TY - JOUR
T1 - In vivo demonstration of maturational changes of the chronotropic response to α-adrenergic stimulation
AU - McCormack, Jorge
AU - Gelband, Henry
AU - Villafañe, Juan
AU - Xu, Hui
AU - Stolfi, Adrienne
AU - Pickoff, Arthur S.
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 1988/7
Y1 - 1988/7
N2 - In vitro studies suggest that neonates and adults may have different cardiac chronotropic responses to α-adrenergic stimulation. To investigate these differences in vivo, three groups of dogs were studied. Group I = 12 puppies, ages 3-7 days; group II = 12 puppies ages 8-15 days, and group III = seven adult dogs. Heart rate and blood pressure determinations were made in the control setting and then after combined β-adrenergic and parasympathetic blockade (propranolol 0.6 mg/kg and bilateral vagotomies). Alpha-stimulation was then achieved with phenylephrine given in doses of 0.5, 1.0, and 10.0 μg/kg/min. A second, high dose of propranolol (1.0 mg/kg intravenously) was administered after the highest phenylephrine infusion dosage to assure complete β-blockade. Finally, α-blockade was achieved with phentolamine (groups I and II: 0.5 mg intravenously; group III: 5.0 mg intravenously). An α-mediated positive chronotropic effect was observed in 42 and 100% of subjects in groups I and II, respectively, but never observed in the adults. Whereas α-blockade with phentolamine resulted in a large decrease in heart rate of all puppies (groups I and II), it had no effect on adults. Blood pressure responses were similar in all three groups. Thus, there are important maturational changes in the chronotropic response to α-adrenergic stimulation and blockade demonstrable in the intact neonatal canine.
AB - In vitro studies suggest that neonates and adults may have different cardiac chronotropic responses to α-adrenergic stimulation. To investigate these differences in vivo, three groups of dogs were studied. Group I = 12 puppies, ages 3-7 days; group II = 12 puppies ages 8-15 days, and group III = seven adult dogs. Heart rate and blood pressure determinations were made in the control setting and then after combined β-adrenergic and parasympathetic blockade (propranolol 0.6 mg/kg and bilateral vagotomies). Alpha-stimulation was then achieved with phenylephrine given in doses of 0.5, 1.0, and 10.0 μg/kg/min. A second, high dose of propranolol (1.0 mg/kg intravenously) was administered after the highest phenylephrine infusion dosage to assure complete β-blockade. Finally, α-blockade was achieved with phentolamine (groups I and II: 0.5 mg intravenously; group III: 5.0 mg intravenously). An α-mediated positive chronotropic effect was observed in 42 and 100% of subjects in groups I and II, respectively, but never observed in the adults. Whereas α-blockade with phentolamine resulted in a large decrease in heart rate of all puppies (groups I and II), it had no effect on adults. Blood pressure responses were similar in all three groups. Thus, there are important maturational changes in the chronotropic response to α-adrenergic stimulation and blockade demonstrable in the intact neonatal canine.
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U2 - 10.1203/00006450-198807000-00013
DO - 10.1203/00006450-198807000-00013
M3 - Article
C2 - 2842725
AN - SCOPUS:0023894732
VL - 24
SP - 50
EP - 54
JO - Pediatric Research
JF - Pediatric Research
SN - 0031-3998
IS - 1
ER -