Seasonal changes of food and water consumption and urine production of the marmot, marmota flaviventris

0300-9629/84 $3.00+ 0.00 mp 1984Pergamon Press Ltd

Camp. Biochem. Physiol. Vol. 77A, No. 4, pp. 735-743, 1984

Printed in Great Britain

SEASONAL CHANGES OF FOOD AND WATER CONSUMPTION AND URINE PRODUCTION OF THE MARMOT, MARMOTA FLAVIVENTRIS MARVIN L. ZATZMAN, GARY V. THORNHILL, WILLIAM J. RAY* and MARK R. ELLERSIEK The University of Missouri Health Sciences Center, Department of Physiology and the Agricultural Experiment Station, University of Missouri School of Agriculture, Columbia, MO 65212, USA Telephone: (3 14) 882-4957 (Receiaed

20 July 1983)

In early spring, food and water consumption and the excretion and clearances of urine and solutes reached maximal rates. Water consumption exceeded food intake and urine production and plasma osmolality was lowest. 2. Toward early and late summer, water intake decreased faster than food consumption and urine production. Urea excretion and clearances diminished with food consumption, while creatinine clearance decreased only slightly. Plasma osmolality increased. 3. The data are consistent with rehydration soon after hibernation is completed, followed by a period of weight gain and dehydration in preparation for the next prolonged period of hibernation.

Abstract-l.

INTRODUCTION In a recent publication (Zatzman and South, 1981) we documented the seasonal nature of renal function and some plasma constituents of the yellow-bellied marmot (M. flaviventris). Although data of seasonal food intake and body weights of some hibernants are available (Pengelly and Fisher, 1963; Davis, 1976; Fall, 1971; Armtage et al., 1976; Young and Sims, 1979; Hock, 1969), the literature contains no information of food and water consumption, urine production or urinary constituents of the M. Jluviventris under laboratory conditions. This report presents the data obtained from two studies of the yellow-bellied marmot: (1) weekly food and water consumption and bimonthly body weights of 18 animals (9 males and 9 females) and (2) weekly food and water consumption, electrolyte intake and excretion, urine production and constituents, bimonthly body weights and monthly determinations of plasma constituents, urea, creatinine, free water, and osmotic clearances in six animals (3 males and 3 females). Of interest in these studies were seasonal changes in: (1) the relation between maximum food intake and body weight; (2) the relation between water and food intake; (3) water, electrolyte, creatinine and urea balances. MATERIALS AND METHODS Animals

Animals were collected with live traps in the area of Red Feather Lakes, Colorado in 1980 (altitude 243%2530m). Animals were housed singly in cages (46 x 61 x 46cm) in the animal care facilities of the Dalton Research Center. The initial series of studies were performed in 1981 with 18 animals approximately 2 years of age. The final series was

performed in 1982 with six of the animals previously studied and were approximately 3 years of age. When the animals were obtained they were dipped to eliminate ectoparasites (Kern-Dip, Vet Kern Co., Dallas, Texas). All animals were placed in quarantine for one month and provided with a 20% sulfaquinoxaline (Merck Chemical Division) in the drinking water to prevent or treat coccidiosis. Following the quarantine period they were placed in the regular animal house facility with a photoperiod of 12L: 12D. At this time we attempted to feed them a commercial rabbit diet (Lab Rabbit Chow, Ralston Purina Co.) which was recommended for Mnrmofa monad by Young and Sims (1979) and Lawless et al. (1982). We found that this species would not consume the diet and began to lose weight. We then changed to a commercial rat diet (Rodent Laboratory Chow, Ralston Purina Co.) which had been used in our earlier studies and found that unlike MOIILIX, ,jkzrirentris gained well and did not become excessively fat. In addition to the rat chow the animals were provided with carrots once a week and vitamins (Vi-Sorbin, Norden Laboratories) in the drinking water once each week. Following the first study and prior to the second one the animals were placed in a hibernaculum (6 ‘C) and permitted to hibernate until early March. Cotton wool bedding was provided as nesting material. Food and water were provided ad libitum. Body weight and ,food and water consumption

