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Biomedical subjects

M Maskrey

Publications and source records attributed to M Maskrey.

33 records · Page 2Linked to original sources
PubMed1978

Blood gas changes during panting in a small East African antelope, the dik-dik.

Five adult male dik-dik (Madoqua kirkii) were exposed in a climatic chamber to an air temperature of 45 degrees C. Measurements were made of rectal temperature (Tre) and respiratory frequency (f) and arterial blood samples taken before and during heat exposure were analyzed for pH, PCO2 and PO2. During exposure, Tre and f increased in all animals. In the first 80 min dik-dik displayed thermal tachypnea and minor changes in blood gases. Continued exposure lead to hyperpnea accompanied by a fall in PaCO2 and a rise in pH. PaCO2 at first fell and then increased toward or above control levels. The dik-dik did not display second phase breathing. This observation confirms that second phase breathing is not essential to the development of respiratory alkalosis. The main conclusion of the study is that the dik-dik, unlike another heat-adapted antelope, the wildebeest (Taylor, Robertshaw, and Hoffmann. Am. J. Physiol. 217:907-910, 1969), is unable to resist alkalosis during heat stress.

Animals↗
PubMed1977

Panting in small mammals: a comparison of two marsupials and the laboratory rabbit.

By use of a barometric technique, tidal volume (VT), minute volume (VE), respiratory frequency (f), and respiratory evaporative heat loss (Eex) were measured from conscious unrestrained potoroos (Potorous tridactylus), barred bandicoots (Perameles gunnii), and New Zealand white rabbits (Oryctolagus cuniculus) at temperatures in and above the thermoneutral zone (TNZ). Rectal temperature (Tre) and oxygen consumption were also measured. VT initially decreased with rising Ta, but in the potoroo and rabbit it then increased past the resting level. VE increased much more in the marsupials than in the rabbit, and higher Eex maxima were also found for the marsupials. The marsupials had high Q10's above the TNZ, and had a panting efficiency of 80%. The rabbits had a Q10 of 1.9 above the TNZ and 100% panting efficiency. The high VE and Eex and low panting efficiency of the marsupials may be due to their lower Tre which allows transfer of heat from the environment to the animal.

Animals↗
PubMed1976

Respiratory and thermoregulatory responses of rabbits breathing carbon dioxide during heat exposure.

1. Rabbits were clipped and exposed in turn to three environmental conditions: control (C), cold exposure (CE) and water deprivation (WD). Following each type of treatment, the rabbits were exposed to an ambient temperature (Ta) of 35 degrees C for 1 hr. Throughout this period they breathed either normal atmospheric air or 6% CO2 in air. 2. During heat exposure, measurements were made of the respiratory responses and of the O2 consumption (Vo2) of the rabbits. Rectal temperature (Tre) was measured immediately before and again immediately after heat exposure. 3. When subjected to cold exposure or water deprivation the rabbits showed an initial decrease in respiratory frequency (RF) and an initial increase in VT when compared with controls. There was no difference in VE. Rabbits breathing 6% CO2 showed an increase in VT and VE and a decrease in RF when compared with rabbits breathing atmospheric air. In all cases a change in VT or RF was associated with a reciprocal change in the other parameter. 4. The respiratory responses to breathing 6% CO2 were essentially similar in treated and control rabbits, from which it is concluded that neither cold exposure nor water deprivation alter the sensitivity of the medullary respiratory centre to the respiratory drive from the central chemosensors. 5. The increase in Tre during heat exposure was significantly less in rabbits breathing 6% CO2 than in rabbits breathing atmospheric air. However, there was no significant over-all difference in VO2 between rabbits breathing CO2 and those breathing air. From this it is concluded that increased ventilation induced by CO2 causes a greater dissipation of heat than does thermally-induced panting. 6. It is concluded that VT is controlled by the level of blood PCO2 whereas RF is controlled by thermoregulatory requirements. It is further concluded that the reciprocal relationship between VT and RF is regulated in such a way as to maintain VE at the appropriate level for effecting gaseous exchange and evaporative heat loss.

Animals↗
PubMed1975

Inhibition of thermal tachypnoea in rabbits following exposure to cold and water deprivation.

