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Dimethylsulfoxide and thermoregulation: Studies on body temperature, metabolic rate and thyroid function
CRYOHIOLOGY,
9,
198-204 (1972)
Dimethylsulfoxide Temperature,
and Thermoregulation Metabolic Rate and
MICHrlEI, Department
of Biology,
M. ORLANDO Georgetown
A number of reports have indicated that dimethyl sulfoxide affects thermoregulation in mammals (1) 3, 7, 10, 13). Studies in our laboratory demonst,rated that DMSO accelerated the cooling rate of rats (8), and depressed oxygen consumption in both rats and hamsters (12). The depression of oxygen consumption, t’ogether with evidence that DMSO inhibited thyroid I311 upt,ake in mice (5)) suggested t’he possibility that t,he thermoregulat’ory effects of DMSO might involve t’he thyroid gland. The studies presented in this paper were undertaken to characterize further the previously reported thermoregulatory effects of DMSO and to determine if t,hese effects might be associated with a depression of thyroid function. MATERIALS
A4ND METHODS
The subjects in these experiments were male, Sprague-Dawley rats weighing between 225 and 275 g. The dimethyl sulfoxide (Crown Zellerbath Corp.) was dose adjusted as a 50% solution in saline and administered by intraperitoneal injection. Subjects were maintained either at ambient temperatures of 2-4°C or 21-25°C. Body temperatures were measured from thermocouples inserted to an intracolonic depth of approximately 4 cm. Control body temperatures were measured in unanesthetized, unt,reated subjects. Oxygen consumption and carbon dioxide production were determined by using a Beckman Model C2 oxygen analyzer and Harvard Model 2000 CO? Analyzer which were connected in series to a metabolism chamber housing the animal. Radioactivity was counted on a Nuclear Chicago Model 181 B Scaler using a well-type detect’or. Thyroid 1311uptake was measured on thyroid glands which were resected from et,her-anest)heReceived April 20,1972. ‘Supported in part by a grant, from the Washington Heart Association and Contract NOO14-69--i0220 from the Office of Naval Research. Copyright. All rights
o-1972 by Academic Press. of reproduction in any form
Inc. rrserved
ASD
: Studies on Body Thyroid Function1 J. A. I’;ZNTTSKA
University,
Washington,
D.C. 20007
tized rats using a method described by Arnot t, and Daniach (2) Serum thyroxine (T4) was detrrmined using the Oxford column chromatography m&hod (Oxford Laboratories) Serum from blood obtained by cardiac puncture immcdiately before thyroid resect,ion was itsed for these determinations. Serum thyroxine (iodine) values were determined calorimetrically and the values are prescnted in optical drnsity units (OD) for more accurate statistical comparison. These optical densities were converted to approximate mirrograms per 100 ml of serum thyroxine by comparison with a linear graph generated from dctermination of standards of known thyrosine concentration. There were two series of experiments. In each series, one group of animals was exposed to a T, of 23°C and another group to Tn 22-26°C. The first series was concerned with the effects of DMSO on body temperature, oxygen consumpt,ion, and respiratory quotient,. Three different doses of DMSO, 0.5, 2.0, and 6.0 g/kg, wrre used at time intervals of 0 (control), 1, 5, 10, and 21 hr for each dose. Cont,rol groups received saline injections. In a second serirs of experiments, t,h\-roid fun&on (*“I uptake and serum T,) was determined, but t)he dose range of DMSO was modified to 0.1, 1.0, and 6.0 g/kg at 3 hr. The effect of the 6.0 g/kg dose was studied at 6 and 24 hr. RESULTS Series 1. Body Temperature, Oxygen Conmmption, and Respiratory Quotient The results of t,he studies on the effect of DMSO on body temperature, oxygen consumption, and respiratory quot,ient are summarized in Tables 1 and 2. Ta 21-2,.5”C. The control value for body temperature was 37.9 ? O.l”C, and no significant change was observed over the 24-hr period. In the group treated with 6 g/kg of DMSO, the
199
Body temperature (“C)
Dose DMSO
Time (hr)
Oh TA = 21-25”CY Control 6 g/kg 2 g/k 0.5 g/kg
TA = 2-6”Cc Cont,rol saline
6 g/k 2 g/kg
0.5 g/kg
37.9 37.9 37.9 37.9
zk Tk & f
1
.l .l .l .I
38.1 33.7 37.6 37.6
.2” .2
37.8 Y!J .4 31.4 52 .4
37.8 * .2 37.8 zk .2
35.6 zt .3 37.6 zt .2
37.8 f 37.8 f
a Values = Mean f Standard Error. Average weight = 230 =t 15 g for TA = * 0 = Control value prior to DMSO c TA = Ambient temperature. d = Control values were determined e = All animals in group died.
f * f zt
5
.l .2 .2 .l
37.7 36.0 37.8 37.4
zk f zk f
10
.l .4 .I .l
37.9 37.5 37.8 37..i
zt zt f 3z
37.9 f 16.5 f
.2 .2
38.1 f 6
37.1 f 37.9 f
.l .2
24
.1 .3 .l .2
37.8 37.9 37.7 37.4
.l
38.2 h e
.l
38.0 zk .2 38.0 zk .l
38.3 f 38.0 f
.2 .2
Xumber = 24 per control group and 6 per UMSO-treated 21-25°C and 288 =t 22 g for TA = 24°C. injection.
* * f. r!z
.I .2 .l .2
group.
1 hr after animals were placed in cold.
