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Biomedical subjects

R Summers

Publications and source records attributed to R Summers.

At least 55 records · Page 3Linked to original sources
PubMed1991

Double blind, placebo controlled trial of metronidazole in Crohn's disease.

A double blind study compared the efficacy of metronidazole in two doses (20 mg/kg, 10 mg/kg) with placebo in patients with Crohn's disease. One hundred and five patients participated but only 56 completed the 16 week study -21 were withdrawn for deterioration of symptoms, 17 for adverse experiences, and 11 for protocol violation. Significant improvement in disease activity as measured by the Crohn's disease activity index (metronidazole 20 mg/kg, 97 units; metronidazole 10 mg/kg, 67 units; placebo -1 unit, p = 0.002) and serum orosomucoid (metronidazole 20 mg/kg/day, 49; 10 mg/kg/day, 38; placebo, -9, p = 0.001)) were detected. Changes in C reactive protein concentrations did not achieve significance when all three groups were considered but were significant when all metronidazole treated patients were grouped and compared with the placebo treated patients (0.8 v -0.9, p less than 0.05). Although patients receiving metronidazole 20 mg/kg/day had a greater improvement in disease activity than those receiving 10 mg/kg/day (difference 30 units (95% confidence intervals -27-87), the small sample size may have precluded the detection of statistical significance. Preliminary analysis suggests that metronidazole was more effective in patients with disease confined to the large intestine or affecting both small and large bowel than in those with small bowel disease only. There were no differences in remission rates between metronidazole and placebo treated patients. We conclude that metronidazole warrants further assessment in the treatment of patients with active Crohn's disease.

Analysis of Variance↗
PubMed1990

Reduction of gastrointestinal symptoms following treatment for panic disorder.

Symptoms of gastrointestinal distress, including those of irritable bowel syndrome, were reported more frequently by patients with panic disorder than by nonanxious controls. Five of 30 subjects with panic disorder met criteria for irritable bowel syndrome, the onset of which coincided with the onset of panic disorder. Effective treatment for the anxiety disorder was accompanied by a reduction in gastrointestinal symptoms in all subjects.

Adult↗
PubMed1988

Persistent beta-adrenoceptor blockade with alkylating pindolol (BIM) in guinea-pig left atria and trachea.

The actions of alkylating pindolol (N8-bromoacetyl-N1-3'-(4-indolyloxy)-2'-hydroxypropyl[z]-1,8- diamino-p-menthane; BIM) have been examined on beta-adrenoceptors in guinea-pig left atria and trachea. In organ bath experiments, addition of BIM (greater than or equal to 0.1 microM), followed by washout, produced concentration-dependent rightward shifts of the dose-response curve to cumulative additions of (-)-isoprenaline and oxymethylene-isoprenaline and reductions in the maximal response. The "apparent" pA2 value for BIM was 9.23 +/- 0.20 (slope = 0.98 +/- 0.20). Changes in the maximal density of beta-adrenoceptor binding sites were determined in guinea-pig left atrial membranes using [125I]-cyanopindolol. BIM (0.1, 1.0 and 10 microM) produced 14, 23 and 41% reductions in Bmax with no change in KD. The binding of [125I]-BIM to guinea-pig left atrial membranes had a high non-specific binding component and a pseudo-Hill coefficient less than unity. The "apparent" KD value of [125I]-BIM at beta-adrenoceptor binding sites was 85.7 +/- 57.9 pM.

Adrenergic beta-Antagonists↗
PubMed1988

Clinical relevance of the substitution of different brands of sustained-release theophylline.

In order to assess whether clinically important changes in serum theophylline concentrations occur when patients switch their brand of slow-release (SR) theophylline, 10 subjects with asthma were administered the same dose of four different SR theophylline formulations for 2-week periods in a random, double-blinded, crossover manner. Analysis of the data revealed significant differences in mean peak-to-trough fluctuations of serum theophylline concentrations between the formulations of SR theophylline, which varied from 60% to 106% of trough concentration (p less than 0.0001, analysis of variance). On at least one occasion in every subject, switching between brands of SR theophylline was responsible for raising the serum theophylline concentrations outside the accepted therapeutic range, and this was associated with symptoms of toxicity in five of the subjects. Worsening pulmonary functions were observed in two of the subjects whose switching resulted in lowered theophylline concentrations. Many of the formulation-related changes in theophylline concentrations appeared to be idiosyncratic and could not be predicted by the overall bioavailability differences between the drugs. These results argue against the open substitution of these formulations and suggest that if patients are switched between different brands of SR theophylline, their serum theophylline concentrations need to be closely monitored.

Adult↗
PubMed1986

Water content and NMR relaxation time gradients in the rabbit kidney.

Magnetic resonance images were made of rabbits at 1.4 tesla for the purpose of measuring the T1 relaxation times of the kidney in vivo with the animal in different states of hydration. In the normally hydrated animal, the outer cortex has a T1 of about 600 msec and there was a steep T1 gradient with an increase to about 1200 msec at the tip of the inner medulla. The relaxation time gradient was not affected by overhydration with intravenous fluid, but dehydration by withholding water for 24 hours decreased the values in the inner medulla. The T1 and T2 relaxation times and total water content were measured in vitro on tissue samples. The values for both T1 and T2 correlated with the regional renal water content.

Animals↗
PubMed1985

Normal values for trabecular and cortical bone in the radius measured by computed tomography.

