According to the studies of Chittenden,(16) low protein diet improves
the general metabolism of the body, fatigue is diminished, and
bodily vigor, therefore, correspondingly increased. The expectation
is, therefore, justified that the defense of the organism against
deleterious substances introduced into the body is much improved
by such a diet, thus increasing its resistance to poisons. Hunt's
experiment on this subject, also quoted by Chittenden, lends support
to this view. He found that mice fed on carbohydrates chiefly, or on
foods containing only a small amount of protein, were more resistant
to acetonitril. It was interesting, therefore, to inquire whether the
toxicity of caffein differs under similar conditions of diet.
A fixed diet of the same calorific value was provided for all dogs
of this series, but the protein content for three of the animals was
approximately one-third of the amount usually fed to dogs. Caffein was
at first administered subcutaneously, but all the dogs on a low protein
diet developed abscesses at the site of injection, while none of those
on high protein diet showed a local reaction. Feeding by mouth was then
begun and continued throughout the experiment in each case. The initial
dose was 50 mg per kilo, which was given daily for seven to nine days.
It was then increased progressively by 25 mg per kilo; 75 mg per kilo
were administered for one to two days, 100 mg for two to three days,
125 mg for one to two days, 150 mg for one to two days, and a single
dose of 175 mg. It will be remarked that sometimes an interval of one
day had to be allowed during which no caffein was fed.
_Dog 30. Black and tan hound, male._
The dog was under observation for about eight weeks before the
experiment was begun and had received a high protein diet. He was then
given 50 mg caffein for nine consecutive days. On the tenth day the
dose was increased to 75 mg per kilo. As no symptoms developed, this
dose was increased to 100 mg per kilo, and was fed one day apart. It
was then raised to 125 mg per kilo. For the first time since the drug
was fed, symptoms appeared; they were noticed a few hours after feeding
and persisted during the next day. Although the appetite was good,
no caffein was given on this day. On the following day this dose was
repeated. As the symptoms were not serious, 150 mg per kilo were given
daily for the next three days, until 175 mg per kilo was reached. This
dose proved fatal within six hours. Record of experiment follows:
October 9: Weight, 9 kilos, on full nitrogen diet, received daily 0.724
gram nitrogen per kilo or 87 calories per kilo, received 18 grams meat
per kilo, 4 grams lard per kilo, 3 grams carbohydrates per kilo, bone
dust, ad libitum.
November 3: Weight, 9.10 kilos.
November 10: Weight, 9 kilos.
November 20: Weight, 9.55 kilos.
November 29: Weight, 8.70 kilos.
December 6, 7, 8, and 9: Received subcutaneously 22 cc 2 per cent
caffein. Condition good, site of injection normal.
December 10, 11, 12, 13, and 14: Received 0.4375 gram caffein by
mouth equal to 0.050 gram per kilo, no symptoms, appetite and general
condition good.
December 15: 11.30 a. m., received 0.6563 gram caffein by mouth, or
0.75 gram per kilo, no symptoms, appetite good, condition excellent.
December 16: 11 a. m., received 0.870 gram caffein by mouth, or 0.1
gram per kilo, weight 8.70 kilos, no symptoms.
December 17: No caffein given.
December 18: Received 0.870 gram caffein, or 0.1 gram per kilo, no
symptoms.
December 20: 2.45 p. m., received 1.0875 grams caffein, or 0.125 per
kilo; 4 p. m., ate food readily, seemed very uncomfortable and sick.
December 21: 9 a. m., stiffness in muscles, but no other symptoms,
appetite good, no caffein given.
December 22: 11 a. m., received 1.0875 grams caffein, or 0.125 gram per
kilo; 3 p. m., depressed in spirits and sick, but no other symptoms
observed.
December 23: 11.30 a. m., received 1.305 grams caffein, or 0.150 gram
caffein per kilo; 1.30 p. m., apparently quite sick, but no other
symptoms, had good appetite.
December 24: 10 a. m., received 0.175 gram caffein per kilo; 4 p. m.,
when about to be fed fell over and died; no autopsy.
The total amount of caffein given dog 30 was 11.3458 grams,
administered for a period of eighteen days. The average daily amount
per kilo was therefore 72 mg. The feces became offensive when the
amounts of caffein were increased to 75 mg per kilo. It will be
observed that in this dog the appetite was uniformly good until the day
of his death. Whether or not this is the cause of his resistance to
caffein will be discussed later.
