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Topographical appearance of adenohypophysial cells with special reference to the development of the portal system.

To determine whether or not the portal vessels play any essential role on the cytogenesis of adenohypophysis through the mediation of hypothalamic neurohormones, chronological and topographical relations between the portal system and adenohypophysial cells have been studied in fetal rats aged from 14.5 to 18.5, by vascular infusion with India ink and by immunohistochemistry. On day 14.5 the intraglandular fossa (Atwell's recess) receives several blood vessels (primitive portal vessels) from the subtuberal capillary plexus and a pair of fine branches from the internal carotid arteries: those blood vessels anastomose within the recess. On day 15.5 the recess becomes narrow but the vasculature extends posteriorly into the growing anterior wall of the rathke's pouch, in which they sprout short branches showing terminal dilations. Immunoreactive ACTH cells first appear in the ventral-middle portion of the pars distalis, where the vascular sproutings are not evident. On day 16.5 the intraglandular blood vessels spread through the pars distalis and connect occasionally with extraglandular venous system suggesting the initiation of the hypophysial portal circulation. TSH cells first appear sporadically in the posterior part of the pars distalis, where blood vessels are still scarce and very occasional cells abut on te sinusoids. On day 17.5, the recess becomes indistinct and pituitary acquires the mature shape. The intraglandular vasculature of the portal system makes a dense meshwork in the adenohypophysis except the pars intermedia. LH cells appear first in the ventral region of the anterior half of the adenohypophysis, where occasional cells appear abutting on the sinusoids. The conclusion is that the portal blood supply, which might convey hypothalamic neurohormones, is not essential or initial cytogenesis of the adenohypophysial cells studied here.