18 animals were used in this study (9 males and 9 females). Each animal was provided with 200 g of commercial rat diet blocks and 450 ml of water daily. The amount of food and water consumed was determined daily between 09:OO and 14:OOhr. Once each week (Monday) water bottles were replaced and 1 ml of a vitamin supplement, Vi-Sorbin, was added to each water bottle. Once each week (Thursday) 100 g of carrot were provided to each animal. The amount consumed was recorded on the following day. Animals were weighed every 2 weeks. The initial weight range of these animals was: males 2.52-6.95 kg, females 2.60-5.10 kg. Body

*Present address: Department of Neurosurgery, Henry Ford Hospital, Room 3088 Benson Ford Education and Research Building, Detroit, MI 48202, USA. c BP 77’4AJ

weight, food and water consumption

und urine pro-

d&on Three animals of each sex were used in this study. The animals were one year older and were randomly selected 735

MARVIN L. ZATZMANet (11.

136

from the group that was used in the previous study. Only six animals comprised this study due to the large number of analyses necessary and because of the limited number of metabolic cages available. Food, water, carrots and vitamins were provided as indicated above. During the first week only five animals were studied. A sixth animal (male) was added in the second week. Animals were housed individually in metabolism cages that were built for this study by the Dalton Research Center shop. Below the screen floor was a fine screen (fiberglass) to catch feces and food crumbs. A funnel-shaped box with a small opening at the bottom was formed of sheet stainless steel. This funnel was situated below the fine screen. Urine collection was made by placing a container below the funnel. The urine collecting containers had in them a layer of water-equilibrated mineral oil to prevent the evaporation of the urine sample (Zatzman and South, 1975). Urine volume was measured daily and an aliquot was frozen (-20’C) for later chemical analysis. Animals were weighed every 2 weeks. The initial weight range was: males 3.8-5.23 kg, females 3.24-4.95 kg. At one month intervals a 4ml blood sample was obtained by cardiac puncture from each of the sedated animals (kctamine 10 mg/kg i.m.). Blood samples were transferred to 5 ml tubes containing ammonium heparin. After centrifugation the plasma was frozen and stored for later analysis. Chemical

Daily consumption and excretion were corrected for body weight by assuming that the change in weight (measured bimonthly) was linear. A weekly average was computed for each animal. Clearances (creatinine, urea, osmotic and free water) were calculated from the average daily excretion rate for the month divided by the average plasma concentration for that period. Weekly averages of daily consumption or excretion were analyzed statistically by the method of repeated measurements described by Gill and Hafs (1971). The method. which is an analysis of variance procedure, permits statistical evaluation of the effect of time as well as the effect of sex. The same statistical procedure was used for bimonthly body weights, monthly plasma concentrations and monthly clearance. Mean separation due to sex was ascertained using Fisher’s least significant difference (LSD). Where appropriate, linear regression lines were calculated and the correlation coefficient was determined. Differences for each animal were calculated for water, Na and K between intake and excretion rates, These differences were also analyzed by the repeated measurements design,

RESUETS Body

analysis

Chemical analysis was performed in the second study; only food and water consumption were determined in the first study. At two week intervals the urine samples were thawed, mixed and the following analyses were performed: osmotic pressure by freezing point depression with a Fiske osmometer, urea nitrogen by the method of Marsh ef al. (1965) and creatinine by an automated procedure developed by the Technicon Instruments Corp.. and sodium and potassium by flame photometry. At the end of the study plasma samples were analyzed by the same methods. In addition, an aliquot of tap water, commercial rat diet and carrot were analyzed for sodium and potassium content. Sodium and potassium intake from carrots were included with the intake from the food eaten.

wei,ght,

.fimd and

Table I. Body weight, average food and water consumption Body weight (kg) Females Males wt SEM Wt SEM

