G. Edgar Folk

Circadian metabolic patterns in cultured hamster adrenal glands

1. 1. Circadian patterns in respiration and steroid secretion have been observed for hamster (Mesocricetus auratus) glands which have been maintained in culture. 2. 2. Reversal of the lighting regimen for young animals reversed the phase profile of adrenal metabolic patterns. 3. 3. Cultured phase-reversed glands did not sustain the reversed metabolic pattern but re-established patterns intermediate between reversed and control times. 4. 4. The biorhythmic property of relative temperature independence was displayed by cultured glands. 5. 5. The secretory pattern profiles resembled respiratory patterns, but did not have the same phase relationships. 6. 6. The relationship between stimulated steroid secretion and oxygen consumption by the cultured glands must be indirect.

Rhythmic changes in rate of the mammalian heart and heart cells during prolonged isolation

Abstract 1. 1. Isolated, perfused rat hearts and heart cell networks in tissue culture are found to display rhytmic changes in rate of contraction under constant conditions. 2. 2. Periodogram analysis reveals an increase in contraction rate every 8–13 hr in isolated hearts and every 12 hr in heart cell networks during the experiment. 3. 3. The isolated hearts and cell networks have similar patterns of activity over the solar day—similar circadian rhythms. 4. 4. The isolated hearts display a distinct day-night setting of heart rate with elevated rates each evening and lower rates during the day. 5. 5. Antibiotics were found to cause a significant lowering of the heart rate and a decrease in the amplitude of rhythmic oscillations. 6. 6. It is hypothesized that the circadian rhythms of resting heart rate are controlled by a “clock” located within the heart cell.

The role of adrenoceptors in norepinephrine-stimulated VO2 in muscle

The purpose of this study was to characterize the norepinephrine (NE)-evoked calorigenic response of an isolated perfused rat muscle preparation into alpha-and/or beta-adrenergic components. Epinephrine was as effective as NE in evoking the increase in oxygen consumption. The alpha-agonist, phenylephrine, was also as effective as NE in eliciting an increase in oxygen consumption by the muscle. Isoproterenol (beta-agonist) had no effect on the VO2 of the preparation. Phentolamine, an alpha-blocker, completely blocked the NE-stimulated VO2. Propranolol (beta-antagonist) could also completely block the NE induced VO2 but this drug was found to be less potent. It was concluded that the NE-induced calorigenic response of muscle cannot be classified either strictly as an alpha-or beta-response, but unlike brown adipose tissue, the alpha-response seems to predominate in skeletal muscle. Also, it appears as though different mechanisms of action may be involved in the NE-stimulated VO2 in skeletal muscle and brown fat.

Induction of summer hibernation in the 13-lined ground squirrel shown by comparative serum transfusions from Arctic mammals

Abstract A “trigger” substance was again indicated to be present in sera of hibernating animals. Sera from the hibernating 13-lined ground squirrel, hibernating woodchuck, hibernating Arctic ground squirrel, and hibernating Arctic marmot were all capable of inducing the 13-lined ground squirrel to hibernate in the summer, a season when that species would normally be active. The hibernation trigger is thus not species specific. It is effective whether drawn from these two Arctic species of hibernators or drawn from these two species of hibernators from the midwestern states. The normothermic Arctic marmot appears to have an “anti-trigger” substance in its serum in the summer, which impedes fall hibernation in the transfused 13-lined ground squirrel. This is similar to the anti-trigger observed in the summer serum of active 13-lined ground squirrels and active woodchucks. With respect to hypothermia, it was induced in Artic marmots and in Arctic foxes at Point Barrow, Alaska, in summer. Though in such cases body temperatures fell significantly (as in hibernation), no trigger was recovered from their hypothermic sera that could be shown to be capable of inducing summer hibernation in the ground squirrel. Neither was anti-trigger found in the serum of hypothermic experimentals. These latter experiments thus suggest that the release of trigger into the blood during hibernation is dependent on a mechanism more complex than simply lowering body temperature.

Humoral induction of mammalian hibernation

Abstract 1. 1. The terminology and physiology of hibernation are briefly reviewed. 2. 2. Entrance into hibernation and possible blood-borne “trigger” substances are discussed. 3. 3. Recent studies on “antabalone” and “hibernation trigger” are reviewed. 4. 4. The role of naturally occurring substances capable of inducing hypothermia is discussed and related to the study of hibernation.

The critical thermal minimum of small rodents in hypothermia

Abstract The resistance times of eight rodent species were compared (including two species of lemmings) at an ambient temperature of −40 °C. Of these, the collared lemming demonstrated a striking ability to withstand extremely cold environmental temperatures. The ecological and behavioral differences between the collared and brown lemming relative to the development of low temperature tolerance are discussed. Cold acclimation (induced in four of the species) increased the resistance time. The greatest magnitude of increase was found in the collared lemming (51 times). Little difference was found among liver temperatures of the eight species at the time of loss of coordination. The lower body temperature at which coordination is lost is redefined here for mammals as the critical thermal minimum.

