Secretion of Pro-Opiocortin Peptides from Isolated Perfused Rat Pars intermedia Cells

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Abstract
The perfused, isolated, pituitary cell column was used to measure the release of .alpha.-MSH-like immunoreactivity (LI), carboxyl terminal ACTH (C-ACTH)-LI, .gamma.-lipotropin (.gamma.-LPH)-LI, .alpha.-endorphin-LI, .beta.-endorphin-LI and amino-terminal pro-opiocortin (N-POC)-LI from rat pars intermedia (PI) cells. Concomitant secretion of all PI peptides was observed during basal release and in response to all applied stimuli. Dopamine (DA) caused a dose-dependent (10-9-10-5 M) simultaneous inhibition of peptide release which was antagonized by haloperidol. Isoprenaline stimulated the release of PI peptides in a parallel, dose-related (10-10-10-6 M) manner and was blocked by propranolol. Stimulation of peptide secretion caused by low concentrations (10-8 M), of adrenaline (AD) [epinephrine] and noradrenaline (NA) [norepinephrine] changed to inhibition at high concentrations (10-5 M) whereas intermediate concentrations (10-6, 10-7 M) possessed both inhibitory and excitatory effects. A 45 mM solution of K+ ions stimulated the release of PI peptides and both the K+-stimulated secretion and basal secretion were Ca2+-dependent. MSH-release-inhibiting factor (MIF) and 5-hydroxytryptamine (5-HT) failed to alter peptide secretion from the perfused PI cells. Pro-opiocortin (POC) peptides are evidently concomitantly from rat PI cells and biogenic amines are involved in their release.