The Inhibiting Action of Calcium and Magnesium on the Movements and
Secretion of the Intestine.
It was first observed by Ringer[49] that the unfavorable effect
produced by pure NaCl solution could be lessened by adding other
salts, notably calcium and potassium. From this observation there was
made the so-called Ringer’s solution, which contains Na, K, and Ca in
proportions which render the solution relatively neutral and innocuous
towards the living tissues.
Howell,[50] working with the heart of the terrapin in various mixtures
of Na, K, and Ca chloride, emphasized the importance of calcium in
the medium in which the heart beat. He concluded from his experiments
that the sodium chloride was mainly instrumental in establishing and
maintaining the proper osmotic conditions, while calcium was the main
factor in initiating and maintaining the beat of the heart. To quote
from his articles:--“The stimulus that leads to a heart contraction
is dependent upon the presence of calcium compounds in the liquids of
the heart; but for rhythmic contractions and relaxations a certain
proportion of potassium compounds is necessary.” “The sodium chloride
seems to be essential only in preserving the osmotic relations between
the tissues and the surrounding liquid.” Similar conclusions were
arrived at by Green.[51]
Loeb,[52] working with Gonionemus, and with the striated muscles of
the frog, arrived at conclusions which are in some respects entirely
opposed to those of Howell. What Loeb spoke of as the toxic effects of
sodium chloride was emphasized by this work. This was especially shown
in the case of Fundulus eggs which, though freshly fertilized, cannot
develop in pure NaCl solution, although they develop in sea-water or
in distilled water. In this case the addition of a small quantity of
calcium chloride to the NaCl rendered development possible. According
to Loeb, the Ca exerted an antitoxic effect and neutralized the
injurious action of the NaCl. Similarly it was found that the apex
of the heart contracts rhythmically in a pure NaCl solution, but
soon came to a standstill. The addition of a small amount of calcium
is sufficient to cause the contractions to persist for a long time.
This again was referred to the toxic and antitoxic effects of the
salts. From these and similar experiments arose the conception of
“physiologically balanced solutions” in which the toxic effect of each
substance in the solution is exactly counteracted by the antitoxic
effect of some other substance in the same solution.
Other experiments by Loeb showed that if the voluntary muscle of a
frog be immersed in a pure NaCl solution, rhythmical twitchings appear
which continue for many hours, or even for days. If, however, a small
quantity of CaCl_{2} be added to the NaCl solution the twitchings
cease, although the muscle remains alive in this mixture longer than it
does in pure NaCl. Similar results were obtained with solutions of the
sodium salts which precipitate calcium, fluoride, oxalate, carbonate,
phosphate, etc. In all of these solutions twitchings developed in the
muscle. Magnesium and strontium act like calcium in inhibiting the
muscular twitchings produced by sodium salts. These experiments led
Loeb to the conclusion that the presence of calcium in the body keeps
the voluntary muscles from constantly twitching or beating rhythmically
in the way the heart does. Calcium, magnesium, and strontium seemed to
have a definite inhibitory action on the muscular contractions.
Loeb further showed that the center of a jellyfish (Gonionemus), which
when isolated from the margin will not contract in sea-water, will beat
rhythmically if placed in pure NaCl solution. If a quantity of CaCl_{2}
or Ca(NO_{3})_{2} be added to the NaCl solution the contractions
are inhibited. Magnesium and strontium behave in this respect like
calcium. If also a sufficient quantity of a calcium precipitating
solution (sodium fluoride, phosphate, etc.) be added to sea-water in
which the center will not beat, rhythmical contractions soon appear,
due apparently to the removal of the calcium from the sea-water and
the tissue. In these experiments, as in those with voluntary muscles,
calcium, magnesium and strontium have apparently an inhibiting action
on muscular contractions.
