Somatostatin acts by inhibiting pituitary TSH cells in female rats

The effects of intracerebroventricularly (i.c.v.) administered synthetic so matostatins (SRIH-14 and SRIH-28) on pituitary TSH cells of adult female ra ts were studied. The animals were i.c.v. injected with three 1.0 mu g (5 mu l) doses of SRIH-14 or SRIH-28 every second day and sacrificed five days a fter the last dose. The controls received an equivalent volume of saline in the same manner according to the same schedule. The pituitary glands were excised and used for immunohistochemical and morphometric evaluation. The r esults obtained demonstrated a somatostatin-related decrease in relative pi tuitary weight. The morphometric analyses showed decreased volumetric densi ty of TSH-immunoreactive cells in SRIH-treated groups, but this difference was more expressed in SRIH-14 treated animals than in those receiving SRIH- 28. On the basis of these results if can be concluded that centrally admini stered somatostatins inhibit TSH cells.