The effects of prolonged chilling upon in vitro Ca2+ accumulation, influx, and growth hormone release in rat adenohypophysis

The exposure of rat adenohypophysial tissue to iced media for periods of 30–60 min causes accumulation of Ca2+ by the tissue and an increased "basal" release of growth hormone into the media. The Ca2+ permeability following the chill, estimated from the uptake of 45Ca2+ by the tissue at 37 °C, is unchanged by the exposure to iced media. This suggests that the accumulation of Ca2+, which occurs during the chill, may be due simply to decreased efflux of Ca2+. The insensitivity of 45Ca2+ influx to the increased cellular content is readily explained if Ca2+ is rapidly sequestered after it has entered the cell. Our previous investigations snowed an increase in 45Ca2+ uptake (permeability) associated with hormone release which had been induced by elevated K+ or by partially purified releasing factor. We used tissue that had been chilled during collection. Our studies here indicate that our previous observations of increased uptake are qualitatively correct despite the cellular accumulation of Ca2+ that must have occurred before exposure to the secretagogues. The release of hormone seems to be related to the absolute cytoplasmic concentration of Ca2+ and release will occur in any circumstance that increases this concentration. The source of Ca2+ is not critical.