共查询到20条相似文献,搜索用时 15 毫秒
1.
P. J. Ponganis G. L. Kooyman L. M. Winter L. N. Starke 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):9-16
California sea lions, Zalophus californianus, were trained to elicit maximum voluntary breath holds during stationary underwater targeting, submerged swimming, and trained
diving. Lowest heart rate during rest periods was 57 bpm. The heart rate profiles in all three protocols were dominated by
a bradycardia of 20–50 bpm, and demonstrated that otariid diving heart rates were at or below resting heart rate. Venous blood
samples were collected after submerged swimming periods of 1–3 min. Plasma lactate began to increase only after 2.3-min submersions.
This rise in lactate and our inability to train sea lions to dive or swim submerged for periods longer than 3 min lead us
to conclude that an aerobic limit had been reached. Due to the similarity of heart rate responses and swimming velocities
recorded during submerged swimming and trained diving, this 2.3-min limit should approximate the aerobic dive limit in these
40-kg sea lions. Total body O2 stores, based on measurements of blood and muscle O2 stores in these animals, and prior lung O2 store analyses, were 37–43 ml O2 kg−1. The aerobic dive limit, calculated with these O2 stores and prior measurements of at-sea metabolic rates of sea lions, is 1.8–2 min, similar to that measured by the change
in post-submersion lactate concentration.
Accepted: 7 July 1996 相似文献
2.
Gordos MA Limpus CJ Franklin CE 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(1):65-73
Changes in heart rate (f
H) and cloacal ventilation frequency (f
C) were investigated in the Fitzroy turtle, Rheodytes leukops, under normoxic (17.85 kPa) and hypoxic (3.79 kPa) conditions at 25°C. Given R. leukops’ high reliance on aquatic respiration via the cloacal bursae, the objective of this study was to examine the effect of varying
aquatic PO2 levels upon the expression of a bradycardia in a freely diving, bimodally respiring turtle. In normoxia, mean diving f
H and f
C for R. leukops remained constant with increasing submergence length, indicating that a bradycardia failed to develop during extended dives
of up to 3 days. Alternatively, exposure to aquatic hypoxia resulted in the expression of a bradycardia as recorded by a decreasing
mean diving f
H with increasing dive duration. The observed bradycardia is attributed to a hypoxic-induced metabolic depression, possibly
facilitated by a concurrent decrease in f
C. Results suggest that R. leukops alters its strategy from aquatic O2 extraction via cloacal respiration in normoxia to O2 conservation when exposed to aquatic hypoxia for the purpose of extending dive duration. Upon surfacing, a significant tachycardia
was observed for R. leukops regardless of aquatic PO2, presumably functioning to rapidly equilibrate blood and tissue gas tensions with alveolar gas to reduce surfacing duration. 相似文献
3.
M. L. Glass F. T. Rantin † R. M. M. Verzola ‡ M. N. Fernandes † A. L. Kalinin † 《Journal of fish biology》1991,39(2):143-149
Moderate hypoxia (Pio2, = 50 mmHg) caused tachycardia in carp, Cyprinus curpio Linnaeus, whereas severe hypoxia (Pio2, from 30 to 5 mmHg) coincided with bradycardia accompanied by alterations of the waveforms of the electrocardiogram. A cardio respiratory synchronization developed during hypoxia and was maintained during bradycardia. The data raised the question: Does hypoxic bradycardia in part result from myocardial dysfunction or only from regulatory adjustments? 相似文献
4.
Harry J. Mangalam David R. Jones 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1984,154(3):243-247
Summary The effects of breathing different levels of O2 and CO2 before forced dives were investigated in 5 dabbling ducks (White Pekin) and 5 deep divers (Double Crested Cormorants). Breathing
and heart rates, blood gases, and blood pH, were monitored. After breathing air before diving, ducks exhibited a slow decrease
in heart rate that reached a minimum of 20 beats·min−1 after 50 s submergence. The development of bradycardia was retarded if the duck breathed a hyperoxic gas mixture before diving
and was accelerated if the gas mixture was hypoxic and hypercapnic. The cormorants' diving heart rate decreased to a minimum
of about 60 beats·min−1 in less than 20 s and development of bradycardia was unaffected by different levels of O2 and CO2 breathed before diving. Consequently, bradycardia in forced dived cormorants was unrelated to changes in blood gases in the
dives which suggests that intravascular chemoreceptors are unimportant in initiating diving bradycardia in cormorants. 相似文献
5.
