Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters (Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 degrees C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures (PT(a)) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT(a) was monitored. After NA injections there was a rapid drop in PT(a), decreasing to approximately 15 degrees C within 10-20 min after each NA injection. Following 4 weeks of acclimation to 10 degrees C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT(a) of approximately 10 degrees C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT(a) after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.     

Nicotinamide and heat preconditioning – Effects on hepatic HSP70, carbohydrate and oxidative disturbances in STZ-induced diabetic rats

ObjectiveNicotinamide (NA) is known to have antioxidant potential and partially to protect insulin-secreting cells against diabetogenic agent STZ (streptozotocin). In a combination to heat stress (HS), NA is also known to induce heat-shock proteins (HSPs) production. Heat preconditioning (HP) and HSPs have cytoprotective effects against development of cellular injury caused by application of subsequent stressor. We aimed to determine if pretreatment with NA and HP (as HSP70 –inducers) can affect STZ-induced diabetic disturbances in rats.MethodsNA-pretreatment (250 mg/kg b.w., 7 days) and heat preconditioning (41 ± 1 °C, 45 min) of diabetic rats was performed. The changes in hepatic carbohydrate- and antioxidative-related enzymes and substrates were investigated.ResultsNA-pretreatment, alone or in combination with HS, resulted in significant increase of HSP70 concentration in the liver of control and diabetic rats. Compared to diabetic controls, pretreatment with NA, in combination with HP, resulted in decrease of blood and liver glucose, increase of glycogen and glucose-6-phosphate level, increase of glycogenolytic/glycolytic enzymes, decrease of gluconeogenic enzymes, as well as an increase of glutathione content and glutathione peroxidase, decrease of glutathione reductase and catalase activities.ConclusionsNA is a potent HSP70 coinducer, alone or in a combination with HS in the liver of both control and diabetic rats. Pretreatment with NA, accompanied by HP, has a pronounced corrective effect on STZ-induced diabetes disturbances in the key hepatic carbohydrate- and antioxidative-related parameters. It seems that this corrective effect is based on the increased production of hepatic HSP70.     

Influence of fasting and dopamine on the tissue catecholamines diurnal variations

To define the role of catecholamines (CA) in the metabolic adaptation to fasting we examined the effect of exogenous dopamine(DA) on heat production(HP) and CA content in the interscapular brown adipose tissue(IBAT) and adrenals of control-fed and 2-day fasted rats in the morning(M) and in the evening(E). DA stimulates HP in fed rats in the M by 45% but the thermogenic effect of this CA is markedly higher in the E. However, DA had no thermogenic effect in fasted rats. The tissue CA in fed rats fluctuates diurnally: in the IBAT noradrenaline(NA) was much higher in the E while adrenaline(A) in adrenals was lower. DA in fed rats did not change the adrenal A but reduced NA content both in the adrenals and in the IBAT all over the day. Fasting depleted A from adrenals but increased NA content both in the M and in the E. Unlike the adrenals in the IBAT fasting did not affect NA content. In the adrenal gland of fasted rats DA significantly increased the A content to the equal degree during the day, while this CA had no effect on NA content of the IBAT.     

Chronic Stress Increases Serotonin and Noradrenaline in Rat Brain and Sensitizes Their Responses to a Further Acute Stress

The effects of 1 h/day restraint in plastic tubes for 24 days on the levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan (TP), and noradrenaline (NA) in six regions of rat brain 20 h after the last restraint period were investigated. The levels of 5-HT, 5-HIAA, and NA but not TP increased in several regions. The effects of 1 h of immobilization on both control and chronically restrained rats were also studied. Immobilization per se did not alter brain 5-HT, 5-HIAA, and TP levels, but decreased NA in the pons plus medulla oblongata and hypothalamus. However, immobilization after chronic restraint decreased 5-HT, increased 5-HIAA, and decreased NA in most brain regions in comparison with values for the chronically restrained rats. We suggest that chronic restraint leads to compensatory increases of brain 5-HT and NA synthesis and sensitizes both monoaminergic systems to an additional acute stress. These changes may affect coping with stress demands.     

