Abstract
In the previous study, we have demonstrated that nicotine hardly induces catecholamine release from adrenal medulla of 21-day-old rats. The present study examined the responsiveness of the adrenal chromaffin cells to acetylcholine in vitro and neostigmine and oxotremorine in vivo in 21-day-old and 8-week-old rats. As assessed by electron microscopy, the number of the chromaffin granules was markedly decreased and the content of adrenaline in adrenals was diminished significantly by oxotremorine treatment in 8-week-old rats, whereas these changes did not occur in 21-day-old rats. Morphological changes of the adrenal chromaffin cells, with respect to exocytosis, were not observed in neostigmine-treated 21-day-old rats and acetylcholine-treated adrenal slices prepared from 21-day-old rats. Catecholamine release was hardly evoked by acetylcholine in these slices as judged by measuring the catecholamine content in the medium. These results indicate that the sensitivity of the chromaffin cells to these secretagogues in 21-day-old rats is very low when compared to that in young adult rats.