body temperature was significantly reduced to 35.7 i 0.2”C (p < ,001) at 1 l1r after the injection. There was a slight increase at 5 hr to 36.0 -C 0.4”C and a return to control levels at 10 and 24 11r. In the groups treated with 2- and 0.5-g/kg doses of DMSO, there were no significant changes in body temperature over the 24-hr period. Thp co11t,rol vulue for oxygen consumpt#ion was 28.3 ? 0.9 ml/min/kg and did not change significantly over tl1e 24-1~ period. In the group treated with 6.0 g/kg of DMSO, a marked depression of oxygen consumption was observed at 1 hr. Tl1e change from control values of 28.3 -I 0.9 to 19.4 * 0.7 ml/min/kg represents a decxrenseof 32% (p < ,001). The oxygen consumption increased to 21.0 ?z 1.4 at 5 lir, 24.8 L 0.9 at 10 hr, and approximated control values at 24 lir. The group trcnt)ed with 2 g/kg of DMSO also 11nd:I marked depression of oxygen consumption at 1 11r to 22.1 c 1.1 ml/min/kg (p < .05). Tl1ere \vas a gradual increase at 5 and 10 hr from t’hc value obtained at 1 hr. At 24 hr, tl1e oxygen consumption 11nd returned to control levels. The respiratory quotient was 0.85 -I- 0.03 in the control group and did not change signifi-
cantly over the 24-hr period. Treatment of the animals with doses of 6.0, 2.0, and 0.5 g/kg 11ad no significant effect on the R/Q over the 24-hr period. T, Z-6°C. In the cold-exposure study, the mean control value for body temperature was 37.8 f 0.2”C after 1 hr of cold exposure. This value did not change significantly over t,he ensuing 24-hr period. In the group treated with 6.0 g/kg of DMSO, a significant decline in body temperature to 31.4 c 0.4”C (p < ,001) was observed at 1 hr, and an even greater depression at 5 hr to 16.5 2 0.2”C (p < ,001). All the animals in t,he group died between the fifth and the tenth hour. The group receiving a 2 g/kg dose of DMSO had a decrease in body temperat,ure at 1 11r to 35.6 ? 0.3”C (p < .05). The body temperature had increased at 5 hr to 37.1 rfr: O.l”C and returned to control values at 10 and 24 hr. Treatment wit,11 a 0.5 g/kg dose of DMSO did not, alter the body temperature o\-er the 24-hr dctermination period. The oxygen consumption of the control groups was 40.4 * 0.7 ml/min/kg. Tl1is value was obtained 1 hr after cold exposure and represents a 30% increase over the control group maintained at room t’emperature. Oxygen consumption in
200
ORLANDO
AND PANUSK.4 TABLE
2
OXYGI,:N CONSIJMPTIONANI) 1:,X1 OF I)MSO-TIII~;~\TI':D KITS Dose DMSO
Oxygen consumption (ml/min/kg) Time (hr) 0
TA = 21L25”C, Control saline 6 g/k 2 g/k!? .i g/kg
28.3 28.3 28.3 28.3
f. f f +
0.9 0.9 0.9 0.9
27.0 19.4 22.1 24.-j
TA = 2Z6”C Control saline 6 g/k 2 g/k 5 g/kg
40.4 40.4 40.4 40.4
f f f +
0.7 0.7 0.7 0.7
40.3 20.2 30.4 36.9
+ 1.0 f
10
5
1
0.7
f
1.1
f
0.9
f
1.5
f
1.0
zt 2.3 zk 1.3
28.2 21.0 22.3 2-5.7
37.5 5.7 37.9 39.5
f
1.1
24
1.1
27.0 24.8 24.2 23.2
i
1.5
37.8 zk 1.3
37.4 f
1.3
* It *
3.9 1.2 2.1
37.3 f 37.9 f
37.1 f 37.8 f
1.4
zt 1.4 xt 1.3
f
f 0.7 zk 0.9 f 1.3
I!Z 1.0
1.4 1.2
29.0 26.8 26.4 26.3
f
1.2
h 1.1 f 1.3 zk 0.7
1.2
R/O (respiratory quotient)
Dose DMSO
Time (hr) 0
1
5
10
24
TA = 21-25X
Control saline
6 g/kg 2 g/k .5 g/kg TA = 2-6X Control saline 6 g/k 2 g/k ..i g/kg
.8d .85 .85 .85
zk f It +
.03 .03 .03 .03
.87 .84 .78 .8,5
f f + zk
.03 .04 .02 .05
.78 f .78 b
.02 .n2
.80 zt .03 .93 f .02
.78 f .78 f
.02 .02
.79 f .77 f
.06 .02
the control group held steady over t,he 24-hr period. In the 0.5 g/kg group, a slight but significant depression of oxygen consumption was seen at 1 hr (36.9 * 1.3 ml/min/kg, p < .05). Control levels of oxygen consumption were observed at 5, 10, and 24 hr. The respiratory quotient of the cold-exposed control group was lower than the group maintainrd at room temperature. The R/Q value was 0.78 * 0.02 and was constant over the 24-hr period. The only significant, change in R/Q for any of the groups was observed in the group treated with 6.0 g/kg of DMSO at 1 hr after the injection. The value obtained was 0.93 * 0.02. Owing to the severe depression of oxygen ronsumption and carbon dioxide production, R/Q
.80 .80 .86 .82
z!z * + f
.02 .04 .03 .05
.79 .89 .78 .84
.81 f
.04
.74 f .70 l
.02 .04
f f zk f
.04 .09 .04 .03
.80 .85 .83 .82
f f zk f
.03 .05 .05 .05
.79 f
.04
.80 f -
.04
.73 f .82 f
.06 .03
.84 f .78 *
.04 .05
values were not determined at 5 hr. All the animals in the group had died by the tenth hour. Series 2. Thyroid ture
Function
and Body Tempera-
The result,s of the studies on t)hyroid function and body temperature in DMSO-t,reated rats are given in Tables 3 and 4. Three-hour study (T, ~145°C). The only significant change in body temperature in these groups was observed in the group treated with 6.0 g/kg of DMSO. The 3-hr determinations indicated n drop in body temperature from 38.0 * O.l”C to 35.0 & 0.3”C (p < ,025). In t)he group treated with 6.0 g/kg of DMSO, there was 54% inhibition of the 3-hr thyroid ‘“‘I uptake when compared with controls. The t,hy-
DMSO AND TEMPERATURE TABLE THYROID
FUNCTION
AND
BODY
3
TEMPERATURE
Av wt. (g)
N
279 f
12
18
6 g/k
273 f
13
10
1 g/kg
289 zk 16
.l g/k
275 zk 10
-
.I-
TA = 21-25°C Control saline
TA = 2-6°C Control
253 zt 21
6 g/kg
249 *
14
1 g/kg
220 f
7
.I g/kg
226 f
8
8
-I
37.9 37.8 38.0 35.0 37.9 38.0 37.8 38.0
3z f f f i f f z!r
0.1 0.1 0.1 0.3 0.1 0.2 0.2 0.2
38.2 38.6 38.0 28.7 38.3 38.1 38.0 38.4
rt f f f f i f f
0.2 0.2 0.2 2.4 0.3 0.2 0.3 0.2
3hr
18,400 , 4,500 8,400 ~ 5,000 13,100
Thyroid serum T/S
Serum 13q kpd
-I- 3 hr
3 hr
.-
RUTS (3
OF DMSO-TREATED
rhyroid 131I (cpm) Dose DMSO
201
REGULATION
I
~
l.i8
1
TJ (serum)
ODc
3 hr
3 hr
4.17 f
HK)@
.41 / ,546 zk .014
xk .19
.618 f
.013
4,600
I 2.88 f
.42 I 648 rt
.022
16,700
3,500
1 4.60 rt
.61 ; ,527 +
.021
9,700
3,900
3,600
7,000
.54 +
.OT
,681 zk ,037
10,200
5,700
1 1.83 f
.21
,543 f
,023
10,200
4,500
( 2.38 f
.34
,472 f
.015
2.66 zt .30
a Values = Means or Means f Standard Error. TA = ambient temperature. 6 = For each group both pre-DMSO (upper figure) and 3 hr post-DMSO (ion-er figure) tures are given.
