AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 6 1050-R1057, Copyright © 1993 by American Physiological Society
Cardiac but not pulmonary receptors mediate depressor response to IV phenyl biguanide in conscious rabbits
L. B. Bell, K. P. O'Hagan and P. S. Clifford
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226.
Phenyl biguanide (PBG) stimulates pulmonary and cardiac receptors in the
cat and rabbit. Previous reports have suggested that pulmonary receptors
mediate the reflex respiratory responses and cardiac receptors mediate the
reflex hypotension and bradycardia. Using selective denervation of the lung
(LDX) and intrapericardial procaine to block cardiac nerves (CDX), we
investigated the specific role of pulmonary and cardiac receptors in the
reflex response to PBG infusion (60 micrograms/kg iv) in the conscious
rabbit. Breathing frequency, arterial pressure, heart rate, and renal
sympathetic nerve activity (RSNA) were recorded before and after LDX and
CDX. Before LDX and CDX, PBG infusion produced tachypnea, hypotension, and
bradycardia. This was accompanied by a withdrawal of RSNA to a level not
different from that evoked by ganglionic blockade. These responses were
preserved after LDX but were abolished after CDX with intrapericardial
procaine. Intrapericardial infusion of PBG produced no response. These
results indicate that in conscious rabbits both the respiratory and
cardiovascular responses to PBG infusion are mediated by cardiac receptors
not accessible from the epicardial surface. Furthermore, the reflex
hypotension is mediated largely by withdrawal of sympathetic nerve activity
resulting in a decreased peripheral resistance.