Loeb has recently made experiments on a jellyfish of the Pacific
(Polyorchis) with results which are somewhat different from those
described for voluntary muscles and Gonionemus. He found that the
normal swimming movements of the uninjured animal could not occur in
solutions which did not contain some proportion of magnesium, and
the presence of magnesium in the sea-water seemed to be the stimulus
for the apparently spontaneous movements of the animal. Calcium and
potassium were found to oppose this action of magnesium. Further with
the isolated center of Polyorchis, which will not beat in pure sugar
solution or in sea-water, it was found that the addition of CaCl_{2},
SrCl_{2}, or BaCl_{2} to either solution caused contractions to appear.
Magnesium chloride did not produce this effect. In pure NaCl solution
also the isolated center will not beat, or beats only after a long
time, while the addition of CaCl_{2} to the NaCl causes it to beat at
once.
Lingle[53] made experiments with the ventricle of the tortoise heart,
which was able to beat for only a short time in pure NaCl solutions.
When a small amount of CaCl_{2} is added, however, the heart may
continue to beat for a long period. Lingle explained this by the
assumption that NaCl is a poison and that calcium acts in an antitoxic
way, a suggestion already offered by Loeb.
Loeb’s experiments on the inhibition of muscular twitchings in
voluntary muscles by calcium and magnesium, as well as the similar
results he obtained with the isolated center of Gonionemus, led me to
test the action of these two substances on the rhythmical movements
of the mammalian intestine. It was found that not only the normal
movements of the intestine, but also those produced by the saline
purgatives such as sodium citrate, sulphate, tartrate, etc., could be
very definitely inhibited by the administration of calcium or magnesium
chloride. This was the case when these latter substances were given in
any way either intravenously, subcutaneously, or applied directly to
the serous surfaces of the intestine. The following experiments will
illustrate this inhibitory action.
A rabbit was anaesthetized by a subcutaneous injection of 4-5 c.c.
1% morphine solution. The intestines were then carefully exposed and
protected in every way from loss of heat and moisture. The method
suggested by van Braam-Houckgeest[54] of opening the abdomen under the
surface of sodium chloride solution is perhaps the most perfect. A
small quantity of m/6 sodium citrate solution (for a rabbit weighing
1,200 g. 2-3 c.c. is sufficient) was injected into a vein of the ear.
The intestines almost immediately began to move actively. There was
then injected 3-4 c.c. m/6 CaCl_{2} solution. The intestines within
2 or 3 minutes came entirely to rest and remained perfectly quiet.
A second injection of a somewhat greater quantity of sodium citrate
caused them to again become active.
A still more striking experiment may be made by exposing the
intestines and pouring a small quantity of sodium citrate solution on
their peritoneal surfaces. Immediately they become extremely active. If
now they be washed off with a little NaCl solution and a few c.c. of a
solution of calcium chloride be poured on them they will come to rest
at once. These solutions must be at body temperature and isotonic with
the blood. If the loops which have been quieted by CaCl_{2} are again
moistened with the citrate solution they will be set into motion as
before, and a subsequent application of CaCl_{2} will again cause all
movement to cease. This may be continued almost indefinitely. I have
set the same loops in motion and stopped them by these solutions as
many as sixteen times in succession.
Magnesium chloride acts in this respect like calcium chloride, and
a similar but slighter action is possessed by strontium chloride.
Magnesium sulphate has a purgative action just as many other sulphates
have. Magnesium citrate also acts in the same way as other citrates.
The action of the magnesium in these cases seems to be subordinate.
In addition to the inhibitory action of calcium and magnesium on
the peristaltic movements of the intestine, these substances also
suppress the secretion of fluid into the intestine. This is shown in
the previous chapter (IV), where tables are given to show the course
of the experiments. According to these experiments, the normal rate
of secretion in an isolated loop was measured. The quantity of fluid
secreted was small, but the application of CaCl_{2} or MgCl_{2} to
the serous surface of the loop stopped the secretion entirely. The
subsequent application of sodium citrate caused it to flow again.
In its counteraction of the effect of saline purgatives, calcium
behaves in the same way. The increased peristalsis or secretion
caused by sodium citrate, sulphate, etc., is entirely suppressed by
the administration of calcium or magnesium chloride. This is not true
to the same extent of those activities produced by barium chloride.
