Immunohistochemical localisation of the 25 kDa heat shock protein in unstressed rats: possible functional implications.

The distribution of the 25 kDa heat shock protein (hsp 25) in a number of tissue types from unstressed rats was investigated. Immunohistochemical analysis showed that hsp 25 was not found in the thymus, brain (cerebral cortex and cerebellum), testis, adrenal, liver, spleen, or kidney. A number of cells in the anterior pituitary showed strong staining. These cells were tentatively identified as being either gonadotropes or thyrotropes. Strong staining was also observed in the blood vessels within these tissues. Hsp 25 was found to be localised predominantly to intestinal smooth muscle of the duodenum and colon and to vascular smooth muscle. Smooth muscle from other sites, such as the trachea, was also intensely stained. Lower and more variable amounts of staining were observed in cardiac and skeletal muscle. These observations suggest that hsp 25 is associated with cytoskeletal elements in muscle, and that the high staining intensity in smooth muscle might be due to the lack of internal architecture present in this muscle type.