Table Of ContentTHE PENNSYLVANIA STATE COLLEGE
THE GRADUATE SCHOOL
DEPARTMENT OF AGRICULTURAL AND BIOLOGICAL CHEMISTRY
SOME COMPARISONS OF THE BIOLOGICAL VALUE OF
GLYCEROL AND PROPYLENE GLYCOL
A Dissertation
Gaylord Purcell Whitlock
Submitted in Partial fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy
December, 1942
Approved:
Professor of Biological Chemistry
Approved:
Head of the Department
Date: y 2—
TABLE OF CONTENTS
Page
I - Introduction .................. •• 1
II - Review of the Literature . . • • • . . • • • • • • • 4
III - Experimental............ • ... 34
A - Methods and Materials • 34
B - Observations on Growth ................ 44
C - Observations on Activity ............ 45
D - Observations on Metabolism 46
E - Observations on Pathology and Bacteriology ... 47
F - Observations on Reproduction.......... 47
IV - Presentation of the Data........... 49.
V - Discussion of the Results • • • • . « • • • • • • • 83
VI - Summary.......... 109
VII - Acknowledgements . . . . . . . . . . . . . . . . . . 115
VIII - Bibliography . . . . . . . . . .................. 116
£54623
I - INTRODUCTION
The major problem of this investigation is concerned with
a comparison of the biological value of propylene glycol and gLycerol
when administered to rats in replacement of part or all of the carbo
hydrate of the diet*
The following formulae show the structures of these two
closely related chemical compounds:
CEjOH CEjOH
CHOH CHOH
I [
CHgOH ch3
GLYCEROL PROPYLENE GLYCOL
Glycerol has long been used as a vehicle in pharmaceutical
preparations* The reasons for its wide use in medicine are derived
from its physical properties, each specific property giving rise to
an entire category of medical and pharmaoeutical preparations, and
frequently, several of the properties are utilized in one prepar
ation* Its hygroscopic nature is perhaps the most important single
property* Glycerol is an excellent solvent* It dissolves many sub
stances that do not readily go into solution with other fluids. Its
syrupy quality makes it useful in preparations that contain substan
ces which would ordinarily settle out. Many of its other properties
are also responsible for its place in pharmacy and medicine*
Propylene glycol, until recently, has commanded little or
no interest in chemistry, pharmacy, or medicine* Zet some of its
physical properties would have suggested its use as a vehicle for
medicinal and food products* However, until recently, it has been
used in such preparations only to a limited extent, hut now has
been replacing glycerol in some preparations* Propylene glycol is
of immediate interest because of the demands of the war industries
for glycerol, and also because of the recent advancements in synthetic
production procedures*
Glycerol, being a normal component of the diet, might be
expected to produce no ill effects in the body* This is not uncon
ditionally true. Studies of the physiological action of glycerol
made in the last ten years indicate it has detrimental effects on
certain functions in different organisms*
It is well to point out that the physiological actions and
pharmacological properties of many compounds are dependent to a
marked degree on the route of administration* Extensive direct
comparisons have not been made of glycerol and propylene glycol when
administered orally*
Since, with a theoretical glycerol shortage, there is like
lihood that more and more propylene glycol will be used in foods and
pharmaceutical preparations as a substitute for glycerol, and since
no comprehensive comparisons have been made on the biological values
of these two substances this study was undertaken to yield more
3
knowledge concerning then when administered orally to rats in replace
ment of part or all of the carbohydrate of the diet*
A
II REVIEW OF THE LITERATURE
i
Until 1932 little experimental work had been reported con
cerning the pharmacological properties of propylene glycol. Its
place in chemistry and in medicine had been comparatively unimportant.
The first reference to the pharmacological properties of propylene
glycol was made by Miura (41) in 1911, who reported that there was
no toxicity from this substance when a 25 cc. portion was mixed with
75 cc. of water and administered gastrically to a rabbit. Similar
bsuits were observed on another occasion when 10 cc. of propylene
glycol mixed with AO cc. of water were administered subcutaneously
to the same rabbit. This author found propylene glycol-monoglucuronic
acid in the urine as a product of metabolism.
Propylene glycol is a colorless, odorless liquid, with a
mildly acrid and sweetish taste. It has about the same density as
water. It is freely miscible with water, glycerol, methyl alcohol,
ethyl alcohol, acetone, ether, chloroform, and ethyl acetate, but is
insoluble in carbon tetrachloride, carbon disulphide and benzene.
Propylene glycol may be expressed by two structural configurations,
namely, the normal form and the trimethylene form. The normal form
. 1
-
is the only one that has been given pharmaceutical consideration.
1
1
In 1932 Seidenfeld and Hanzlik (4-6) reported on the general
1
properties, actions, and the toxicity of propylene glycol. They re
ported that the usual form was less toxic than the trimethylene form.
5
These authors used humans, rabbits, and white rats in their studies
concerning local irritant action, the acute toxicity, and the effects
of continued drinking of propylene glycol. In the first of these
studies nine human subjects received 2 cc. of propylene glycol by
intramuscular injection. One half of them complained of more pain
and burning in the areas injected with propylene glycol than with
ethylene glycol. In all cases the Irritant action was fleeting
(5-10 minutes) and no after effects were noted either looally or
systematically. In animals propylene glycol was reported by these
authors to be more irritant than ethylene glycol or glycerol. The
Irritant action was judged by restlessness, limping, and lifting of
the extremities.