,520 zt ,030
body tempera-
c OD = Optical density (units were converted to pg T&00 ml serum by comparing with a standard graph
(Fig. 1). These values
are given in the Results
roid-serum ratio of ?I (cpm) was significantly reduced from 4.17 t 0.41 in the controls to 1.78 -C 0.19 in the DMSO-treated group (p < .OOl). The serum thyroxine values are given in the table as optical density units but are discussed here as micrograms per 100 milliliters of serum (pg/lOO ml). The control group had a serum thyroxine value of 1.90 pg/lOO ml serum, while the group treated with 6.0 g/kg of DMSO had a value of 1.25 pLg/lOOml (p < .05). In the group receiving 1 g/kg of DMSO, there was a 28% reduction of I”1 uptake as compared to controls. The thyroid-serum ratio was reduced to 2.88 + 0.42. This value was significantly lower than controls (p < .05), but not as low as that obtained in the 6.0 g/kg group. Serum thyroxine in this group (1.0 g/kg) was 1.05 yg/lOO ml which was significantly less than the controls (p < .05).
The group treated with 0.1 g/kg did not show changes in any of the parameters from values obtained for controls.
section.
Three-hour study (TA Z-PC). In the coldexposed control group, the 3-hr thyroid ‘“‘I was lower than in the control group maintained at room temperature. There was also a lower serum ‘Y value resulting in a thyroid-serum ratio of 2.66 2 0.30 which indicates a significant change from the 4.17 & 0.41 (p < .05) in the roomtemperature control group. The serum thyroxine value was 2.10 pg/lOO ml in the control group of the cold-exposed animals. The administration of a 6.0 g/kg dose of DMSO resulted in a 63% inhibition of I”1 uptake and a decreasein the thyroxine-serum ratio from 2.66 & 0.30 to 0.54 + 0.07 (p < ,001). The mea,nserum thyroxine value obtained for the 6.0 g/kg dose group was 0.78 pg/lOO ml which indicates a significant decrease from the controls (p < .05). In the group treated with 1.0 g/kg of DMSO, the ?t uptake was not significantly different from controls, but the serum ‘“I was higher, resulting in an over-all thyroid-serum ratio de-
ORLANDO AND PANUSKA
202
THYROID
FUNCTIOK
TA = 21-25°C
DOS?
DMSO -___~
Control
Av wt. (9)
Body
1 -1-v.
BODY
TABLE 4 OF DMSO-TIW.~TEDRATS (6 hr and 24 hr)a
TEMPERATURE
Thyroid 13’1 (cpm)
temperature (“W
6 Hi-
1 21Hr
6 Hr
24 HI
Thyroid serum (T/s) 6 Hi-
1 24 Hr
1 I
6 Nr
1
Ta (serum)
24 HI
OD
6 Hr
24 Hr
~_____
18 38.1
279 f
6 g/k
LND
12
273 zt 13
*
8
37.7 .2
37.9 f .3 37.9 f .3 35.8 f .2
f
40,700
47,700
.2
37.5 f .2 37.6 f .4 37.8
3.1
f
21,800
40,300
2,500
840 8.9
f 1.1
58.5 f 3.4
54.0
f 9.5
zk
.516 ,044
f
,530 .036
f
3~
.542 ,025
,520 .027
+ .l
I = Values = Mean or Mean & Standard Error. TA = ambient temperature. b For each group both pre-DMSO (upper figure) and 6 hr and 24 hr post-DMSO (lower figure) body temperatures are given. crease to 1.83 * 0.21. Serum thyroxine was 1.92 pg/lOO ml, approximating control values. Treatment with 0.1 g/kg of DMSO did not result in changes in any of the thyroid parameters when compared to controls. The only significant change in body temperat,ure observed was in the group given the 6.0 g/kg dose of DMSO. In this group the body temperature declined from 38.0 & 0.02 to 28.7 e 2.4O"C at 3 hr (p < .OOl).
DISCUSSION
It is apparent from these studies that DMSO interfered with normal thermoregulatory processesin the rat. The action of DMSO resulted in a transient depression of body temperature which was associated with a similar effect on metabolic rate. These responseswere observed in rats maintained at ambient temperatures within their thermoneutral zones and were markedly accentuated by cold exposure. The thyroid studSix-hour and 24 hour studies (TA 91-25°C). ies demonstrated that the depression of thermoThe body temperature of the group treated with genesis caused by DMSO treatment was both 6.0 g/kg of DMSO was lower than controls at 6 dose and time correlated with a depression of hr (37.9 + 0.3 and 35.8 + 0.2”C), but no differ- thyroid function. ence was observed at 24 hr. The thyroid I”1 An important finding was that the DMSO-inuptake in the controls increased at 6 and 24 hr duced decline in body temperature even initially from the values obtained at 3 hr. The X311 uptake was accompanied by a similar decline in metain t,he DMSO-treated group increased at 6 and bolic rate. A normal rat experiencing an acceler24 hr but the increase was less than that of the ated heat loss which threatens its thermal homecontrols. The thyroid-serum ratio in the control ostasis responds by increasing metabolic rate to group was 18.1 -C 3.1 at 6 hr and 58.5 + 3.4 at increase heat production. This was observed in 24 hr. The group treated with 6.0 g/kg of the cold-exposed control group whose oxygen DMSO had a T/S ratio of 8.90 r+ 1.10 at 6 hr consumption increased by 30% after 1 hr of cold which is significantly lower than the controls (p exposure. The attempt to increase heat produc< .05) and a 24-hr value of 54.0 * 9.5, which is tion is normally accompanied by other physionot different from the control group. logic adjustments to decreaseheat loss (e.g., peThe serum thyroxine in the control group did ripheral vasoconstriction) as part of the mechanot show any significant change at 6 and 24 hr nism for maintaining thermal homeostasis. Since from the values obtained at 3 hr. The 6-hr serum thyroxine value was 2.15 pg/lOO ml and this increase in metabolic rate was not seen in the 24-hr value was 1.90 pg/lOO ml. In the DMSO-treated rats, it can be assumed that at DMSO-treated group, the serum thyroxine value least part of the effect of DMSO on thermoreguwas 2.00 pg/lOO ml at 6 hr and 2.10 pg/lOO ml lation is due to interference with heat production. at 24 hr.