T. E. Shumilova G. B. Weinstein V. N. Semernya V. I. Shereshkov A. D. Nozdrachev I. N. Yanvareva A. A. Panov 《Journal of Evolutionary Biochemistry and Physiology》2006,42(4):424-430
Microhemodynamics and oxygen tension (pO2) in the brain cortex tissues as well as the heart rate were studied in rodents with different ecological specialization during hypoxia produced by subcutaneous injection of sodium nitrite (3 mg/100 g body mass). It was shown that the blood flow in animals with low (rats) and high (muskrats) resistance to hypoxia decreased by the 30th min of the nitrite action, with its subsequent restoration to 85% and 83% of the initial level by the 60th min. The interspecies difference consisted in an increase of the brain blood flow (by 24%) in muskrats and a decrease (by 33%) in rats 15 min after the injection. In rats, simultaneously with the blood-flow dynamics, a pO2 increase was observed in some brain cortex microareas, while in others—a pO2 decrease 15 min after the NaNO2 injection: meanwhile, in muskrats, at this time period a significant pO2 decrease was observed on the background of a blood flow increase. In both animal species, the pO2 minimal value was reached by the 45th min, while restoration almost to the initial levels—by the 60th min of the nitrite action. Changes in the rats, synchronous and unidirectional with the heart rate frequency, of the brain blood-flow, as well as tachycardia developing throughout the whole experiment in rats allow suggesting that restoration of the oxygen regime in the brain cortex microareas is provided by activation of systemic mechanisms of regulation of circulation. 相似文献
6.
Faouzi Horchani Samira Aschi-Smiti Renaud Brouquisse 《Acta Physiologiae Plantarum》2010,32(6):1113-1123
The putative role of nitrate and nitrate reductase in the tolerance to prolonged hypoxia was investigated in tomato plants.
Nitrogen nutrition has been modified either by deprivation of nitrate or by addition of tungstate—an inhibitor of nitrate
reductase (NR)—in the culture medium. In the absence of nitrate as well as in the presence of tungstate, plant growth was
significantly disturbed. In the presence of nitrate, the growth of hypoxic plants maintained, nitrate absorption and NR activity
increased and a significant release of nitrite into the medium was observed. This mechanism of nitrate reduction, called nitrate
respiration, could be an alternative pathway to oxygen-dependent respiration during root hypoxia and a transient adaptation
of tomato roots to hypoxic conditions. 相似文献
7.
T. E. Shumilova V. I. Shereshkov A. D. Nozdrachev 《Journal of Evolutionary Biochemistry and Physiology》2011,47(5):464-473
The systemic and peripheral hemodynamics was studied in male white rats under conditions of acute nitrite hypoxia (subcutaneous
administration of sodium nitrite at doses of 1, 3, and 5 mg/100 g body mass). By the electrocardiographic, rheographic, and
other methods there were recorded the heart rate (HR), minute circulation volume (MCV), cardiac output (CO), skeletal muscle
circulation (SMC), brain circulation (BC), and systemic arterial pressure (AP). Nitrite was shown to produce a fast, dose-dependent
AP fall accompanied by a decrease of MCV due to development of bradycardia and a fall of CO. At the phase of the steady hypotension,
MCV increased due to a significant rise of CO on the background of the continuing bradycardia. The systemic circulatory effects
of NaNO2 were found to be accompanied by a redistribution of peripheral circulation in the form of a dose-dependent increase of BC
and a sharp fall of MCV. It was shown that 1–1.5 h after the nitrite injection the parameters of systemic and peripheral hemodynamics
approached the initial levels. Possible triggering mechanisms of the initial stage of the rat cardiovascular adaptation to
conditions of acute nitrite hypoxia are discussed. 相似文献
8.
