Different Effects of K+ and Ca++ on α-MSH and ACTH Release from Superfused Neurointermediate Lobe of the Rat Hypophysis

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Abstract
The effects of K+-enhanced and Ca++-free media on α-MSH and adrenocorticotropic hormone (ACTH) release from superfused neurointermediate lobe (NIL) were studied in the same experiments. High K+ caused reversible and repeatable inhibition of α-MSH release and stimulation of ACTH release. Removal of Ca++ impaired the effect of K+, irreversibly for α-MSH and reversibly for ACTH. The existence of both melanotrophic and corticotrophic cells within the intermediate lobe (IL) of rat hypophysis could account for the different effects of ionic modifications on in vitro α-MSH and ACTH release.