DMSO
AIND TEMPERATURE
In the groups maintained at 21-25”C, the threshold dose necessary to depress body temperature and metabolic rate was between 1.0 and 2.0 g/kg, while the peak effect of the drug occurred between 1 and 5 hr after treatment. The response in each case was transient despite the apparent dose dependence. The depression of thyroid function was also most marked during t#he first few hours afber t,reatment and began to diminish by the sixth hour. Cold exposure resulted in a lower threshold dose, a more pronounced peak effect, and a more sustained effect with each dose of the drug. In the cold-exposed animals which received a 6.0 g/kg dose, the depression of body temperature was irreversible and the animals died in profound hypothermia. This was probably the result of a critical body temperature being reached at which all thermoregulatory processes broke down despite the transience of the DMSO actions. Under these conditions of depressed metabolism, the elimination of the drug from its site of action or the body in general will also be reduced and the longer exposure to higher concentrations will compound the problems of thermoregulation. The question of the role of the thyroid gland in the observed thermogenic action of DMSO is interesting. There are three possible explanations for the apparent relationship between depressedthyroid function and depressedmetabolic rat’e. First, the inhibition of thyroid fun&on could be responsible for the metabolic rate depression. There was evidcncc of decreased circulating thyroid hormone within 3 hr after DMSO treatment, which apparently returned to normal by 24 hr. This correlated well with the inhibition of thyroid “I uptake. The explanation for t’his depression of circulating thyroxine might be that the decreased output from the thyroid gland was coupled with increased peripheral turnover or elimination. The increased turnover might be associated with the met#abolic demand imposed by t,he threat to thermal homeostasis. However, the observed decreasesin serum thyroxine with the 6.0 g/kg dose were large, and another more speculat,ive explanation might be offered. Since DMSO is known to alter protein configuration (6), it might be postulated that the t’hyroxine binding proteins are modified resulting in a decreased binding affinity for thyroxine. Unbound
REGULATIOX
203
thyroxine is apparently eliminated more rapidly than that bound to plasma protein (11). The decrease of serum thyroxine observed in the DMSO-treated animals was probably not the cause of the metabolic-rate and body-temperature depression. These effects were observed Jvithin 3 hr and most experimental evidence suggests that the metabolic actions of the thyroid hormones take place only aftscr a lag period of 45 hr or more (9). The mechanism for this latent, action has not been established and t’he question of thyroid-induced metabolic rate changes associated with endogenous hormone secretion remains unresolved. A second possible explanation for the experimental results is that t’he decreasein metabolism is a generalized cellular effect and that t’he function of the thyroid gland might also be depressed accordingly. This would imply a specific action of DMSO on cell metabolism, an effect which had not been supported by in viva experiments (4). A third and more att,ractil-e cxplanat’ion for the results is that the action of DMSO is at a specific site which would be directly involved with the control of cellular metabolism as well as other aspect,sof thermoregulation including heat conservation, heat loss, and thyroid function. The hypothalamus has been shown to be the control cent’er for thermoregulation and an action of DMSO at this level could explain all of the observed effects. The depression of thyroid function and metabolic rate in animals whose thermal homeostasis is being threatened is indeed paradoxical. It is possible that DMSO acts in such a way that the hypothalamic “output” institutes heat-loss mechanisms and slows down processesinvolved in heat production. Another relevant finding was that the R/Q in the DMSO-treated animals was not changed despite the significant decrease in metabolic rate. Under these conditions of stress, it would be reasonable to expect hypothalamicmoderated release of catecholamines into the peripheral circulation with the resultant increased utilization of lipids in metabolic pathways in an effort to gain more efficient energy production. The apparent stability of the R/Q, despite the t,hermal challenge, suggests the stress response was not initiated. It, was also observed that the DMSO-treated rat’s did not increase their motor activity or assume a hunched posture but remained inxni-
204
ORLANDO
AND PANUSKA
mate with their paws extended while experiencing a profound decrease in body temperature. Likewise, shivering was not observed in these animals during the course of the experiments. The absence of these behavioral and physiologic adjustments in view of the threat to thermal homeostasis suggests an aberrant control mechanism. Perhaps, DMSO acts on the hypothalamus either directly or indirectly causing inappropriate thermoregulatory responses. SUMMARY It has been demonstrated that intraperitoneal injections of DMSO to rats results in a dose-dependent transient depression of thyroid function which is both dose and time correlated with similar effects on body temperature and metabolic rate. At this time, no cause and effect relationships have been established for these effects of DMSO. However, the evidence indicates that the DMSO-treated animals did not elicit a number of normal responses for maintaining body temperature within the homeothermic range. Since these responses are coordinated by hypothalamic control, it has been suggested that the actions of ,DMSO on thermoregulation might be at that level. REFERENCES 1. Altland, P. O., Highman, B., and Parker, M. Induction of hypothermia by dimethyl sulfoxide in rats exposed to cold: tissue and exzyme changes. Proc. Xoc. Exp. Biol. Med. 123,%3-859 (1966). 2. Arnott, D. G., and Daniach, I. The effects of compounds allied to resorcinol upon the uptake of radioactive iodine Pa1by the thyroid of the rat. Biochem. J. 50,473 (1951).
3. Ashwood-Smith, M. J. The radioprotective action of dimethyl sulfoxide and various other sulfoxides. Int. (1961).
J. Radiat.
Biol.
3, 41-48
4. Gerhards, E., and Gibian, H. The metabolism of dimethyl sulfoxide and its metabolic effects in man and animals. Ann. N. Y. Acad. Sci. 141, U-76 (1961). 5. Hagemann, R. F., and Evans, T. C. Reversible inhibition of thyroidal uptake of I’” by dimethyl sulfoxide. Proc. Sot. Exp. Biol. Med. 128, 1008-1010 (1968). 6. Hamaguchi, K. Structure of muramidase (lysozyme): Effect of dimethyl sulfoxide on the stability of muramidase. J. Biochem. 56, 441-449 (1964). 7. Orlando, M. M., and Panuska, J. A. Cardiovascular and respiratory function of hypothermic rabbits, as influenced by dimethyl sulfoxide. Cryobiology 7,216-222 (1971). 8. Panuska, J. A., Malinin, T. I., and Mentx, R. J. Effects of dimethylsulfoxide on cooling rates 2, 345-350 of unrestrained rats. Cryobiology (1966). 9. Pitt-Rivers, R., and Trotter, W. R. “The Thyroid Gland,” Vol. I-II. Butterworth, Washington, DC., 1964. 10. Smith, E. R., Hadidian, Z., and Mason, M. M. The single and repeated dose toxicity of dimethyl sulfoxide. Ann. N. Y. Acad. Sci. 141,96-109 (1967). 11. Tat, F. R. Intracellular and extracellular mechanism for the ut,ilization and action of thyroid hormones. Recent Progr. Horm. Res. 18: 187-268 ( 1962). 12. Walker, T. M., Albrigo, F. L., and Panuska, J. A. The effect of dimethyl sulfoxide on oxygen consumption in cold exposed rats and hamsters. Crybiology 3,265-268 (1966). 13. Worthley, E. G., and Schott, C. D. The toxicity of four concentrations of DMSO. TOXicol. Appl. Pharmacol. 15, 275-281 (1969).