E. M. Tsoi R. I. Kovalenko D. A. Kuz’min 《Journal of Evolutionary Biochemistry and Physiology》2008,44(4):476-483
The study is carried out on Wistar white rats non-adapted to oxygen deficit and on semiaquatic rodents muskrats adapted to periodic arrest of respiration during diving under conditions of Nembutal narcosis. It has been revealed that 1 h after a subcutaneous injection of sodium nitrite (3 mg/100 g body mass), intensification of lipid peroxidation (LPO) in the muskrat brain is absent, the activity of the antioxidant enzyme catalase increasing 16 times (p < 0.01) as compared with control injected with equivalent saline volume. In heart and liver, there was a statistically significant decrease of the content of LPO products active in the test with 2-thiobarbituric acid; in the femoral muscle tissue, the LPO intensity did not change. In rats, unlike muskrats, after injection of sodium nitrite, an increase of LPO is recorded in brain, while a decrease of the LPO product content in the femoral muscle; in liver the LPO intensity did not change. In muskrats, the sodium nitrite administration led to a decrease of the leukocyte spontaneous mobility, of lymphocyte cytokine-producing activity, and of neutrophil bactericidal activity (by the content of cationic proteins in neutrophilic phagocytes), whereas in rats the leukocyte mobility did not change, only the blood neutrophil bactericidal activity decreased. The ability of neutrophils to produce the superoxide anion during the nitrite intoxication did not change both in rats and in muskrats. The obtained data allow concluding that under conditions of Nembutal narcosis the leukocyte functional activity on the background of nitrite intoxication is suppressed to the greater degree in the muskrats genotypically adapted to oxygen deficit than in immunocompetent cells of the rodents not adapted to hypoxia. 相似文献
9.
Nina K. Iversen David J. McKenzie Hans Malte Tobias Wang 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(4):495-502
Most teleost fish reduce heart rate when exposed to acute hypoxia. This hypoxic bradycardia has been characterised for many
fish species, but it remains uncertain whether this reflex contributes to the maintenance of oxygen uptake in hypoxia. Here
we describe the effects of inhibiting the bradycardia on oxygen consumption (MO2), standard metabolic rate (SMR) and the critical oxygen partial pressure for regulation of SMR in hypoxia (Pcrit) in European
eels Anguilla anguilla (mean ± SEM mass 528 ± 36 g; n = 14). Eels were instrumented with a Transonic flow probe around the ventral aorta to measure cardiac output (Q) and heart rate (f
H). MO2 was then measured by intermittent closed respirometry during sequential exposure to various levels of increasing hypoxia,
to determine Pcrit. Each fish was studied before and after abolition of reflex bradycardia by intraperitoneal injection of
the muscarinic antagonist atropine (5 mg kg−1). In the untreated eels, f
H fell from 39.0 ± 4.3 min−1 in normoxia to 14.8 ± 5.2 min−1 at the deepest level of hypoxia (2 kPa), and this was associated with a decline in Q, from 7.5 ± 0.8 mL min−1 kg−1 to 3.3 ± 0.7 mL min−1 kg−1 in normoxia versus deepest hypoxia, respectively. Atropine had no effect on SMR, which was 16.0 ± 1.8 μmol O2 kg−1 min−1 in control versus 16.8 ± 0.8 μmol O2 kg−1 min−1 following treatment with atropine. Atropine also had no significant effect on normoxic f
H or Q in the eel, but completely abolished the bradycardia and associated decline in Q during progressive hypoxia. This pharmacological inhibition of the cardiac responses to hypoxia was, however, without affect
on Pcrit, which was 11.7 ± 1.3 versus 12.5 ± 1.5 kPa in control versus atropinised eels, respectively. These results indicate,
therefore, that reflex bradycardia does not contribute to maintenance of MO2 and regulation of SMR by the European eel in hypoxia. 相似文献
10.
Regulation of the systemic and peripheral hemodynamics in the conditions of acute nitrite hypoxia (doses of NaNO2 10, 30, and 50 mg/kg of the body mass) were studied on white male rats. It was shown that NaNO2 causes a quick dose-dependent decrease in the blood pressure with an intensification of the parasympathetic tonus and development of bradycardia. The hemodynamics was restored as the oxygen capacity of the blood decreased with an increase in the sympathetic tonus and development of tachycardia. The role of intracardial metasympathetic structures and the renin-angiotensin system in cardiovascular adaptation to hypoxia was established. Adaptation to nitrite hypoxia is accomplished by a coordinated interaction of neurogenic and humoral factors. A combination of pharmacological agents, which include separate links of regulator systems of the organism, leads to failure of the adaptation process. 相似文献
11.
