[Analysis of changes in heart rate and temperature of the ground squirrel Citellus undulatus in various physiological states]. / Analiz izmenenii chastoty serdtsebienii i temperatury susslika Citellus undulatus v razlichnykh fiziologicheskikh sostoianiiakh.

Heart rate (HR) of ground squirrel C. undulatus was studied in dependence of season, level of activity, physiological state and air temperature (T). In summer HR varies from 110-130 beat/min in sleep up to 420 beat/min at flight from danger. During winter hibernation HP was minimal (3-5 beat/min) at T 1-4 degrees C, the increase in T induced the growth of HP in correspondence to the Arrenius van't Hoff law. The temperature of the body in hibernation exceeded T on 1.5-3 degrees C. The time of getting off the hibernation increased with the decrease in T (6-7 hours at -1 degree C and 2.5-3 hours at +18 degrees C). At phase of increased thermogenesis during arousal heart temperature exceeded rectal one on 10-12 degrees C and heart rate run up to 360-420 beat/min i.e. 2-3 time higher than in active state. The decrease in T stimulated the increase in HP up to 3.8 in winter and 5.3 beat/min/degree C in summer. The highest values of Q10 for HP were revealed at the beginning of hibernation (15-20) and at the beginning of arousal (6-7), in other periods Q10 was similar to the normal biological values (2-2.5). Thus, at the beginning of transitional periods changes of HP were determined mainly by endogenic mechanisms that inhibited myocardium at the beginning of hibernation and activated in arousal. Some mechanisms of coordination between activities of heart and other systems of organism are considered. The features of hit exchange providing the hibernation in wide range of T are discussed.

[Biologically active substances in the tissues of hibernating animals]. / K voprosu o biologicheski aktivnykh veshchestvakh v tkaniakh zimospiashchikh.

It was supposed that the transitional period from euthermia to hibernation rather than the period of winter hibernation is optimal for the secretion of biologically active substances in rodent tissues. This hypothesis was tested in experiment. The maximal O2 consumption suppression was noted in mice after I. P. Injection of blood plasma from suslik Citellus undulatus at the beginning of its entering into hibernation. Low-molecular peptide fraction appearance in C. undulatus blood before hibernation was revealed by electrophoresis in gel and autoradiography. But its traces disappear by the end of bout. The endogenic inhibitory factor's maximal influence in early bout was shown by experiments with TRH and neoklotorphin (NKT). I.P. injections of these substances to C. undulatus were ineffective in the beginning of entering into hibernation, but clearly caused awakening after hibernation, has started. KT, being a fragment of NKT, inhibited suslik's heart rate when the awakening was provoked in the middle, but not in the end of bout. Possible transformation of biologically active substances in winter-hibernating rodents tissues is discussed. The KT "inhibitor" and NKT "stimulator" are supposed to pertain to the special type of regulatory peptides, that manage the hibernation cycle. One of the ways of inactivation of endogenic "hibernation trigger" is its removal from the organism with urine. The urine, taken from suslik immediately after hibernation proved to produce the greatest hypothermic effect on mice, I.P. injected with it.

[The dependence of the rate of heart contractions in the long-tailed Yakutsk suslik Citellus undulatus on environmental temperature]. / Zavisimost' chastoty serdechnykh sokrashchenii iakutskogo dlinnokhvostogo suslika Citellus undulatus ot temperatury vneshnei sredy.

Decrease of ambient temperature (Ta) leads to the increase of the heart rate (HR) in active ground squirrels C. undulatus by 5.3/min/1 degree C in summer and by 3.8/min/1 degree C in winter. In a hibernation state, the dependence of the HR on Ta was in a good agreement with equation HT = 2.53.exp.(0.1.Ta). On entering into hibernation and on arousal, the HR change outruns the corresponding body temperature (Tb) change by 1.5-2 hours. A maximum HR level (up to 400/min and more) was registered on arousal when Tb reached 17-20 degrees C. A minimal HR level (4-5/min) was observed during hibernation at Ta 2-5 degrees C. The maximum Ta, at witch C. undulatus was hibernating, reached 23-24 degrees C, the HR being 23-25/min.

[The hypometabolic effect of the blood plasma from a hibernating suslik Citellus undulatus. Neokyotorphin activates cardiac and respiratory activities in the suslik during arousal from hibernation]. / Gipometabolicheskii éffekt plazmy krovi giberniruiushchego suslika Citellus undulatus. Neokiotorfin aktiviruet deiatel'nost' serdtsa i dykhaniia suslika pri vykhode iz spiachki.

The effect of intraabdominal injection of the blood serum from ground squirrels Citellus undulatus obtained at various stages of the baut has been studied on the level of oxygen consumption in albino mice. The strongest hypometabolic effect exhibited the blood plasma from animals at the beginning of the baut. The onset of baut was used in further experiments on C. undulatus for investigation of activating effects of neokiotorphin (Thr-Ser-Lys-Tyr-Arg) which was earlier found in the brain of the ground squirrel. It was shown that intraabdominal injection of this peptide to hibernating animals facilitates their arousal stimulating both the cardiac activity and respiration. The strongest effect was noted with neokiotorphin of [D-Ser] 2-modification which is more stable to proteolysis.

[The effect of serotonin on the heart contraction frequency in the suslik Citellus undulatus depends on the environmental temperature]. / Vliianie serotonina na chastotu serdechnykh sokrashchenii suslika Citellus undulatus zavisit ot temperatury sredy.

In experiments on active ground squirrels, it has been shown that the effect of intraperitoneal injection of serotonin on the heart rate depends on the dose and the environmental temperature. At relatively low doses and high environmental temperature, serotonin increases the heart rate and body temperature; on the contrary, with the increase in the dosage and the decrease in the environmental temperature the heart rate and body temperature of animals decrease. It is suggested that this relationship serves as one of the factors which enhance the transition of animals from one level of activity to another during the beginning and the end of hibernation.