9,
198-204 (1972)
Dimethylsulfoxide Temperature,
and Thermoregulation Metabolic Rate and
MICHrlEI, Department
of Biology,
M. ORLANDO Georgetown
A number of reports have indicated that dimethyl sulfoxide affects thermoregulation in mammals (1) 3, 7, 10, 13). Studies in our laboratory demonst,rated that DMSO accelerated the cooling rate of rats (8), and depressed oxygen consumption in both rats and hamsters (12). The depression of oxygen consumption, t’ogether with evidence that DMSO inhibited thyroid I311 upt,ake in mice (5)) suggested t’he possibility that t,he thermoregulat’ory effects of DMSO might involve t’he thyroid gland. The studies presented in this paper were undertaken to characterize further the previously reported thermoregulatory effects of DMSO and to determine if t,hese effects might be associated with a depression of thyroid function. MATERIALS
A4ND METHODS
The subjects in these experiments were male, Sprague-Dawley rats weighing between 225 and 275 g. The dimethyl sulfoxide (Crown Zellerbath Corp.) was dose adjusted as a 50% solution in saline and administered by intraperitoneal injection. Subjects were maintained either at ambient temperatures of 2-4°C or 21-25°C. Body temperatures were measured from thermocouples inserted to an intracolonic depth of approximately 4 cm. Control body temperatures were measured in unanesthetized, unt,reated subjects. Oxygen consumption and carbon dioxide production were determined by using a Beckman Model C2 oxygen analyzer and Harvard Model 2000 CO? Analyzer which were connected in series to a metabolism chamber housing the animal. Radioactivity was counted on a Nuclear Chicago Model 181 B Scaler using a well-type detect’or. Thyroid 1311uptake was measured on thyroid glands which were resected from et,her-anest)heReceived April 20,1972. ‘Supported in part by a grant, from the Washington Heart Association and Contract NOO14-69--i0220 from the Office of Naval Research. Copyright. All rights
o-1972 by Academic Press. of reproduction in any form
Inc. rrserved
ASD
: Studies on Body Thyroid Function1 J. A. I’;ZNTTSKA
University,
Washington,
D.C. 20007
tized rats using a method described by Arnot t, and Daniach (2) Serum thyroxine (T4) was detrrmined using the Oxford column chromatography m&hod (Oxford Laboratories) Serum from blood obtained by cardiac puncture immcdiately before thyroid resect,ion was itsed for these determinations. Serum thyroxine (iodine) values were determined calorimetrically and the values are prescnted in optical drnsity units (OD) for more accurate statistical comparison. These optical densities were converted to approximate mirrograms per 100 ml of serum thyroxine by comparison with a linear graph generated from dctermination of standards of known thyrosine concentration. There were two series of experiments. In each series, one group of animals was exposed to a T, of 23°C and another group to Tn 22-26°C. The first series was concerned with the effects of DMSO on body temperature, oxygen consumpt,ion, and respiratory quotient,. Three different doses of DMSO, 0.5, 2.0, and 6.0 g/kg, wrre used at time intervals of 0 (control), 1, 5, 10, and 21 hr for each dose. Cont,rol groups received saline injections. In a second serirs of experiments, t,h\-roid fun&on (*“I uptake and serum T,) was determined, but t)he dose range of DMSO was modified to 0.1, 1.0, and 6.0 g/kg at 3 hr. The effect of the 6.0 g/kg dose was studied at 6 and 24 hr. RESULTS Series 1. Body Temperature, Oxygen Conmmption, and Respiratory Quotient The results of t,he studies on the effect of DMSO on body temperature, oxygen consumption, and respiratory quot,ient are summarized in Tables 1 and 2. Ta 21-2,.5”C. The control value for body temperature was 37.9 ? O.l”C, and no significant change was observed over the 24-hr period. In the group treated with 6 g/kg of DMSO, the
199
Body temperature (“C)
Dose DMSO
Time (hr)
Oh TA = 21-25”CY Control 6 g/kg 2 g/k 0.5 g/kg
TA = 2-6”Cc Cont,rol saline
6 g/k 2 g/kg
0.5 g/kg
37.9 37.9 37.9 37.9
zk Tk & f
1
.l .l .l .I
38.1 33.7 37.6 37.6
.2” .2
37.8 Y!J .4 31.4 52 .4
37.8 * .2 37.8 zk .2
35.6 zt .3 37.6 zt .2
37.8 f 37.8 f
a Values = Mean f Standard Error. Average weight = 230 =t 15 g for TA = * 0 = Control value prior to DMSO c TA = Ambient temperature. d = Control values were determined e = All animals in group died.
f * f zt
5
.l .2 .2 .l
37.7 36.0 37.8 37.4
zk f zk f
10
.l .4 .I .l
37.9 37.5 37.8 37..i
zt zt f 3z
37.9 f 16.5 f
.2 .2
38.1 f 6
37.1 f 37.9 f
.l .2
24
.1 .3 .l .2
37.8 37.9 37.7 37.4
.l
38.2 h e
.l
38.0 zk .2 38.0 zk .l
38.3 f 38.0 f
.2 .2
Xumber = 24 per control group and 6 per UMSO-treated 21-25°C and 288 =t 22 g for TA = 24°C. injection.
* * f. r!z
.I .2 .l .2
group.
1 hr after animals were placed in cold.
