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Species differences in circulatory responses to nasopharyngeal perfusion with smoke
Camp. Biochrm P/wsio/. Vol. 78C. No. I, pp. 133-135. Printed m Great B&in
0306-4492/84 $3.00 + 0.00 s:<;:!’ 1984 Pergamon Press Ltd
1984
SPECIES DIFFERENCES IN CIRCULATORY RESPONSES TO NASOPHARYNGEAL PERFUSION WITH SMOKE D. FRED Department
PETERSON, JACQUE L. BERGMAN and HUGH
of Physiology,
Oral
Roberts
University
School
G. TESTER
of Medicine,
7777 South
Lewis,
Tulsa, OK 74171, USA (Receiwd 23 September 1983) Abstract-l. Cardiovascular changes were observed in five species of laboratory mammals during upper airway perfusion with cigarette smoke. 2. Apnoea occured, both before and after vagotomy, in all species. 3. Blood pressure always went up in rabbits, rats and hamsters but was not much affected in cats and guinea-pigs. 4. Before vagotomy heart rate fell in rabbits and rats, rose in hamsters but did not change in cats and guinea-pigs. Vagotomy affected heart rate changes only in rabbits and rats. 5. Results demonstrate markedly different autonomic responses in different species.
INTRODUCTION
It is now well established that stimulation of upper respiratory irritant receptors in the rabbit produces a predictable pattern of cardiovascular changes. When cigarette smoke enters the nares, blood pressure rises, heart-rate falls and apnoea occurs. These responses have been observed in conscious (White and McRitchic, 1973) and anesthetized (Robleto and Peterson, 1981) animals. The rise in blood pressure is due to a dramatic increase in total peripheral resistance as a result of vasoconstriction in most of the peripheral vasculature (White et al., 1974). The fall in heart rate is largely due to increased parasympathetic (vagal) activity to the heart (Robleto and Peterson, 1981) although it is also partly due to decreased cardiac sympathetic nerve activity (Peterson pt al., 1983). Whether or not this pattern of autonomic responses is unique to the rabbit is not known. Much less profound heart rate and blood pressure responses have been observed in dog and man (White and McRitchie, 1973). In the present series of experiments responses were compared between the rabbit and four other species of common laboratory animals. Ail were challenged with cigarette smoke and their respiratory and cardiovascular responses observed.
used to maintain spontaneous ventilation of room air. The cranial cannula permitted the delivery of unfiltered cigarette smoke to the trachea and out through the nostrils. Each animal was instrumented to measure arterial pressure either via a femoral or carotid cannula. ECG was recorded using subcutaneous pin electrodes. Heart rate was measured continuously from the ECG using a cardiotachometer. Respiratory movements were obtained by measuring tracheal airflow temperature changes with a thermocouple placed in a sidearm of the tracheal cannula. All measurements were recorded continuously on a Beckman Instruments eight-channel Dynograph, Model R612. Experimental cigarettes (code 32, National Cancer Institute) were used in these experiments. The delivery of smoke was accomplished by drawing non-filtered smoke into a glass syringe. The smoke was then immediately forced through the trachea-to-nostrils cannula by hand at a relatively constant rate over a period of 10 sec. Smoke was thus prevented from being inspired into the lungs of the animal. Within 5 set after the delivery of smoke. room air was used to flush out any remaining smoke from the upper airway compartment. Occasionally, during infusion, smoke was observed to be escaping from the mouth. All such data collected in these animals were discarded. The smoke exposure was repeated 24 times both before and after bilateral cervical vagotomy. Paired or unpaired r-tests were used. as appropriate. for statistical analysis of results. Differences were considered significant when P < 0.05. Values are expressed as mean f SE.