Robert A. MacArthur 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(5):593-599
Summary The oxygen storage capacity and partitioning of body oxygen reserves were compared in summer-and winter-acclimatized muskrats (Ondatra zibethicus). Blood volume, blood oxygen capacity, and skeletal muscle myoglobin content were higher in December than in July (P<0.02). Total lung capacity increased only slightly in winter (P>0.05). The oxygen storage capacity of a diving muskrat was calculated at 25.2 ml O2 STPD · kg-1 in July, compared to 35.7 ml O2 STPD · kg-1 in December. Blood comprised the major storage compartment in both seasons, accounting for 57% and 65% of the total oxygen stores in summer and winter, respectively. Based on available oxygen stores and previous estimates of the cost of diving, the aerobic dive limit (ADL) increased from 40.9 s in July to 57.9 s in December. Concurrent behavioral studies suggested that most voluntary diving by muskrats is aerobic. However, the proportion of dives exceeding the calculated ADL of these animals was shown to vary with the context of the dive. Only 3.5% of all dives initiated by muskrats floating in the water exceeded their estimated ADL. Provision of a dry resting site and access to a submerged food source increased this proportion to 18–61%, depending on the underwater distance that foraging muskrats were required to swim. Serial dives exceeding the estimated ADL were not accompanied by extended postdive recovery periods.Abbreviations
ADL
acrobic dive limit
-
Hb
hemoglobin
-
Hct
hematocrit
-
Mb
myoglobin
-
PaO2
arterial O2 tension
-
STPD
standard temperature and pressure, dry 相似文献
12.
T. E. Shumilova V. I. Shereshkov I. N. Yanvareva A. D. Nozdrachev 《Journal of Evolutionary Biochemistry and Physiology》2010,46(2):179-188
In anesthetized male rats the arterial blood pressure in femoral artery and electrocardiogram in standard leads were recorded
uninterruptedly for 1–1.5 h under conditions of acute nitrite intoxication produced by a subcutaneous injection of water solution
of sodium nitrite (donor of nitric oxide) at concentrations of 10, 30, and 50 mg/kg body mass. Results of the study have shown
dose-dependent changes of arterial pressure as well as of time and amplitude characteristics of electrocardiogram under effect
of NaNO2. At the threshold hypoxic dose, an increase of amplitude of R and S waves was observed by the 30–45th min, while at the maximal
NaNO2 dose, amplitude of all waves rose by the 15th min of intoxication. High nitrite doses often caused an elevation of the ST
segment above the isoelectric line and a rise of the amplitude of the T wave, on which a notch appeared in some cases. The
change of the ECG time parameters was expressed in the dose-dependent development of bradycardia for the first 4–7 min; its
level correlated with the progressively decreasing arterial pressure in the beginning (the 2–4th min) of nitrite intoxication.
Variation analysis of the heart rate spectral characteristics by Baevskii’s method has revealed a rise of the total spectral
power of pulse oscillations. Under effect of nitrite, in the specter of cardiointervals, the slower oscillations have been
revealed with frequency of 0.15–0.2 Hz in the LF diapason with subsequent recovery of the normal ECG specter at the end of
the experimental period. The maximal nitrite dose produced more pronounced shifts of the heart rate specter towards the LF
and VLF diapasons that were not restored for 1 h of experiment. Transitory processes of readjustment of the cardiac rhythm
had discrete character. The nitrite dose of 100 mg/kg body mass increased the RR-interval after 4–7 min with amplitude steps
of 3–5 imp/s and the time constant of 20–40 s. The revealed ECG changes had the reflex (enhancement of parasympathetic tonus)
and metabolic (the hypoxic and histotoxic damage of myocardium) nature. 相似文献
13.
In 8 unanesthetized dogs, 10-21 days post pancreatectomy, the cardiac chronotropic response to rapid infusion of a pharmacological dosage of Adrenaline was begun. During the subsequent month, the response was recorded electrocardiographically on 19 occasions. On 8 occasions, animals were treated with continuous intravenous administration of fluids and insulin up to the time of the test; on 11, insulin was omitted for 18 hours before Adrenaline injection. Insulin treated animals responded with the typical brief initial bradycardia, followed by some 2 minutes of ventricular tachycardia, and restoration of preinjection heart rate and electrocardiograph pattern within 5 minutes. On those occasions when insulin was omitted, the tachycardia was replaced by ventricular bradycardia. The altered chronotropic response of non-insulin treated dogs indicates impairment of their cardiac beta receptors. 相似文献
14.
Akiyama R Mitsubayashi H Tazawa H Burggren WW 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(2):85-92
Normal heart rate (HR), and the HR responses to hypoxia and hyperoxia during early heart development in chick embyros have
not been studied in detail, particularly in undisturbed embryos within the intact egg. HR was measured in day 3–9 chick embryos
at 38 °C using relatively noninvasive impedance cardiography. Embryos were exposed to air (control) and to hypoxic (10% O2) or hyperoxic (100% O2) gas for a 2-h or 4-h period, during which HR was continually monitored. Control (normoxic) HR increased from about 150 beats
per min (bpm) on day 3 to about 240 bpm on days 7–9. HR in very early embryos showed a variety of moderate responses to hypoxia
(all survived), but as development progressed beyond day 6, hypoxic exposure induced a profound bradycardia that frequently
terminated in death before the end of the measurement period. In contrast to the marked developmental changes in hypoxic sensitivity,
HR showed little response to hyperoxia throughout development, suggesting no “hypoxic drive” to HR. We speculate that hypoxia
has little effect early in development because of the embryo's small absolute O2 demand, but as the embryo grows, hypoxia represents a progressively more severe perturbation. Although general trends were
identified, there was considerable variation in both HR and HR responses to ambient O2 changes between individuals of the same developmental stage.