body temperature was significantly reduced to 35.7 i 0.2”C (p < ,001) at 1 l1r after the injection. There was a slight increase at 5 hr to 36.0 -C 0.4”C and a return to control levels at 10 and 24 11r. In the groups treated with 2- and 0.5-g/kg doses of DMSO, there were no significant changes in body temperature over the 24-hr period. Thp co11t,rol vulue for oxygen consumpt#ion was 28.3 ? 0.9 ml/min/kg and did not change significantly over tl1e 24-1~ period. In the group treated with 6.0 g/kg of DMSO, a marked depression of oxygen consumption was observed at 1 hr. Tl1e change from control values of 28.3 -I 0.9 to 19.4 * 0.7 ml/min/kg represents a decxrenseof 32% (p < ,001). The oxygen consumption increased to 21.0 ?z 1.4 at 5 lir, 24.8 L 0.9 at 10 hr, and approximated control values at 24 lir. The group trcnt)ed with 2 g/kg of DMSO also 11nd:I marked depression of oxygen consumption at 1 11r to 22.1 c 1.1 ml/min/kg (p < .05). Tl1ere \vas a gradual increase at 5 and 10 hr from t’hc value obtained at 1 hr. At 24 hr, tl1e oxygen consumption 11nd returned to control levels. The respiratory quotient was 0.85 -I- 0.03 in the control group and did not change signifi-
cantly over the 24-hr period. Treatment of the animals with doses of 6.0, 2.0, and 0.5 g/kg 11ad no significant effect on the R/Q over the 24-hr period. T, Z-6°C. In the cold-exposure study, the mean control value for body temperature was 37.8 f 0.2”C after 1 hr of cold exposure. This value did not change significantly over t,he ensuing 24-hr period. In the group treated with 6.0 g/kg of DMSO, a significant decline in body temperature to 31.4 c 0.4”C (p < ,001) was observed at 1 hr, and an even greater depression at 5 hr to 16.5 2 0.2”C (p < ,001). All the animals in t,he group died between the fifth and the tenth hour. The group receiving a 2 g/kg dose of DMSO had a decrease in body temperat,ure at 1 11r to 35.6 ? 0.3”C (p < .05). The body temperature had increased at 5 hr to 37.1 rfr: O.l”C and returned to control values at 10 and 24 hr. Treatment wit,11 a 0.5 g/kg dose of DMSO did not, alter the body temperature o\-er the 24-hr dctermination period. The oxygen consumption of the control groups was 40.4 * 0.7 ml/min/kg. Tl1is value was obtained 1 hr after cold exposure and represents a 30% increase over the control group maintained at room t’emperature. Oxygen consumption in
200
ORLANDO
AND PANUSK.4 TABLE
2
OXYGI,:N CONSIJMPTIONANI) 1:,X1 OF I)MSO-TIII~;~\TI':D KITS Dose DMSO
Oxygen consumption (ml/min/kg) Time (hr) 0
TA = 21L25”C, Control saline 6 g/k 2 g/k!? .i g/kg
28.3 28.3 28.3 28.3
f. f f +
0.9 0.9 0.9 0.9
27.0 19.4 22.1 24.-j
TA = 2Z6”C Control saline 6 g/k 2 g/k 5 g/kg
40.4 40.4 40.4 40.4
f f f +
0.7 0.7 0.7 0.7
40.3 20.2 30.4 36.9
+ 1.0 f
10
5
1
0.7
f
1.1
f
0.9
f
1.5
f
1.0
zt 2.3 zk 1.3
28.2 21.0 22.3 2-5.7
37.5 5.7 37.9 39.5
f
1.1
24
1.1
27.0 24.8 24.2 23.2
i
1.5
37.8 zk 1.3
37.4 f
1.3
* It *
3.9 1.2 2.1
37.3 f 37.9 f
37.1 f 37.8 f
1.4
zt 1.4 xt 1.3
f
f 0.7 zk 0.9 f 1.3
I!Z 1.0
1.4 1.2
29.0 26.8 26.4 26.3
f
1.2
h 1.1 f 1.3 zk 0.7
1.2
R/O (respiratory quotient)
Dose DMSO
Time (hr) 0
1
5
10
24
TA = 21-25X
Control saline
6 g/kg 2 g/k .5 g/kg TA = 2-6X Control saline 6 g/k 2 g/k ..i g/kg
.8d .85 .85 .85
zk f It +
.03 .03 .03 .03
.87 .84 .78 .8,5
f f + zk
.03 .04 .02 .05
.78 f .78 b
.02 .n2
.80 zt .03 .93 f .02
.78 f .78 f
.02 .02
.79 f .77 f
.06 .02
the control group held steady over t,he 24-hr period. In the 0.5 g/kg group, a slight but significant depression of oxygen consumption was seen at 1 hr (36.9 * 1.3 ml/min/kg, p < .05). Control levels of oxygen consumption were observed at 5, 10, and 24 hr. The respiratory quotient of the cold-exposed control group was lower than the group maintainrd at room temperature. The R/Q value was 0.78 * 0.02 and was constant over the 24-hr period. The only significant, change in R/Q for any of the groups was observed in the group treated with 6.0 g/kg of DMSO at 1 hr after the injection. The value obtained was 0.93 * 0.02. Owing to the severe depression of oxygen ronsumption and carbon dioxide production, R/Q
.80 .80 .86 .82
z!z * + f
.02 .04 .03 .05
.79 .89 .78 .84
.81 f
.04
.74 f .70 l
.02 .04
f f zk f
.04 .09 .04 .03
.80 .85 .83 .82
f f zk f
.03 .05 .05 .05
.79 f
.04
.80 f -
.04
.73 f .82 f
.06 .03
.84 f .78 *
.04 .05
values were not determined at 5 hr. All the animals in the group had died by the tenth hour. Series 2. Thyroid ture
Function
and Body Tempera-
The result,s of the studies on t)hyroid function and body temperature in DMSO-t,reated rats are given in Tables 3 and 4. Three-hour study (T, ~145°C). The only significant change in body temperature in these groups was observed in the group treated with 6.0 g/kg of DMSO. The 3-hr determinations indicated n drop in body temperature from 38.0 * O.l”C to 35.0 & 0.3”C (p < ,025). In t)he group treated with 6.0 g/kg of DMSO, there was 54% inhibition of the 3-hr thyroid ‘“‘I uptake when compared with controls. The t,hy-
DMSO AND TEMPERATURE TABLE THYROID
FUNCTION
AND
BODY
3
TEMPERATURE
Av wt. (g)
N
279 f
12
18
6 g/k
273 f
13
10
1 g/kg
289 zk 16
.l g/k
275 zk 10
-
.I-
TA = 21-25°C Control saline
TA = 2-6°C Control
253 zt 21
6 g/kg
249 *
14
1 g/kg
220 f
7
.I g/kg
226 f
8
8
-I
37.9 37.8 38.0 35.0 37.9 38.0 37.8 38.0
3z f f f i f f z!r
0.1 0.1 0.1 0.3 0.1 0.2 0.2 0.2
38.2 38.6 38.0 28.7 38.3 38.1 38.0 38.4
rt f f f f i f f
0.2 0.2 0.2 2.4 0.3 0.2 0.3 0.2
3hr
18,400 , 4,500 8,400 ~ 5,000 13,100
Thyroid serum T/S
Serum 13q kpd
-I- 3 hr
3 hr
.-
RUTS (3
OF DMSO-TREATED
rhyroid 131I (cpm) Dose DMSO
201
REGULATION
I
~
l.i8
1
TJ (serum)
ODc
3 hr
3 hr
4.17 f
HK)@
.41 / ,546 zk .014
xk .19
.618 f
.013
4,600
I 2.88 f
.42 I 648 rt
.022
16,700
3,500
1 4.60 rt
.61 ; ,527 +
.021
9,700
3,900
3,600
7,000
.54 +
.OT
,681 zk ,037
10,200
5,700
1 1.83 f
.21
,543 f
,023
10,200
4,500
( 2.38 f
.34
,472 f
.015
2.66 zt .30
a Values = Means or Means f Standard Error. TA = ambient temperature. 6 = For each group both pre-DMSO (upper figure) and 3 hr post-DMSO (ion-er figure) tures are given.
