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Comparison of the Effects of ATP, Mg2+, and MgATP on the Release of Luteinizing Hormone‐Releasing Hormone from Isolated Hypothalamic Granules

Abstract: The effect of ATP, Mg2+, or MgATP on the release of luteinizing hormone‐releasing hormone (LH‐RH) from hypothalamic granules was examined under in vitro conditions. Granules, isolated from adult male hypothalami, were incubated at 37°C in a buffered (pH 7.8) medium containing 0.15 m‐KCl. The addition of ATP to the incubation mixture did not stimulate the release of LH‐RH. In contrast, the addition of MgATP stimulated the release of LH‐RH, the release being 62% greater than control. The addition of Mg2+ to the incubated granules also stimulated the release of LH‐RH. However, the magnitude of this Mg2+‐stimulated release of LH–RH was significantly (P < 0.01) lower than that of the MgATP‐stimulated release, indicating that ATP stimulates LH‐RH release in a Mg2+‐dependent manner. As both MgATP and Mg2+ alone stimulated LH‐RH release, we characterized further these two release processes by incubating the granules under one of the following conditions: incubation at 4°C in a buffered medium containing 0.15 m‐KCl or incubation at 37°C in a medium that does not contain KCl. Under these two incubation conditions, the MgATP‐stimulated release of LH‐RH was not manifested, whereas the Mg2+‐stimulated release of LH‐RH was manifested. On the basis of these differences, we propose that two different processes can lead to the release of LH‐RH from isolated hypothalamic granules: one process involves ATP and Mg2+ (MgATP) and another process involves Mg2+ alone.