Calcium modifies the effects of thyroliberin and somatostatin on hormone release from cell cultures of the rat anterior pituitary.

Role of calcium (Ca2+) in the effects of thyroliberin (TRH) and somatostatin (SRIF) on the release of growth hormone (GH), prolactin (PRL) and thyroid stimulating hormone (TSH) from the rat adenohypophyseal cells in primary monolayer cultures has been studied. Decrease of extracellular Ca2+ diminished the stimulatory effects of TRH on TSH and PRL release. Ca2+ is also an important factor in the mechanism of SRIF action. Data obtained in the experiments with high Ca2+ levels in the medium indicate that some antagonistic interrelationship exists between Ca2+ and SRIF. These results suggest that the participation of cAMP alone is not sufficient for stimulus-secretion coupling. Another messenger, namely Ca2+, is necessary for the effects of hypothalamic hormones. On the other hand, the contribution of Ca2+ to the secretory process in mammotrophs, somatotrophs and thyrotrophs is not equal. PRL and TSH secretion is more dependent on the presence of extracellular Ca2+ than the release of GH.