Week

Date

1 2 3 4 5 6 7 8 9 10

3!553111 3:12-3118 3;19-3,125 3:2&4;1 41’2&4:8 4/9-4;15 4/l&4/22

4.36 4.37

0.56 0.52

3.72 3.81

0.27 0.24

4.37

0.51

3.86

0.24

4.62

0.53

4.12

0.25

4123-4129

4.76

0.54

4.29

0.26

4.95

0.55

4.39

0.33

5.19

0.59

4.61

0.27

5.39

0.61

4.61

0.27

5.45

0.64

4.62

0.31

5.50

0.67

4.62

0.33

5.46

0.6X

4.54

0.34

5.29

0.66

4.37

0.36

5.33 5.32

0.65 0.63

4.30 4.33

0.33 0.35

II

12 I3 14 15 16 17 I8 19 20 21 22 23 24 25

4/3@5,‘6 5/7-5113 s/145/20 5!21-5/27 51286,‘3 6&6/10 6il l-6127 6/18-6124 6,25~7,‘1 7;‘227:8 719-7/15 71167122 7123%7,‘29 7i3&8/5 8:68jl2 X/13-8:19 8/2&8!26

*i.e. 5 March-11

March.

water

consumption

Average body weights of males (Table I and Fig. 1) exceeded that of females (P = 0.02) throughout the period when measurements were made (8 March-23 August). Peak weight of males and females was achieved between late June and the third week in July (Table I and Fig. I). There was no significant difference of food consumption between males and females when food consumption was corrected to body weight (Fig. 2, top panel). However, peak food consumption occurred in both sexes much earlier (29 March-24 May) than the maximum increase in weight. Water consumption, on a body weight basis, demonstrated the same pattern as did food consumption (Fig. 2, middle panel). by IX marmots

Av. food consumption (g/day) Females Males SEM SEM 62.2 63.4 66.4 91.6 96.3 108.6 104.1 117.8 119.4 122.0 126.6 120.6 114.2 104.9 97.1 92.8 87.2 81.6 66.9 57.0 40.3 39.5 32.8 32.9 19.8

9.3 8.6 7.X 9.9 9.0 9.9 11.3 12.3 11.x 14.7 15.1 18.1 19.6 16.8 16.8 17.7 18.2 19.8 17.5 13.9 IO.2 II.5 9.0 9.0 5.7

77.9 79.9 81.9 101.2 113.6 110.2 106.7 116.8 99.3 99.2 9x.2 101.0 97.2 81 .O 6X.2 58.2 46.8 44.8 28 8 27.0 20 I 16.4 9.0 6.2 5.6

12.x 14.3 12.9 14.3 18.2 12.2 12.1 13.0 3.9 6.4 Il.3 11.5 15.5 17.0 15.0 15.6 14.4 12.9 Y.? 9.6 6.4 6.0 2.7 24 I.6

Av. water consumption (mljday) Males Females SEM SEM I28 138 I27 193 I52 I91 192 211 216 231 22X 22X 212 187 145 145 124 117 107 X9 63 59 50 41 34

25 41 21 47 28 26 26 40 34 34 37 43 44 41 35 41 37 40 36 35 27 29 20 22 17

128 134 129 I82 191 213 206 205 168 186 163 150 139 124 93 69 63 44 2X ?I II 6 4 5 4

IX 22 21 21 20 23 24 25 14 26 20 25 26 2X 22 17 18 13 IO 8 4 2 I 2 3

Food 6.5

and water

consumption

of the marmot

r

6.0

-

55-

5.0 -

BODY

WT

4.5-

(kg)

4.0

-

3.5 -

WEEK

OF STUOY

Ll I

11

2

3/15

OAT E

3

”

4

SR9

5

1

6

‘VI2

” 7

0 4/C%

”

9

10 wlo

”

,I

I2 5/24

”

I3

14 6/7

”

15

16 vzl

”

17

IS v/s

”

19

20 VI9

Fig. 1. Bimonthly body weights of M. Jlaviuenfris. A---A males (N = 9); n --a *Difference between male and female weight are significant (P < 0.02). Verticasl

”

21

22 e/z

’

23

”

24

25

Ma

females (N = 9). bars are SEM.

