Interaction of calcium and cyclic nucleotides in thyroliberin-stimulated prolactin release |
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Authors: | R H Matthews K A Kiefer W B Malarkey |
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Institution: | Departments of Physiological Chemistry and Medicine, The Ohio State University, Columbus, Ohio 43210, USA |
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Abstract: | The object of the present study was to determine the relative importance of Ca++ and cyclic nucleotides as “second messengers” in thyroliberin (TRH)-mediated prolactin (PRL) release in the GH3 and GH4 rat pituitary tumor cell lines. PRL, cyclic adenosine 3': 5'-monophosphate (cAMP), and cyclic guanosine 3': 5'-monophosphate (cGMP) were measured by radioimmunoassay (RIA) following TRH stimulation. TRH increased PRL release and cAMP levels in GH3 and GH4 cells, but cGMP increases were variable. Treatment with 1 mM theophylline increased PRL release and raised cAMP and cGMP. Addition of TRH to theophylline-pretreated cells produced further significant increases in PRL release without any additional increases in cAMP and cGMP. Co++, a Ca++ antagonist, abolished TRH-induced PRL release in a dose-dependent manner. The Co++ inhibition was partially reversed by Ca++ in GH3 or GH4 cells. Furthermore, the Ca++ ionophore A23187 stimulated PRL release. We conclude that Ca++ is the primary “second messenger” for TRH-mediated PRL release from GH3 or GH4 cells. |
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