Effect of retrotestosterone on accessory sex organs & spermatogenesis of rat

Retrotestosterone (17beta-hydroxy 9beta 10alpha androst 4-en 3 one) (RT), testosterone propionate (TP), and a combination of TP and RT were administered to adult male rats in order to study the effects of such treatment on male sex organs and spermatogenesis. Although TP treatment did not produce significant reduction in testis weight, RT and RT+TP did. Seminal vesicle (SV) weight was increased by TP treatment and TP+RT treatment, but it was decreased with the RT treatment. Ventral prostate (VP) weight was increased significantly by TP and TP+RT treatment, whereas RT did not alter VP weight. The The pituitary weight of RT- and RT+TP-treated rats was significantly reduced but that of the TP rats was unaltered. Resting spermatocytes, pachytene spermatocytes, Stage 7 spermatids, and spermatogonia were increased in all treatment groups. In castrated rats, the increase in VP and SV weight was significant in the group treated with TP, but in the RT-treated group, S V and VP weights were significantly reduced. Simultaneous administration of TP and RT in 1:1, 1:4, and 1:8 ratios failed to produce statistically significant increases in SV and VP weight. The group treated with 1:20 ratio of RT:TP produced highly significant incre ases in SV and VP weights. In the spermatodynamic study, results showed that RT is comparatively more potent than TP in stimulating spermatogenesis. RT+TP treatment produced maximum increase in the count of resting and pachytene spermatocytes, whereas spermatogonia and Stage 7 spermatids were more than in the TP-treated group but less than in the RT-treated group. The findings indicate that RT is weakly androgenic and unable to stimulate accessory organs but that it is able to block the effect of endogenous androgen on the target tissue.     

Core temperature is regulated, although at a lower temperature, in rats exposed to hypergravic fields

1. In rats acclimated to 23 degrees C (RT rats) or 5 degrees C (CA rats), core temperature (Tc), tail temperature (Tt) and oxygen consumption (VO2) were measured during exposure to a hypergravic field. 2. Rats were exposed for 5.5 h to a 3 g field while ambient temperature (Ta) was varied. For the first 2 h, Ta was 25 degrees C; then Ta was raised to 34 degrees C for 1.5 h. During this period of warm exposure, Tc increased 4 degrees C in both RT and CA rats. Finally, Ta was returned to 25 degrees C for 2 h, and Tc decreased toward the levels measured prior to warm exposure. 3. In a second experiment at 3 g, RT and CA rats were exposed to cold (12 degrees C) after two hours at 25 degrees C. During the one hour cold exposure, Tc fell 1.5 degrees C in RT and 0.5 degree C in CA rats. After cold exposure, when ambient temperature was again 25 degrees C, Tc of RT and CA rats returned toward the levels measured prior to the thermal disturbance. 4. Rats appear to regulate their temperature, albeit at a lower level, in a 3 g field.     

Changes in body temperature of rats acclimated to heat with different acclimation schedules

Male Wistar rats, initially maintained at an ambient temperature (Ta) of 23.8 degrees C, were subjected to one of seven different heat acclimation schedules under a 12:12-h light-dark cycle (lights on at 0600 h). Two groups of rats were exposed to Ta of 32.4 degrees C all day for 5 (HC5) or 10 (HC10) days. The other four groups were exposed to Ta of 32.8 degrees C for 5 h/day during the last half of the dark phase for 5 (NI5) or 10 (NI10) consecutive days or during the last half of the light phase for 5 (DI5) or 10 (DI10) consecutive days. Control rats (C) were kept at 23.8 degrees C throughout the experiment. Hypothalamic temperature (Thy) was measured every 5 min with a chronically implanted thermocouple from 1 day before the beginning to 2 days after the end of the heat acclimation periods. During the heat acclimation periods, daily mean Thy rose significantly in HC5 and HC10 rats but decreased significantly in NI5 and NI10 rats. Daily mean Thy did not change in C, DI5, and DI10 rats. Thy in HC10 rats sharply decreased at the end of the heat acclimation periods and remained at low levels for approximately 3 h. On the 2nd postacclimation day, however, mean Thy returned and remained at a significantly higher level. In NI10 rats, the mean Thy in the postacclimation period was significantly lower than the preacclimation values. No such changes in mean Thy were observed in DI10 rats. Five-days of heat exposure had little effect on the postacclimation Thy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of survival time of rats in severe heat.