FOOD CONSUMED t~,“+.gBw-

day-11 IS

WATER

CONSUMED (ml It9 SW-’ day-‘1

1

Fig. 2. Food consumption; consumption.

TT

and water consumption of 9 male and 9 female M. Jlaviventris. Upper panel-food middle panel-water consumption; lower panel-ratio of water consumption to food *Significant difference between males and females (P -z 0.05). Vertical bars are SEM.

MARVIN L. ZATZMANet ul.

738

However, an analysis of the ratio of water:food consumption (Fig. 2, bottom panel) indicates that during late winter and early spring about 2 ml of water was consumed for each gram of food eaten; by late summer the ratio fell to 0.5-1.0 indicating that water consumption decreased faster than food consumption (see Fig. 2, upper and middle panels). In addition, this group of animals demonstrated that the ratio of water to food consumption decreased more in females toward late summer than males (P < 0.05). Food consumption, water consumption, body weight and ratio of water to food consumption changed significantly (P < 0.001) with time. By the end of this study the animals were lethargic and ready for hibernation. Body weights, food and water consumption production

and urine

This study was initiated about one month later than the first one because of delay in obtaining metabolism cages. One animal (male) was added to the study in the second week. The average results are indicated in Table 2 and Figs 3-5. Since no differences were noted between the sexes the values in the table and figures are the overall averages. The patterns of body weight, food and water consumption (Figs 3 and 5) of these older animals were similar to that observed in the initial study, although peak body weight occurred about I month earlier and averaged approximately 0.5 kg as compared to 1.0 kg in the younger marmots. Because of the small number of animals in this study there was no significant difference in the body weights of males as compared to females although the mean body weights of males exceeded that of females. The ratio of water:food consumption demonstrated a pattern similar to that observed with the larger group of animals (compare Fig. 2, bottom panel and Fig. 3, middle panel). Except where noted, all measured values demonstrated significant changes with time. Plasma constituents Figure 4 contains the plasma concentrations of urea nitrogen (U), creatinine (Cr), sodium (Na), potassium (K) and the plasma osmotic pressure (P,,). All except Na (P = 0.09) and K (P = 0.12) concentrations demonstrated a change with time (P < 0.01) although the time of the minimum concentration of sodium and the potassium peak agrees with that found in a study with a larger animal population (Zatzman and South, 1981). Plasma urea concentrations gradually decreased from early April to the middle of August. On the other hand, both plasma creatinine concentration and osmolality of the plasma demonstrated an increase over the same period. Intake and excretion The intake tion of these Fig. 5. They with time (P

of water and electrolytes

of water and electrolytes and the excrematerials are indicated in Table 2 and all demonstrated a significant change < 0.0001).

As indicated in the inserts of Fig. 5, there was a reasonable balance between the consumption of water, Na and K and their excretion. The same lot of commercial diet was used throughout the study and contained 0.127 mEq Na/g and 0.215 mEq K/g. Carrots contained 0.01 mEq Na/g and 0.07 mEq K/g. Tap water, which was provided for drinking, contained undetectable concentrations of Na and K. The daily intake of water and the excretion of urine by each animal demonstrates an overall significant difference (P cc 0.0001) between these two processes. Initially (1 I April-21 April) there was a greater water intake than urine production (P values ranged from 0.0001 to 0.04). Late in the study (16 July-27 August) it appeared that urine loss exceeded water uptake; however, the differences were small (as were the absolute values), and were not significantly different from each other. Since there may have been a gradual dehydration of the animals due to a cumulative difference between water consumption and urine production, we tested (paired t-test) the difference between the sums of water consumed and urine produced during that period and found that the cumulative urine loss exceeded intake (t = 2.88; P < 0.05). Potassium intake and excretion demonstrated the same pattern seen in water intake and urine excretion. Potassium intake exceeded excretion (P values between 0.02 and 0.0001) between weeks three and six (23 April-14 May). Although the slight excessive increase in K excretion was not significant, the total excretion from 11 May to 27 August exceeded the intake during the same period (t = 2.78; P cc 0.05). Although Na intake and excretion decreased from spring through late summer (P < 0.0001) there was no evidence of a significant difference between these processes (P > 0.20). Osmotic, ,frer wuter, creatinine

