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Biomedical subjects

G Jennings

Publications and source records attributed to G Jennings.

159 records · Page 9Linked to original sources
PubMed1976

Oral disopyramide in prophylaxis of arrhythmias following myocardial infarction.

Oral disopyramide given prophylactically following myocardial infarction has been compared with placebo in a double-blind trial using continuous-tape monoriting of the electocardiogram. It caused a significant reduction in the incidence of ventricular arrhythmias and of the various degrees of heart-block. There was a significant reduction of reinfarction during hospital stay in patients who had received disopyramide. Disopyramide appears to be a safe and effective oral therapy in the prevention of potentially serious arrhythmias following myocardial infarction.

Administration, Oral↗
PubMed1976

Lithium and the antidiuretic hormone.

The effect of lithium on the urine concentrating response to antidiuretic hormone (ADH) and the excretion of ADH has been studied in rats and man. The maximum urine osmolarity following 18 h dehydration and Pitressin (5 u) was decreased in three out of four patients during lithium treatment compared to their response to the same test in the absence of lithium. In a fifth patient, tested only during lithium treatment, the urine remained hypotonic to plasma throughout this test. Lithium increased the excretion of ADH in non-polyuric patients from 9-22 mu/24 h in the absence of lithium to 36-202 mu/24 - during lithium treatment. In four patients with lithium-induced polyuria, a diuretic acting on the distal tubules, clorexolone, reduced the polyuria. Lithium increased urine volume and the excretion of ADH in four rats receiving lithium in their diet. The response to exogenous ADH was decreased during lithium administration.

Animals↗
PubMedDate not supplied

Assessment of neuronal uptake of noradrenaline in humans: defective uptake in some patients with essential hypertension.

1. Disappearance of tritiated noradrenaline from plasma, after infusion to steady-state, was studied to assess neuronal uptake of noradrenaline inessential hypertension. 2. Plasma tritiated noradrenaline disappearance was biexponential. Rapid removal was dependent on neuronal uptake, being slowed both in normal subjects after desipramine, and in patients with sympathetic nerve dysfunction (autonomic insufficiency). 3. In nine of thirty-eight hypertensive patients the t1/12 similarly was prolonged. Endogenous noradrenaline escaping uptake after release, and spilling over into plasma, was increased in these patients. 4. Defective neuronal uptake of noradrenaline, by exposing adrenergic recepotors to high local transmitter concentration, may be important in the pathogenesis of essential hypertension in some patients.

Adult↗
PubMedDate not supplied

Differing noradrenaline kinetics in essential hypertension and depressive illness, two diseases in which the plasma concentration of noradrenaline is sometimes elevated.

1. The rate of spill-over of noradrenaline to plasma, and neuronal noradrenaline uptake, which influences spill-over, were studied in patients with essential hypertension and depressive illness. 2. Noradrenaline spill-over was increased in seven of thirty-four patients with essential hypertension and five of eleven patients with primary depressive illness, compared with values in seventeen normal subjects (range 1.0-3.63 nmol/min per m2). 3. Faulty neuronal reuptake of noradrenaline seemed to be the cause of higher noradrenaline spill-over in patients with essential hypertension. Increased sympathetic nerve firing rates apparently were responsible in the primary depressives, despite their normal blood pressure. 4. These puzzling findings suggest that hypertension occurs when neurotransmitter excess is due to defective noradrenaline reuptake (in essential hypertension), but not chronically increased nerve firing (in depressive illness).

Adult↗
PubMedDate not supplied

Evaluation of the CO2 rebreathing method for the non-invasive measurement of resting cardiac output in man.

We have compared the indirect Fick, a non-invasive CO2 rebreathing method for measuring resting cardiac output, with the thermodilution method in eleven subjects including some with cardiac and pulmonary disease. Three alternative methods for calculating veno-arterial CO2 content difference were used: (i) from end-tidal and rebreathing bag equilibrium PCO2 modified from the equations developed for use during exercise by Jones et al. (1975); (ii) by using the uncorrected difference between end-tidal and equilibrium PCO2 and the standard CO2 dissociation curve; (iii) by direct measurement of arterial PCO2. Each method was satisfactory in that reproducibility was similar to thermodilution (5-10%) and the equations relating thermodilution to indirect Fick cardiac output were linear with slope and intercept, close to 1 and 0, respectively. End-tidal PCO2 accurately predicted arterial PCO2 except in five patients with liver disease. Direct measurement of arterial PCO2 is recommended in such patients. In other subjects there was no advantage in either correcting non-invasive measurements of alveolar gas to obtain veno-arterial CO2 content difference, or in direct measurement. The indirect Fick is an accurate method for measuring cardiac output at rest in normal subjects and those with cardiovascular disease. Its use can be extended to other groups by a single arterial blood sample.