CaCl_{2} as far as I have been able to determine only partially
counteracts the effect of BaCl_{2}. That an antagonism does exist
cannot be doubted, but the violent peristaltic movements brought about
by BaCl_{2} cannot be fully suppressed by CaCl_{2} or MgCl_{2}. As
mentioned above, BaCl_{2} in extremely small doses causes an increased
flow of urine.[55] This can be partially inhibited by CaCl_{2}. With
slightly larger doses of barium, the flow of urine often ceases
abruptly, due probably to the contraction of the musculature of the
urinary passages, or possibly to a contraction of the blood vessels
of the kidney. This condition is relieved by the administration of
CaCl_{2}, that is, the calcium merely counteracts the effect of the
barium on the musculature of the urinary passages or blood vessels,
whichever it may be.
Experiments have recently been made to test the effect of adding
calcium salts to barium chloride and feeding the two mixed with some
edible substance to mice. BaCl_{2} is a common poison to employ for
mice and rats. It was found that the mice eating food containing
barium carbonate alone died, while those eating the mixture of calcium
carbonate and barium carbonate in the food were unharmed.[56]
When loops of the intestine are entirely removed from the body and
placed in sodium chloride solution, active movements begin, as will
be described in detail in a later chapter. These movements continue
40 to 45 minutes or longer if the proper conditions of temperature,
etc., are preserved. If, however, CaCl_{2} be added to this solution
the movements are inhibited. Also loops placed in pure m/6 CaCl_{2}
solution lie perfectly quiet.
A peculiar action of calcium which will be described in detail later
on is shown in the following experiments: A loop of rabbit’s intestine
was removed from the body and placed in a solution of m/6 LiCl. After
moving rhythmically for about 15 seconds the loop came to rest. A
loop similarly placed in m/6 CaCl_{2} solution showed no movements.
In a mixture, however, of 50 c.c. m/6 LiCl + 5 c.c. m/6 CaCl_{2} the
initial movements seen in the pure LiCl solution were absent and the
loop remained quiet for 10-15 minutes. Then sudden sharp constrictions
appear in the loop, followed by violent contractions of the whole loop.
The loop twists and coils upon itself and continues to move in this
extremely active manner for 30-45 minutes or longer. The control loops
in pure LiCl and pure CaCl_{2} remain motionless during all this time.
A similar phenomenon occurs with a mixture of NaCl and CaCl_{2}. In
NaCl, however, the initial movements are much more conspicuous and may
continue for an hour. These are inhibited in the mixture of NaCl and
CaCl_{2}, and after 10-15 minutes movements of an entirely different
character appear, resembling those described for mixtures of LiCl and
CaCl_{2}. Sharp constrictions and violent twistings persist for 30 or
40 minutes.
These peculiar contractions do not occur in mixtures of LiCl and NaCl,
nor in mixtures of CaCl_{2} and MgCl_{2}.
In addition to their action on the intestine, calcium and magnesium
have a very definite action on other organs of the body, more
especially the kidney. It was found[57] that both calcium and magnesium
chlorides inhibit the flow of urine. This is shown in the following
tables taken from the paper referred to.
Rabbit--cannula placed in bladder. No urine flowed in the first or
second periods of 10 minutes before the NaCl solution was injected.
Time Salts other than m/6 NaCl Urine
NaCl injected injected in c.c. in c.c.
10:10 10
10:15 10
10:20 5 0.5
10:40 10 0.8
11:00 10 0.5
11:20 5 1.0
11:40 10 2.8
12:00 10 6.0
12:00 5 c.c. m/6 CaCl_{2}
intravenously
12:05 5 c.c. 5m/6 CaCl_{2}
subcutaneously
12:20 5 0.2
12:40 10 1.8
1:00 10 0.8
1:00 5 c.c. m/6 sodium citrate
intravenously
1:20 10 2.2
1:40 5 3.6
In this case, although the flow of urine was considerably increased
by the injection of NaCl solution, and although the injection was
continued, the introduction of CaCl_{2} caused the flow to almost
cease. This action was quite constant and was obtained in a large
number of experiments. MgCl_{2} has a similar but less powerful effect.
