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.