Effects of chronic hypoxia during maturation on the negative chronotropic effect of [H+] on the rabbit sino-atrial node.
Previous studies in our laboratory have shown an effect of 12 weeks of hypoxia on the electrophysiology of the heart. This study was designed to determine the effects of hypoxia for shorter periods (1, 2, 3 and 6 weeks) on the neonatal heart as well as the chronotropic effects of [H+] on sino-atrial automaticity. Rabbits (2 days of age) were raised for 1, 2, 3 or 6 weeks in either a normal or hypoxic environment. At the end of 1, 2, 3 or 6 weeks, they were killed and studied using an isolated sino-atrial tissue preparation and standard microelectrode techniques. Measurements of hematocrit, ventricular weight and ventricular total protein were made. Right ventricular hypertrophy appeared at 2 and 3 weeks in the hypoxic hearts. There was no difference in left ventricular weight or total protein between normal and hypoxic groups over the time studied. Both the basal and maximal (isoproterenol stimulated) spontaneous rates decreased with age. The baseline and maximal rates from hypoxic rabbits were significantly less than those from normal rabbits at 3 and 6 weeks (p less than 0.05). The net negative chronotropic effect of elevated [H+] was more pronounced in the hypoxic than the normal preparations at 3 and 6 weeks. In summary, neonates raised in hypoxia for as short a period as 3 weeks show right ventricular hypertrophy and a decrease in sino-atrial automaticity. The net negative chronotropic effect of [H+] is enhanced with development and chronic hypoxia.
Posner
P
P
Department of Physiology, University of Florida Health Sciences Center, Gainesville.
Baker
S P
SP
Epstein
M L
ML
MacIntosh
B R
BR
Buss
D D
DD
D000138:Acidosis / Q000209:etiology; D000818:Animals; D000831:Animals, Newborn; D001835:Body Weight; D002907:Chronaxy / Q000187:drug effects; D005260:Female; D006340:Heart Rate, Fetal / Q000187:drug effects* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000150:complications / Q000503:physiopathology*; D009924:Organ Culture Techniques; D009929:Organ Size; D011247:Pregnancy; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects* / Q000502:physiology