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

Abstract

The pigeon crop-sac is a n 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.The most widely used procedures for testing the direct effects of hormones and growth factors on cell metabolism and/or proliferation involve in vitro methods with primary culture or established cell lines. Other in vitro studies apply similar analyses to tissue slices or fragments. Although these techniques yield useful information about actions of and interactions between or among hormones and growth factors on various cell functions, concern exists about the physiological significance of some results from such studies because the in vitro environment does not duplicate conditions found in vivo.The pigeon crop-sac is a unique structure because it allows the direct effects of hormones and growth factors on proliferation and the differentiated functions of a specialized cell type to be studied in vivo. The crop is found in all birds and in many species it is used as a temporary storage site for food. In some species it is also used as a display organ during courtship. In pigeons and doves, the crop-sac is further specialized to carry out an additional function-the nourishment of their young (Bernard, 1859; Beams and Meyer, which is used to feed the young squabs or nestlings. In 1935, W.R. Lyons discovered that if PRL was injected intradermally over the crop-sac, it caused local proliferation of mucosal cells under the site of injection (Lyons and Page, '35). Because of the bi-lobed nature of this structure (Fig. 1) it is possible to compare the activities of two different preparations in the same birds by injecting them over each lobe of the crop. It is also possible to test interactions between or among hormones or growth factors that are applied directly to the tissues or by injection of one preparation over the crop while a second substance is administered at a distant site so that it has systemic actions. Thus, the crop-sac allows for various kinds of analysis in vivo that could not be duplicated in vitro. Various injection schedules and procedures of response quantification have been used in studying the direct actions of PRL on the crop-sac (see Hiroi, '71; Nicoll, '73). METHODSThe procedure which we routinely use involves removing the feathers that overlie the crop of the pigeons on the day prior to the beginning of the series of four local injections. After the first intracutaneous injection is given the injection site is marked so...

Effects of Recombinant Ovine Interferon Tau, Placental Lactogen, and Growth Hormone on the Ovine Uterus1

“…Hyperprolactinemia causes endometrial hypertrophy and glandular differentiation and alters secretions found in the uterine lumen in both the rabbit and pig [27,28,[58][59][60]. In ruminants, PL may act on the endometrial GE to stimulate morphogenesis and differentiated function in a manner similar to that observed for PRL in its effects on the pigeon crop sac [71] and mouse mammary gland [73].…”

“…In other epitheliomesenchymal organs, PRL induces mitogenesis and alters postdifferentiation gene expression programs. For instance, in the pigeon crop sac, PRL stimulates proliferation of mitogenically competent germinal layer cells and causes the differentiated cells to enter an altered program of gene expression and phenotypic differentiation leading to production of large volumes of crop milk [67,71,72]. Hyperprolactinemia causes endometrial hypertrophy and glandular differentiation and alters secretions found in the uterine lumen in both the rabbit and pig [27,28,[58][59][60].…”

Ovine Placental Lactogen Specifically Binds to Endometrial Glands of the Ovine Uterus1

“…In other epitheliomesenchymal organs, PRL induces mitogenesis and alters postdifferentiation gene expression programs. For instance, in the pigeon crop sac, PRL stimulates proliferation of mitogenically competent germinal layer cells and causes the differentiated cells to enter an altered program of gene expression and phenotypic differentiation leading to production of large volumes of crop milk [47,49]. Hyperprolactinemia causes endometrial hypertrophy and glandular differentiation and alters secretions found in the uterine lumen of both the rabbit and pig [50][51][52][53].…”

“…Hyperprolactinemia causes endometrial hypertrophy and glandular differentiation and alters secretions found in the uterine lumen of both the rabbit and pig [50][51][52][53]. In ruminants, PL may act on the endometrial GE to stimulate morphogenesis and differentiated functions in a manner similar to effects of PRL on the pigeon crop sac [49] and mouse mammary gland [54].…”