and ureu clearances

Osmotic and free water clearance, excretion and clearances of creatinine and urea are shown on Fig. 6. Osmotic clearance (upper panel) decreased dramatically throughout the study (P < 0.0001) and was accompanied by an increasing (P < 0.001) free water clearance. Free water clearance, however, never became positive, thus indicating a maintained but diminished water reabsorption. The maintenance of water reabsorption throughout the study is supported by the fact that urine osmolality never fell below 430 mOsm/kg (range 430-2500 mOsm/kg). The weekly average of urine osmolality remained surprisingly constant in the face of diminished urine flow (Table 2). Creatinine excretion (P < 0.0001) and clearance (P < 0.01) decreased throughout the study (Fig. 6, middle panel). The general shape of the clearance pattern was similar to that found with exogenous creatinine clearance (Zatzman and South, 1981), but the absolute values were somewhat reduced. Urinary concentration of creatinine increased 4-fold by the end of the study (Table 2) while its excretion rate halved (Fig. 6). The excretion of urea nitrogen (Fig. 6, lower panel) very closely paralleled food consumption (r = 0.95, P < 0.001) with a peak at week four (30 April), a

4/9$ 4/16 4/23 4/30 s/7 5/14 5121 S/28 6/4 6/11 6/1X 6125 712 7;/9 7116 7123 7/30 S/6 8/13 8/20 8127 913

4.64 to.52 4.70f0.44

4.80+0.45

4.81 +O.Sl

4.88 f0.52

4.92 + 0.52

5.OOiO.50

5.09io.47

5.04+0.43

4.95 ? 0.42

4.51 kO.35 4.71 +0.40

‘Food or water intake tUrine flow. fDate (month/day).

2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21

I

Week

Body wt (kg)

94* 11 109113 118+1X l24i 18 95* 13 X9? I8 79* 15 74i 18 45k I6 so+ I5 40+ I4 37 f IO 32 +_ IO 25i 11 19+6 l3_+3 12+3 1523 II +2 IOk2 14 * 5

(g/day)

Food in.*

166i I8 174 2 20 169 + 27 161 f 27 99521 126i30 105 i 29 75i21 46 _+22 59 + 29 48 + 26 38t II 31+_9 IX & I4 15*5 7~2 11 _t2 5+1 fI+2 7+2 1055

Water in.*

t/t

109.26 f 6.35 106.55 k 13.30 105.52 f 18.71 110.07 * 18.16 76.07 & 16.26 90.38 i 26.27 84.08 + 23.30 66.09 f 17.55 45.46 f 17.96 42.12 i 13.62 34.38 i I I .58 32.30 k 9.67 33.50 * 8.04 23.48 f 4.4X 19.36k4.10 15.42 5 3.68 10.68 * 2.00 16.00 i 2.01 12.62 + 1.59 11.54+ I.51 15.15* 1.94

bWW

120.2 * 5.99 123.2 f 10.71 126.7 i 12.89 138.659.13 138.2_+9.15 145.2 k 19.81 135.9 f 11.24 140.5 f 8.61 158.78 i 12.95 178.2 i 12.9 19X.08 & 30.68 163.5 f 24.26 144.0 k 14.16 159.5 k 26.71 130.68 i 18.28 105.7 F 16.79 110.9 k 9.32 137.2 f 24.56 9l.Of 11.58 121.6i 13.02 124.2 i 15.46

(m&/l)

IJ N>

Table 2. Body weight, average

13.63 iO.93 16.16&0.X1 17.83 k 1.53 19.88f 1.22 25.65 & 1.02 21.35i 1.74 20.72 k 1.94 23.07+ 1.44 26.12 f 1.44 23.03 f 1.70 24.68 i I.83 20.67 _+ 1.79 22.15k2.77 20.13 +2.43 18.23 k 2.09 19.40F2.44 21.93 5 2.54 16.23 k 2.87 16.85 f 2.41 15.40f2.03 18.05i 1.66