_Dog 32. White, male, young._
Although he was growing rapidly this dog's weight was constant, but
he looked anemic. He received a high protein diet until December 3,
when the rations were increased by one-third. This dog was under
observation from October 26 to December 6 when the administration of
caffein was begun. He then received 50 mg caffein per kilo daily for
nine days consecutively without showing any effects, when the dose was
increased to 75 mg per kilo, then to 100 mg per kilo. This dose was
further increased to 150 mg per kilo without causing symptoms, which
was repeated the next day. No symptoms having been observed after such
amounts of caffein, 175 mg per kilo were fed. This dose, however,
proved fatal within two hours. Record of experiment follows:
October 26: Weight, 6.90 kilos.
November 3: Weight, 6.90 kilos.
November 10: Weight, 6.90 kilos.
November 20: Weight, 6.90 kilos.
November 29: Weight, 6.55 kilos.
December 3: Put into cage, diet increased one-third.
December 6, 7, 8, 9: Weight 6.30 kilos; 12.30 p. m., received 16 cc 2
per cent caffein by subcutaneous injection in back, no symptoms of any
kind noticed, site of injection normal.
December 10, 14: 0.05 gram caffein per kilo.
December 15: Received 0.4725 gram caffein by mouth, no symptoms.
December 16: Received 0.655 gram caffein, 0.100 gram per kilo.
December 17: No caffein given.
December 18: Received 0.655 gram caffein daily, 0.100 gram per kilo, no
symptoms.
December 20: Received 0.8188 gram caffein, 0.125 gram per kilo, no
symptoms, appetite good.
December 21: Received 0.9825 gram caffein, 0.150 gram per kilo,
somewhat uncomfortable, no other symptoms.
December 22: Received 0.9825 gram caffein, 0.150 gram per kilo, no
symptoms except some uneasiness.
December 23: 9 a. m., no symptoms, appetite good; 11.30 a. m.,
received 1.146 grams caffein, 0.1759 gram per kilo; 1.30 p. m., died
while making an effort to get out of cage, tonic contraction of limbs
observed before death.
The amount of caffein received during the entire experimental period
was 9.2223 grams, or an average per day approximately of 80 mg per
kilo, and therefore 10 per cent more than dog No. 30 received. It will
be observed that the appetite in dog No. 32 was likewise uniformly
good, and that he received a very high protein diet which was also of a
very high calorific value.
_Autopsy (dog 32)._--Stomach presented a severe inflammation of
the mucosa, especially in the fundus and pyloric portions. The
gastritis was more marked in pyloric portion, and the inflammatory
condition extended along the whole course of small intestines, which
presented numerous hemorrhagic areas, and a thick catarrhal exudate
on the mucosa. The large intestine contained quite a large number of
parasites, probably round worms. The liver was enlarged and the gall
cyst well filled. The spleen was also considerably engorged, kidneys
appeared normal, other organs all appeared normal.
_Dog 31. Black spaniel, male._
This dog had been under observation one month previous to the
experiments with caffein. The usual initial dose was then administered
for nine days. There were no signs of local irritation when the drug
was given subcutaneously, but symptoms of toxicity were present. These
disappeared, however, when the drug was administered by mouth. The
dose was therefore increased to 75 mg per kilo. This, as will be seen,
proved fatal within six hours. High nitrogen diet, same as No. 30.
November 3: Weight 10.250 kilos.
November 10: Weight, 10.25 kilos.
November 20: Weight, 10.30 kilos.
December 1: Put in cage.
December 6, 7, 8, 9: Weight, 10.20 kilos; received 26 cc 2 per cent
caffein subcutaneously, site of injection normal.
December 6: Very restless and excited, whined when handled as though
muscles were sore, appeared to be sick.
December 10-14: Condition good, received 0.51 gram caffein by mouth
daily, no noteworthy symptoms, appetite continues good, somewhat
restless at intervals.
December 15: 11.30 a. m., received 0.765 gram caffein per mouth
(0.075 gram per kilo); 2 p. m., depressed in spirit, seemed sick and
uncomfortable; 4.15 p. m., when about to feed, animal jumped up, then
fell back dead.
_Autopsy (dog 31)_: Lungs congested; heart filled with blood and
contained small amount of blood-stained fluid in pericardial sac. Liver
deeply congested, soft and friable; gall bladder distended with bile;
kidneys showed inflammation of cortex; spleen pale, normal in size
and consistency; stomach practically empty, the mucosa of the pyloric
portion exhibited severe gastritis, with thick catarrhal exudate. This
catarrhal inflammation extended through the duodenum; remaining portion
of small intestine showed mild inflammation; large intestine appeared
practically normal. The total amount of caffein received by dog 31
during 10 days was 5.395 mg, or a daily average of 53.9 mg per kilo.
