PubMed Health⌕ Search

Biomedical subjects

J M Elliott

Publications and source records attributed to J M Elliott.

At least 109 records · Page 6Linked to original sources
PubMed1983

A comparison of alpha 2-adrenoreceptor binding characteristics of intact human platelets identified by [3H]-yohimbine and [3H]-dihydroergocryptine.

The binding characteristics of [3H]-yohimbine on intact human platelets were investigated and compared to those of [3H]-dihydroergocryptine. A significant correlation (r = 0.92, P less than 0.01, n = 7) was observed between the inhibition of [3H]-yohimbine binding and of noradrenaline-induced platelet aggregation, indicating that [3H]-yohimbine binds to the alpha 2-adrenoreceptor responsible for noradrenaline-induced platelet aggregation. The binding capacity of [3H]-yohimbine in 20 young male volunteers was 39 +/- 2.2 fmol/10(8) platelets (mean +/- s.e.m.). This is considerably lower than the binding capacity of [3H]-dihydroergocryptine previously reported. Simultaneous analysis of [3H]-yohimbine and [3H]-dihydroergocryptine binding in 10 subjects showed a significantly lower binding capacity for [3H]-yohimbine (P less than 0.001, paired t-test). This difference was not present in every subject, and was consistent within individuals on repeated testing. Possible causes of this difference in radioligand binding are discussed.

Adult↗
PubMed1982

Baroreceptor reflexes in conscious guinea-pigs are unaffected by depletion of cardiovascular substance P nerves.

Adult guinea-pigs were injected with doses of capsaicin increasing from 10 mg/kg to 400 mg/kg over 6-days. The guinea-pigs were supplied with indwelling arterial cannulae 14 days later and the next day cardiovascular function was assessed in the conscious animals. Resting blood pressures and heart rates were recorded and then baroreceptor reflex function was evaluated by recording the changes in heart period which were evoked by blood pressure responses to injections of phenylephrine and glyceryl trinitrate. Substance P was measured by radioimmunoassay and its localization examined by immunohistochemistry. The capsaicin treatment caused a substantial reduction in substance P levels in vascular and cardiac nerves. However, there were no changes in resting heart rate, blood pressure or baroreceptor sensitivity. It is concluded that the widespread substance P nerves associated with the heart and blood vessels are not necessary for baroreceptor reflex function. Their role or roles remain unknown.

Animals↗
PubMed1982

The binding characteristics of [3H]-dihydroergocryptine on intact human platelets.

1 We have characterized the binding of [3H]-dihydroergocryptine to intact human platelets. 2 The values of the association and dissociation rate constants, affinity and capacity of specific [3H]-dihydroergocryptine binding on intact cells closely resemble those previously reported on the human platelet lysate preparation. 3 The affinity of alpha-adrenoceptor antagonists, determined from inhibition of [3H]-dihydroergocryptine binding, is similar in intact and lysed platelet preparations, but the affinity of agonists is considerably lower in intact cells. 4 The potency of alpha-adrenoceptor antagonists as inhibitors of noradrenaline-induced platelet aggregation and as inhibitors of [3H]-dihydroergocryptine binding on intact platelets demonstrate a significant correlation (r = 0.92, p less than 0.01). 5 The affinity and capacity of [3H]-dihydroergocryptine binding to platelets from a group of healthy, young, male subjects show a high degree of consistency both between subjects (Kd = 2.81 +/- 0.27 nM; Bmax = 63 +/- 3 fmol/10(8) platelet: mean +/- s.e. mean, n = 10) and between sampling occasions in a single subject (Kd = 3.28 nM +/- 13%; Bmax = 70 fmol/10(8) platelet +/- 16%: mean +/- coefficient of variation, n = 5). 6 There is no significant difference in the binding capacity of platelets from a group of elderly male subjects (mean age 73) compared to those from young males (mean age 27) or elderly females (mean age 77). The affinity of binding is slightly but significantly (P less than 0.05) higher in the elderly male group compared to the two other groups. 7 We conclude that [3H]-dihydroergocryptine binds to the alpha 2-adrenoceptor of intact human platelets which is responsible for noradrenaline-induced platelet aggregation. The high consistency of the binding characteristics of [3H]-dihydroergocryptine indicate that this assay may be useful as a monitor of platelet alpha-adrenoceptor sensitivity in clinical investigation.

