The work described in the papers submitted was
begun in 1950 when radioactive isotopes of sodium
and potassium first became available for biological
research. The initial investigations were made
with ²⁴Na and methods were developed leading to the
measurement of the amount of sodium in the human
body that was free to exchange with the isotope.
This afforded a means of ascertaining the amount of
metabolically active sodium in the body and is
commonly referred to as "exchangeable sodium" or
Naₑ. During the course of this work it was found
that there was a large amount of sodium in bone but
that about 75 per cent was not available for
exchange. This was confirmed by the use of
the long half-life isotope ²²Na. The
significance of the large amount of sodium in bone
could not be investigated in man but studies in
rats under various experimental conditions showed
that in states of acute depletion sodium was withdrawn from the bones especially in young
animals . This work demonstrated that ²²Na
is not safe for use in man as a small amount may be
retained in bone for a long period.The amount of exchangeable potassium in the
body can likewise be measured with the isotope ⁴²K.
Practically all the potassium in animals was
available for exchange. When exchangeable
sodium and potassium are measured simultaneously,
as is often required, special techniques must be
developed because the half lives of the isotopes
²⁴Na and ⁴²K (15.0 and 12.3 hours) are close.
The introduction of tetraphenyl boron proved
extremely satisfactory for the separation of
potassium from sodium in biological fluids.
Rubidium was thought to have a similar distribution
to potassium in the body but investigations with
the isotope ⁸⁶Rb showed that it was not a reliable
alternative to ⁴²K.Previous to the use of sodium and potassium
radioisotopes the only way to study the metabolism of these electrolytes in the human body was by
cumulative metabolic balance methods. In long
term investigations this is extremely laborious.
However, measurements of Naₑ, and Kₑ at intervals can
demonstrate cumulative changes, are simpler and less
time consuming, and gave results in good agreement
with the balance method. Furthermore, the
isotope techniques yielded a measure of the amounts
of sodium and potassium in the body . The
potassium content of the body was related to the
lean tissue mass; in comparison with healthy males
the amount of potassium was reduced in females and
in those with wasting diseases. In chronic disease
there was an increase in the proportion of sodium
in the body and this was seen to the greatest extent
in oederenatous states.Characteristic changes in sodium and potassium
metabolism take place after the infliction of an
injury or a surgical operation (12, 13). These
consisted in a retention of sodium and an enhanced excretion of potassium lasting over a few days.
These changes are probably related to the levels
of adrenocortical hormones in the blood as trauma
increases adrenal secretion, but this response was
detected in patients undergoing bilateral
adrenalectomy and in patients with Addison's disease
(adrenal insufficiency) given a constant exogenous
supply of adrenal steroids during an operation. It is now known that the blood levels
are elevated by surgical operation even in these
circumstances as the metabolism and excretion of the
steroids are delayed.Electrolyte metabolism may be deranged in thyroid
disorders and accordingly measurements were made of
exchangeable sodium and potassium in hypothyroidism
and hyperthyroidism before and after treatment.
Treatment of hypothyroidism with thyroxine led to a
decrease in both Naₑ and Kₑ due probably to a loss
of myxoedematous tissue. Successful therapy of
hyperthyroidism was associated with an increase in Kₑ due to restoration of lost muscular tissue.
Changes in Naₑ were variable and not readily
interpreted. In some patients there was little
change but in many there was a moderate decrease
in Naₑ on return to health. Decalcification of
the skeleton may occasionally occur in
hyperthyroidism and it was considered possible
that some of the difficulties in interpretation of
Naₑ changes might be due to alteration in bone
sodium content. However, experimental studies in
rats given large doses of thyroxine did not
demonstrate any effects on bone sodium metabolism. A mild degree of cardiac failure occurs in
many thyrotoxic patients and the decrease in
Naₑ is probably related to a loss of a small amount
of latent oedema. This has been confirmed in
subsequent unpublished observations.A similar pattern of changes in body electrolyte
composition, namely an excess of sodium and a loss
of potassium, has already been noted in cardiac patients . It was particularly evident in
patients with severe mitral stenosis and after
successful surgical treatment serial measurements
showed a gradual restoration of the body composition
towards normal. A delay in the excretion of
ingested sodium is a recognised early feature of
congestive cardiac failure and it was thought that
this might be related to the increased sodium content
of the body. This was investigated in dogs with
experimental valvular lesions of the heart.
Considerable changes in the ability to excrete sodium
developed without any gross alterations in the amount
of exchangeable sodium in the body. The reduction
in sodium excretion rate could not be attributed to
the dilution of infused sodium in an expanded body
sodium pool. The abnormality was apparently due to
a direct effect of the cardiac lesions on renal function.The introduction of chlorothiazide, an effective
oral diuretic, constituted a considerable advance in
aiding the excretion of the excess of sodium present in cardiac failure. However, chlorothiazide often
caused a considerable excretion of potassium as well
as sodium which is particularly disadvantageous in
the depleted cardiac patient. This potassium loss
was attributed to the carbonic anhydrase inhibitor
activity of chlorothiazide. However, a later
derivative, hydroflumethiazide, which was a negligible
carbonic anhydrase inhibitor, nevertheless under
certain circumstances caused a marked loss of
potassium. The liability to lose potassium
was thought not to be related so much to the choice
of the thiazide diuretic as to the circumstances
under which it was given. This hypothesis was
tested experimentally in normal men and it was
demonstrated that the extent of potassium loss
following the administration of a thiazide diuretic
was related to adrenal mineralocorticoid activity.
Excessive potassium loss may be prevented by giving
an aldosterone antagonist. Triamterene, a
recently introduced oral diuretic enhances sodium excretion but depresses potassium excretion; this
was probably due to a direct action on the distal
renal tubule. It may be used in conjunction
with a thiazide and together they may promote a large
sodium diuresis without excessive potassium loss.
This recent work on the action of diuretics in relation
to the excretion of sodium and potassium has been
reviewed in the Bradshaw lecture
