Effect of early versus delayed hypoxic environment on neonatal rabbits.

We developed a low-cost, nonsurgical small animal model simulating the condition of cyanotic heart disease. Six groups of New Zealand white rabbits were studied: Group (1-C), 1-week-old control rabbits (n = 9) reared in room air; Group (1-H), 1-week-old rabbits placed in a hypoxic environment (10% O2) at birth (n = 5); Group (1-H-3), 1-week-old rabbits (n = 11) reared in room air for 3 days and then placed under hypoxic conditions identical to those for Group (1-C); Group (4-C), 4-week-old control rabbits (n = 12); Group (4-H), 4-week-old rabbits placed in hypoxia since birth (n = 11); Group (4-H-3), 4-week-old rabbits kept in room air after birth for 3 days (n = 7) before being exposed to hypoxia. Animals were anesthetized, heparinized, and instrumented for measurement of hemodynamic parameters. Right ventricular (RV) hypertrophy and hematocrit were assessed. Lung tissue was analyzed using quantitative morphometric techniques to assess arterial size, number, and muscularity. Group (1-H) and Group (4-H) developed RV hypertrophy, pulmonary hypertension, and erythrocytosis. The RV hypertrophy developed rapidly, as early as 1 week of age and became so pronounced by 4 weeks as to result in high mortality rate (35%). None of the animals in Groups (1-H-3) or (4-H-3) died while chronic changes of hypoxemia still developed. Placing rabbits after birth in room air for 3 days before exposing them to hypoxia appeared to play a protective role, moderating the development of pulmonary hypertension and severe RV hypertrophy. The effects of hypoxia appear to be at least partially dependent on the time of exposure. Utilizing our low-cost model will allow future work, including study of the effects of chronic hypoxemia on systemic ventricle exposed to an ischemic insult.