The above authors injected five to fifteen rats and three
rabbits intravenously and intramuscularly with propylene glycol in
doses ranging between 1 and 20 oc. per kg. body weight. No symptoms
were observed in the rats until 6 to 7 cc. were injected, intramus
cularly. Toxicity was judged on increase of respiration, loss of
equilibrium, followed by depression, and after highest doses, coma
ani death. Since 80 percent of the rats died when an intramuscular
injection of 14*7 g. of propylene glycol was made, this quantity was
considered the minimum fatal dose, MFD. The MFD for ethylene glycol
had been Similarly found to be 1.2 6* par kg. body weight, or
approximately three times as toxic as propylene glyool. With rabbits,
71-100 percent died when levels of 7.1 g. of propylene glycol, and
6
6.3 g. of ethylene glycol, respectively, were administered. These
authors Interpreted their animal data in terms of human reaction
and concluded that a dose just sufficient to cause comparable
symptoms would be 490 cc., or more than a pound, and that a probable
fatal does would be more than two pounds of propylene glycol. By
intravenous injections the MFD of propylene glycol was established
at 16.3 g. for rats, and 5.25 g. for rabbits. In comparison with
previous results this would indicate that propylene glycol is
approximately one-third as toxic as ethylene glycol. According to
these results 294 g* of propylene glycol and 73*5 g» of ethylene
glycol would be the maximum non-toxic dose for humans.
These same authors studied the cumulative effects on rats
as reflected by growth and body weight after drinking propylene
glycol solutions (in water) for long periods. The amounts of propylene
glycol drunk were 9/10, 1/2, 1/4, and l/lO of the MFD, without demon
strable effect. No effect was shown when 13*3 g. per kg. of body
weight of propylene glycol was ingested per day, but 2.2 g. per kg.
body weight of ethylene glycol resulted in stunted growth. Practic
ally no pathological changes in the kidneys, heart, spleen, and liver
were noted after continued drinking of the various solutions during
1/8 of the normal life span. It was shown that both ethylene glycol
and propylene glycol are for the most part completely oxidized in the
body to COg and HgO. Intermediate products for propylene glycol
might be lactic acid and pyruvic acid, and that these are less objec
tionable than the oxalic acid formed from the ethylene glycol.
7
la 1930 Hunt wrote a letter to the editor of the Journal
of Industrial and Engineering Chemistry, but the letter was not
published until 1932 (26) in the hope that further experiments would
he carried out. Hunt stated in this letter that ethylene glycol
had little or no narcotic or other immediate visible effects but was
inherently dangerous chronically. By various methods of injection
into rats, mice, guinea pigs, rabbits, and cats, this compound was
found to be distinctly poisonous. This poisonous action was said to
be due to the formation of oxalic acid, an oxidation product. The
kidneys were found to be severely injured, and eventually this injury
was the cause of death. Hunt found no poisonous action of propylene
glycol in similar experiments. Bats grew at a normal rate and reached
maturity when the only liquid they received was a 5 percent solution
of propylene glycol. Hunt suggested that the propylene glycol might
have energy value.
Hanzlik (17) replied to this letter of Hunt pointing out
that Hunt had not made any literature references, yet investigators
at the Stanford University School of Medicine had reported on similar
observations the previous year (4&)• (This misunderstanding was due
to the delay in the publication of Hunt's first letter.) Hanzlik
indicated that the margin of safety in the internal administration
of ethylene glycol was vastly greater than had been sometimes erroneous
ly supposed. This investigator found that propylene glycol was com
paratively less toxic than ethylene glycol, but possessed more local
irritation properties (17).
8
Hunt’s reply followed (27) and this Investigator substan
tiated the work of Hanzlik, Seidenfeld, and Johnson (20). Hunt
pointed out the error of applying the results of animal experiment
directly to humans* Bint also reported that toxicity may he greatly
Influenced by malnutrition (vitamin A deficiency, for example).
Johnson, Carlson, and Johnson (28) have reviewed the liter
ature prior to 1933 on the physiological action of glyeerol. Intra-
vaneous injection of glycerol has been found to lower the resistance
to bacterial infection (39)• Likewise it has been reported that
glycerol administration leads to the destruction of red blood cells,
albuminuria, fever, and (in large doses, 8-15 g* per kg. body weight)
tachycardia, vomiting, muscular weakness, convulsions, and even death.
For the previous list of effects the specific point of administration
has not been pointed out. Osmosis alone is believed to cause fatal
change if large amounts are ingested.
The experiments of Johnson, Carlson, and Johnson (28) repre-
' sent the type of research that was needed and is still needed in the
field of pharmacology. These authors studied the physiological action
of glycer&L on the animal organism. In their observations on rats
they used a standard diet, and modified this control diet by the sub
stitution of varying amounts of glycerol for starch. The standard diet
consisted of starch, 18% casein, 1055 butter, 555 yeast, U% inorganic
salts, and 255 agar. The modified diets were such that instead of 6L%