Adult↗
PubMed1982

The effects of monovalent and divalent cations on the alpha-adrenoceptor of intact human platelets.

1 We have examined the effects of monovalent and divalent cations and purine nucleotides on the binding of agonists and antagonists to the alpha-adrenoceptor of intact human platelets. 2 Replacement of Na+ (150mM) by NH4+ (150mM) in the incubation medium significantly reduced the binding affinity of [3H]-dihydroergocryptine (P less than 0.05) but did not alter the binding capacity. The competitive binding affinity of adrenaline and noradrenaline was unaltered. 3 The addition of Ca2+ (1mM) or Mg2+ (1mM) to the platelet suspension significantly reduced the platelet alpha-adrenoceptor capacity as indicated by either [3H]-dihydroergocryptine (P less than 0.05) or [3H]-yohimbine (P less than 0.01; Ca2+ only). 4 The addition of Ca2+ (1mM) or Mg2+ (1mM) had no effect on the binding affinity of [3H]-dihydroergocryptine but significantly reduced that of [3H]-yohimbine (P less than 0.05). The competitive affinity of adrenaline and noradrenaline determined by inhibition of [3H]-dihydroergocryptine binding, was unchanged in the presence of either cation. 5 Addition of the purine nucleotides ADP, ATP, GDP or GTP (final concentration 10 microM), either alone or in the presence of 1 mM Ca2+ or 1 mM Mg2+, had no effect on the binding of [3H]-dihydroergocryptine or on the competitive affinity of adrenaline or noradrenaline. 6 We conclude that the alpha-adrenoceptor of intact human platelet displays the binding characteristics of the alpha 2L form of the receptor previously identified in the platelet lysate preparation.

Adult↗
PubMed1980

Oestrogen and progesterone change the binding characteristics of alpha-adrenergic and serotonin receptors on rabbit platelets.

The binding characteristics of the alpha-adrenergic and serotonin receptors on intact rabbit platelets were identified using [3H]-dihydroergocryptine and [3H]-5-hydroxytryptamine respectively. In untreated female rabbits a single slpha-adrenoceptor and two serotonin receptors were identified with ligand affinities similar to those in human platelets. The effects of oestrogen and/or progesterone on the alpha-adrenergic and serotonin receptors of rabbit platelets were studied. Oestrogen alone increased the capacity of serotonin receptors but reduced that of the alpha-adrenoceptor. Oestrogen plus progesterone reduced the capacity of both receptors and reduced the affinity of the alpha-adrenoceptor. The possible mechanisms of the steroid-induced changes and the implications of these with regard to the effects of the oral contraceptive pill are discussed.

Animals↗
PubMed1980

Cigarettes and accelerated hypertension.

The smoking and drinking habits of 58 patients with accelerated hypertension were compared with those of a control group of 58 patients with benign hypertension, each individually matched for age, sex and date of presentation. Thirty-eight (66 percent) of the patients with accelerated hypertension were regular smokers compared to 26 (45 percent) of the control group. This excess of smokers was significant, but the average number of cigarettes smoked by smokers in the two groups was similar. The number of patients known to consume alcohol was the same in the two groups; and there were no significant differences in amount of alcohol drunk. Smoking and alcohol habits were not related. Thirty-six patients (62 percent) with accelerated hypertension had serum creatinine levels greater than 0.12 mmol/l compared with nine (16 percent) of the control group. Seventeen (29 percent) patients with accelerated hypertension were known to have died compared with five (9 percent) of the control group. This survey confirms that, as shown by recent studies in Britain, smoking is more common in patients presenting with accelerated than with benign hypertension. It appears that hypertensive patients who smoke regularly are more likely to develop the accelerated phase than those who do not.

Alcohol Drinking↗
PubMed1979

Effect of oral contraceptives on platelet noradrenaline and5-hydroxytryptamine receptors and aggregation.

Characteristics of receptor sites on platelets for noradrenaline (NA) and serotonin (5-HT) changed significantly between day 21 and day 28 of treatment in healthy women taking oral contraceptives. NA-induced and 5-HT-induced platelet aggregation and 5-HT uptake vaired accordingly. In untreated women with normal cycles no changes in either receptor site or in platelet function occurred between the luteal and postmenstrual phases. It is concluded that the observed changes are due to a pharmacological effect of the oral contraceptive rather than a normal physiological variation.