Adult↗
PubMedDate not supplied

Norepinephrine kinetics in essential hypertension. Defective neuronal uptake of norepinephrine in some patients.

To assess sympathetic nervous system function in essential hypertension, we measured the rates of release to and removal from plasma of the sympathetic neurotransmitter, norepinephrine. In normal subjects, disappearance of tritiated l-norepinephrine from plasma, after infusion to steady state, was biexponential, with t1 1/2 = 2.0 +/- 0.4 minutes (mean +/- standard deviation) and t2 1/2 = 33 +/- 15 minutes. The rapid component of removal seemed to represent neuronal uptake of norepinephrine: the t1 1/2 was lengthened by the selective inhibitor of neuronal norepinephrine uptake, desipramine; it was not changed by the extraneuronal uptake blocker, cortisol; and it was prolonged in patients with peripheral sympathetic nerve dysfunction (idiopathic autonomic insufficiency). In eight of 37 hypertensive patients, the t1 1/2 was greater than 2.8 minutes (range, 3.3-6.0 min), longer than in any normal subject; this appears to be presumptive evidence of the existence of defective neuronal norepinephrine uptake. In these patients the rate of spillover of norepinephrine to plasma, of transmitter escaping uptake after release, was 0.73 +/- 0.39 micrograms/m2/min (4.3 +/- 2.3 nmoles/m2/min), higher than in normal subjects, 0.36 +/- 0.14 micrograms/m2/min (2.1 +/- 0.8 nmoles/m2/min) (p less than 0.01). A defect in neuronal uptake of norepinephrine, by exposing adrenergic receptors to high local norepinephrine concentration, may be important in the pathogenesis of blood pressure elevation in some patients with essential hypertension.

Adolescent↗
PubMedDate not supplied

Effect of dietary restriction on the response of alpha 2-macroglobulin during an acute phase response.

The effects of aseptic abscesses induced by subcutaneous injections of turpentine (5 mL/kg body weight) on the acute-phase protein response (alpha 2-macroglobulin, alpha 2-M) and on the circulating albumin and total protein concentrations were assessed in young rats that were made malnourished by restricting dietary intake to an extent that either impaired growth (60% of normal intake) or caused weight loss (0% to 45% of normal intake). The measurements were obtained daily during a period of 4 days in malnourished rats that had lost about 25% body weight but had maintained a stable weight thereafter, or in rats that had lost about 12% body weight and were continuing to lose weight at various rates at the time of the turpentine injection. In animals that were injected while they maintained a stable weight after losing about 25% body weight, the alpha 2-M response was attenuated fourfold to eightfold compared with control animals (the area under the 4-day alpha 2-M curve in control rats was 23.3 +/- 2.3 g/L/d). In the depleted animals that were injected while they were actively losing weight (approximately 12.5% weight loss), the attenuation of the alpha 2-M response was related to the rate of weight loss or to the extent of dietary restriction (area under the 4-day alpha 2-M curve ranged from 5.7 +/- 1.4 g/L/d in animals receiving 15% restricted diet to 15.6 +/- 1.5 g/L/d in animals receiving the 45% restricted diet).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute-Phase Reaction↗
PubMedDate not supplied

Central nervous system monoamine neurotransmitter turnover in primary and obesity-related human hypertension.

Recent experiments in laboratory animals have challenged the conventional view that the dominant effect of CNS noradrenergic neurons in cardiovascular control is sympathetic nervous inhibition and blood pressure reduction, describing instead sympathetic activation. We have tested whether such a stimulant effect on sympathetic outflow is also evident in human hypertension. CNS norepinephrine turnover was estimated from the combined overflow of norepinephrine, MHPG and DHPG into the internal jugular veins. Cerebral blood flow scans allowed differentiation between cortical and subcortical jugular venous drainage. In patients with pure autonomic failure, jugular overflow of norepinephrine and metabolites was not reduced, indicating brain neurons and not cerebrovascular sympathetics was the source. In healthy men, CNS norepinephrine turnover and muscle sympathetic nerve activity were directly related (p < 0.02). Administration of the ganglion blocker, trimethaphan, caused a compensatory five-fold increase in jugular overflow of MHPG. Conversely, intravenous clonidine reduced CNS norepinephrine turnover by approximately 50%, this possibly representing a mechanism of drug action. In cardiac failure patients, sympathetic nervous activation was associated with a trebling of CNS norepinephrine turnover (p < 0.01). In untreated patients with essential hypertension, the sympathetic activation present was associated with 250% higher CNS norepinephrine turnover (p < 0.01), but in subcortical brain regions only. A close and direct relation exists between brain norepinephrine turnover and human sympathetic nervous activity. CNS release of norepinephrine, presumably in the forebrain where noradrenergic neurons are sympathoexcitatory and pressor, mediates increased sympathetic nerve firing in patients with essential hypertension.