196.1 f 12.00 200.3* 14.34 196.8k20.24 217.9* 13.78 214.4 k 9.95 220.4k24.13 241.3 523.89 256.9i 17.01 259.6 i 24.06 293.9k27.16 293.8 k 30.49 297.X f 38.96 251.4i29.40 262.5-27.22 270.4 + 34.85 218.3f 16.68 253.3 525.68 248.0 + 27.50 229.4 i 13.66 212.7k22.34 267.2k30.07

L’,I

Owdml)_

(mEq/U

UK

food and water consumption

0.76 iO.07 0.79kO.05 0.75_+0.09 0.76f0.10 I.19 f 0.16 1.11 F0.20 1.14iO.20 1.34+0.20 1.97 + 0.30 1.76 kO.33 2.06 i 0.40 1.95 iO.43 248f0.46 2.65 kO.58 2.52 f 0.29 3.64kO.55 4.31 +0.63 2.98 kO.29 3.38 k 0.37 3.47f0.32 3.19iO.35


u ci

and average

127X.32+ 55.1X1362.74+80.72 1424.36+_ 126.59 1575.67i77.63 1637.85 i 75.69 1579.49* 127.92 1585.24f 135.16 1781.88k94.58 1814.69 + 98.68 1834.1 F 126.94 1827.7 + 129.87 1751.15? 146.12 1612.16f 161.64 1607.14f 145.15 1639.95 _+ 151 .I2 1508.55* 118.13 1710.92 + 154.95 1386.26 +_ 168.09 1410.31 F 124.45 1411.68 k 162.11 1449.96f 117.14

(mO&/kg)

UOP

urine production

1.18

I48 f 1.05

l52k

149iO.70

14X* 1.30

149& 1.17

148~0.60

(mh/l)

Pt4*

of 6 marmots PK

P,

0.34+0.02

0.28;0.02

(mg!ml)

0.19iO.01

4.31 k 0.13 0.23 +0.02

4.78iO.18

0.25+_0.03

1.13 0.32kO.02

5.02&0.27

6.5i

4.95kO.35

4.28iO.07

@WI)

PO

0.012 &O.OOl

0.011 f0.0008

0.009iO.0004

0.009f0.006

0.008~0.0006

O.OOX+O.O~l

(m&/ml)

P OF

I.31

1.49

317 +_ 1.36

314i

317S2.25

316_+ 1.82

317+

30X_+ 1.28

(mOsm;kg)

P

ii

3 E

E

0,

6 ‘cf t. :

z

6

z

6 a --S w

?1 8 a

MARVIN L. ZATZMAN el al.

740

FOOD CONSUMED lqm kg-’ day-‘)

t 15 -

t?

T

WATER/FOOD LmVgml 10 -

6.0 h LmEq/L)

IJJddj-/ T .-. 1,.

kg)*s-• Ti/ 405.0 =-

BODY

WEIGHT

T

6 o

1~

I R

Fig. 3. Food consumption (upper panel); ratio of water to food consumption (middle panel) and mean body weight of 6 M.jauiventris (3 males, 3 females). Since no sex differences were noted, figures contain overall means. Vertical bars are SEM.

decrease to week sixteen (23 July) and then a plateau for the remaining time of the study. Urea clearance, however continued to diminish throughout the study (Fig. 6, lower panel), due principally to the reduction in urine flow since urine urea nitrogen concentrations remained relatively stable (Table 2). * DISCUSSION

Seasonal alteration of body weights of hibernants (Pengelly and Fischer, 1963: Davis, 1976; Fall, 1971; Armitage et al., 1976; Young and Sims, 1979; Hock, 1969) including M. monax (Davis, 1976; Fall, 1971; Armitage et al., 1976; Snyder et a/., 1961) and M. flauiuentris (Armitage et al., 1976; Hock, 1969) have been documented. In general, male marmots are larger than females (Armitage et al., 1976) in agreement with our results (Fig. 1). There are, however, discrepancies in the literature concerning the time at

