Pigeon crop-sac as a model system for studying the direct and indirect effects of hormones and growth factors on cell growth and differentiation in vivo.

The pigeon crop-sac is an underappreciated and underutilized model that can be used to study the direct and indirect effects of hormones, growth factors, and other agents on cell proliferation and differentiative processes in vivo. It can thus allow the uncertainties that attend many in vitro methods to be avoided. In addition, the crop mucosal cells are homogeneous and the organ is structurally much less complex than most other hormone-responsive target organs, such as the mammary gland or prostate. The organ is well suited for various other studies such as analysis of second-messenger systems for PRL and growth factors and the effects of growth-inhibitory substances.