1. Rabbits were clipped and exposed in turn to four environmental conditions: control (C), cold exposure (CE), water deprivation (WD) and water deprivation and cold exposure together (WD/CE). 2. Following each type of treatment, the rabbits were exposed for 1 hr to an ambient temperature (Ta) of 35 degrees C. During this time, respiratory frequency (RF), rectal temperature (Tre), activity and oxygen consumption (V02) were recorded. 3. It was found that under both cold exposure and water deprivation conditions, the mean respiratory frequency during the first 30 min of heat exposure was reduced when compared with controls. This was associated with a delay in the onset of thermal tachypnoea. Under conditions of water deprivation and cold exposure together, the mean respiratory frequency was further reduced and the length of the delay was increased. 4. Previous cold exposure led to an increase in the V02 measured at 35 degrees C, whereas the V02, after water deprivation and water deprivation and cold exposure together were not significantly different from the control. 5. Neither the initial Tre nor the change in the Tre during the course of the heat exposure were significantly different from the controls under any of the experimental conditions. 6. It is concluded that both water deprivation and previous cold exposure cause a block to panting in the heat and that the blocking mechanisms involved are closely interrelated. It is also concluded that neither the metabolic rate of the animal nor its initial or final Tre are important factors in determing the degree to which thermal tachypnoea is inhibited.

Animals↗
PubMed1971

Influence of ambient temperature on the thermoregulatory responses to 5-hydroxytryptamine, noradrenaline and acetylcholine injected into the lateral cerebral ventricles of sheep, goats and rabbits.

1. The influences of ambient temperature (T(a)) on the thermoregulatory effector activities and the body temperature (T(b)) of intraventricular injections into the sheep, goat and rabbit of 5-hydroxytryptamine (5-HT), noradrenaline (NA), acetylcholine (ACh), carbachol and eserine, have been interpreted in terms of a simple neuronal model of the pathways between thermosensors and thermoregulatory effectors.2. In all three species 5-HT in minimal doses caused a rise in respiratory frequency (RF) and a fall in T(b) at high T(a), and a reduction in EMG activity and a fall in T(b) at low T(a). These effects could be interpreted as those of an excitatory transmitter acting on the warm receptor-heat loss pathway.3. In all three species NA caused a reduction in RF and a rise in T(b) at high T(a), and a reduction in EMG activity and a fall in T(b) at low T(a). These effects are interpreted as those of an inhibitory transmitter acting both on the warm sensor-heat loss pathways and on the cold sensor-heat production pathway.4. The effects of ACh and the cholinomimetic substances carbachol and eserine are complex and more difficult to interpret. In small doses the effects on the sheep and goat are those of an excitatory transmitter on the cold sensor-heat production pathway. There was an increase in EMG activity and a rise in T(b) at low T(a), and a reduction in RF and a rise in T(b) at high T(a). At higher dose levels in the goat and at all dose levels in the rabbit these substances had the reverse effects which are attributed to a synaptic block due to the excess of the excitatory substance.5. The effects of ambient temperature and injected substances upon ear temperature are consistent with the predictions of the model if it is assumed (a) that at high and low ambient temperatures direct thermal effects on ear vessels dominate those of the sympathetic innervation, and (b) that the warm sensor influence is to lower peripheral vasomotor tone, and the cold sensor influence is to increase it.6. The conclusion reached is that when consideration is given to species differences in the thermoneutral ambient temperature and to the possibility that excitatory substances have reversed effects at high dose levels, the effects of 5-HT, NA and ACh in the control of body temperature are very similar in the sheep, goat and rabbit: 5-HT is excitatory on the heat loss pathway, ACh is excitatory on the heat production pathway and NA has an inhibitory influence on both pathways.

Acetylcholine↗
PubMedDate not supplied

Dual effect of aminophylline on the ventilatory response to hypoxia in the rat.

Male Hooded Wistar rats were exposed to three five-minute periods of hypoxia in which they breathed a gas mixture comprising 7% O2 and 93% N2. Before the second and third hypoxic exposures rats were injected (i.m.) with aminophylline (an adenosine antagonist) at a dose of 15 mg.kg-1. In control animals, hypoxia caused an increase in ventilation which was greater during the first than during the fifth minute of hypoxia. Each injection of aminophylline significantly increased ventilation in air-breathing rats. However, the first dose of the drug did not significantly alter the hypoxic ventilatory response. The second dose of aminophylline had two effects on ventilation during hypoxia. It reduced the ventilatory response during the first minute of hypoxia, and also prevented the fall in ventilation between the first and fifth minute of exposure. Ethylenediamine injections had no effect on ventilation or the responses to hypoxia. The results suggest that adenosine has a dual role in respiratory control during hypoxia, one excitatory and the other inhibitory. Although previous studies have already identified such roles for adenosine, the present study may represent the first time in which these have been demonstrated in a single animal model.

Aminophylline↗