Zinc in the Anterior Pituitary of Rat: A Histochemical and Analytical Work

Abstract

Recent studies have suggested zinc to be a possible modulator of hormone secretion from the anterior pituitary. The three aims of the present study were: (1) to estimate the total amount of zinc in the gland by instrumental analysis; (2) to visualize the zinc at light and electron microscopical levels, and (3) to estimate the amount of zinc that can be visualized by histochemical techniques. PIXE measurement showed the total amount of zinc to be 74 ng/mg dry weight in males and 100 ng/mg dry weight in females, which is a highly significant difference. Histochemically, the zinc was shown by a modified Timm method and the selenium method to be localized to the secretory granules, and to a smaller extent to the Golgi apparatus of the somatotrophs, corticotrophs and thyrotrophs. Chelation of tissue zinc by intravital dithizone treatment effectively blocked subsequent selenium and Timm staining in the secretory granules, and PIXE assays of the chelated metal (extracted into CCU) showed it constitued less than 5% of the total zinc in the tissue. It is concluded from the study that zinc is present in the anterior pituitary of rats in rather high amounts and that loosely bound zinc, which is suggested to exert a biological effect by itself, can be located to the parts of the cells responsible for production, storing and release of hormones.

Zinc regulation of aminopeptidase B involved in neuropeptide production

“…AP-B is predicted to be regulated by zinc metal ion for its activity, as predicted from its HEXXH metallopeptidase motif. The presence of endogenous zinc in neuropeptide-containing secretory granules [11][12][13] that contain AP-B [6,15] raised the question of how AP-B activity may be regulated by zinc.…”

“…At this range of zinc concentration, AP-B in secretory vesicles would be partially inhibited by zinc, as shown in this study. Zinc is also present in secretory granules of pituitary and pancreas that store and secrete peptide hormones [12,13]. AP-B has been demonstrated in such endocrine secretory vesicles [15].…”

Cobalt-mediated Dimerization of the Human Natural Killer Cell Inhibitory Receptor

“…To detect potential dimer formation of KIR2DL1 in the presence of Zn 2ϩ and its related metal ions, soluble KIR2DL1 was incubated with various divalent metal ions and then chemically cross-linked with the reagent BS 3 (bis(sulfosuccinimidyl) suberate) to stabilize any dimer formation, if it exists. The physiological concentration of free Zn 2ϩ ion has been estimated to be approximately 0.25-1 M (28), based on the fact that 95% of zinc in serum is complexed with proteins (29,30). A much higher concentration of Zn 2ϩ (0.2 mM) was needed for measurements here to allow visualization of the effect of Zn 2ϩ on the oligomeric state of KIR2DL1, although some cross-linking was evident at 10 M Zn 2ϩ .…”

An Overview of a Wide Range of Functions of ZnT and Zip Zinc Transporters in the Secretory Pathway

“…16,19,22) Among vertebrates, some highly specialized cell types have cytoplasmic vesicles/granules accumulating high zinc contents. For example, pancreatic cells, 50) specialized glutamatergic neurons, 51) epithelial cells of the lateral prostate, 52) pigment epithelial cells in the retina, 53,54) granular convoluted tubule cells of submaxillary gland, 55) pituitary secretory cells, 56) sperm cells, 57,58) mast cells 59,60) and secreting mammary epithelial cells 61) are known to have zinccontaining vesicles/granules. These are controlled as part of the regulated secretory pathway, and hence specialized specific zinc transporters must be in operation.…”