This unusually low resistance to caffein (which was practically the
only case in all the experiments on dogs presented in this research)
suggests the presence of some abnormal condition. The bloody exudate
in the pericardial cavity indicating pericarditis, which is likely to
induce secondary changes of cardiac muscle, may be considered as a
possible cause of the increased toxicity of caffein in this case.
_Dog 29. Male fox terrier, black._
This dog was kept on a low nitrogen diet for nearly five weeks before
the feeding of caffein was begun. The administration of 50 mg of
caffein per kilo was then carried on for eight days without showing any
symptoms of toxicity. The usual increase of dose was then given--75
mg per kilo--which was followed by a manifestation of symptoms.
Further increase, however, to 100 mg per kilo had no visible effect.
Nevertheless it was considered advisable to suspend the feeding of
caffein for one day. The same amounts were then repeated on two
consecutive days. No symptoms having been observed, 125 mg per kilo
were given. As symptoms of toxicity and especially loss of appetite
were observed, the dog was not given any caffein the next day. Since
his appetite had now improved, the experiment with larger doses was
resumed. Death followed after the second dose of 150 mg per kilo.
Protocol follows:
Weight, 9.90 kilos. One-third nitrogen diet. Receives 0.269 gram
nitrogen per kilo (88.269 calories per kilo).
November 3: Weight, 9.85 kilos.
November 10: Weight, 9.55 kilos.
November 12: Weight, 9.40 kilos.
November 29: Weight, 9.85 kilos.
December 6: Weight, 9.90 kilos; 11.35 a. m., received 25 cc 2 per
cent caffein solution by subcutaneous injection in back; 4 p. m., no
symptoms, appetite good.
December 7-9: Received 25 cc caffein 2 per cent solution--subcutaneous
injection, no symptoms, area of injection inflamed and swollen.
December 10, 13: Site of injection showed increased inflammation,
received 0.495 gram caffein (50 mg per kilo) in 30 grams meat daily
without showing any symptoms.
December 14: 12 noon, received 0.7425 gram caffein by mouth (0.075 per
kilo); 2.30 p. m., restless and uneasy.
December 15: 11.30 a. m., received 0.7425 gram caffein by mouth;
2 p. m., depressed in spirits, although continues to have good
appetite.
December 16: Weight, 9.50 kilos; 3.15 p. m., received 0.9509 gram
caffein by mouth; 4.50 p. m., no symptoms.
December 17: Animal rested.
December 18: Received 0.950 gram caffein by mouth, no symptoms.
December 19: Received 0.9509 gram caffein by mouth, no symptoms.
December 20: 2.45 p. m., received 1.1875 grams caffein (0.125 gram per
kilo); 4 p. m., restless and quite sick; ate only a little food.
December 21: 9 a. m., still uncomfortable, allowed to rest, no caffein
given, gradually recovered appetite.
December 22: 11 a. m., received 1.875 grams caffein; 3 p. m., seemed
sick, but showed no other symptoms, appetite fair.
December 23: 9 a. m., showed no symptoms from the day before, ate food
gradually, seemed sick; 11.30 a. m., received 1.425 grams caffein
(0.150 gram per kilo); 1.30 p. m., looked and behaved as if very sick,
no other symptoms; 3.45 p. m., in attempting to get out of box fell over
on back, had convulsions, whined, dyspnoea, died within 30 seconds.
_Autopsy_: Stomach exhibited mild inflammation; small intestine
inflamed and hemorrhagic areas on mucosa; liver engorged and friable;
spleen normal; kidneys slightly congested; other organs appeared
normal. The total amount of caffein fed to Dog 29 was 12.135 grams,
which was given in 18 days. The average daily amount per kilo was
therefore 67.68 mg.
_Dog 28. Male fox terrier._
Low nitrogen diet was begun about four weeks before the feeding of
caffein; 50 mg of caffein was then fed for seven consecutive days.
Partial loss of appetite was observed after the first dose. As the
experiment progressed the desire for food steadily diminished, and the
feces became fetid. Symptoms of intoxication manifested themselves
early in the experiment, and vomiting occurred after the fourth
dose. The dog was then put on a diet exclusively of meat. After an
intermission of 10 days 109 mg caffein per kilo were given. Since there
were no symptoms, the following day the amount was increased to 125 mg
per kilo. This dose proved fatal within 16 to 20 hours.
