Download The Time Course of Contraction in Heart Muscle Preparations

Medical Research Society
supports the theory that the high level of IgE in this
community is due to parasitic infestations. However,
cutaneous reactions to D. pteronyssinus were larger
in the asthmatics than in the controls which indicates
that asthmatics may also have increased levels of I&
speci6c for this allergen.
The low prevalence of asthma in New Guineans
does not appear to be explained by a reduced atopic
tendency and, though ethnic factors cannot be
excluded, it is likely that this is mainly due to environmental factors.
2. THE INFLUENCE O F BRONCHOMOTOR
TONE ON BRONCHIAL REACTIVITY
MALCOLM
K. BENSON
Cardiovascular Research Institute, Uniuersity of
California, San Francisco, California
(Introduced by N.B. PRIDE)
The parasympathetic nervous system has been shown
to have an important influence on resting bronchomotor tone and to mediate reflex bronchoconstriction.
Airway responses to various stimuli are frequently
studied before and after vagal blockade and it is often
implied that a reduction in response indicates a
reflex mechanism. However, vagal blockade also
reduces airway tone and thus alters baseline conditions. This in itself may alter the response to bronchoconstrictor stimuli.
The effect of changes in bronchomotor tone on
histamine induced bronchoconstriction was examined
by measurement of changes in bronchial diameter in
dogs in whom airways were outlined by tantalum dust.
In each dog the airway response was taken as the
change seen in twenty airways randomly selected and
ranging in size from the main bronchi to airways
2 mm in internal diameter. Bilateral vagotomy was
performed and reactivity to inhaled histamine
measured (1) without vagal stimulation and (2) with
electrical stimulation of the distal ends of the cut vagi.
In seven dogs when vagal tone was induced in this
way airway calibre was reduced as expected (mean
reduction 0.9k0.36mm). Doses of histamine which
had little effect on airway diameter when the vagi
were unstimulated (mean reduction 0 3 k 0 1 4 mm)
produced significantly greater changes during vagal
stimulation (mean reduction 1-2f 044mm) (P.c 0~001,
paired t test). In three dogs a wide range of histamine
doses were studied and dose-response awes were
constructed with and without vagal tone. Adding
vagal tone decreased the threshold dose of histamine
required to reduce airway diameter.
This study demonstrates that variations in the level
of resting bronchomotor tone will alter bronchial
reactivity to bronchoconstrictor stimuli. The ‘reflex
blockade’ produced by atropine could also be explained on this basis.
1 3 ~
3. THE TIME COURSE OF CONTRACTION IN
HEART MUSCLE PREPARATIONS EQUILIBRATED WITH STRONTIUM
A. H. HENDERSON
and M. R. CATTELL
Department of Cardiology, Welsh National School of
Medicine
(Introduced by J. R. MUIR)
Mechanical performance of cat and frog ventricular
muscle preparations has been studied after equilibration with strontium in place of calcium in order to
gain insight into underlying control mechanisms. The
onset of mechanical activity is slowed in cat but not
in frog heart muscle. This supports the view that
activating cation is derived mainly from internal
stores in mammalian but not in frog heart muscle,
where the sarcoplasmic reticulum is poorly developed.
The duration of contraction is prolonged in both
species. In cat but not in frog heart muscle, a separate
twitch and plateau phase of contraction can then be
distinguished. The plateau phase is augmented in the
first contraction after adding adrenaline whereas the
twitch phase is increased more in subsequent contractions. The plateau can also be augmented by
adrenaline added during the course of contraction.
These observations support the view that influx of
cations can contribute directly to mechanical activation.
4. SOME EFFECTS OF DISODIUM ETHANE-1-
HYDROXY-1,I-DIPHOSPHONATE (EHDP) ON
CALCIUM METABOLISM IN MAN
R. J. WALTON,R. G. G. RUSSELL,R. SMITHand G.
WARNER
Nufield Departments of Orthopaedic Surgery and
Medicine, University of Oxford
EHDP is able to inhibit calcification and bone resorption in experimental animals and is currently under
investigation in man as a treatment for Paget’s
disease of bone and other conditions.
At the commonly used dose of 20 mg/kg/day by
mouth, EHDP consistently produces a marked rise
in plasma inorganic phosphate. This is due to an
alteration in the renal tubular handling of phosphate
and does not appear to be caused by altered plasma
levels of parathyroid hormone, growth hormone,
thyroid hormones or cortisol. There is no comparable
consistent change in the total plasma concentration or
renal handling of calcium.
EHDP has no significant effect on the 24-h urine
excretion of calcium or on the intestinal absorption of
calcium as measured by the whole body retention of
oral 47Ca. It therefore seems unlikely that EHDP
has any marked effect on the production of 1,25-