The response pattern of the rectal temperature of unanesthetized rats exposed to an acute heat in a room of 42.5 degrees C, rh 40% was analyzed in relation to survival time (S), equilibrium rectal temperature (Te), rise in Te from the initial temperature (Delta Te), and the slope of the changes in rectal temperature during the equilibrium period (Gt). A very wide fluctuation of the survival time (from 46.8 to 250.0 min) was observed between individual rats. For prediction of the survival time, following formula was obtained: log(S) = K1 - K2 times log (Te) - K3 times log (Delta Te) + k4 times 10- minus Gt. K1-4 are constants which differ according to sex. The predicted survival time showed highly constant results in individual rats when measured by repeated exposures. The predicted time coincided well with the survival time actually measured, the difference between the two (measured minus predicted) being 2.2 plus or minus 21.7 min (mean plus or minus SD) IN 77 RATS. There was also a significant correlation between the survival time predicted for acute heat exposure and the actual survival time of individual rats when they were exposed to a chronic heat by daily elevation of the rearing room temperature by 1.0 degrees C.     

PP and PT Intervals and TP Segment in Human Electrocardiogram under Experimental Acute Normobaric Hypoxia

Seven male volunteers aged 22–27 years took part in the laboratory experiment for the determination of body response to acute normobaric hypoxia where they inhaled an oxygen–nitrogen gas mixture (9% of О₂) for 25 min. At least 100 cardiac cycles at each of six experimental time points have been recorded by using an electrocardiogram (ECG) recording technique in standard lead II. Mean heart rate (±SD) before hypoxia was 64 ± 2 bpm; the duration of the PP interval was 0.94 ± 0.07 s, that of the PT interval was 0.51 ± 0.02 s, and that of the TP segment was 0.41 ± 0.07 s. Five minutes after hypoxia, it has been found that heart rate (HR) increased by 19%; the duration of the PP and PT intervals and TP segment decreased by 16%, 6%, and 30%, respectively. Twenty minutes after hypoxia, all the parameters reached their initial values. Five and fifteen minutes after hypoxia, HR reached 59 ± 3 bpm; PP interval and TP segment increased by 9% and 14%, respectively, compared to the initial values; PT interval was the same as the initial value at the baseline. The correlation coefficient r_p (PP/PT) was 0.10–0.54; r_p (PP/TP) was 0.94–0.99. The intervals PP and TP were found to be identical.     

Use of the comet-FISH assay to demonstrate repair of the TP53 gene region in two human bladder carcinoma cell lines

The alkaline single-cell gel electrophoresis (comet) assay can be combined with fluorescence in situ hybridization (FISH) methodology to investigate the localization of specific gene domains within an individual cell. The position of the fluorescent hybridization spots in the comet head or tail indicates whether the sequence of interest lies within or in the vicinity of a damaged region of DNA. In this study, we used the comet-FISH assay to examine initial DNA damage and subsequent repair in the TP53 gene region of RT4 and RT112 bladder carcinoma cells after 5 Gy gamma irradiation. In addition to standard comet parameter measurements, the number and location of TP53 hybridization spots within each comet was recorded at each repair time. The results indicate that the rate of repair of the TP53 gene region was fastest during the first 15 min after damage in both cell lines. When compared to overall genomic repair, the repair of the TP53 gene region was observed to be significantly faster during the first 15 min and thereafter followed a rate similar to that for the overall genome. The data indicate that the TP53 domain in RT4 and RT112 cells is repaired rapidly after gamma irradiation. Furthermore, this repair may be preferential compared to the repair of overall genomic DNA, which gives a measure of the average DNA repair response of the whole genome. We suggest that the comet-FISH assay has considerable potential in the study of gene-specific repair after DNA damage.     