Accepted: 16 December 1998 相似文献
15.
T. I. Baranova R. I. Kovalenko A. V. Mitrofanova I. N. Yanvareva 《Journal of Evolutionary Biochemistry and Physiology》2010,46(5):489-500
Studies of the diving reflex in comparative evolutionary terms have shown that a complex of reactions providing the oxygen-saving
effect during diving is inherent in human as well as in the secondary-aquatic mammals. This is confirmed by study of peculiarities
of energy metabolism the simulated diving (it is the breath holding with face immersed into the cold water—what we call the
cold-hypoxic-hypercapnic effect, CHE). Data of gas analysis have shown that the oxygen consumption rate during the diving
imitation is statistically significantly lower than during the usual expiration delay (Genche’s test). We have revealed that
under effect of adaptation to CHE, on the background of a reduction of the total energy consumption by the organism there
occurs a slight increase in contribution of aerobic processes to its energy supply. Adaptation to CHE has been shown to be
accompanied by a decrease in reactivity of the parasympathetic chain of regulation of the heart chronotropic function and
by an increase of duration of apnea. The apnea duration is directly correlated with level of insulin—the hormone stimulating
activity of the anaerobic energy pathway provision. Under effect of adaptation to CHE there has been established an increase
of the organism resistance to stress actions, which is confirmed by the lower levels of cortisol and thyroid hormones in representatives
of the experimental group as compared with the control one. 相似文献
16.
Neurotensin (NT) infusions into isolated, perfused, spontaneously beating hearts of guinea pigs evoked a concentration-dependent, positive chronotropic effect which was preceded in some hearts by transient bradycardia. The tachycardia caused by NT was not affected by propranolol, cimetidine, indomethacin, a mixture of methysergide and morphine or by atria removal. The incidence and amplitude of bradycardia caused by NT were increased by neostigmine but reduced by atropine. Neostigmine and atropine also tended to decrease and increase respectively, the tachycardia caused by NT. These results suggest that the positive chronotropic effect of NT in guinea pig isolated heart results from a direct effect on the specialized conduction system of the heart while its negative chronotropic effect is likely to reflect the activation by NT of cardiac vagal cholinergic neurons. 相似文献
17.
Eme J Altimiras J Hicks JW Crossley DA 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2011,160(3):412-420
Hypoxia is a naturally occurring environmental challenge for embryonic reptiles, and this is the first study to investigate the impact of chronic hypoxia on the in ovo development of autonomic cardiovascular regulation and circulating catecholamine levels in a reptile. We measured heart rate (f(H)) and chorioallantoic arterial blood pressure (MAP) in normoxic ('N21') and hypoxic-incubated ('H10'; 10% O(2)) American alligator embryos (Alligator mississippiensis) at 70, 80 and 90% of development. Embryonic alligator responses to adrenergic blockade with propranolol and phentolamine were very similar to previously reported responses of embryonic chicken, and demonstrated that embryonic alligator has α and β-adrenergic tone over the final third of development. However, adrenergic tone originates entirely from circulating catecholamines and is not altered by chronic hypoxic incubation, as neither cholinergic blockade with atropine nor ganglionic blockade with hexamethonium altered baseline cardiovascular variables in N21 or H10 embryos. In addition, both atropine and hexamethonium injection did not alter the generally depressive effects of acute hypoxia - bradycardia and hypotension. However, H10 embryos showed significantly higher levels of noradrenaline and adrenaline at 70% of development, as well as higher noradrenaline at 80% of development, suggesting that circulating catecholamines reach maximal levels earlier in incubation for H10 embryos, compared to N21 embryos. Chronically elevated levels of catecholamines may alter the normal balance between α and β-adrenoreceptors in H10 alligator embryos, causing chronic bradycardia and hypotension of H10 embryos measured in normoxia. 相似文献
18.
