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

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Abstract
The effect of ATP, Mg2+ or MgATP on the release of LHRH from rat hypothalamic granules was examined under in vitro conditions. Granules, isolated from adult male hypothalami, were incubated at 37.degree. 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 LHRH. The addition of MgATP stimulated the release of LHRH, the release being 62% greater than control. Addition of Mg2+ to the incubated granules also stimulated the release of LHRH. The magnitude of this Mg2+-stimulated release of LHRH was significantly (P < 0.01) lower than that of the MgATP-stimulated release, indicating that ATP stimulates LHRH release in a Mg2+-dependent manner. As both MgATP and Mg2+ alone stimulated LHRH release, these 2 release processes were characterized by incubating the granules under one of the following conditions: incubation at 4.degree. C in a buffered medium containing 0.15 M-KCl or incubation at 37.degree. C in a medium that does not contain KCl. Under these 2 incubation conditions, the MgATP-stimulated release of LHRH was not manifested, whereas the Mg2+-stimulated release of LHRH was manifested. On the basis of these differences, it is proposed that 2 different processes can lead to the release of LHRH from isolated hypothalamic granules: 1 process involves ATP and Mg2+ (MgATP) and another process involves Mg2+ alone.