METHODS Four
of each species were used in these experiincluded male albino rabbits, Orycrolqus cuniculus (I .9-2.7 kg), male SpragueeDawley rats, Rartus norce,qicus (354-425 g), malt golden hamsters, Mesocriceru.s uurutus (122-135 g), one male and three female cats, Felis c~utus(2.9-3. I kg) and two male and two female guinea pigs, Cork parcel/us (6 IO- I I50 g). Each animal was anesthetized with sodium pentobarbital either i.p. or i.v. A femoral or jugular catheter was inserted in order to administer supplemental anesthesia. Through a midcervical incision the trachea, carotid arteries, and vagi were exposed and carefully isolated from one another and from surrounding tissue. Two cannulae were inserted into the midcervical trachea. The caudal one was
RESULTS
animals
ments. They
Eflkct on respiration
Each species underwent a period of apnoea following upper air-way perfusion with cigarette smoke. The duration of apnoea was longest in rabbits and shortest in rats and hamsters (Table I). The onset of apnoea was different between species (Table 1). Rabbits and rats responded in about I set after perfusion began. Cats, hamsters and guinea-pigs were slower to respond (2.1-3.3 set). Only the guinea-pig seemed influenced by vagotomy. The mean time to onset was much slower (Table 1). This was largely influenced by 133
D. F. PETERSON et al.
134 Table I. Respiratory
changes associated with upper airway perfusion smoke Time of onset of apnoea (=I Intact Vagotomized
Rabbit Rat Guinea-pig Hamster Cat *Indicates
I.1 0.9 3.3 2.1 2.7
kO.2 f 0.2 k 0.8 * 0.4 k 0.4
1.2 * 0.6 k 9.1 i I .6 i 3.4 i
that the value is significantly
one individual which did not become 20 set after perfusion began.
apnoeic
0.2 0.2 2.9* 0.4 0.8 dXerent
until
Arterial pressure responses were not uniform between species. Large significant rises were observed in rabbits, rats and hamsters. This was true whether or not the vagi were intact (Table 2). In the guinea-pig there was no significant change in blood pressure due to smoke whether or not the vagi were intact. This was true in spite of the fact that the guinea-pig’s resting blood pressure was much lower than any other species. The cat underwent a small but significant rise in blood pressure due to smoke when vagi were intact. This rise was not present when the vagi were cut. However, cutting the vagi itself caused a significant rise in the blood pressure of the cat (Table 2).
in resoonse
to stimulation
Intact Rabbits Rat &mea-pig Hamster Cat
Resting
Response
106+2 120*5 61 k5 117*4 146k2
140*2 162k3 54 * 7 172k5 155*3
as a result of vagotomy.
Results of this study demonstrate that all five species of laboratory mammals tested undergo a period of apnoea when cigarette smoke is passed through the upper airways. Thus it is likely that all of these species, which represent three different phylogenetic orders, possess similar irritant receptors in the nasopharynx. These receptors have trigeminal afferent pathways in the rabbit (White and McRitchic, 1973) and the response is not influenced by olfactory receptors (McRitchie and White, 1974). Dog and man seem to possess similar receptors but do not always respond with apnoea (White and McRitchie, 1973). The reason for species differences in onset and duration of apnoea in our study is not clear. Presumably it is related to differences in location or sensitivity of the receptors in the nasopharynx. There appears to be parasympathetic vagal involvement in only two of the species studied. Both the rabbit and the rat underwent dramatic bradycardia with the vagi intact whereas the magnitude of the bradycardia was much reduced in the rabbit and abolished in the rat after vagotomy. The smaller but significant bradycardia which persisted in the rabbit
on heart rate
oressure chances
34.2 f 3. I 10.5 f 1.3 31.4k7.1 12.0 + 1.5 18.4 + 2.9
i_ 2.8 i 1.3 k 5.0 k I.8 * 1.9
DISCUSSION
There was striking differences in heart rate responses between species (Table 3). With vagi intact, rabbits and rats underwent large drops in heart rate. No significant changes occured in heart rates of guinea-pigs or cats but hamsters had a significant rise in heart-rate. Vagotomy itself did not change the resting heart rate of any species. There continued to be no heart rate responses to smoke in either the guinea-pig or cat. There was still a significant fall in heart rate in the rabbit but this change was not as profound as before vagotomy. There was significant Table 2. Mean arterial
Intact 26.5 9.8 21.7 10.0 14.3
of apnoea (se@ Vagotomized
tachycardia in the rat after vagotomy which was the reverse of the response observed beforehand. Heart rate in the hamster went up just as it did prior to vagotomy.
