Ultrastructural localization of thyrotropin (TSH)-like immunoreactivity in specific secretory cells of the hypophyseal pars tuberalis in the Djungarian hamster, Phodopus sungorus.

Specific secretory cells in the hypophyseal pars tuberalis of Djungarian hamsters maintained under different photoperiods were investigated immunocytochemically by means of the colloidal gold technique using antibodies against rat thyrotropin (TSH). Secretory cells of animals kept under long photoperiods (LD16:8) showed positive staining of secretory granules (diameters 90-130 nm), whereas other intracellular structures were free of immunoreactivity. In animals kept under short photoperiods (LD8:16) secretory cells displayed increased numbers of secretory granules, but these organelles were devoid of immunoreactivity. In contrast, immunoreactivity of thyrotropes in the pars distalis did not differ between the two groups of animals investigated. The present results confirm earlier light-microscopical studies that in the pars tuberalis specific secretory, cells show TSH-like immunoreactivity; however, they differ in their reactivity pattern from classical thyrotropes in the pars distalis.