus and levator ani muscles of the adult male rat were examined. After castration, no change was observed in the number of sites or the binding affinity of [125I]-monoiodo-alpha-bungarotoxin to the nicotinic cholinergic receptor population of the slow fiber muscle (soleus). The two fast fiber muscles (extensor and levator) showed no change in binding affinity but a significant change in the number of sites. In these two fast fiber muscles, the number of sites begins to increase within the first few days after castration, peaks at 14 days and begins to decline. The results presented in this report demonstrate three major concepts: 1) influences on skeletal muscle mediated by one receptor population can change the characteristics of another receptor population; 2) at least some androgen effects on skeletal muscle are fiber type specific; and 3) the development of extrajunctional receptors is not solely the function of the nerve-muscle relationship.

Animals↗
PubMed1976

Cholinergic sites in skeletal muscle. I. Denervation effects.

Cholinergic interactions in systems derived from rat skeletal mixed muscle are detailed. The isotherms of the binding of [125I]diiodo-alpha-bungarotoxin over the range of 10(-10)-10(-5) M toxin have been separated into a "nonspecific" component exclusive to the toxin and a "specific" component that binds both the toxin and d-tubocurarine. The "specific" component appears to reflect two independent sets of binding sites. One of the sets has an affinity constant on the order of 10(9) M-1. Following denervation, the number of sites in this high-affinity set begins to increase after 3 days, reaches a peak (28-fold higher than normal) on the 8th day, and begins to decline. Similar results are obtained when sensitivity of this set to an antibody derived from patients with myasthenia gravis is examined. This sensitivity is reflected by the inhibition of the alpha-bungarotoxin binding by the myasthenic IgG fraction. Following denervation, sensitivity first appears on day 3 progresses coincidentally with the increase in new sites in the set. The charcteristics of this set suggest that it represents the acetylcholine receptor and that the new sites appearing during the course of denervation are extrajunctional receptor sites. The interaction with the myasthenic IgG indicates an antigenic difference between junctional and extrajunctional receptors. The second set of specific binding sites has an affinity constant on the order of 10(5) M-1. The number of sites in this set increases only fivefold as a result of denervation. The increase also begins between days 2 and 3. The definition of this low affinity set of sites is not presently clear.

Animals↗
PubMed1976

Cholinergic sites in skeletal muscle. II. Interaction of an agonist and two antagonists with the acetylcholine site.

The equilibrium interactions of alpha-bungarotoxin, d-tubocurarine, and carbamylcholine with junctional and extrajunctional skeletal muscle acetylcholine receptors were examined. d-Tubocurarine is a competitive inhibitor of the bindings of alpha-bungarotoxin to the acetylcholine receptor. No substantive difference was observed in the association of d-tubocurarine with the junctional and extrajunctional receptors. In contrast, the carbamylcholine inhibition of toxin binding is not competitive. The data indicate that either the single set of alpha-bungarotoxin and d-tubocurarine bindings sites contains two subsets of carbamylcholine sites or that the carbamylcholine binds in a cooperative manner to a single set of sites. In addition, the affinity of carbamylcholine for extrajunctional receptors may be higher than the affinity for junctional receptors.

Acetylcholine↗