Simultaneous measurements of heart rate and oxygen consumption in black-tailed prairie dogs (Cynomys ludovicianus).

1. 1. Studies were conducted to explore the potential for using telemetry of heart rates as an index of rates of energy expenditures in free-ranging black-tailed prairie dogs (Cynomys ludovicianus). 2. 2. For periods of 1 hr with activities varying spontaneously or by exciting the animal, heart rate and oxygen consumption were highly correlated with coefficients averaging >0.9. 3. 3. The relationships appeared stable for one to a few days but differed over weeks or longer. 4. 4. Relative comparisions of costs for behaviors over circadian cycles and a few days would seem feasible by the heart rate index method in prairie dogs.

OBSERVATIONS ON THE DAILY RHYTHMS OF BODY TEMPERATURE-LABILE MAMMALS*

Many biologists interested in circadian rhythms have studied the effects of varying body temperature upon these rhythms in higher animals. Two earlier symposia include accounts of circadian rhythms in higher animals with periods that are essentially unchanged as body temperatures are 10wered.l-~ After describing one of the earliest of these experiments, which demonstrated that fiddler crabs had a circadian rhythm of color change a t different ambient temperatures, Brown4 suggested that the accurate measurement of time under these circumstances represents a biological process independent of temperature. This means that the internal synchronizers of circadian rhythms in some animals are biological mechanisms that function independently of changes in metabolic state of the whole animal; this description applies equally well to “constituent biological oscillators which compensate for temperature,” or cells or sense organs that are capable of responding effectively a t a cold temperature “to pervasive geophysical factors.” During the last 5 years it has been shown not only that invertebrates have temperature-independent synchronizers but that heterothermic mammals also can measure time when they have a body temperature of about 5” C. to 10” C. (deer mouse and hamster,’ ground squirrel,8 and bat3i9). Heterothermic mammais have a labile body temperature (not fixed a t one point).’O There now remain two pathways for the investigator: (1) to seek the mechanism of temperature compensation of the “clock” in mammals or lower animals or (2) to describe the importance of temperature independence of the “clock” in mammals. The proof that it exists in this group has been obtained under distinctly artifical and frequently unbiological circumstances for the experimental animals. In our laboratory, we attempt to divide our experiments on biological rhythms between the study of mechanism and description. In this paper, some experiments to elucidate the mechanism of temperature compensation will first be presented (Section I) , including data on a comparison of the response of heart and brain activity during hypothermia of cats and the temperature-labile 13-lined ground squirrel. Secondly, a description will be presented of the activity rhythms of the arctic ground squirrel, Citeltus parryi, when this animal is exposed in outdoor enclosures to the continuous light of the Arctic (Section 11). * The experimental work on the 13-lined ground squirrels and cats was supported in part by the National Science Foundation. The investigations on Alaskan mammals in the Arctic and in the Physiological Laboratories of the University of Iowa were supported by the Arctic Institute of North America uuder contractual arrangements with the Office of Naval Kesearch. Reproduction of this paper in whole or in part is permitted for any purpose of the United States Government.

Effects of photoperiod, cold acclimation and melatonin on the white rat.

Abstract 1. The combined stimuli of short day (9L:15D) and cold exposure (8 ± 2°C) produced a positive response to norepinephrine resulting in nonshivering thermogenesis (metabolic rate 23% above basal metabolic rate), stimulated growth of brown adipose tissue and effectively raised the mean lowest daily rectal temperatures of the white rat over warm-acclimated conditions (21 ± 2°). 2. Exogenous melatonin was effective in depressing the mean daily lowest rectal temperature under warm acclimated conditions and raising the mean daily lowest rectal temperatures of long day rats under cold conditions. It apparently overrode the effect of a long day. 3. The combination of cold acclimation and short day potentiated by melatonin induced an increase ( P > 0.02) in mean pineal weight over long day, melatonin-treated, cold-acclimated rats. 4. Although the short day, warm experiment did not produce “cold acclimation without cold” as shown in other laboratories, the short day, cold experiment did produce indices of cold acclimation not seen in the long day, cold experiment. This would be predicted from adaptation observed in mammals in the free environment.

The Dental Tissues of Wild and Laboratory-raised Hibernating and Non-hibernating 13-lined Ground Squirrels

The 13-lined ground squirrel, Cittelus tridecemlineatus, is a valuable animal for laboratory investigations because it hibernates at low room temperatures. Although today it is a common laboratory animal, few reports are available pertaining to its dental tissues. Schourl described the changes seen in the incisor of the 13-lined ground squirrel following gonadectomy, and Mayer and Bernick2, studied the periodontal tissues and caries incidence of the Arctic ground squirrel. The 13-lined ground squirrel has a dental formula of incisors 2/2, premolars 4/2, and molars 6/6. The anatomy of the animals posterior teeth is similar to the corresponding posterior teeth of human beings. This report is one of several originating in the laboratories of G. E. Folk, Jr., and concerned with the effects of hibernation on metabolic and physiologic activities of the ground squirrel.4