Effect on mean arterial pressure
Efects
Duration
with cigarette
Change
N
34 * 4*** 42 k 3*** -7*5 56 i 3*** 9*2**
12 12 12 I2 I2
of irritant
Vagotomized Resting I05 i 2 I21 i4 59 i 5 114*5 162i8t
receotors Response l38k3 167k3 54 * 7 163 k5 l63+6
‘Indicates a significant change from resting values. **P < 0.01, ***P -c 0.001. flndicates that the value is significantly different as a result of vagotomy; P < 0.05; each value is averaged number of tnals. Table 3. Mean heart rate changes
in resoonse
to stunulatlon
of irritant
Intact Rabbits Rat Guinea-pig Hamster cat
Resting
Response
254 i 374 * 237 i 331 * 179*9
133 230 228 361 I81
5 9 4 I4
+- I6 i 32 i 6 f II i8
Change ~ I21 + 15*** - 145 k 29*** -9*5 31 * 5** 3+1
with smoke
receotors
N II II I2 IO 8
from four animals.
N = total
with smoke
N
Resting
Vdgotomized Response
I2 I2 I2 I2 I2
252 5 6 375 * 12 236 i_ 3 309 * 9 169i9
207 393 232 343 169
+ + + * k
Change 33 * 2*** 46 & 3*** -5i4 49 * 4*** I*2
q I* 4 II IO
Change
N
-45 + 4***tt I8 ; 4**Wt -4?3 34 f 5*** Okl
II II I2 IO 8
*Indicates a significant change from resting values. **P < 0.01; ***P i 0.001. tlndications that the change intact was significantly greater than after vagotomy: ttP < 0.01; PttP < 0.001. $Indicdtes that the value is significantly diKerent as a result of vagotomy. pP < 0.001. Each value is averaged from four animals. number of trials.
N = total
Species differences
after vagotomy confirms previous findings (Robleto and Peterson, 1981), and supports the earlier conclusion that there is a withdrawal of sympathetic activity to the heart as part of the reflex pattern in the rabbit (Peterson et al., 1983). Sympathetic withdrawal was not supported in any other species. In the rat and hamster there was evidence of sympathetic excitation to the heart. In the hamster, heart rate rose to the same extent both before and after vagotomy, indicating no vagal influence on heart rate. In the rat bradycardia was reversed and became tachycardia after vagotomy indicating vagally mediated slowing which was competing with sympathetically mediated tachycardia. The sympathetic excitation was unmasked by vagotomy. There was no evidence of vagal or sympathetic influences on heart rate in response to smoke in either the guinea pig or cat. Blood pressure responses indicated that sympathetic vasoconstriction was a likely part of the reflex pattern in the rabbit, rat and hamster. The blood pressure rise was dramatic and similar before and after vagotomy. The small blood pressure rise observed in cats which was not present after vagotomy suggests that it may have occurred in response to stimulation of vagally mediated intrathoracic receptors activated by apnoea or secondary to apnoea. The majority of vagally mediated reflexes that have been reported produce a fall in blood pressure (Brown, 1979). Pressor reflexes have been reported in response to chemical stimulation in or near the coronary vasculature (Armour et al., 1977). There was no evidence for a sympathetic effect on blood pressure in the guinea-pig. Our results suggest several clearly different patterns of autonomic responses all activated by stimulation of irritant receptors in the upper airways. None of the species mimics the previously reported responses for the rabbit which include vagal and sympathetic slowing of the heart rate but sympathetic excitation to resistance vessels causing the blood pressure rise (Robleto and Peterson, 1981). Rats underwent strong vagal slowing of the heart but sympathetic excitation of the heart and periphery. Guinea-pigs and cats showed no clear evidence of vagal or sympathetic responses as a direct result of irritant receptor stimulation.
in response
135
to smoke
It is not possible to generalize that phylogenic differences explain differences in pattern of responses. The two species that had no apparent autonomic responses to smoke were not closely related: cat (carnivore) and guinea-pig (rodent). The species most closely related, rodents, had very different responses: rat, vagal and sympathetic components; hamster, sympathetic, guinea pig, neither. It appears that there are clearly unique differences between species in the organization of autonomic responses to stimulation of upper respiratory irritant receptors. There is no easy explanation for the meaning of these differences. Our findings do confirm, however, that generalizations between species are extremely risky when comparing autonomic responses to a given sensory stimulus using a common anesthesia.
