Morphoangiogenesis: a unique action of growth hormone.

A new form of angiogenesis, morphoangiogenesis (M-A), produces stem cells in vivo in adults. M-A was first identified in the knees of adult rabbits used to test intraarticular growth hormone (IAGH) injections as a method of regenerating articulophyseal cartilage (APC). M-A produces two structures capable of generating the stem cells. The first structure, which resembles cartilage canals normally observed only in fetuses, starts to develop 24 h after an IAGH injection. The second structure, which resembles renal glomeruli, develops several weeks later. Both structures contained thin-walled fenestrated capillaries and produced stem cells which contributed to the cascade generating articular cartilage. It was thought that other uses for morphoangiogenesis could be developed. These include tissue and organ formation using stem cells produced by M-A and the obstruction of neovascularization of cancers by M-A's ability to form structures which would obstruct nutritive vessels and thereby starve tumors.