Growth hormone as an autocrine/paracrine factor in chick embryogenesis: a retinal model

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This proposal is an extension of an ongoing program of research on the physiology of GH secretion and action. In postnatal development, GH is secreted from the pituitary gland (at the base of the brain) into the bloodstream, through which it gains access to every tissue in the body. These tissues express receptors that mediate the actions of pituitary GH on cellular growth and differentiation. However, while these 'endocrine' actions of pituitary GH are obligatory for postnatal development, embryonic or fetal growth is thought to be a 'growth-without-GH-syndrome', since it occurs prior to the development of the circulatory system and the differentiation of the pituitary gland. Embryonic or fetal growth is thus thought to be induced locally by tissue growth factors. Growth in the embryo may not, however, be 'paradoxical' since it may be mediated by local actions of GH produced in early embryonic tissues.