Preparation and characterization of modified hydroxyapatite particles by heparin.

Heparin-modified hydroxyapatite (HAP-HP) particles were prepared by an in situ coprecipitation method and were characterized by Fourier transform infrared spectrometry, x-ray diffraction and transmission electron microscopy. The heparin content in the particles was determined by a colorimetric assay and energy dispersive x-ray spectroscopy. Final results indicated that the crystallinity and crystal size decreased as both the Ca/P molar ratio and sulfur content increased by adding heparin. Blood compatibility of the HAP-HP particles was evaluated by activated partial thrombin time and prothrombin time. The clotting time of HAP-HP was prolonged remarkably compared with that of HAP. Above all, this novel HAP-HP material can be potentially applied as compatible blood materials for drug carriers of intravenous injection and artificial blood vessels.

The in vitro effect of leptin on growth hormone secretion from primary cultured ovine somatotrophs.

Although existing data suggest an influence of leptin on circulating levels of growth hormone (GH), the action site and properties of leptin are still controversial. Using primary cultured ovine pituitary cells, we studied the direct effect of leptin on the secretion of GH. Pituitary cells were dissociated by collagenase and subjected to Percoll gradient centrifugation to enrich the somatotroph population to 60-80% of cells. Treatment of primary cultured ovine somatotrophs with leptin (10(-9)-10(-7) M) for 30 min did not affect basal, GH-releasing hormone (GHRH) (10(-7) M)- or GH-releasing peptide-2 (GHRP-2)(10(-7) M)-stimulated GH secretion. Following treatment of cells for 1-3 d with leptin, GHRH-stimulated GH secretion was reduced and GHRP-2-stimulated GH secretion increased. The combined effect of GHRH and GHRP-2 on GH secretion was not altered by the treatment of cells with leptin for 3 d. GHRH receptor mRNA levels in cultured somatotrophs were decreased but GHRP receptor mRNA levels were increased by 3-d leptin treatment. These results suggest that leptin has a long-term effect on somatotrophs to reduce GHRH receptor synthesis leading to a decrease in GHRH-stimulated GH secretion. Leptin appears, however, to have an opposite effect on GHRP receptor synthesis leading to an increase in GHRP-stimulated GH secretion.

An immunological study on chromogranin A and B in human endocrine and nervous tissues.

Antisera were raised against synthetic peptides derived from the primary amino acid sequence of human chromogranin B. These antisera recognized in one- and two-dimensional immunoblotting a component previously designated as chromogranin B. In human chromaffin granules, the major endogenous processing product of chromogranin B is formed by proteolytic cleavage of the protein near the C-terminus. Immunohistochemical localizations were obtained with antisera against human chromogranins A and B and against a synthetic peptide corresponding to the B sequence. In human tissues, chromogranin B is co-stored with chromogranin A in the adrenal medulla, the anterior pituitary, parafollicular cells of the thyroid, in some cells of the endocrine pancreas and in some enterochromaffin cells, whereas only chromogranin A is found in the parathyroid gland and enterochromaffin cells of the gastric corpus mucosa. In the nervous system, no immunostaining was observed for chromogranin A and only a weak one for chromogranin B in some cells of the spinal cord. However, the Purkinje cells of the cerebellum were strongly positive for chromogranin B.