,520 zt ,030
body tempera-
c OD = Optical density (units were converted to pg T&00 ml serum by comparing with a standard graph
(Fig. 1). These values
are given in the Results
roid-serum ratio of ?I (cpm) was significantly reduced from 4.17 t 0.41 in the controls to 1.78 -C 0.19 in the DMSO-treated group (p < .OOl). The serum thyroxine values are given in the table as optical density units but are discussed here as micrograms per 100 milliliters of serum (pg/lOO ml). The control group had a serum thyroxine value of 1.90 pg/lOO ml serum, while the group treated with 6.0 g/kg of DMSO had a value of 1.25 pLg/lOOml (p < .05). In the group receiving 1 g/kg of DMSO, there was a 28% reduction of I”1 uptake as compared to controls. The thyroid-serum ratio was reduced to 2.88 + 0.42. This value was significantly lower than controls (p < .05), but not as low as that obtained in the 6.0 g/kg group. Serum thyroxine in this group (1.0 g/kg) was 1.05 yg/lOO ml which was significantly less than the controls (p < .05).
The group treated with 0.1 g/kg did not show changes in any of the parameters from values obtained for controls.
section.
Three-hour study (TA Z-PC). In the coldexposed control group, the 3-hr thyroid ‘“‘I was lower than in the control group maintained at room temperature. There was also a lower serum ‘Y value resulting in a thyroid-serum ratio of 2.66 2 0.30 which indicates a significant change from the 4.17 & 0.41 (p < .05) in the roomtemperature control group. The serum thyroxine value was 2.10 pg/lOO ml in the control group of the cold-exposed animals. The administration of a 6.0 g/kg dose of DMSO resulted in a 63% inhibition of I”1 uptake and a decreasein the thyroxine-serum ratio from 2.66 & 0.30 to 0.54 + 0.07 (p < ,001). The mea,nserum thyroxine value obtained for the 6.0 g/kg dose group was 0.78 pg/lOO ml which indicates a significant decrease from the controls (p < .05). In the group treated with 1.0 g/kg of DMSO, the ?t uptake was not significantly different from controls, but the serum ‘“I was higher, resulting in an over-all thyroid-serum ratio de-
ORLANDO AND PANUSKA
202
THYROID
FUNCTIOK
TA = 21-25°C
DOS?
DMSO -___~
Control
Av wt. (9)
Body
1 -1-v.
BODY
TABLE 4 OF DMSO-TIW.~TEDRATS (6 hr and 24 hr)a
TEMPERATURE
Thyroid 13’1 (cpm)
temperature (“W
6 Hi-
1 21Hr
6 Hr
24 HI
Thyroid serum (T/s) 6 Hi-
1 24 Hr
1 I
6 Nr
1
Ta (serum)
24 HI
OD
6 Hr
24 Hr
~_____
18 38.1
279 f
6 g/k
LND
12
273 zt 13
*
8
37.7 .2
37.9 f .3 37.9 f .3 35.8 f .2
f
40,700
47,700
.2
37.5 f .2 37.6 f .4 37.8
3.1
f
21,800
40,300
2,500
840 8.9
f 1.1
58.5 f 3.4
54.0
f 9.5
zk
.516 ,044
f
,530 .036
f
3~
.542 ,025
,520 .027
+ .l
I = Values = Mean or Mean & Standard Error. TA = ambient temperature. b For each group both pre-DMSO (upper figure) and 6 hr and 24 hr post-DMSO (lower figure) body temperatures are given. crease to 1.83 * 0.21. Serum thyroxine was 1.92 pg/lOO ml, approximating control values. Treatment with 0.1 g/kg of DMSO did not result in changes in any of the thyroid parameters when compared to controls. The only significant change in body temperat,ure observed was in the group given the 6.0 g/kg dose of DMSO. In this group the body temperature declined from 38.0 & 0.02 to 28.7 e 2.4O"C at 3 hr (p < .OOl).
DISCUSSION
It is apparent from these studies that DMSO interfered with normal thermoregulatory processesin the rat. The action of DMSO resulted in a transient depression of body temperature which was associated with a similar effect on metabolic rate. These responseswere observed in rats maintained at ambient temperatures within their thermoneutral zones and were markedly accentuated by cold exposure. The thyroid studSix-hour and 24 hour studies (TA 91-25°C). ies demonstrated that the depression of thermoThe body temperature of the group treated with genesis caused by DMSO treatment was both 6.0 g/kg of DMSO was lower than controls at 6 dose and time correlated with a depression of hr (37.9 + 0.3 and 35.8 + 0.2”C), but no differ- thyroid function. ence was observed at 24 hr. The thyroid I”1 An important finding was that the DMSO-inuptake in the controls increased at 6 and 24 hr duced decline in body temperature even initially from the values obtained at 3 hr. The X311 uptake was accompanied by a similar decline in metain t,he DMSO-treated group increased at 6 and bolic rate. A normal rat experiencing an acceler24 hr but the increase was less than that of the ated heat loss which threatens its thermal homecontrols. The thyroid-serum ratio in the control ostasis responds by increasing metabolic rate to group was 18.1 -C 3.1 at 6 hr and 58.5 + 3.4 at increase heat production. This was observed in 24 hr. The group treated with 6.0 g/kg of the cold-exposed control group whose oxygen DMSO had a T/S ratio of 8.90 r+ 1.10 at 6 hr consumption increased by 30% after 1 hr of cold which is significantly lower than the controls (p exposure. The attempt to increase heat produc< .05) and a 24-hr value of 54.0 * 9.5, which is tion is normally accompanied by other physionot different from the control group. logic adjustments to decreaseheat loss (e.g., peThe serum thyroxine in the control group did ripheral vasoconstriction) as part of the mechanot show any significant change at 6 and 24 hr nism for maintaining thermal homeostasis. Since from the values obtained at 3 hr. The 6-hr serum thyroxine value was 2.15 pg/lOO ml and this increase in metabolic rate was not seen in the 24-hr value was 1.90 pg/lOO ml. In the DMSO-treated rats, it can be assumed that at DMSO-treated group, the serum thyroxine value least part of the effect of DMSO on thermoreguwas 2.00 pg/lOO ml at 6 hr and 2.10 pg/lOO ml lation is due to interference with heat production. at 24 hr.