REFERENCES
Armour J. A., Wurster R. D. and Randall W. C. (1977) Cardiac reflexes. In Neural Regulation of the Heart (Edited by Randall W. C.). Oxford University Press, New York. Brown A. M. (1979) Cardiac reflexes. In Handbook qf Physiology Section 2: The Cardiovascular System, Vol 1. The Heart (Edited by Berne R. M.). American Physiological Society, Bethesda, Maryland. McRitchie R. J. and White S. W. (1974) Role of trigeminal, olfactory, carotid sinus and aortic nerves in the respiratory and circulatory response to nasal inhalation of cigarette smoke and other irritants in the rabbit. Aust. J. exp. Biol. med. Sci. 52, 127-140. Peterson D. F., Coote J. H., Gilbey M. P. and Futuro-Neto H. A. (1983) Differential pattern of sympathetic outflow during upper airway stimulation with -smoke. Am. J. Physiol. 245, R433-R437. Robieto D. 0. and Peterson D. F. (1981) Reduction in cardiac contractility during upper respiratory stimulation with cigarette smoke. Am. J. Physiol. 240, H584H589. White S. W. and McRitchie R. J. (1973) Nasopharyngeal reflexes: integrative analysis of evoked respiratory and cardiovascular effects. Aust. J. exp. Biol. med. Sci. 51, 17-31. White S. W., McRitchie R. J. and Franklin D. L. (1974) Autonomic cardiovascular effects of nasal inhalation of cigarette smoke in the rabbit. Aust. J. exp. Biol. med. Sci. 52, 111-126.
0306-4492/84 $3.00 + 0.00 s:<;:!’ 1984 Pergamon Press Ltd
1984
SPECIES DIFFERENCES IN CIRCULATORY RESPONSES TO NASOPHARYNGEAL PERFUSION WITH SMOKE D. FRED Department
PETERSON, JACQUE L. BERGMAN and HUGH
of Physiology,
Oral
Roberts
University
School
G. TESTER
of Medicine,
7777 South
Lewis,
Tulsa, OK 74171, USA (Receiwd 23 September 1983) Abstract-l. Cardiovascular changes were observed in five species of laboratory mammals during upper airway perfusion with cigarette smoke. 2. Apnoea occured, both before and after vagotomy, in all species. 3. Blood pressure always went up in rabbits, rats and hamsters but was not much affected in cats and guinea-pigs. 4. Before vagotomy heart rate fell in rabbits and rats, rose in hamsters but did not change in cats and guinea-pigs. Vagotomy affected heart rate changes only in rabbits and rats. 5. Results demonstrate markedly different autonomic responses in different species.
INTRODUCTION
It is now well established that stimulation of upper respiratory irritant receptors in the rabbit produces a predictable pattern of cardiovascular changes. When cigarette smoke enters the nares, blood pressure rises, heart-rate falls and apnoea occurs. These responses have been observed in conscious (White and McRitchic, 1973) and anesthetized (Robleto and Peterson, 1981) animals. The rise in blood pressure is due to a dramatic increase in total peripheral resistance as a result of vasoconstriction in most of the peripheral vasculature (White et al., 1974). The fall in heart rate is largely due to increased parasympathetic (vagal) activity to the heart (Robleto and Peterson, 1981) although it is also partly due to decreased cardiac sympathetic nerve activity (Peterson pt al., 1983). Whether or not this pattern of autonomic responses is unique to the rabbit is not known. Much less profound heart rate and blood pressure responses have been observed in dog and man (White and McRitchie, 1973). In the present series of experiments responses were compared between the rabbit and four other species of common laboratory animals. Ail were challenged with cigarette smoke and their respiratory and cardiovascular responses observed.