Hindle AG Senkiw RW Macarthur RA 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2006,144(2):232-241
We tested the hypothesis that immersion hypothermia enhances the diving capabilities of adult and juvenile muskrats by reducing rates of oxygen consumption (V O2). Declines in abdominal body temperature (T(b)) comparable to those observed in nature (0.5-3.5 degrees C) were induced by pre-chilling animals in 6 degrees C water. Pre-chilling did not reduce diving V O2 of any animal tested in 10 degrees C or 30 degrees C water, irrespective of the nature of the dive. Most behavioural indices of dive performance, including average and cumulative dive times, were unaffected by T(b) reduction in adults, but depressed in hypothermic juveniles (200-400 g). Hypothermia reduced diving heart rate only on short (<25s) dives (16% reduction, P=0.01), but did not affect the temporal onset of diving bradycardia. Post-immersion V O2 was higher for pre-chilled than for normothermic muskrats, but the difference became insignificant on longer (>90 s) dives. Our findings suggest that the mild hypothermia experienced by muskrats in nature has minimal effect on diving and post-immersion metabolic costs, and thus has little impact on the dive performance of this northern semi-aquatic mammal. 相似文献
19.
Eme J Hicks JW Crossley DA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(7):981-990
Hypoxia is a naturally occurring environmental challenge for embryonic non-avian reptiles, and this study is the first to
investigate the impact of chronic hypoxia on a possible chemoreflex loop in a developing non-avian reptile. We measured heart
rate and blood pressure in normoxic and hypoxic-incubated (10% O2) American alligator embryos (Alligator mississippiensis) at 70 and 90/95% of development. We hypothesized that hypoxic incubation would blunt embryonic alligators’ response to a
reflex loop stimulated by phenylbiguanide (PBG), a 5-HT3 receptor agonist that stimulates vagal pulmonary C-fiber afferents. PBG injection caused a hypotensive bradycardia in 70
and 95% of development embryos (paired t tests, P < 0.05), a response similar to mammals breathing inspired air (all injections made through occlusive catheter in tertiary
chorioallantoic membrane artery). Hypoxic incubation blunted the bradycardic response to PBG in embryos at 95% of development
(two-way ANOVA, P < 0.01). We also demonstrated that the vagally mediated afferent limb of this reflex can be partially or completely blocked
in ovo with a 5-HT3 receptor blockade using ondansetron hydrochloride dihydrate (OHD), with a ganglionic blockade using hexamethonium, or with
a cholinergic blockade using atropine. Atropine eliminated the hypotensive and bradycardic responses to PBG, and OHD and hexamethonium
significantly blunted these responses. This cardiovascular reflex mediated by the vagus was affected by hypoxic incubation,
suggesting that reptilian sympathetic and parasympathetic reflex loops have the potential for developmental plasticity in
response to hypoxia. We suggest that the American alligator, with an extended length of time between each developmental stage
relative to avian species, may provide an excellent model to test the cardiorespiratory effects of prolonged exposure to changes
in atmospheric gases. This extended period allows for lengthy studies at each stage without the transition to a new stage,
and the natural occurrence of hypoxia and hypercapnia in crocodilian nests makes this stress ecologically and evolutionarily
relevant. 相似文献
20.
The present study was done to characterize the effects of endogenous tachykinins on heart rate in urethane-anesthetized guinea pigs. Intravenous injection of capsaicin (32 nmol/kg) was used to evoke release of tachykinins and calcitonin gene-related peptide (CGRP) from cardiac sensory nerve fibers. Such injections caused a brief decrease in heart rate (− 37 ± 7 beats/min, n = 6) that was followed by a more prolonged increase (+ 44 ± 10 beats/min). Blood pressure was lowered by − 11 ± 2 mmHg. Bilateral vagotomy did not affect the chronotropic or depressor responses to capsaicin, but atropine (1 µmol/kg) nearly abolished the bradycardic response (− 8 ± 3 beats/min, n = 7). Combined blockade of NK2 and NK3 receptors, with SR48968 and SR14801 respectively, also caused a significant reduction of capsaicin-evoked bradycardia (− 14 ± 3 beats/min, n = 4) but did not affect bradycardia evoked by vagal nerve stimulation. Blockade of CGRP receptors eliminated capsaicin-evoked tachycardia and prolonged the capsaicin-evoked bradycardia. These findings suggest that capsaicin-evoked bradycardia in the anesthetized guinea pig is mediated by tachykinins that stimulate cardiac cholinergic neurons. This effect appears to be truncated by the positive chronotropic action of CGRP that is also released from cardiac afferents by capsaicin. 相似文献