Fig. 4. Plasma levels of: urea nitrogen (upper panel), creatinine (Panel 2). sodium (Panel 3), potassium (Panel 4) and osmolality (bottom panel). Vertical bars are SEM.

which peak weight is achieved. Studies in the field (Davis, 1976; Armitage et a/., 1976; Snyder et al., 1961) indicate that both M. monax and M.,flacicentris continue to increase body weight until hibernation ensues. Captive animals, however, demonstrate peak weight sometime before hibernation begins and actually lose weight prior to the hibernation period (Davis, 1976; Young and Sims, 1979). This pattern was reproduced by our studies (Fig. 1 and Fig. 3). The larger group of animals (2 years old) reached peak weight late in June or early in July, while the older animals reached peak weight about a month earlier. Thus, under conditions of constant photoperiod our animals demonstrated an I1 month cycle of weight gain as investigators have found with other hibernants (Pengelley and Fisher, 1963; Davis, 1976). The literature contains no data on food and water consumption of M. ,jfat;iuentris. There is some variability in the literature concerning feeding patterns of woodchucks. One study indicates a gradual increase in food intake until May to July and then a gradual decrease in food consumption until hibernation starts (Fall, 1971). In another by Davis (1976) food consumption reached its maximum level in August under conditions of decreasing day length. A group of

Food and water consumption of the marmot

URINE

EiCkETlON

(ml k.q“ day-‘)

Nq INTAKE EX%ETlON hEq

kg-’ day-‘)

K INTAKE OR EXCRETION (mEq kg4 dcy

Fig. 5. Water intake and urine excretion, *P < 0.01, **P < 0.05 between intake and excretion (upper panel); sodium intake and excretion (middle panel); potassium intake and excretion, *P -c 0.02, between intake and excretion (lower panel); l ---@ intake, x ---X excretion. Vertical bars are SEM. animals under constant conditions of L:D of 16: 8 continued to increase food consumption until mid September. In a recent study, in which light approximated seasonal cycles, Young and Sims (1979) found that maximal food consumption occurred in mid May followed by a gradual decline to September when food consumption ceased. This latter pattern in the woodchuck is supported by studies that indicate maximal metabolic rates during May (Bailey, 1965). Maximal food consumption of M. ,flaviventris occurs earlier than in monax (Figs 2 and 3) and may have been influenced by the shorter natural feeding season of these animals (Armitage et al., 1976). An unusual finding in our study and that of Young and Sims (1979) is the continued increase of body weight for a month or more beyond the peak food consumption. We found, as did others working with M. monax, that food consumption of males was slightly higher but not significantly different from that of females

741

either on the basis of intake per day or intake per kg of body weight per day (Figs 2 and 3). No studies have been reported of water consumption in hibernants under laboratory conditions. Water consumption by M. ji’aviventris generally follows food consumption (Figs 2 and 5), but decreases more than food consumption between April and August. In the study with the larger group of animals the water: food consumption ratio decreased more in the female than male population. Decreased water consumption was associated with a decrease in urine flow and osmotic clearance (Fig. 6). Although free water clearance remained negative, water reabsorption diminished by a factor of seven and may have contributed to the gradual rise in plasma osmotic pressure since respiratory (Benedict and Lee, 1938) and fecal water loss may have been significant. In addition to the relative decrease in total body water, the plasma osmotic pressure could have been increased due to an increase in plasma albumin which was demonstrated in the 13-lined ground squirrel throughout the late spring and into the winter months (Galster and Morrison, 1966). It appears that one of the preparative features for hibernation is a relative dehydration of the animal which is supported by the work of Jameson and Mead (1964) who found a 13% decrease in the total body water of C. lateralis prior to hibernation. Excess intake of water in the initial part of the study may be necessary for rehydration of the marmot following hibernation. In addition, since some growth occurs after emergence in the spring, the positive K balance may be associated with the increased requirement for incorporation into new cellular elements. There were significant alterations in the relation between K intake and excretion. Potassium loading was apparent at the time of rehydration and a cumulative loss of K prior to hibernation. Due to the relative stability of plasma K (PK) in the face of larger alterations of intake or excretion, P, did not show significant changes. Sodium balance was better maintained than that of either water or potassium, with no apparent excesses in either intake or excretion. The obvious reciprocal relation between P,, and P, demonstrated in our previous study (Zatzman and South, 1981) is not as clear. However, the minimum P,, coincides with the peak of P, at about the same time that these changes occurred in the report mentioned. We hoped to clarify the process which produced those changes in plasma electrolytes. They cannot be accounted for by alterations in the relation between intake and output. In addition, urine concentrations of Na and K (Table 2) do not help in the determination of the factors responsible for the alteration of plasma K and Na noted previously. Urinary Na and K concentrations tended to be lowest at the initiation of the study when urine flow was greatest and at the end when urine flow was lowest. Unfortunately, no data are as yet available of seasonal plasma aldosterone concentrations which may play an important role in governing the P,, and P, levels. The decrease noted in plasma urea nitrogen levels are essentially continuous with those we observed during hibernation of this suecies (Kaster et al.. 1978): A high correlation between fdod intake and the excretion of urea nitrogen (r = 0.95) argues