used to maintain spontaneous ventilation of room air. The cranial cannula permitted the delivery of unfiltered cigarette smoke to the trachea and out through the nostrils. Each animal was instrumented to measure arterial pressure either via a femoral or carotid cannula. ECG was recorded using subcutaneous pin electrodes. Heart rate was measured continuously from the ECG using a cardiotachometer. Respiratory movements were obtained by measuring tracheal airflow temperature changes with a thermocouple placed in a sidearm of the tracheal cannula. All measurements were recorded continuously on a Beckman Instruments eight-channel Dynograph, Model R612. Experimental cigarettes (code 32, National Cancer Institute) were used in these experiments. The delivery of smoke was accomplished by drawing non-filtered smoke into a glass syringe. The smoke was then immediately forced through the trachea-to-nostrils cannula by hand at a relatively constant rate over a period of 10 sec. Smoke was thus prevented from being inspired into the lungs of the animal. Within 5 set after the delivery of smoke. room air was used to flush out any remaining smoke from the upper airway compartment. Occasionally, during infusion, smoke was observed to be escaping from the mouth. All such data collected in these animals were discarded. The smoke exposure was repeated 24 times both before and after bilateral cervical vagotomy. Paired or unpaired r-tests were used. as appropriate. for statistical analysis of results. Differences were considered significant when P < 0.05. Values are expressed as mean f SE.
METHODS Four
of each species were used in these experiincluded male albino rabbits, Orycrolqus cuniculus (I .9-2.7 kg), male SpragueeDawley rats, Rartus norce,qicus (354-425 g), malt golden hamsters, Mesocriceru.s uurutus (122-135 g), one male and three female cats, Felis c~utus(2.9-3. I kg) and two male and two female guinea pigs, Cork parcel/us (6 IO- I I50 g). Each animal was anesthetized with sodium pentobarbital either i.p. or i.v. A femoral or jugular catheter was inserted in order to administer supplemental anesthesia. Through a midcervical incision the trachea, carotid arteries, and vagi were exposed and carefully isolated from one another and from surrounding tissue. Two cannulae were inserted into the midcervical trachea. The caudal one was
RESULTS
animals
ments. They
Eflkct on respiration
Each species underwent a period of apnoea following upper air-way perfusion with cigarette smoke. The duration of apnoea was longest in rabbits and shortest in rats and hamsters (Table I). The onset of apnoea was different between species (Table 1). Rabbits and rats responded in about I set after perfusion began. Cats, hamsters and guinea-pigs were slower to respond (2.1-3.3 set). Only the guinea-pig seemed influenced by vagotomy. The mean time to onset was much slower (Table 1). This was largely influenced by 133
D. F. PETERSON et al.
134 Table I. Respiratory
changes associated with upper airway perfusion smoke Time of onset of apnoea (=I Intact Vagotomized
Rabbit Rat Guinea-pig Hamster Cat *Indicates
I.1 0.9 3.3 2.1 2.7
kO.2 f 0.2 k 0.8 * 0.4 k 0.4
1.2 * 0.6 k 9.1 i I .6 i 3.4 i
that the value is significantly
one individual which did not become 20 set after perfusion began.
apnoeic
0.2 0.2 2.9* 0.4 0.8 dXerent
until
Arterial pressure responses were not uniform between species. Large significant rises were observed in rabbits, rats and hamsters. This was true whether or not the vagi were intact (Table 2). In the guinea-pig there was no significant change in blood pressure due to smoke whether or not the vagi were intact. This was true in spite of the fact that the guinea-pig’s resting blood pressure was much lower than any other species. The cat underwent a small but significant rise in blood pressure due to smoke when vagi were intact. This rise was not present when the vagi were cut. However, cutting the vagi itself caused a significant rise in the blood pressure of the cat (Table 2).
in resoonse
to stimulation
Intact Rabbits Rat &mea-pig Hamster Cat
Resting
Response
106+2 120*5 61 k5 117*4 146k2
140*2 162k3 54 * 7 172k5 155*3
as a result of vagotomy.
