The role of calcium in gonadotropin releasing hormone-induced luteinizing hormone secretion from the bovine pituitary /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1986.
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| Subjects: | |
| Online Access: | Link to ProQuest copy Link to OAKTrust copy ProQuest, Abstract |
| Abstract: | The hypothesis was tested that GnRH acts to release LH by increasing calcium uptake by the gonadotroph which in turn stimulates calcium-calmodulin activity and results in LH release from bovine pituitary cells as it does in the rat. Pituitary glands of calves (4-10 months of age) were enzymatically dispersed (0.2% collagenase) and grown for 5 days to confluency in multiwell plates (3x10^5/well). Cells treated with GnRH (10-1000 ng/ml in Hank's Balanced Salt Solution), Ca++ ionophore A23187 (2.5-10 μM), and ouabain (0.1-1 μM) all produced significant releases of LH. Extracellular Ca++ as low as 46 μM permitted GnRH-induced LH release in a pronounced "all or none" fashion, while thorough washing of the cells with 0.5 mM EGTA in Ca++-free media prevented the action of GnRH. GnRH (100 ng/ml) caused a rapid efflux (15 seconds) of ^45Ca++. Both GnRH-stimulated 45Ca efflux and LH release could be partially blocked by verapamil (10^-5 M). GnRH-induced LH release could also be blocked by nifedipine (10^-7-10^-5 M) and tetrodotoxin (10^-9 10^-7 M), although these agents did not affect 45Ca efflux. The calmodulin antagonists calmidazolium (10^-9-10^-8M) and W7 (10^-6-10^-5 M) were found to block GnRH induced LH release, as well as LH release induced by theophylline (1 mM), KC1 (25 mM), PGE2 (1 μM) and estradiol (25 ng/ml). These data indicated that: (1) calcium is required for GnRH action, but extracellular Ca++ does not regulate LH release; (2) GnRH elevates intracellular Ca++ by opening both voltage sensitive and receptor mediated Ca++ channels; (3) activation of calmodulin is one mechanism involved in GnRH-induced LH release. |
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| Item Description: | "Major subject: Veterinary Physiology." Typescript (photocopy). Vita. |
| Physical Description: | x, 175 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 117-158). |