Age-related effects of cardiac sympathetic denervation on the responses to cardiopulmonary receptor stimulation in piglets

The effects of right stellate ganglionectomy (RSG) and bilateral stellate ganglionectomy (BSG) on cardiovascular responses to phenyl biguanide (PBG, 80 micrograms/kg) were studied in 1- and 8-wk-old piglets. Animals were anesthetized with Saffan, paralyzed, thoractomized, and ventilated with 100% O2. Recordings of the ECG (lead II) and aortic pressure (AoP) were used to compute the maximum R-R interval, heart rate (HR), and mean AoP, and to determine the occurrence of atrioventricular conduction block (AVB). Right atrial injections of PBG in 1-wk-old piglets elicited AVB as well as decreases in AoP and HR in all animals; this response pattern was not altered by either RSG or BSG. The PBG response of neurally intact 8-wk-old animals was comprised of a decrease of HR without change in AoP; AVB occurred in three of six animals. After RSG or BSG, AoP decreased along with decreased HR, and now AVB occurred in all animals; changes of AoP and maximum R-R interval were greater after BSG than after RSG. These results suggest that the stellate ganglia exert a neuroprotective influence on cardiovascular function, requiring some degree of maturation for expression. Our findings support the hypothesis that an imbalance of cardiac autonomic innervation favoring parasympathetic activity may produce immature responses to cardiopulmonary afferent stimulation in older maturing animals.