Adult↗
PubMed1978

The effect of visual frame of reference on a judgement of plane stimulus orientation by children.

Three studies are reported with children aged 4 1/2 to 9 1/2 years and also with educationally subnormal children, in which it was found that up to about 7 years children's selection of one of a pair of line stimuli as 'falling over' is affected by the nature of the visual surround contours provided. Both the form of the stimulus surround and the presence or absence of a baseline tilted 45 degrees relative to the horizontal were found to affect the children's judgements. The plane (horizontal or vertical) in which the stimuli were presented had no effect on the results. It is argued that while the results show the influence of the visual surround on children's comprehension of 'falling over', this may not be wholly explicable in terms of surround contour matching, as conventionally correct judgements were obtained in the absence of all straight line contours in the immediate surround.

Age Factors↗
PubMed1978

Changes in muscarinic ligand binding to intestinal muscle strips produced by pre-exposure to hypotonic conditions.

The extent of the binding of [3H]propylbenzilylcholine mustard (3H-PrBCM) to muscarinic receptors in longitudinal muscle strips from guinea-pig small intestine is increased by nearly 50% when the strips are preexposed to distilled water before measurement of 3H-PrBCM binding in Krebs-Henseleit solution. The apparent rate constant for 3H-PrBCM-receptor complex formation is more than double that of intact strips. The curves for the inhibition of 3H-PrBCM binding by methylatropinium bromide in normal and treated strips are superimposable, but, in contrast, distilled water pretreatment shifts the inhibition curve for carbachol to lower concentrations by a factor of 5-6. The inhibition curve for methylfurmethide is also shifted, by a factor of approximately 4, but the effect on the curve for hexyltrimethylammonium (C6TMA) is slight. The relative inhibition produced by benzhexol in the two preparations was variable. Comparison of the rate of equilibration of benzhexol with muscarinic receptors in intact and in distilled water pretreated muscle indicates that this inconsistency is unlikely to be due to incomplete equilibration.

Animals↗
PubMed1977

Changes in rat hind limb vascular resistance following intracerebroventricular drug administration.

The right hind limbs of rats (which had previously implanted intraventricular guide cannulae) were isolated from the systemic circulation, but with the nerves to the limb remaining intact, and perfused using a constant output blood pump. Using this preparation, changes in vascular resistance, blood pressure and heart rate were monitored following injection of noradrenaline, phentolamine and propranolol into the lateral cerebral ventricles (i.c.v.) of rats anaesthetised with alpha-chloralose. All three drugs lowered blood pressure. Noradrenaline administered i.c.v. induced a nervously mediated vasocilatation and an insignificant fall in heart rate whereas i.c.v. phentolamine administration was followed by a nervously mediated vasoconstriction in the isolated hind limb and a gradual rise in heart rate. After i.c.v. administration of propranolol there was no evidence of an immediate nervously mediated vasodilatation but heart rate fell significantly. Following i.c.v. phentolamine or propranolol vasodilatation did not occur in the hind limb until after the time taken for circulating blood ro reach the isolated vascular bed. The vasodilatatory and hypotensive responses to i.c.v. noradrenaline were not evident following prior i.c.v. injection of phentolamine. These results indicate the suitability of this preparation for investigations of central actions of other drugs.

Animals↗
PubMed1976

Rat liver cells in culture: effect of storage, long-term culture, and transformation on some enzyme levels.

Aryl hydrocarbon hydroxylase (AHH) and tyrosine aminotransferase (TAT) activities were determined in rat liver cell lines after frozen storage, long-term culture, and transformation in vitro. Levels of AHH activity after 17 months in frozen storage were comparable to levels prior to freezing. During long-term culture the AHH levels of the cell lines tended to decrease. Transformed lines had variable levels of AHH activity. Cell lines retained measurable TAT activity following long-term culture and frozen storage. TAT activity of transformed cells was comparable to that of normal lines. Prolonged frozen storage did not induce transformation up to one year.

Animals↗
PubMed1968

Pica and pregnancy.

Explore the source record for details and available documents.

Anemia, Hypochromic↗