text: Growth factor and clotting factors are paracrine signaling agents. The local action of growth factor signaling plays an especially important role in the development of tissues. Also, retinoic acid, the active form of vitamin A, functions in a paracrine fashion to regulate gene expression during embryonic development in higher animals. 
  In insects, Allatostatin controls growth through paracrine action on the corpora allata.
  In mature organisms, paracrine signaling is involved in responses to allergens, tissue repair, the formation of scar tissue, and blood clotting. Histamine is a paracrine that is released by immune cells in the bronchial tree. Histamine causes the smooth muscle cells of the bronchi to constrict, narrowing the airways.