Biomedical subjects
Publications and source records attributed to Y Hatada.
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The effects of A23187 and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the phosphorylation of proteins in normal rat anterior pituitary cells were compared. A23187 rapidly activated the phosphorylation of at least 5 proteins (45, 47, 53, 54 and 58 kDa), which reached the maximal level in 2-10 min, and decreased gradually thereafter. In contrast, TPA activated the phosphorylation of at least 6 proteins (45, 62, 64, 72, 76 and 82 kDa), which were mostly distinguished from those activated by A23187. TPA-induced response was elicited more slowly, reached a plateau after about 10 min, and was sustained thereafter. These results suggest that the protein phosphorylation stimulated by A23187 and TPA is conducted by different mechanisms.
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The intermediate lobe of the rat pituitary gland is a homogeneous population of cells which synthesize and secrete various peptides related to ACTH and lipotropin derived from a common precursor, proopiomelanocortin. Catecholamine beta-receptor (beta-adrenoceptor) and dopamine receptor which are present in the intact cells of the intermediate lobe, remain functional in the enzymatically dispersed cells. In this study we investigated the mechanism by which beta-endorphin is released from the dispersed cells of the neurointermediate lobe of the rat pituitary gland. 1-Isoproterenol stimulated the release of immunoreactive beta-endorphin-like peptide (IR-beta-Ep) and the accumulation of adenosine 3', 5'-monophosphate (cAMP). On the other hand, dopaminergic drugs, apomorphine, bromocriptine, dopamine, lergotrile and lisuride, decreased the rate of release of IR-beta-Ep. Dopamine also inhibited the stimulatory effects of 1-isoproterenol on the release of IR-beta-Ep and cAMP accumulation. Dopamine antagonists, fluphenazine and sulpiride, diminished the inhibitory effects of dopamine on the release of IR-beta-Ep and cAMP accumulation which were stimulated by 1-isoproterenol. it has been reported that cholera toxin enhanced the release of IR-beta-Ep and the accumulation of cAMP in the rat neurointermediate lobe. After preincubation in the incubation medium containing 30 nM cholera toxin for 2 hours, the cells (CT cells) showed spontaneous release of IR-beta-Ep and cAMP accumulation. 1-Isoproterenol had no effect on the release of IR-beta-Ep and cAMP accumulation in CT cells. Dopamine, however, inhibited both the release of IR-beta-Ep from CT cells and cAMP accumulation in CT cells. These results suggest that dopamine may be involved in the regulatory mechanism of IR-beta-Ep release from the dispersed cells of the rat neurointermediate lobe.
The presence of Ca2+ in the incubation medium was required for stimulation of the release of the immunoreactive beta-endorphin-like peptide (IR-beta-EP) from the dispersed cells of the neurointermediate lobe of rat pituitary gland by adenosine 3',5'-monophosphate (cAMP) analogs, a phosphodiesterase inhibitor, L-isoproterenol, cholera toxin and forskolin. The basal release observed in the absence of the stimulants was also dependent on the addition of Ca2+. A calcium antagonist (verapamil) inhibited the effects of the stimulants. A calcium ionophore (A23187) enhanced the release of IR-beta-EP, but did not stimulate the formation of cAMP. These findings suggest that Ca2+ has the essential role in the release of beta-endorphin from the neurointermediate lobe of rat pituitary gland.
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The intermediate lobe cells of pituitary gland synthesize and secrete bioactive peptides derived from proopiomelanocortin. In the present study, we investigated the effects of cholera toxin on the release of beta-endorphin (beta-Ep) from dispersed-intermediate lobe cells of rats. Cholera toxin added into culture medium, enhanced the intracellular accumulation of adenosine 3', 5'-monophosphate (cAMP) and the release of beta-endorphin like immunoreactive substance (beta-END-LIS). A positive dose-response relationship existed between the concentration of cholera toxin and the release of beta-END-LIS or the accumulation of cAMP. Maximal response was obtained with approximately 3 X 10(-10) M (in beta-END-LIS release) and 1 X 10(-9) M (in cAMP accumulation) concentration of cholera toxin. Incubation with cholera toxin (3 X 10(-8) M) resulted in a significant rise of cAMP accumulation after 20-30 min, and a 2-2.5 fold increase of beta-END-LIS release occurred after 60 min in comparison with nontreated cells. cAMP analog and phosphodiesterase inhibitor also increased the beta-END-LIS release). These results suggested the close relationship between cAMP accumulation and its biological effect (i.e. beta-END-LIS release).
Calmodulin and Ca2+- and calmodulin-dependent protein kinase were identified in the rat anterior pituitary gland. The concentration of calmodulin was 1.18 +/- 0.11 microgram/mg protein (n = 7) in the cytosol fraction. The calmodulin of the anterior pituitary gland co-migrated with brain calmodulin on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The Ka value of the partially purified enzyme for Ca2+ was 3.3 microM in the presence of 0.30 microM calmodulin. Trifluoperazine and chlorpromazine, calmodulin-interacting agents, inhibited enzyme activity, with Ki values of 1.3 and 2.6 X 10(-5) M, respectively. The enzyme was resolved into two peaks of activity, with sedimentation coefficients of 5.5 S and 16.5 S, by sucrose density gradient centrifugation. At least nine proteins were phosphorylated by the enzyme in a Ca2+- and calmodulin-dependent manner. In light of these results, the possibility that calmodulin and the calmodulin-activatable protein kinase system are involved in the mediation of the Ca2+ effect on hormone release from the anterior pituitary gland must be given consideration.