Animals↗
PubMedDate not supplied

[Rilmenidine sympatholytic activity preserves mental and orthostatic sympathetic response and epinephrine secretion].

BACKGROUND: Heightened central sympathetic nervous outflow is common in essential hypertension, contributing to hypertension development and perhaps also to complications. Acute sympathetic nervous activation is a proven trigger for adverse cardiovascular events. Accordingly, antihypertensive drugs inhibiting sympathetic outflow represent a theoretically attractive therapeutic option. OBJECTIVES: To study the sympatholytic and blood pressure lowering activity of the imidazoline binding agent rilmenidine at rest and during reflex sympathetic activation. DESIGN AND METHODS: The HERA study (Hyperium Effect on the sympathetic Reflex activation and Adrenaline) is a randomised, double-blind, 6-week cross-over trial, with a 1-week placebo run-in period, two 2-week active treatment intervals (rilmenidine 1 mg bid, placebo) and intervening one week placebo wash-out. In 15 hypertensive patients, noradrenaline and adrenaline plasma kinetics and intra-arterial blood pressure measurements were performed at rest, after mental stress (difficult mental arithmetic) and during head-up tilting, at the end of the 2-week dosing periods. RESULTS: The noradrenaline spillover rate, indicative of whole body sympathetic activity, was reduced 35% by rilmenidine at rest (p<0.01) and remained significantly lower during mental stress and tilting, although the increases in noradrenaline spillover with both stimuli were preserved. The effects on intraarterial blood pressure ran in parallel, a fall in supine resting pressure, but no reduction in BP rise during mental stress and a lack of fall in BP with tilting. On placebo, adrenaline secretion was 162 +/- 27 ng/min (mean, SE) at rest, increased by 77 +/- 42 ng/min with mental stress (p=0.019) and was unchanged with tilting. Rilmenidine left adrenaline secretion untouched under all conditions. CONCLUSIONS: This study confirms a sympatholytic effect of rilmenidine during supine rest but demonstrates that sympathetic responses during mental stress and tilting are preserved, the latter underlying a perhaps surprising absence of postural hypotension on the drug. The absence of suppression of reflexive sympathetic responses contrasts with the effects of rilmenidine in experimental animals, and emphasises the previously demonstrated unique importance in humans of suprabulbar noradrenergic neuronal projections from the brainstem, which are inhibited by imidazoline binding agents, in regulating tonic sympathetic activity in essential hypertension. Sympathetic nervous inhibition with rilmenidine contrasted with an absence of suppression of the secretion of adrenaline affirming that here, as elsewhere, sympathetic nervous and adrenal medullary function can be disconnected.

Adult↗
PubMedDate not supplied

Independent effects of protein and energy deficiency on acute-phase protein response in rats.

The effect of restricting either protein intake alone or all dietary constituents on the acute-phase protein response was assessed during a 3-wk period after a standardized "injury" (i.e., subcutaneous injection of turpentine 0.5 ml/kg body wt) to rats. Sequential measurements were made of the circulating concentrations of alpha 2-macroglobulin (alpha 2-M), albumin, and total protein. Results were compared with those obtained from normally fed rats that were also injected with turpentine and with saline-injected rats (controls) receiving each dietary regimen. Turpentine-treated rats showed a decrease in albumin concentration by approximately 10 g/L within 2-4 days. In the protein-deficient rats, recovery to preinjection levels had not occurred by 3 wk, but in the other groups, it was complete by 7-9 days. The protein-deficient animals also showed an attenuated response in alpha 2-M and total protein and delay in their recovery toward normal. Maximal alpha 2-M and total-protein responses in this group of animals was only 44 and 39%, respectively, of those found in the control group. We conclude that protein deficiency attenuates the magnitude and alters the time profile of the positive (alpha 2-M and total protein) and negative (albumin) acute-phase protein responses to injury, independent of the severity of the stimulus.

Acute-Phase Proteins↗