Intracisternal TRH analog increases gastrin release and corpus histidine decarboxylase activity in rats

Thyrotropin-releasing hormone (TRH) acts in brain stem nuclei to induce vag ally mediated stimulation of gastric secretion. The effects of intracistern al injection of the TRH analog RX-77368 on plasma gastrin levels and corpus histidine decarboxylase (HDC) activity were studied in 48-h fasted conscio us rats. RX-77368 (25-100 ng) increased plasma gastrin levels by threefold at 30 min, which remained significantly higher than control at 2 and 4 h po stinjection. Corpus HDC activity began to increase at 2 h and reached a pea k at 4 h postinjection with a 21-fold maximum response observed at 50 ng. M orphological changes in the appearance of corpus HDC-immunoreactive cells c orrelated well with HDC activity. Pretreatment with gastrin monoclonal anti body completely prevented RX-77368 stimulatory effects on HDC activity. Atr opine significantly attenuated gastrin increase at 30 min by 26%. These res ults indicated that in conscious fasted rats, TRH analog acts in the brain to increase corpus HDC activity in the enterochromaffin-like cells, which i nvolves gastrin release stimulated by central TRH analog.