Restoration of contractions of isolated heart arrested in result of progressing hypothermia with electrical stimuli and no warming up of the heart

In the rat isolated heart, the effect of cooling with the velocity 0.2 degrees C/min and its stimulation with rectangle electrical pulses (19 Hz, 100 ms, 1-5 V amplitude) on the heart mechanical activity in mcWatt/g was studied as the product of heart shortening on contraction strength and heart rate. The heart shortening was measured by the Langendorf method. Heart contractions activated the recording system with the aid of a hook at the apex. The Ringer-Lokk solution served as perfusate pumped with peristaltic pump. After cold arrest of automatic contractions (on the average at 9.3 +/- 0.7 degrees C), the heart continued to respond with contractions to electrical pulses of 5 V amplitude, the power of the heart contractions at 10 degrees C being on the average 35 % of the initial power at 20 degrees C. Excitability and contractility of the heart terminate at 5.3 +/- 0.4 degrees C.     

Effect of perfusate ionized calcium on mechanical activity of the rat heart in deep hypothermia

Effects of different concentrations of ionized calcium ([Ca2+]) in perfusion fluid and of the heart temperature on the systolic pressure (Psyst), heart rate (Vc) and their product as general index of the heart mechanical activity (HMA) of the rat isovolumetrically contracting isolated heart preparations were examined in condition of retrograde perfusion at constant volume with a modified Krebs-Heseleit buffer. An increase of [Ca2+] from 0.62 to 2.5 mM (mmol/l) in the normothermia (38 degrees C) augments Psyst and HMA. Heart rate does not change. An increase of [Ca2+] from 0.62 to 4.5 mM at 20 degrees C augments Vc and HMA. An increase [Ca2+] at 15-11 degrees C decreases psyst and HMA. [Ca2+] does not affect the temperature of the heart arrest.     

Development of deep hypothermia in rats with limited motor activity

Changes of the main organism functions (breathing frequency, heart rate and shivering) were investigated under hypothermia in two groups of rats. Animals of the first group were fixed rigidly on the special platform with fixing of head and limbs, and those of the second one--the rats, were placed in a punched cylindrical chamber, inside which they could move freely forward and back. In 2.5-3.0 hours after anaesthesia the rats were placed in a refrigerator (-5 degrees C) until they stop breathing. Cessation of breathing of the first group rats occurred in 1.7 +/- 0.3 hours from the beginning of cooling at body temperature 17.3 +/- 0.6 degrees C and the brain temperature 15.7 +/- 0.5 degrees C. In the second group, a prolonged activation of the frequency of breathing, heart rate and intensity of electrical activity of muscles during 2.5-3.0 hours, was observed. Only in 4.5-5.0 hours, the breathing stopped at rectal temperature 12.3 +/- 1.1 degrees C and the brain temperature 12.9 +/- 0.9 degrees C. In these animals, the time of survival in the cold environment increased considerably and the temperature thresholds of the termination of breathing were lowered. Thus, the activation in the thermo-regulative muscle tone and in shivering muscles provides the most effective resistance against cooling of rats, reducing a surface of heat, dissipation and keeping the temperature of internal areas of body.     

Study of contractile activity of the crayfish heart with the aid of a new non-invasive technique

The dynamics of the numbers of the decapod crustacean populations depends essentially on the anthropogenous load on inner reservoirs. This process affects the most substantially the crayfish speciesAstacus astacus L. that is aboriginal for the North-West of Russia. The sensitivity of these crayfish to changes of the water quality in the ecosystems has been noted by many authors [1, 11, 15]. For an ecophysiological monitoring of the reservoirs as well as for a nature-protective and aquacultural activity necessary, is necessary to have methods and means of determination of quantitative parameters of responses of animal life-providing systems, for example, the cardiovascular system. In the present work, a new non-invasive technique is proposed for recording parameters of the crayfish heart activity. The method is based on measurement of the laser emission of the near-infrared diapason, which is scattered in the reverse direction. This paper describes the instrumental part of the complex and exposes some preliminary data obtained with the aid of the used method of recording the crayfish heart activity. This method is shown to permit not only recording the crayfish heart rate under conditions of free behavior, without any harm to the animals, but also tracing changes of the shape and amplitude parameters of the response, which characterize the animal state.     

In vivo brown fat response to hypothermia and norepinephrine in the ovine fetus

The goal of this study was to assess the response of fetal brown fat in vivo to hypothermia and norepinephrine infusion. In 10 unanaesthetized, chronically-prepared fetal sheep (133 +/- 2 days of gestation) cold water was passed through tubing encircling the fetus in utero and plasma glycerol concentration was measured as an indicator of brown fat activity. Following cooling for 60 min, amniotic fluid temperature fell 7.79 degrees C to 31.66 +/- 1.73 degrees C (n = 8, P less than 0.001) and maternal temperature fell 0.63 degree C to 38.63 +/- 0.08 degrees C (n = 9, P less than 0.001). Eight of the fetuses were subjected to a second experiment in which norepinephrine was infused intravenously for 15 min. During infusion fetal arterial temperature fell 0.38 degrees C to 39.05 +/- 0.25 degrees C (n = 7, P less than 0.05). Amniotic fluid temperature (n = 7, NS) and maternal arterial temperature (n = 7, NS) remained constant. Glycerol concentration during the infusion increased from 0.73 to 1.27 mg/dl, a 74% increase over control (n = 8, P less than 0.001). Although clearly detectable, these glycerol responses to hypothermia and norepinephrine stimulation are one-third or less of those achieved after birth, indicating that thermogenesis remains quiescent in the near-term fetal sheep, despite powerful stimuli for activation.     

The specific activity of retained and released norepinephrine in dog saphenous vein prelabeled with radiolabeled norepinephrine

The specific activities of released and retained norepinephrine (NE) in the isolated superfused dog saphenous vein preparation, prelabeled with [³H]NE, have been determined. Norepinephrine was isolated from extracts of vein superfusate and its concentrations were measured by high pressure liquid chromatography with electrochemical detection. The specific activity of NE in superfusate collected under basal conditions was lower than that of NE in veins after electrical stimulation or in parallel unstimulated veins. However, NE released during electrical stimulation had a specific activity 1.5 to 3 times higher than the NE in the veins. Thus, NE taken up by neuronal uptake in the prelabeling procedure enters a pool from which is preferentially released by electric stimulation. In addition, NE is released from different compartments during basal conditions and during electric stimulation.