Involvement of Calcium in the Release of Immunoreactive β-Endorphin-Like Peptide from Dispersed Cells of the Neurointermediate Lobe of the Rat Pituitary Gland

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The presence of Ca²⁺ in the incubation medium was required for stimulation of the release of the immunoreactive β-endorphin-like peptide (IR-β-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-β-EP, but did not stimulate the formation of cAMP. These findings suggest that Ca²⁺ has the essential role in the release of β-endorphin from the neurointermediate lobe of rat pituitary gland.