Thyroxine replacement after hypophysectomy alters the pattern of enkephalin localisation in the adrenal medulla of the fetal sheep

Presence of ten isoforms of monocarboxylate transporter (MCT) family in the bovine adrenal gland

This study provides novel information regarding the existence and precise cellular localization of various monocarboxylate transporters (MCTs) in the mammalian adrenal gland. RT-PCR results revealed that 10 MCT isoforms, namely MCT1, MCT2, MCT3, MCT4, MCT5, MCT8, MCT9, MCT10, MCT13, and MCT14 are expressed in the bovine adrenal gland. MCTs (MCT1-MCT8) proteins were examined by Western blot analysis in the bovine adrenal gland. The precise cellular localization of six MCT isoforms (MCT1-MCT5 and MCT8) within the different zones of the adrenal gland has been determined by immunohistochemical and immunofluorescence confocal laser microscopy analyses. To gain insight on the species differences for the expression profiles of MCT isoforms in this vital organ, we also examined the expression and cellular localization of MCT1-MCT8 in the rat adrenal gland. Some discrepancies in MCTs profiles between cattle and rat have been observed in the different zones of the adrenal gland. The tissue distribution pattern of MCT isoforms in the steroid-secreting adrenal cortex and catecholamine-secreting adrenal medulla suggests that they may play distinct roles in the regulation of the different hormone biosynthesis in the adrenal gland. Also, it is possible that different MCT isoforms in adrenal gland can be differentially regulated under acute or chronic conditions. This report can form the basis for future research on the regulation of these transporters in the adrenal gland.

Adrenal gland SNAP-25 expression is altered in thyroid hormone receptor knock-out mice

SNAP-25 is a protein in neurons and neuroendocrine cells, which is involved, together with syntaxin and VAMP, in neurotransmitter release and neurite outgrowth. Since the thyroid hormone receptors TR alpha and TR beta are essential for nervous system development, their possible role in regulating the expression of these vesicle trafficking proteins was examined by analysing SNAP-25 levels in TR alpha and TR beta knock-out mice. Immunoblotting and RT-PCR showed that SNAP-25 levels are increased in the adrenal gland, but not in cerebellum, in knock-out mice, while syntaxin-1 and VAMP-2 are unaffected in either tissue. Treatment of the pheochromocytoma-derived cell line PC12 with the thyroid hormone L-3,5,3'-triiodothyronine (T3) decreased SNAP-25 expression. Together, these data suggest that thyroid hormones exert a negative regulatory effect on SNAP-25 in adrenal medullary neuroendocrine cells.