Dual effects of manganese on prolactin secretion.
The effect of Mn2+ (a commonly used Ca2+ antagonist) on prolactin secretion from pituitary cells was investigated. In the presence of normal extracellular Ca2+ levels (2.5mM), Mn2+ inhibited basal, TRH- and K+- stimulated prolactin secretion. The Ca2+ ionophore, A23187, partially overcame the inhibitory effect of Mn2+. However, in the presence of low extracellular Ca2+ (less than 100 microM), which decreased basal prolactin secretion and abolished any stimulatory effects of TRH or K+, a paradoxical stimulatory effect was observed with Mn2+ in the presence of A23187. In the presence of Ca2+, Mn2+ appeared to be inhibitory due to its Ca2+ antagonistic effects, but at low Ca2+ levels, intracellular stimulatory effects of Mn2+ became apparent.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D000001:Calcimycin; D008345:Manganese; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D011188:Potassium; D002118:Calcium