Hypoxia-induced cardiac hypertrophy in rabbits treated with verapamil and nifedipine.

Young rabbits were exposed, eight at a time, to 310 h of hypoxia (O2 at 70-80 torr), at atmospheric pressure. The animals were injected with 1 mg kg-1 nifedipine (F) or 5 mg kg-1 verapamil (V) or an equivalent volume of the vehicle (H) (Cremophor EL), i.p. twice a day. A fourth group (N), also injected with vehicle, was not made hypoxic. The animals were from 6 litters, 6 rabbits in each litter, and were distributed so that every group had litter mates in the other groups. Right ventricular hypertrophy was induced in all the hypoxic groups (H, +39%; V, +46%; F, +44%). Differences between groups were not statistically significant, but all were significantly hypertrophied relative to their normoxic litter mates (N). The right atria were less hypertrophied (H, +3.6%; V, +20%; F, +21.6%), but there was no left ventricular or left atrial hypertrophy. There was also a small increase in haematocrit in the hypoxic groups (H, +20.6%; V, +17.5%; F, +28.8%). The doses administered were equivalent to the highest used clinically producing blood levels of verapamil and nifedipine within or above the clinical range and had no effect on the development of cardiac hypertrophy.