Changes of impulse activity recorded from the rat vagus nerve during short-lasting total cooling

Gradual cooling of anesthetized rats followed by a drop in rectal temperature (RT) increased the frequency of efferent impulses and decreased the frequency of afferent impulses in the vagus nerves. Preliminary short-lasting (5 h) moderate cooling of the animals in a thermochamber to +5°C (RT did not change), or intensive cooling to −20°C (RT dropped to 32°C) changed the response of efferent nerve fibers to cooling of the body. Under these conditions, a drop in RT to 29°C was followed by a significant increase in efferent discharges in the vagus nerve after additional cooling throughout the experiment, while an initial cooling phase (RT was equal to 35-30°C) was followed by some inhibitory effect. At the same time, the changes in the afferent link were different. As in the control, gradual cooling decreased frequency of afferent impulses, although the intensity of the effects was different. The involvement of the vagus nerve system in the maintenance of temperature homeostasis during body cooling has been discussed.     

Characterization of the effects produced by neurokinins and three agonists selective for neurokinin receptor subtypes in a spinal nociceptive reflex of the rat

In the awake restrained rat the intrathecal (i.th.) administration of 6.5 pmol-40 nmol of substance P (SP), neurokinin A (NKA) or one of two selective NK-1 receptor agonists [Pro9, Met(O2)11]SP, denoted ana1 and [beta-Ala4, Sar9, Met(O2)11]SP , denoted ana2 decreased reaction time (RT) to a noxious radiant heat stimulus in a dose-related manner. The following rank order of potency was observed in relation to this response: ana1 = ana2 greater than SP much greater than NKA. The decrement of tail-flick latency was greatest at 1 min and RT returned to the basal level within 6-11 min post-administration. However, in some rats SP produced a small increase in RT (anti-nociception) at 6-11 min post-administration. The i.th. administration of neurokinin B (NKB) or a selective NK-3 receptor agonist [beta-Asp4, MePhe7]NKB), denoted ana3 induced an antinociceptive effect which was greatest at 1 min and lasted less than 11 min after NKB or more than 30 min after ana3 administration. The magnitude of the increase in RT produced by 65 pmol-40 nmol doses of these peptides is ana3 much greater than NKB much greater than SP. The effect of NKB (8.0 nmol) was significantly blocked (P less than 0.005) by prior i.th. administration of naloxone (opioid antagonist) but not by idazoxan (alpha 2-adrenoceptor antagonist), [Thi5,8, D-Phe7]BK (kinin antagonist), or following bilateral adrenalectomy. From these results, we conclude that NKB-induced antinociception is mediated by the spinal release of an opioid and not through a BK or NA mechanism. The results also suggest that the nociceptive and antinociceptive effects of neuro-kinins are mediated by the activation of NK-1 and NK-3 receptor subtypes respectively, in the rat spinal cord.     

Development of autonomic and behavioural thermoregulation in turkeys (Meleagris gallopavo)

1. 1.|Heat production (HP) and body temperature (T_b) measurements were conducted at ambient temperatures (T_a) between 10 and 40°C. In addition preference temperatures (PT) were determined in a temperature channel and T_b was measured at preferred T_a

2. 2.|The influence of age on T_b at constant, as well as at PT, was proved. Increasing age was accompanied by an elevation of T_b whereas HP remained constant in the mid-range of T_a

3. 3.|The lower T_b in the first days of life is suggested to result from a lower thermoregulatory set point during the postnatal period.

4. 4.|The PT were different for the observed types of behaviour. The PT at rest was higher than the PT during locomotion, food intake and drinking.

Hormonal growth-promotant effects on grain-fed cattle maintained under different environments

Six steers (3/4 Charolais×1/4 Brahman) (mean body weight 314±27 kg) and six spayed heifers (3/5 Shorthorn×2/5 Red Angus) (mean body weight 478±30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; °C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9±0.9°C ambient temperature (T_A) and 61.7±22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2±4°C (T_A) and 78.3±13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6±0.9°C (T_A) and 63.4±1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P<0.05) on cold days and greater (P<0.05) on hot days compared to TNL. On hot days, RTs, were 0.62°C higher after compared to before implanting. Across all conditions, RTs were >0.5°C greater (P<0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were >0.8°C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2–0.35°C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P<0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P<0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.     