MARVIN

142

L.

ZATZMAN

ef

ul.

T

T .

\ cos.

(ml kg-’

-r-_--i

/’ T,/’

60

day-‘)

/

50

-30

P

CFW

T,“’ i //#

-40 (ml kg-’ day-l)

\

‘I;’

Cr (mq

\

ill

cc,

EXCRETION kg-’

-so

day-‘1

( L kg-’ day-‘)

UREA EXCRETION (mg kg-’

CU

Fig. 6. Osmotic clearance, excretion,

e--e;

kg-’ day-‘)

day”)

@--a;

and creatinine urea clearance,

and free water clearance, x ~-- x (upper panel); credtinine clearance, x --- x (middle panel); urea excretion, 0-a; and x ~-- x (lower panel). Vertical bars are SEM.

against urea recycling which has been implicated in rodent hibernant metabolic activity (Riedesel and Steffen, 1980). Rather, urea clearance and excretion rate appear to be much more influenced by food intake than alteration in renal function. This is similar to the effect seen in humans with varying degrees of renal insufficiency on differing protein diets (Dossetor, 1966; Kopple and Coburn, 1974). Plasma creatinine concentration, on the other hand, is sensitive to alterations in renal function during the time that muscle mass is relatively constant (Dossetor, 1966). Since glomerular filtration rate diminishes throughout the entire study period (Zatzman and South, 1981 and see Fig. 6, middle panel) increasing plasma creatinine levels are not surprising. In summary, we have examined the food and water consumption, urine production, urine and plasma constituents of some electrolytes, creatinine and urea. Shortly after arousing from hibernation water and food consumption increase with a greater intake of water than food. During this period water and potas-

sium intake exceeded urinary excretion. Plasma osmotic pressure was low, as was plasma creatinine. Urea, creatinine and osmotic clearances were high; free water clearance was very low. During this period the marmot appeared to be rehydrating, protein intake and thus urea nitrogen excretion and plasma urea nitrogen were high and glomerular filtration rate was at its maximum (Zatzman and South, 1981). As the season progressed from late winter to late summer, food and water intake diminished. Water intake fell faster than food consumption, free water clearance became less negative and urine production exceeded water intake; total body water probably decreased (Jameson and Mead, 1964). Associated with the decreased food consumption was a fall in urea nitrogen excretion, clearance and plasma level. Glomerular filtration rate reached its nadir by the end of the study in September with a concomitant decrease in creatinine excretion and clearance and an increase in plasma creatinine concentration and plasma osmotic pressure.

Food

and water

consun nption

Alteration of plasma electrolytes cannot be as clearly delineated because of unknown hormonal changes that may occur during this cycle of events.

Acknowledgements-The authors wish to thank MS Renee Dowd and Mr Robert Elder for their assistance in the preparation of the manuscript. This work was supported by grant PCM 7912322 from the National Science Foundation, HL30491 from the National Institutes of Health, and a grant from the University of Missouri Health Sciences Center Research Council.

REFERENCES

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of the marmot

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