Results of this study demonstrate that all five species of laboratory mammals tested undergo a period of apnoea when cigarette smoke is passed through the upper airways. Thus it is likely that all of these species, which represent three different phylogenetic orders, possess similar irritant receptors in the nasopharynx. These receptors have trigeminal afferent pathways in the rabbit (White and McRitchic, 1973) and the response is not influenced by olfactory receptors (McRitchie and White, 1974). Dog and man seem to possess similar receptors but do not always respond with apnoea (White and McRitchie, 1973). The reason for species differences in onset and duration of apnoea in our study is not clear. Presumably it is related to differences in location or sensitivity of the receptors in the nasopharynx. There appears to be parasympathetic vagal involvement in only two of the species studied. Both the rabbit and the rat underwent dramatic bradycardia with the vagi intact whereas the magnitude of the bradycardia was much reduced in the rabbit and abolished in the rat after vagotomy. The smaller but significant bradycardia which persisted in the rabbit
on heart rate
oressure chances
34.2 f 3. I 10.5 f 1.3 31.4k7.1 12.0 + 1.5 18.4 + 2.9
i_ 2.8 i 1.3 k 5.0 k I.8 * 1.9
DISCUSSION
There was striking differences in heart rate responses between species (Table 3). With vagi intact, rabbits and rats underwent large drops in heart rate. No significant changes occured in heart rates of guinea-pigs or cats but hamsters had a significant rise in heart-rate. Vagotomy itself did not change the resting heart rate of any species. There continued to be no heart rate responses to smoke in either the guinea-pig or cat. There was still a significant fall in heart rate in the rabbit but this change was not as profound as before vagotomy. There was significant Table 2. Mean arterial
Intact 26.5 9.8 21.7 10.0 14.3
of apnoea (se@ Vagotomized
tachycardia in the rat after vagotomy which was the reverse of the response observed beforehand. Heart rate in the hamster went up just as it did prior to vagotomy.
Effect on mean arterial pressure
Efects
Duration
with cigarette
Change
N
34 * 4*** 42 k 3*** -7*5 56 i 3*** 9*2**
12 12 12 I2 I2
of irritant
Vagotomized Resting I05 i 2 I21 i4 59 i 5 114*5 162i8t
receotors Response l38k3 167k3 54 * 7 163 k5 l63+6
‘Indicates a significant change from resting values. **P < 0.01, ***P -c 0.001. flndicates that the value is significantly different as a result of vagotomy; P < 0.05; each value is averaged number of tnals. Table 3. Mean heart rate changes
in resoonse
to stunulatlon
of irritant
Intact Rabbits Rat Guinea-pig Hamster cat
Resting
Response
254 i 374 * 237 i 331 * 179*9
133 230 228 361 I81
5 9 4 I4
+- I6 i 32 i 6 f II i8
Change ~ I21 + 15*** - 145 k 29*** -9*5 31 * 5** 3+1
with smoke
receotors
N II II I2 IO 8
from four animals.
N = total
with smoke
N
Resting
Vdgotomized Response
I2 I2 I2 I2 I2
252 5 6 375 * 12 236 i_ 3 309 * 9 169i9
207 393 232 343 169
+ + + * k
Change 33 * 2*** 46 & 3*** -5i4 49 * 4*** I*2
q I* 4 II IO
Change
N
-45 + 4***tt I8 ; 4**Wt -4?3 34 f 5*** Okl
II II I2 IO 8
*Indicates a significant change from resting values. **P < 0.01; ***P i 0.001. tlndications that the change intact was significantly greater than after vagotomy: ttP < 0.01; PttP < 0.001. $Indicdtes that the value is significantly diKerent as a result of vagotomy. pP < 0.001. Each value is averaged from four animals. number of trials.