Reversal of photoschedule in spring does not prevent photorefractoriness in Siberian hamsters

We studied the influence of light-dark (L:D) cycle reversal on daily variations in the brown adipose tissue (BAT) capacity for nonshivering thermogenesis (NST) in Siberian hamsters (Phodopus sungorus). Continuous and simultaneous measurements of BAT temperature (T(BAT)) and preferred ambient temperature (PT(a)) were made after noradrenaline (NA) injections administered every 4 hr. First, hamsters were acclimated for 4 weeks to an ambient temperature (T(a)) of 23 degrees C and 12L:12D, and then to a reversed photoschedule 12D:12L for 8 weeks. The same was done after a 4- and 8-week acclimation period at the same T(a). We found that after photoschedule reversal, the re-entrainment of T(BAT) and PT(a) rhythms preceded re-entrainment of the NST rhythm. The daily rhythms of T(BAT) and PT(a) were fully re-entrained after 4 weeks of acclimation to the reversed photoschedule, but rhythmicity of the response to NA disappeared. This rhythm was restored in hamsters acclimated to a reversed photoschedule for 8 weeks. We suggest that the daily rhythm of NST capacity is not responsible for generating the rhythm of body temperature (T(b)). Rather, it is a result of the daily rhythm of T(b), but adjusts to the new environment more slowly than the T(b) rhythm. When a daily rhythm of NST was present, the increase in T(BAT) after NA injection was inversely correlated with the pre-injection T(BAT). In addition, NA-induced changes in PT(a) reflected the intensity of NST in BAT; namely, increased T(BAT) was correlated with the post-injection decrease in PT(a). When the increase in T(BAT) was large, animals chose a lower T(a) to dissipate excessive heat and prevent overheating. In the course of the experiments, we recorded a decreased mean NST capacity and increased body mass of hamsters. These changes are representative of the time of photorefractoriness and a transition to a summer status. Despite prolonged exposure to an intermediate day length (12 hr of light) and photoschedule reversal, hamsters continued to change towards their summer condition and were able to acclimate to the new D:L cycle.     

Catecholamine content (as measured by the HPLC method) in brain and blood plasma of the eel: effects of 101 ATA hydrostatic pressure

The catecholamine content (noradrenaline, NA; adrenaline, A; dopamine, DA, and its metabolite, DOPAC) was measured, by the HPLC method, in brain and blood plasma of eels studied at atmospheric pressure (1 ATA) or at 101 ATA of hydrostatic pressure (HP). In the brain, HP induces a slight but significant increase (P less than 0.05) in A and DA contents but NA and DOPAC levels are not modified at 101 ATA when compared to 1 ATA. In the plasma, only A and NA are detected, adrenaline being the predominant amine. In eels exposed to 101 ATA HP, A and NA are strongly increased (+100%; P less than 0.01). The significance of the catecholamine increase in brain and plasma of the eels under HP is discussed.     

Changes of characteristics of preoptic neurons and NA metabolism in hypothalamus of ground squirrel (Citelleus Dautieus) in different seasons and hibernating phases

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Effect of essential fatty acid deficiency on G-proteins, cAMP-dependent protein kinase activity and mucin secretion in the rat submandibular salivary glands

Studies were conducted to determine whether β-adrenergic cell signalling is altered in submandibular salivary glands (SMSG) is essential fatty acid (EFA) deficiency. Three groups of rats were fed diets which were deficient in EFA (EFAD), marginally deficient in EFA (MEFAD) or contained sufficient amount of EFA (Control). Rats were killed after 20 wk on diets, SMSG were dissected out and cyclic AMP-dependent protein kinase (PKA) activity was measured. The specific enzyme activities were higher in the homogenates and supernatant fractions of the gland from EFAD and MEFAD rats compared with the controls. The relative levels of guanine nucleotide-binding regulatory proteins (Gs and Gi) were also measured in the SMSG membranes of rats fed the 3 diets. The levels of Gs were significantly higher in the EFAD and MEFAD groups than in the controls. No significant differences were observed in the secretion of trichloroacetic acid-phosphotungstic acid (TCA-PTA) precipitable glycoproteins from the SMSG slices among the 3 dietary groups.