DMSO
AIND TEMPERATURE
In the groups maintained at 21-25”C, the threshold dose necessary to depress body temperature and metabolic rate was between 1.0 and 2.0 g/kg, while the peak effect of the drug occurred between 1 and 5 hr after treatment. The response in each case was transient despite the apparent dose dependence. The depression of thyroid function was also most marked during t#he first few hours afber t,reatment and began to diminish by the sixth hour. Cold exposure resulted in a lower threshold dose, a more pronounced peak effect, and a more sustained effect with each dose of the drug. In the cold-exposed animals which received a 6.0 g/kg dose, the depression of body temperature was irreversible and the animals died in profound hypothermia. This was probably the result of a critical body temperature being reached at which all thermoregulatory processes broke down despite the transience of the DMSO actions. Under these conditions of depressed metabolism, the elimination of the drug from its site of action or the body in general will also be reduced and the longer exposure to higher concentrations will compound the problems of thermoregulation. The question of the role of the thyroid gland in the observed thermogenic action of DMSO is interesting. There are three possible explanations for the apparent relationship between depressedthyroid function and depressedmetabolic rat’e. First, the inhibition of thyroid fun&on could be responsible for the metabolic rate depression. There was evidcncc of decreased circulating thyroid hormone within 3 hr after DMSO treatment, which apparently returned to normal by 24 hr. This correlated well with the inhibition of thyroid “I uptake. The explanation for t’his depression of circulating thyroxine might be that the decreased output from the thyroid gland was coupled with increased peripheral turnover or elimination. The increased turnover might be associated with the met#abolic demand imposed by t,he threat to thermal homeostasis. However, the observed decreasesin serum thyroxine with the 6.0 g/kg dose were large, and another more speculat,ive explanation might be offered. Since DMSO is known to alter protein configuration (6), it might be postulated that the t’hyroxine binding proteins are modified resulting in a decreased binding affinity for thyroxine. Unbound
REGULATIOX
203
thyroxine is apparently eliminated more rapidly than that bound to plasma protein (11). The decrease of serum thyroxine observed in the DMSO-treated animals was probably not the cause of the metabolic-rate and body-temperature depression. These effects were observed Jvithin 3 hr and most experimental evidence suggests that the metabolic actions of the thyroid hormones take place only aftscr a lag period of 45 hr or more (9). The mechanism for this latent, action has not been established and t’he question of thyroid-induced metabolic rate changes associated with endogenous hormone secretion remains unresolved. A second possible explanation for the experimental results is that t’he decreasein metabolism is a generalized cellular effect and that t’he function of the thyroid gland might also be depressed accordingly. This would imply a specific action of DMSO on cell metabolism, an effect which had not been supported by in viva experiments (4). A third and more att,ractil-e cxplanat’ion for the results is that the action of DMSO is at a specific site which would be directly involved with the control of cellular metabolism as well as other aspect,sof thermoregulation including heat conservation, heat loss, and thyroid function. The hypothalamus has been shown to be the control cent’er for thermoregulation and an action of DMSO at this level could explain all of the observed effects. The depression of thyroid function and metabolic rate in animals whose thermal homeostasis is being threatened is indeed paradoxical. It is possible that DMSO acts in such a way that the hypothalamic “output” institutes heat-loss mechanisms and slows down processesinvolved in heat production. Another relevant finding was that the R/Q in the DMSO-treated animals was not changed despite the significant decrease in metabolic rate. Under these conditions of stress, it would be reasonable to expect hypothalamicmoderated release of catecholamines into the peripheral circulation with the resultant increased utilization of lipids in metabolic pathways in an effort to gain more efficient energy production. The apparent stability of the R/Q, despite the t,hermal challenge, suggests the stress response was not initiated. It, was also observed that the DMSO-treated rat’s did not increase their motor activity or assume a hunched posture but remained inxni-
204
ORLANDO
AND PANUSKA
mate with their paws extended while experiencing a profound decrease in body temperature. Likewise, shivering was not observed in these animals during the course of the experiments. The absence of these behavioral and physiologic adjustments in view of the threat to thermal homeostasis suggests an aberrant control mechanism. Perhaps, DMSO acts on the hypothalamus either directly or indirectly causing inappropriate thermoregulatory responses. SUMMARY It has been demonstrated that intraperitoneal injections of DMSO to rats results in a dose-dependent transient depression of thyroid function which is both dose and time correlated with similar effects on body temperature and metabolic rate. At this time, no cause and effect relationships have been established for these effects of DMSO. However, the evidence indicates that the DMSO-treated animals did not elicit a number of normal responses for maintaining body temperature within the homeothermic range. Since these responses are coordinated by hypothalamic control, it has been suggested that the actions of ,DMSO on thermoregulation might be at that level. REFERENCES 1. Altland, P. O., Highman, B., and Parker, M. Induction of hypothermia by dimethyl sulfoxide in rats exposed to cold: tissue and exzyme changes. Proc. Xoc. Exp. Biol. Med. 123,%3-859 (1966). 2. Arnott, D. G., and Daniach, I. The effects of compounds allied to resorcinol upon the uptake of radioactive iodine Pa1by the thyroid of the rat. Biochem. J. 50,473 (1951).
3. Ashwood-Smith, M. J. The radioprotective action of dimethyl sulfoxide and various other sulfoxides. Int. (1961).
J. Radiat.
Biol.
3, 41-48
4. Gerhards, E., and Gibian, H. The metabolism of dimethyl sulfoxide and its metabolic effects in man and animals. Ann. N. Y. Acad. Sci. 141, U-76 (1961). 5. Hagemann, R. F., and Evans, T. C. Reversible inhibition of thyroidal uptake of I’” by dimethyl sulfoxide. Proc. Sot. Exp. Biol. Med. 128, 1008-1010 (1968). 6. Hamaguchi, K. Structure of muramidase (lysozyme): Effect of dimethyl sulfoxide on the stability of muramidase. J. Biochem. 56, 441-449 (1964). 7. Orlando, M. M., and Panuska, J. A. Cardiovascular and respiratory function of hypothermic rabbits, as influenced by dimethyl sulfoxide. Cryobiology 7,216-222 (1971). 8. Panuska, J. A., Malinin, T. I., and Mentx, R. J. Effects of dimethylsulfoxide on cooling rates 2, 345-350 of unrestrained rats. Cryobiology (1966). 9. Pitt-Rivers, R., and Trotter, W. R. “The Thyroid Gland,” Vol. I-II. Butterworth, Washington, DC., 1964. 10. Smith, E. R., Hadidian, Z., and Mason, M. M. The single and repeated dose toxicity of dimethyl sulfoxide. Ann. N. Y. Acad. Sci. 141,96-109 (1967). 11. Tat, F. R. Intracellular and extracellular mechanism for the ut,ilization and action of thyroid hormones. Recent Progr. Horm. Res. 18: 187-268 ( 1962). 12. Walker, T. M., Albrigo, F. L., and Panuska, J. A. The effect of dimethyl sulfoxide on oxygen consumption in cold exposed rats and hamsters. Crybiology 3,265-268 (1966). 13. Worthley, E. G., and Schott, C. D. The toxicity of four concentrations of DMSO. TOXicol. Appl. Pharmacol. 15, 275-281 (1969).