This dog was stout and strong, weight 12.25 kilos, received daily 0.269
gram nitrogen per kilo (88.269 calories per kilo).
November 3: Weight, 11.75 kilos.
November 10: Weight, 11.95 kilos.
November 20: Weight, 11.20 kilos. All through this period had been kept
in a cold, poorly ventilated room, put in a warm room, with bedding and
good ventilation.
November 29: Weight, 11.95 kilos.
December 1: Put in a cage; weight, 11.95 kilos.
December 6: Weight, 11.95 kilos; 11.45 a. m., received 0.050 gram
caffein per kilo; then received 30 cc 2 per cent caffein (0.6 gram) in
practically one subcutaneous injection; 4.30 p. m., ate only part of
food.
December 7: 10.25 a. m., received 30 cc 2 per cent caffein by
subcutaneous injection (0.6 gram, or 50 mg, per kilo); 1.45 p. m.,
seemed sensitive to touch, no desire for food, depressed in spirit.
December 8: 11.40 a. m., received 30 cc 2 per cent caffein by
subcutaneous injection (50 mg per kilo); 1 p. m., depressed in spirit,
hind legs seemed somewhat stiff, no desire for regular food, site of
injection inflamed.
December 9: 10.50 a. m., received 30 cc 2 per cent caffein by
subcutaneous injection (50 mg per kilo); 2.30 p. m., had vomited, no
desire for regular food.
December 10: Inflammation of site of injection, and swelling very
pronounced; 2 p. m., received 0.5975 gram caffein, or 50 mg per kilo,
with 30 grams of meat, refused regular food.
December 11, 12: Received 0.5975 gram caffein by mouth, no symptoms
except refusal of regular food, feces fetid.
December 13-22: Put on meat diet exclusively, high temperature, no
caffein, weight 10 kilos, appetite good, feces fetid.
December 22: 12 a. m., weight 11 kilos, received 1.2 grams caffein by
mouth (0.109 gram per kilo); 4 p. m., no symptoms.
December 23: 11.30 a. m., received 1.375 grams caffein (0.125 gram per
kilo) had vomited food of the day before, but could notice no caffein
or capsules in vomit; 4.30 p. m., no symptoms, seemed in good spirits,
appetite good, had no meat to feed with, so was given low nitrogen
feed, of which he ate about one-fourth.
December 24: 9 a. m., found dead, stiff, and cold. The most striking
effect of caffein in this dog is the increased intestinal putrefaction.
The feces were still fetid 10 days after the administration of caffein
was stopped.
_Autopsy, dog 28_: Stomach partially filled with an undigested food
mass; mucosa showed severe inflammation; small intestines presented
a hemorrhagic enteritis along whole extent; large intestine also
exhibited mild inflammation; liver was engorged; spleen appeared
normal; kidneys slightly congested in cortical portion; other organs
appeared normal.
_Dog 24. White and tan male_: Was put on low protein diet six weeks
before experiments with caffein were begun. The initial dose of 50 mg
per kilo was then administered on eight consecutive days. The only
symptoms observed during this period of caffein administration were
those of intestinal putrefaction. Fetid feces were noticed already
after the first dose of caffein was injected. When the second dose of
75 mg of caffein was repeated, mild symptoms appeared, but none have
been observed even with increased amounts of caffein.
One-third nitrogen diet. Received daily 0.269 gram nitrogen per kilo
(88.269 calories per kilo).
October 26: Weight 11.15 kilos. Food consisted of 5 grams cracker meal
per kilo; meat, 3 grams per kilo; lard, 2 grams per kilo; tapioca,
10.69 grams per kilo. Kept in a cold, damp room with poor ventilation
until November 20.
November 3: Weight, 11 kilos.
November 10: Weight, 10.75 kilos.
November 20: Weight, 10.55 kilos; changed to a warm room, with bedding
and good ventilation.
November 29: Weight, 10.85 kilos.
December 1: Put into a cage.
December 6: Weight, 10.90 kilos; 11.25 a. m., received 28 cc 2 per
cent caffein subcutaneously in side, below the shoulders, area washed
with alcohol and ether, approximately 50 mg per kilo administered, no
symptoms.
December 7: 10.15 a. m., received 28 cc 2 per cent caffein injected
subcutaneously; feces soft and very fetid; 1 p. m., depressed in
spirit, eyes dull.
