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Biomedical subjects

R J Summers

Publications and source records attributed to R J Summers.

At least 163 records · Page 9Linked to original sources
PubMed1979

Investigation of the role of calcium in the supersensitivity produced by cocaine in cat spleen strips.

1. Cocaine (2 x 10(-6) M and 10(-5) M) produced 2 and 7 fold shifts to the left of the dose-response curve to (-)-noradrenaline recorded isotonically in isolated splenic capsular strips of the cat. 2. The same concentrations of cocaine also produced increases in the maximum response of the tissue to 117% and 126.7% of control. 3. Desmethylimipramine (DMI, 10(-7) to 10(-6) M) produced no significant potentiation of the response of cat spleen strips to (-)-noradrenaline. At 10(-5) M DMI decreased the maximum response. 4. Cocaine (10(-5) M) produced a 3.3 fold shift to the left of the dose-response curve whereas DMI (10(-6) M) had no effect on the dose-response curve to oxymetazoline in cat splenic capsular strips. 5. Cocaine (10(-5) M) in the presence of phentolamine (10(-6) M) produced a shift to the left and an increase in the maximum response to K+, an agonist which is believed to produce muscle contraction by increasing the membrane calcium flux. 6. Cocaine (10(-5 M) had no effect on the dose-response curve to angiotensin which is believed to contract vascular muscle by releasing calcium from intracellular storage sites. 7. The potentiating effect of cocaine (10(-5) M) on responses of spleen strips to (-)-noradrenaline was blocked by the calcium flux inhibitor SKF 525A (2.65 x 10(-5) M). 8. It is concluded that the results are compatible with the view that cocaine enhances the influx of calcium across the cell membrane during responses to agonists that utilize the extracellular pool of calcium and that this effect is responsible for a large part of the potentiation of the response.

Angiotensin II↗
PubMed1979

The effects of alpha-adrenoceptor agonists and antagonists on responses of transmurally stimulated prostatic and epididymal portions of the isolated vas deferens of the rat.

1 The effects of alpha-adrenoceptor agonists and antagonists on contractile responses of transmurally stimulated prostatic and epididymal portions of the rat isolated vas deferens were examined. 2 Responses to single stimuli consisted of two phases, the first predominant in the prostatic and the second in the epididymal portion. The first phase was resistant to alpha-adrenoceptor antagonists but the second was reduced in a dose-related manner in the order of potency prazosin greater than azapetine greater than phentolamine greater than labetalol greater than yohimbine. 3 Both phases of the response to a single stimulus were reduced by clonidine but only the first could be reliably restored by yohimbine. 4 Trains of transmural stimuli produced biphasic responses, an early rapid component predominant in the prostatic and a slow secondary component predominant in the epididymal portion. The effects of alpha-adrenoceptor antagonists on these responses were complex. Prazosin produced the most straightforward inhibition of responses with relative resistance of the early rapid component. Only yohimbine and phentolamine produced increases in responses which could be pre-junctional in origin. 5 The alpha-adrenoceptor agonists, oxymetazoline and clonidine, reduced while phenylephrine increased responses to trains of stimuli. 6 These results are discussed in relation to the nature of the innervation of rat vas deferens and the usefulness of the preparation in pharmacological tests for activity at alpha-adrenoceptors.

Adrenergic alpha-Agonists↗
PubMed1979

Macromolecular composition of a Cellulomonas sp. cultivated in continuous culture under glucose and zinc limitation.

The mutant strain of Cellulomonas sp. (ATCC 21399) was cultivated under glucose and zinc limitation at a variety of growth rates in continuous culture. The growth characteristics and macromolecular composition of the population varied with the limitation imposed and the growth rate. Glucose- and zinc-limited cultures maintained a constant relative protein content. The relative ribonucleic acid content increased, whereas the carbohydrate and deoxyribonucleic acid contents decreased with an increase in the population growth rate in glucose-limited cultures. Free unbound lipid remained constant. The maximum population growth rate in zinc-limited cultures was directly proportional to the zinc concentration and demonstrated a traditional steady-state function. The nucleic acid content increased with increased growth rate; however, the relative nucleic acid content was significantly depressed when compared to glucose limited cells. This manner of cultivation may prove to be a useful tool for the production of single cell protein with lowered nucleic acid content and the elucidation of micronutrient involvement in growth-related processes.

Actinomycetales↗
PubMed1979

Continuous Cultivation for Apparent Optimization of Defined Media for Cellulomonas sp. and Bacillus cereus.

Steady-state continuous culture was used to optimize lean chemically defined media for a Cellulomonas sp. and Bacillus cereus strain T. Both organisms were extremely sensitive to variations in trace-metal concentrations. However, medium optimization by this technique proved rapid, and multifactor screening was easily conducted by using a minimum of instrumentation. The optimized media supported critical dilution rates of 0.571 and 0.467 h for Cellulomonas and Bacillus, respectively. These values approximated maximum growth rate values observed in batch culture.

Journal Article↗
PubMed1979

The actions of the beta-adrenoceptor blocking agents propranolol and metoprolol in the maximally exercised horse.