N = total
Species differences
after vagotomy confirms previous findings (Robleto and Peterson, 1981), and supports the earlier conclusion that there is a withdrawal of sympathetic activity to the heart as part of the reflex pattern in the rabbit (Peterson et al., 1983). Sympathetic withdrawal was not supported in any other species. In the rat and hamster there was evidence of sympathetic excitation to the heart. In the hamster, heart rate rose to the same extent both before and after vagotomy, indicating no vagal influence on heart rate. In the rat bradycardia was reversed and became tachycardia after vagotomy indicating vagally mediated slowing which was competing with sympathetically mediated tachycardia. The sympathetic excitation was unmasked by vagotomy. There was no evidence of vagal or sympathetic influences on heart rate in response to smoke in either the guinea pig or cat. Blood pressure responses indicated that sympathetic vasoconstriction was a likely part of the reflex pattern in the rabbit, rat and hamster. The blood pressure rise was dramatic and similar before and after vagotomy. The small blood pressure rise observed in cats which was not present after vagotomy suggests that it may have occurred in response to stimulation of vagally mediated intrathoracic receptors activated by apnoea or secondary to apnoea. The majority of vagally mediated reflexes that have been reported produce a fall in blood pressure (Brown, 1979). Pressor reflexes have been reported in response to chemical stimulation in or near the coronary vasculature (Armour et al., 1977). There was no evidence for a sympathetic effect on blood pressure in the guinea-pig. Our results suggest several clearly different patterns of autonomic responses all activated by stimulation of irritant receptors in the upper airways. None of the species mimics the previously reported responses for the rabbit which include vagal and sympathetic slowing of the heart rate but sympathetic excitation to resistance vessels causing the blood pressure rise (Robleto and Peterson, 1981). Rats underwent strong vagal slowing of the heart but sympathetic excitation of the heart and periphery. Guinea-pigs and cats showed no clear evidence of vagal or sympathetic responses as a direct result of irritant receptor stimulation.
in response
135
to smoke
It is not possible to generalize that phylogenic differences explain differences in pattern of responses. The two species that had no apparent autonomic responses to smoke were not closely related: cat (carnivore) and guinea-pig (rodent). The species most closely related, rodents, had very different responses: rat, vagal and sympathetic components; hamster, sympathetic, guinea pig, neither. It appears that there are clearly unique differences between species in the organization of autonomic responses to stimulation of upper respiratory irritant receptors. There is no easy explanation for the meaning of these differences. Our findings do confirm, however, that generalizations between species are extremely risky when comparing autonomic responses to a given sensory stimulus using a common anesthesia.
REFERENCES
Armour J. A., Wurster R. D. and Randall W. C. (1977) Cardiac reflexes. In Neural Regulation of the Heart (Edited by Randall W. C.). Oxford University Press, New York. Brown A. M. (1979) Cardiac reflexes. In Handbook qf Physiology Section 2: The Cardiovascular System, Vol 1. The Heart (Edited by Berne R. M.). American Physiological Society, Bethesda, Maryland. McRitchie R. J. and White S. W. (1974) Role of trigeminal, olfactory, carotid sinus and aortic nerves in the respiratory and circulatory response to nasal inhalation of cigarette smoke and other irritants in the rabbit. Aust. J. exp. Biol. med. Sci. 52, 127-140. Peterson D. F., Coote J. H., Gilbey M. P. and Futuro-Neto H. A. (1983) Differential pattern of sympathetic outflow during upper airway stimulation with -smoke. Am. J. Physiol. 245, R433-R437. Robieto D. 0. and Peterson D. F. (1981) Reduction in cardiac contractility during upper respiratory stimulation with cigarette smoke. Am. J. Physiol. 240, H584H589. White S. W. and McRitchie R. J. (1973) Nasopharyngeal reflexes: integrative analysis of evoked respiratory and cardiovascular effects. Aust. J. exp. Biol. med. Sci. 51, 17-31. White S. W., McRitchie R. J. and Franklin D. L. (1974) Autonomic cardiovascular effects of nasal inhalation of cigarette smoke in the rabbit. Aust. J. exp. Biol. med. Sci. 52, 111-126.