2004 年 37 巻 4 号 p. 227-239
The pars tuberalis has been generally understood as a simple forward elongation of the glandular pituitary that develops into an architecturally similar structure. In rats, it is also believed that the pars tuberalis completely encircles the infundibular stalk at the ventral portion of hypothalamus. Intact Wistar-Imamichi rats were used in the present study, and frontal and sagittal serial sections of the pituitary gland/brain complex were prepared. Serial sections were stained with hematoxylin-eosin and with antibodies to LH-RH, S-100 protein or LH-RH receptor. Electron microscopic analyses were also conducted. The anatomical end of the epithelial structure of the pars tuberalis was observed at approximately 1 mm behind the optic chiasm. At this point, both the capillaries and the pars tuberalis spread and interdigitated over the median eminence. The pars tuberalis did not, however, completely encircle the pituitary stalk. Electron microscopic observations revealed some profiles of neuroendocrine nerve elements that were also present between the agranular cells of the pars tuberalis. A few LH-RH-positive nerve fibers were initially found just behind the optic chiasm, while the number of LH-RH-positive reactions increased around the capillary vessels. These reactions then decreased significantly and were sparsely distributed both in the diencephalon and in the area near the pituitary stalk where the two separated. LH-RH receptors were observed on S-100 protein-positive cells in the pars tuberalis.
The present observations show the significance of the pars tuberalis and its relationship between the anterior pituitary gland and the hypothalamus as organs that possibly form another collaborating mechanism for the regulation of hormone secretion of the anterior pituitary gland.