The action of the CaCl_{2} is temporary and wears off after a little
time, as shown in the following table taken from the same paper.
It represents only the latter half of the experiment, the regular
injection of 2 c.c. NaCl solution per minute gradually increasing the
rate of flow as shown, until the quantity of fluid excreted almost
equals that injected.
Rabbit--cannula in bladder--injections intravenous.
Time Salts other than m/6 NaCl Urine
NaCl injected injected in c.c. in c.c.
9:25
11:40 150 64.5
11:45 10 6.6
11:50 10 5.6
11:55 10 6.2
12:00 10 7.4
12:05 10 9.5
12:05 5 c.c. m/6 CaCl_{2}
12:10 5 2.2
12:15 10 0.8
12:20 10 1.2
12:25 10 1.6
12:30 10 2.8
12:35 8 3.0
12:40 5 4.5
12:45 0 4.8
12:50 0 5.1
12:55 0 6.2
It was found in another series of experiments[58] that the
haemoglobinuria caused by saponin and by quillain, which is a dried
extract of Quillaja bark, may be inhibited by calcium chloride.
The intravenous injection of 2 c.c. ¹⁄₄% quillain always produced
haemoglobinuria in a rabbit weighing about 1,200 g. If the dilution
of the quillain were made with m/6 CaCl_{2} instead of water, _e.g._,
2 c.c. 1% quillain + 6 c.c. m/6 CaCl_{2} and 2 c.c. of this injected
intravenously, no haemoglobinuria resulted, although the concentration
of the quillain was the same in both cases. The CaCl_{2} does not stop
the excretion of the haemoglobin by the kidneys, for if the saponin
or quillain be given first and the haemoglobinuria established, the
subsequent injection of CaCl_{2} does not stop the excretion of
haemoglobin. This is explained by a large number of experiments in
which it was shown that the haemolysis caused by saponin, quillain,
or digitalin is particularly inhibited by calcium chloride and
magnesium chloride. This can be seen in the following table in which
defibrinated rabbit’s blood is used, and the effects of CaCl_{2} and
MgCl_{2} are compared with that of NaCl.
1 c.c. blood 1 c.c. blood 1 c.c. blood
Time 5 c.c. m/6 NaCl 5 c.c. m/6 MgCl_{2} 5 c.c. m/6 CaCl_{2}
3 drops 0.5% saponin 3 drops 0.5% saponin 3 drops 0.5% saponin
A.M.
10:22
10:24 change of color no change no change
10:27 almost transparent no change no change
10:30 laking almost complete no change no change
10:45 laking complete no change no change
P.M.
1:00 laking complete corpuscles settled same as MgCl_{2}
to bottom; supernatant mixture
fluid
colored; mixture
quite opaque on
shaking
It is of considerable interest to note that these substances, saponin,
quillain, and digitalin, act not only as haemolytics, but also as
diuretics. This was shown in a number of experiments.[59] As shown in
the following table, the injection of a very small quantity of saponin
produces a distinct increase in the quantity of urine excreted.
m/6 NaCl injected
Time intravenously Urine
10:15
10:20 10 c.c. 2 c.c.
10:25 20 c.c. 4 c.c.
10:30 20 c.c. 6 c.c.
10:35 10 c.c. 7.5 c.c.
10:40 10 c.c. 8.0 c.c.
10:45 10 c.c. 8.2 c.c.
10:50 10 c.c. 7.9 c.c.
10:56 Injected 2 c.c. ¹⁄₂₀% saponin in m/6 NaCl
11:00 10 c.c. 10.5 c.c.
11:05 10 c.c. 11.0 c.c.
11:10 10 c.c. 11.0 c.c.
11:15 10 c.c. 11.0 c.c.
11:16 Injected 1 c.c. ¹⁄₂₀% saponin
11:20 10 c.c. 12.2 c.c.
11:25 10 c.c. 13.2 c.c.
11:30 10 c.c. 12.0 c.c.
11:35 10 c.c. 12.5 c.c.
