Effect of centrally administered somatostatin on pituitary thyrotropes in male rats

The effects of intracerebroventricularly administered somatostatin (SRIH-14 or -28) on growth and function of pituitary thyrotropes (TSH-cells) were e xamined in adult male Wistar rats. The animals were implanted with an intra cerebroventricular cannula and after a recovery period, administered three 1 mug doses of SRIH-14 or -28 dissolved in 5 mul saline every second day. C ontrols were treated in the same way with the same volume of saline only. T SH-producing cells were studied using the peroxidase-antiperoxidase immunoh istochemical procedure. Blood samples were collected for hormone (TSH) anal yses 5 days after the last injection. Both SRIH-treatments significantly de creased (p < 0.05) all morphometric parameters obtained for TSH-cells in co mparison with controls. The volume of TSH-cells decreased by 27%, nuclei by 44% and volume density by 33% in animals treated with SRIH-14. In animals treated with SRIH-28, these parameters were also significantly decreased (p < 0.05) (22%, 31%, and 25% respectively) compared to control rats. Serum c oncentrations of TSH were significantly decreased (p < 0.05) by 15% in SRIH -14- and by 12% in SRIH-28-treated animals in comparison with the controls. These observations suggest that centrally administered SRIH-14 or -28 is s pecifically involved in the control of growth and secretory activity of TSH cells.