Microvascular development in chick anterior latissimus dorsi following hypertrophy.

Right (hypertrophied) and left (control) anterior latissimus dorsi muscles (ALD) were injected with India ink to visualise microvascular geometry in these muscles. The ALD muscles have multiple feeding arterioles that branch into meshworks of arcade arterioles. Transverse arterioles arise from the arcade system and give rise to capillaries. Hypertrophy is attended by an increase in the combined length of arterioles in the arcade system due to an increase in the number of arcade segments. Morphometric characteristics of each segment remained constant. Hypertrophy produced a significant increase in the numbers of capillaries per individual muscle fibre due to an increase in number of transverse arterioles and an increase in number of capillaries per transverse arteriole. However, the increased numbers of capillaries per fibre just matched fibre hypertrophy, so that the number of exchange vessels per cross sectional area of muscle remained constant. These results are consistent with the argument that muscle growth is the primary determinant of capillarity.