It is possible that it is by no means a coincidence that these
substances which are powerful haemolytics act also as diuretics; and
that CaCl_{2} and MgCl_{2}, which inhibit the secretion of urine, also
to some extent inhibit the haemolytic action. It is difficult to say by
what process the haemoglobin is liberated from the red blood corpuscle,
as indeed it is difficult to state definitely how fluid passes from
the blood into the urine. It is sufficient to call attention to the
fact that the liberation of haemoglobin and the flow of urine may be
to some extent controlled by the same conditions. If the haemolytics
such as saponin cause haemolysis by increasing the permeability of
the membranes of the red blood corpuscles, it seems possible that the
diuretic effect of these substances may be due to a similar process
in the kidney. If this be true, changes in permeability must play
an important part in the action of these diuretics. And it is not
impossible that the inhibition of the haemolytic action of saponin,
etc., as well as the inhibition of the flow of urine by CaCl_{2} and
MgCl_{2}, may be due to a decreased permeability of the red blood
corpuscle on the one hand, and of the kidney cells on the other.
With these numerous experiments with calcium and magnesium it is
still impossible to make a general statement as to the nature of
their action. Since the chemical conditions existing in the tissues
of animals and of various parts of animals are largely a matter of
conjecture, we cannot predict how these substances will act; nor can
we say that because calcium, for example, has a certain action in one
animal or on one organ it will necessarily have the same action in
other animals or in other organs.
In the experiments on the rabbit’s intestine, however, calcium and
magnesium have been shown to have an action which can only be described
as inhibitory. In an animal as highly organized as the rabbit, the
intestine is an extremely complex organ; it is not only a muscular
and a glandular organ, but contains a complicated nervous mechanism
peculiar to itself which is entirely inseparable from the other parts.
It is not possible here to mechanically isolate a part which shall
be free from the nervous system as can be done almost completely in
the center of the jellyfish and the apex of the heart. We are dealing
with an entire organ which must be considered as an indicator by
which comparative results may be obtained. So many unknown conditions
exist in such an organ that it is impossible to say what tissue is
acted on primarily, whether the nervous system on the one hand, or
the glandular and muscular tissues on the other. There are, however,
two indicators in the intestine by which the comparative actions of
substances can be studied, namely, the muscular movements, and the
secretion of fluid, both of which by various chemical substances may be
increased or lessened; or, in other words, they may be stimulated or
inhibited. These terms are entirely comparative. The fact that calcium
and magnesium act as inhibitors for both the muscular and secretory
activities of the intestine does not imply that they have a similar
action in other organs or in all animals. It can only be said with
certainty that the chemical conditions under which the intestines of
the rabbit live are fairly constant, so that the addition of calcium or
magnesium in some way constantly inhibits the activity of both muscular
and glandular tissues, and the addition of certain purgative salts
constantly stimulates them to greater activity.
FOOTNOTES:
[49] Journal of Physiology, Vols. 4, 5, 6, 8, 16, 17, and 18, 1883-1895.
[50] Amer. Journ. Physiol., Vol. 2, 1898, p. 47.
[51] Amer. Journ. Physiol., Vol. 2, 1898, p. 82.
[52] Festschrift f. Fick, 1899. Chicago Decennial Publications, 1902,
and Pflüger’s Archiv, Bd. 91, S. 248, 1902. Amer. Journ. Physiol., Vol.
5, 1901.
[53] Amer. Journ. Physiol., Vol. 4, p. 265, 1900; Vol. 8, p. 75, 1902.
[54] Pflüger’s Archiv, Bd. 6, 1872; and Bd. 8, 1874.
[55] MACCALLUM, J. B.: Journal exp. Zoology, No. 1, 1905.
[56] STOVER, F. H.: Bulletin of Bussey Institution, Vol. II, Part IV,
1884.
[57] MACCALLUM, J. B.: Journal Exp. Zoology, Vol. I, No. 1, 1904.
[58] MACCALLUM, J. B.: University of California Publications,
Physiology, Vol. II, 1905, p. 93.
[59] MACCALLUM, J. B.: _Loc. cit._