Sasaki F, Nishioka S
Department of Veterinary Anatomy, College of Agriculture, Osaka Prefecture University, Japan.
Anat Rec. 1998 Jun;251(2):143-51. doi: 10.1002/(SICI)1097-0185(199806)251:2<143::AID-AR1>3.0.CO;2-#.
The pituitary gland of the dog is different from all animals and is described as "typical" for mammals. How might this complex pituitary gland of the dog be formed in fetal life? The current study examined the fetal development of the complex and unique dog pituitary and the ontogeny of specific cell types in the pars distalis.
Adenohypophysis of the beagle, from 25 to 60 days of gestation and at 2 days of age, was studied by immunocytochemical and histological staining.
At 25 days gestation, the primordium (Rathke's pouch) of the adenohypophysis began to form by an upward evagination from the epithelium of the primary oral cavity. At 38 days, the pituitary gland showed the same morphology as in adult dogs, being merely smaller. Five walls of Rathke's pouch (anterior wall [A], lateral walls [L], posterior wall [P], and upper wall [U] were found at 25 days, and by 38 days they had specialized into specific regions of the adenohypophysis through complex and unique processes. The pars intermedia was derived from the U and the dorsal area of the A. The pars tuberalis was derived from the dorsal area of the A. The pars distalis was formed by more singular processes: the peripheral areas of the pars distalis were first formed by A and P; then the ventral lumen of the extensive Rathke's lumen surrounded by these areas was filled up by proliferation of cells, although the dorsal lumen remains as Rathke's lumen after 38 days. The blood capillaries may play an important role in the development of parencymal cells in the Rathke's pouch during canine fetal life. At 30 days gestation, the first adrenocorticotropic hormone cells were found in the anterior- and posterior-ventral regions (derived from middle and ventral areas of the A and the P) of the pars distalis anlage, and blood capillaries invaded the parenchymal cells from the mesencyme surrounding the anlage. At 38 days, portal vessels without capillary loops in the median eminence had appeared, and growth hormone and luteinizing hormone cells appeared in the ventral areas of A and P in the pars distalis. By 52 days, when capillary loops were seen in the portal vessels in the median eminence, these types of cells spread through the whole pars distalis.
These areas in the epithelium of Rathke's pouch at 25 days may differentiate into specific regions of the pars distalis during subsequent fetal life, through complex processes that are characteristics to the canine species.
犬的垂体与所有其他动物不同，被描述为哺乳动物的“典型”垂体。犬的这种复杂垂体在胎儿期是如何形成的呢？本研究考察了犬复杂且独特的垂体的胎儿发育过程以及远侧部特定细胞类型的个体发生。
采用免疫细胞化学和组织学染色方法，研究了妊娠25至60天以及出生2天的比格犬腺垂体。
妊娠25天时，腺垂体原基（拉特克囊）由原始口腔上皮向上内陷开始形成。38天时，垂体呈现出与成年犬相同的形态，只是体积较小。妊娠25天时可发现拉特克囊的五壁（前壁[A]、侧壁[L]、后壁[P]和上壁[U]），到38天时，它们通过复杂而独特的过程特化形成腺垂体的特定区域。中间部源自上壁和前壁的背侧区域。结节部源自前壁的背侧区域。远侧部的形成过程更为独特：远侧部的周边区域首先由前壁和后壁形成；随后，被这些区域包围的宽大拉特克腔的腹侧腔隙被细胞增殖填满，不过38天后背侧腔隙仍保留为拉特克腔。在犬胎儿期，毛细血管可能在拉特克囊实质细胞的发育中起重要作用。妊娠30天时，在远侧部原基的前腹侧和后腹侧区域（源自前壁和后壁的中部和腹侧区域）发现了第一批促肾上腺皮质激素细胞，并且毛细血管从原基周围的间充质侵入实质细胞。38天时，正中隆起处出现了没有毛细血管袢的门静脉，生长激素细胞和促黄体生成素细胞出现在远侧部前壁和后壁的腹侧区域。到52天时，当正中隆起处的门静脉中出现毛细血管袢时，这些类型的细胞扩散至整个远侧部。
妊娠25天时拉特克囊上皮中的这些区域，在随后的胎儿期可能通过犬类特有的复杂过程分化为远侧部的特定区域。
