TY - JOUR
T1 - The roles of adenosine in regulating the respiratory and cardiovascular systems in chronically hypoxic, adult rats
AU - Thomas, Teresa
AU - Marshall, Janice M.
PY - 1997
Y1 - 1997
N2 - 1. We have investigated the roles of adenosine in regulating the respiratory and cardiovascular systems of rats that were made chronically hypoxic for 3-4 weeks from 6 weeks of age (CH rats) in an hypoxic chamber at 12% O2. They were studied under anaesthesia while breathing 12% O2 and during acute hypoxia (breathing 8% O2 for 5 min) before and after addition of the adenosine receptor antagonist 8-phenyltheophylline (8-PT, 10 mg kg-1). The results were compared with those obtained from normoxic (N) rats in a previous study. 2. CH rats breathing 12% O2 had greater minute ventilation (V̇(E)) than N rats breathing air, but their levels of arterial blood pressure (ABP), heart rate (HR), femoral vascular conductance (FVC) and cerebral vascular conductance (CVC) were fully comparable. 8-PT increased tidal volume (V(T)) in CH rats indicating a greater tonic central inhibitory influence of adenosine on V(T) than in N rats. However, 8-PT had no effect on cardiovascular variables, indicating no tonic cardioinhibitory or vasodilator influence of adenosine in CH rats. 3. Acute hypoxia in CH rats increased V̇(E) such that at the 5th minute of 8% O2 absolute V̇(E) was comparable to that of N rats breathing 8% O2. Moreover, in CH rats 8-PT increased V(T) at the 5th minute of 8% O2 indicating that the central inhibitory influence of adenosine limits the ability to maintain V(T) in acute hypoxia as it does in N rats. 4. Eight per cent O2 also produced a fall in ABP in CH rats that was comparable to that induced in N rats by the larger change from air to 8% O2. However, the changes in HR were similar in CH and N rats while the increases in FVC and CVC were smaller in CH rats. This suggests that the ability of the secondary effects of hyperventilation and of the baroreceptor reflex to maintain cardiac output and thereby ABP is reduced in CH rats. 5. Whereas 8-PT substantially reduced the hypoxia-induced increases in FVC and CVC in N rats, it had a small effect in CH rats (P = 0.054 and 0.06, respectively). Further, acute hypoxia in CH rats had no effect on the K+ concentration in the venous efflux of hindlimb K+ (K(v)+) before or after 8-PT treatment. We suggest that in CH rats, the dilator influence of adenosine in acute hypoxia occurs via actions on the blood vessel walls: there was no evidence that adenosine can release dilator concentrations of K+ from skeletal muscle fibres in CH rats as proposed for N rats.
AB - 1. We have investigated the roles of adenosine in regulating the respiratory and cardiovascular systems of rats that were made chronically hypoxic for 3-4 weeks from 6 weeks of age (CH rats) in an hypoxic chamber at 12% O2. They were studied under anaesthesia while breathing 12% O2 and during acute hypoxia (breathing 8% O2 for 5 min) before and after addition of the adenosine receptor antagonist 8-phenyltheophylline (8-PT, 10 mg kg-1). The results were compared with those obtained from normoxic (N) rats in a previous study. 2. CH rats breathing 12% O2 had greater minute ventilation (V̇(E)) than N rats breathing air, but their levels of arterial blood pressure (ABP), heart rate (HR), femoral vascular conductance (FVC) and cerebral vascular conductance (CVC) were fully comparable. 8-PT increased tidal volume (V(T)) in CH rats indicating a greater tonic central inhibitory influence of adenosine on V(T) than in N rats. However, 8-PT had no effect on cardiovascular variables, indicating no tonic cardioinhibitory or vasodilator influence of adenosine in CH rats. 3. Acute hypoxia in CH rats increased V̇(E) such that at the 5th minute of 8% O2 absolute V̇(E) was comparable to that of N rats breathing 8% O2. Moreover, in CH rats 8-PT increased V(T) at the 5th minute of 8% O2 indicating that the central inhibitory influence of adenosine limits the ability to maintain V(T) in acute hypoxia as it does in N rats. 4. Eight per cent O2 also produced a fall in ABP in CH rats that was comparable to that induced in N rats by the larger change from air to 8% O2. However, the changes in HR were similar in CH and N rats while the increases in FVC and CVC were smaller in CH rats. This suggests that the ability of the secondary effects of hyperventilation and of the baroreceptor reflex to maintain cardiac output and thereby ABP is reduced in CH rats. 5. Whereas 8-PT substantially reduced the hypoxia-induced increases in FVC and CVC in N rats, it had a small effect in CH rats (P = 0.054 and 0.06, respectively). Further, acute hypoxia in CH rats had no effect on the K+ concentration in the venous efflux of hindlimb K+ (K(v)+) before or after 8-PT treatment. We suggest that in CH rats, the dilator influence of adenosine in acute hypoxia occurs via actions on the blood vessel walls: there was no evidence that adenosine can release dilator concentrations of K+ from skeletal muscle fibres in CH rats as proposed for N rats.
UR - http://www.scopus.com/inward/record.url?scp=0030959205&partnerID=8YFLogxK
U2 - 10.1111/j.1469-7793.1997.439bn.x
DO - 10.1111/j.1469-7793.1997.439bn.x
M3 - Article
C2 - 9192314
AN - SCOPUS:0030959205
SN - 0022-3751
VL - 501
SP - 439
EP - 447
JO - Journal of Physiology
JF - Journal of Physiology
IS - 2
ER -