Effect of prolonged beta-adrenoceptor blockade on heart weight and ultrastructure in young rabbits.

1 Young rabbits were treated for 30 days or 6 weeks with propranolol or oxprenolol to provide dose-levels similar to those used clinically. 2 Relative to litter matched controls the treated rabbits exhibited a reduced rate of growth. 3 Morphometric studies showed that prolonged beta-adrenoceptor blockade had no effect on the myofibrillar volume as a proportion of cell volume. 4 Prolonged beta-blockade increased the proportion of the extracellular space occupied by vascular tissue.