December 9: 10.45 a. m., received 25 cc 2 per cent caffein solution
subcutaneously, feces still fetid, site of injection inflamed and
swollen, no other symptoms.
December 10: Inflammation of area of injection more pronounced;
2 p. m., given 0.5449 gram caffein and 30 grams of meat; 4 p. m., fed,
no symptoms, feces fetid.
December 11: 12 a. m., given 0.5459 gram caffein and 30 grams of meat, no
symptoms, feces fetid.
December 12, 13: Given 0.5459 gram caffein daily, without noticing any
symptoms.
December 14: 12 a. m., received 0.817 gram caffein (75 mg per kilo); 2.30
p. m., restless and uncomfortable, no other symptoms.
December 15: 11.30 a. m., received 0.8175 gram caffein by mouth;
2 p. m., depressed in spirit, acted as though sick, no other symptoms.
December 16: Weight, 11 kilos; 11 a. m., received 0.100 gram caffein
per kilo (1.100 grams) by mouth, no symptoms.
December 17: Rested.
December 18: 2.30 p. m., received 1.100 grams caffein by mouth; 4 p. m.,
no symptoms.
December 19: 12 noon, received 1.100 grams caffein by mouth; 4.15 p. m.,
no symptoms.
December 20: 2.45 p. m., given 1.375 grams caffein (0.125 gram per
kilo); 3.45 p. m., vomited--one of the capsules being found intact,
the other broken open; 4 p. m., given regular diet, containing 1.3757
grams caffein in capsules, ate most of this during the night, whined at
intervals, coordination disturbed, appeared very sick, but exhibited no
other symptoms.
December 21: 9 a. m., found dead, stiff, and cold.
The total amount of caffein received by dog 24 was between 10.109 and
11.484 grams. As one of the capsules vomited was intact and the other
broken open, the amount was probably about 10.75 grams. The fatal dose
in this case was undoubtedly less than 185 mg per kilo--somewhere
between 125 and 185 mg. Autopsy showed heart in diastole; posterior
lobe of right lung deeply congested; liver engorged; gall cyst filled;
spleen appeared normal; stomach well filled with semifluid mass;
pyloric portion of stomach exhibited a severe inflammation of mucosa;
mucosa of duodenum greatly inflamed and showed hemorrhagic areas and
catarrhal exudate; remainder of small intestine also exhibited mild
inflammation; kidneys deeply engorged, mesentery injected.
A comparison of the fatal doses of caffein in the experiments on high
and low protein diet does not show much difference in the resistance to
caffein, since 175 mg per kilo proved fatal to Nos. 30 and 32, while
No. 29 died after receiving 150 mg per kilo, and No. 24 received 125
to 185 mg per kilo. Moreover, No. 28, which was changed from low to
high protein diet, succumbed when given 125 mg per kilo. Observations
made during the experimental period indicate, however, greater toxicity
of caffein in the subjects on low protein diet. Dog 30 showed the
effects of the drug when the dose was increased to 125 mg of caffein
per kilo, while in No. 32, 150 mg per kilo were received without any
manifestation of symptoms. Dog 31, which was likewise on a high protein
diet, is evidently an exception, and its low resistance to caffein
may be accounted for by the condition found at autopsy. In other dogs
on low protein diet symptoms of intoxication appeared early in the
experiment. In Nos. 29 and 24 it was observed as soon as the amount of
caffein was increased to 75 mg per kilo. In dog 28 the first dose of
caffein 50 mg per kilo was toxic. The symptoms of gastro-intestinal
disturbance were especially marked after caffein on low protein diet.
This may seem to contradict the results of experiments on dogs 11
and 20, in which larger doses of caffein failed to induce symptoms
of intoxication. But it should be observed that the diet, which
consisted almost exclusively of carbohydrates, was given only during
the administration of caffein, while in the experiments of series B
the subjects received a low protein diet for several weeks before the
administration of caffein was begun, and it was continued through
the entire caffein period. It will be remarked that the absence of
cumulative action in the experiments of the preceding series was also
observed in dogs on high as well as on low protein diet. The appearance
of symptoms after smaller doses of caffein in the latter experiments
might suggest cumulative action, but since these symptoms disappeared
on continued administration of the substance cumulation is clearly
not indicated. The gastrointestinal lesions observed on post-mortem
examination were, it will be recalled, also found in rabbits similarly
treated. The explanation suggested probably applies also in the case of
dogs.