The effects of two beta-adrenoceptor antagonists, propranolol (0.2 mg/kg) and metoprolol (0.2 mg/kg) on some physiological and metabolic changes produced by maximal exercise in the horse were investigated. Both drugs reduced the elevation in heart rate seen immediately following exercise and reduced performance as was seen by the increased time taken to perform each gallop. The rise in plasma glucose, glycerol and lactate, and the fall in blood pH seen following exercise were attenuated by both drugs. However, a greater increase in plasma free fatty acids occurred. Exercise produced a nine- to 12-fold increase in plasma noradrenaline levels. Neither drug had any effect on resting levels of noradrenaline but after metoprolol the levels during exercise were increased.

Animals↗
PubMed1978

Evaluation of the adverse effects of long-term hyposensitization.

This study was undertaken to determine if long-term hyposensitization causes late sequelae, particularly those reflecting aberrant immunologic responses. Atopic individuals receiving five or more years of hyposensitization with allergenic extracts showed no increased autoimmune, collagen vascular, or lymphoproliferative disease. In addition, chronic hyposensitization did not have adverse effects on immunologic reactivity as assessed by a number of immune parameters. Particularly noteworthy was the absence of immune complexes in the serum of patients undergoing long-term hyposensitization. This study represents the first systematic investigation of potential adverse effects of long-term hyposensitization.

Adolescent↗
PubMed1978

The effects of piperoxan on uptake of noradrenaline and overflow of transmitter in the isolated blood perfused spleen of the cat.

1 The competitive alpha-adrenoceptor blocking agent, piperoxan, in concentrations up to 2 x 10(-4) M, produced large dose-dependent increases in transmitter overflow from the isolated blood perfused spleen of the cat following nerve stimulation at 10 hertz. 2 At concentrations greater than 2 x 10(-4) M, piperoxan produced a rise in perfusion pressure, a contraction of the splenic capsule, and a marked dose-dependent decrease in transmitter overflow. 3 Phenoxybenzamine (10(-4) M) and desmethylimipramine (3 x 10(-5) M) produced further increases in transmitter overflow when added after piperoxan. 4 Piperoxan (5.8 to 6.6 x 10(-6) M) had no effect on the recovery of 3H in the venous blood following the close arterial infusion or injection of (3H)-(--)-noradrenaline, indicating that the drug does not inhibit uptake of the amine. 5 Piperoxan produced dose-dependent inhibition of responses of the splenic vasculature to close arterial injection of 1 microgram of (--)-noradrenaline but was much less effective at inhibiting responses to nerve stimulation. At 2 x 10(-6) M piperoxan produced a considerable reduction of the response to injected noradrenaline but potentiated the response to nerve stimulation. 6 In isolated strips of cat splenic capsule, piperoxan produced a shift to the right of the dose-response curve to noradrenaline with no change of the maximum response. There was no evidence of a postsynaptic sensitizing effect of the type observed in the rat vas deferens.

Animals↗
PubMed1977

The effects of labetalol (AH 5158) on adrenergic transmission in the cat spleen.

1. The competitive alpha- and beta-adrenoceptor blocking agent labetalol, in concentrations up to 10(-4) M, produced dose-dependent increases in transmitter overflow from the isolated blood perfused spleen of the cat following nerve stimulation at 10 and 30 Hz. 2. At concentrations above 10(-4) M labetol produced a pronounced decrease in transmitter overflow. 3. Labetalol (1.5 X 10(-4) M) increased the recovery of 3H label in the venous blood following the close-arterial infusion of [3H]-(-)-noradrenaline indicating that the drug inhibits uptake of the amine. 4. Both labetalol (3.8 X 10(-5) M) and piperoxan (7.4 X 10(-6) M) produced parallel shifts to the right of the dose-response curves to noradrenaline and oxymetazoline in isolated strips of cat splenic capsule. In this preparation both drugs acted as competitive postsynaptic alpha-adrenoceptor blocking agents. 5. Labetalol (3.3 X 10(-5) M) increased the transmitter overflow following stimulation of the splenic nerves with 200 impulses at 10 Hz. The overflow could be further increased by subsequent addition of piperoxan (7.2 X 10(-6 M). Piperoxan (5.7 X 10(-6) M) alone produced a marked increase in transmitter overflow which could be further increased by subsequent addition of desmethylimipramine (DMI; 3.2 X 10(-5) M). Cocaine (1.5 X 10(-5) M) or DMI (5.4 X 10(-5 M) produced a small increase in transmitter overflow which was not further increased by addition of labetalol (2.8 X 10(-5) M). 6. Labetalol produced a biphasic effect on the responses of the isolated blood perfused spleen of the cat to nerve stimulation. With low doses (up to 10(-4) M) vascular responses were potentiated and with high doses (greater than 10(-4) M) inhibited. The potentiation was related to uptake blockade and the inhibition to decreased transmitter overflow and postsynaptic alpha-adrenoceptor blockade. 7. Labetalol appears to act as a postsynaptic alpha-adrenoceptor antagonist in the isolated blood perfused spleen of the cat with little effect on presynaptic alpha-adrenoceptors. The moderate elevation of transmitter overflow by the drug is related to the inhibitory effect of the drug on neuronal uptake rather than on presynaptic alpha-adrenoceptors.

Animals↗