A Morphological Study On The Releasing Pattern And Transport Route For Secretory Granules Of Polypeptide Hormones Of Neurohypophysis

Objective: To explore the structural foundations or the morphological evidences of the releasing pattern and extracellular normal transport route for secretory granules of polypeptide hormones of neurohypophysis. Methods: We observed the microstructure of the neurohypophysis of rat with HE stain by light microscope(LM). Ultrastructure of neurohypophysis was also observed by transmission and scanning electron microscope(TEM/SEM). We identified the type of the blood capillaries and studied the distribution of the secretory granules of polypeptide hormones in the neurohypophysis, expecting to find intact secretory granules coated with membrane in the perivascular space and in the interspace of tissue. By scanning the capsule of neurohypophysis, structural foundations of the extracellular normal transport route for polypeptide hormones or secretory granules were reseached.Result: The neurohypophysis is composed of unmyelinated nerve fibers, pituicytes and connective tissue abound in blood capillaries. The unmyelinated nerve fibers either terminate around the blood capillaries or approach near pituicytes. The endothelium of the blood capillaries belongs to the fenestrated (50nm)type, separated from the perivascular connective tissue by basement membrane. The intact secretory granules(100~300nm)coated with membrane exist not only in the endings or varicosities of the unmyelinated nerve fibers but also occasionally in the perivascular space. The pituitary capsule is composed of simple squamous epithelial cells, among which there are many irregular epithelial openings(2~5μm). Secretory granules can be seen frequently near the epithelial openings. There are many macrophages on the surface of the pituitary capsule whose shapes vary according to their distinct functions. Under the epithelia is loose connective tissue whose chief elements are collagen fibers.Conclusion: These findings indicate that the releasing pattern of polypeptide hormones or secretory granules of neurohypophysis involves a whole-releasing together with granular membrane. After releasing, the polypeptide hormones or secretory granules enter easily into cerebrospinal fluid(CSF)via the perivascular space, interspace of tissue and epithelial openings rather than directly into blood circulation through the walls of blood capillaries.