Quantities related to the amount of trabecular bone in the distal radius and cortical bone in the radius mid-shaft have been measured in 262 normal adults of both sexes aged 21-89 years by computed tomography (CT). A special-purpose CT system (ISOTOM) which incorporated a source of 125I (29 keV) was used to make the measurements. The relationships between these quantities and age, weight, height and surface area have been evaluated, and the results have been used to draw conclusions on the significance of values measured in female patients with osteoporosis, Colles' fracture of the wrist and generalised osteoarthritis.

Absorption↗
PubMed1984

The involvement of central alpha adrenoceptors in the antihypertensive actions of methyldopa and clonidine in the rat.

The antihypertensive effects of methyldopa and clonidine result from agonist activity at alpha adrenoceptor sites within the brain. Methyldopa is converted enzymatically to alpha-methylnoradrenaline in noradrenergic neurones in rat brain and replaces the natural transmitter, noradrenaline. Radioligand receptor studies show that alpha-methylnoradrenaline differs from noradrenaline in being much more selective (70 times) for the alpha 2 subclass of adrenoceptors than noradrenaline and it is likely that the antihypertensive action of methyldopa results from selective activation of alpha 2 adrenoceptors by alpha-methylnoradrenaline in the nucleus tractus solitarius and the anterior hypothalamus. Radioligand studies also show that clonidine is a selective alpha 2 adrenoceptor agonist although it probably interacts with alpha 1 adrenoceptors at higher concentrations. With regard to a withdrawal syndrome after cessation of clonidine treatment, the cardiovascular and behavioural components can now be characterised in a rat model. The components include increases in basal blood pressure and heart rate, as well as increases in cardiovascular reactivity and also increases in rapid eye movement (REM) sleep, body shakes and tremor which is reminiscent of an opiate withdrawal syndrome. Increased central noradrenergic activity is involved in this syndrome and alpha 1 and alpha 2 adrenoceptors mediate opposing effects on the REM sleep rebound component.

Animals↗
PubMed1983

Thiomolybdates in rumen contents and rumen cultures.

Examination of direct and (Cu)-difference spectra of i) the aqueous supernatants of in vitro cultures of bovine rumen contents incubated with MoO42- and potential sources of S2- and ii) samples drawn directly from the rumen of animals receiving high Mo diets yielded evidence of the presence of thiomolybdates. Only MoS42- was detected in the soluble phase of in vitro cultures. Although intense and variable background absorbance precluded full characterization of thiomolybdate species in samples drawn directly from the rumen, both spectral data and the biochemical and clinical responses of animals given high Mo diets were consistent with the conclusion that MoS42- rather than MoOS32- was the predominant thiomolybdate species present in the aqueous phase. Addition of Ca2+ either to rumen cultures before incubation or as a supplement to diets high in MoO42- content inhibited the appearance of MoS42- in the aqueous phase. Evidence of the sequestration of MoS42- and MoOS32- by particulate or microbial fractions of rumen contents is considered in relation to the inhibitory action of Mo upon Cu absorption by ruminants.

Animals↗
PubMed1981

Effects of vasopressin on human memory functions.

Arginine vasopressin and a number of its synthetic analogs augment memory functions in experimental animals. One of these analogs, 1-desamino-8-D-arginine vasopressin (DDAVP), influences human learning and memory. Cognitively unimpaired, as well as cognitively impaired adults, treated with DDAVP for a period of several days, learn information more effectively, as measured by the completeness, organization, and consistency (reliability) of recall. DDAVP also appears to reverse partially the retrograde amnesia that follows electroconvulsive treatment.

Adult↗
PubMed1981

Effects of infused histamine on asthmatic and normal subjects: comparison of skin test responses.

The effect of histamine infused intravenously at sequentially increasing concentrations (0.05, 0.1, 0.25, 0.5, and 1 microgram/kg/min) on the wheal responses to intradermal histamine and compound 48/80 in eight normal and five asthmatic subjects and to allergen skin tests in five asthmatic subjects was measured. These measurements were repeated following pretreatment with the H-1 antagonist hydroxyzine or the H-2 antagonist cimetidine, either alone or in combination. Histamine infused in progressively increasing concentrations had no effect on histamine, compound 48/80, or allergen skin tests either before or after H-1 or H-2 antihistamine treatment. No significant difference was found in the concentration of histamine or compound 48/80 required to elicit a 10-mm wheal in normal or asthmatic patients. Pretreatment with the H-2 antagonist alone had no effect on histamine or compound 48/80 skin tests in either group. However, the H-1 antagonist significantly reduced the wheal response to histamine (p less than 0.05 normal; p less than 0.025 asthmatics) and compound 48/80 (p less than 0.05 normal; p less than 0.025 asthmatics) in both groups. The combination of H-1 and H-2 histamine antagonists was not significantly different from the H-1 antagonist alone. Antigen skin testing was suppressed 82% by the hydroxyzine alone; no significant suppression was induced by cimetidine alone, and the combination of hydroxyzine plus cimetidine was only slightly more effective than hydroxyzine alone. The results indicate that blockade of histamine H-2 receptors with cimetidine has little or no additive effect on H-1 antagonist-suppressed skin test responses to histamine, compound 48/80, or antigen. Furthermore, the capacity of histamine to suppress histamine release in vitro from basophils was not demonstrated in vivo assessing skin mast cell responses. This observation combined with earlier studies on the human lung mast cell, which also failed to demonstrate that histamine had an inhibitory action, suggests that the human mast cell may not respond to histamine like the basophil and that this discrepancy may represent a fundamental difference in the cell types.

Adolescent↗