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Nongenomic Actions of Testosterone on a Subset of Lactotrophs in the Male Rat Pituitary¹

Department of Human Anatomy and Genetics, University of Oxford, Oxford, United Kingdom OX1 3QX

Address all correspondence and requests for reprints to: Prof. John F. Morris, Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford, United Kingdom OX1 3QX. E-mail: john.morris{at}anat.ox.ac.uk

Rapid, nongenomic effects of testosterone on PRL release in vitro were investigated. Anterior pituitary tissue from adult male rats was stimulated in vitro for 5 or 20 min with testosterone (T; 1 or 100 nM) or testosterone-BSA (T-BSA; 1 or 100 nM) with or without 1.2 mM tannic acid, which enables visualization of secretory granule exocytosis. Within 5 min, both concentrations of T and T-BSA stimulated exocytosis from type 2 lactotrophs (characterized by small spherical granules), but not from type 1 lactotrophs (characterized by large polymorphic granules). The effects of T on type 2 lactotrophs could be blocked by preincubation with dopamine (500 nM), but were not time or concentration dependent, and could not be inhibited by 1) removal of extracellular Ca²⁺, 2) the L-type Ca²⁺ channel blocker nifedipine (100 nM), 3) the Ca²⁺-adenosine triphosphatase inhibitor thapsigargin (150 nM), 4) the PKC inhibitor retinal (10 µM), or 5) the -aminobutyric acid_A chloride channel blocker picrotoxin (100 µM). T-BSA (0.1 nM to 1 µM) for 5 or 20 min also caused an increased release of immunoreactive PRL into the medium compared with control incubations. T and T-BSA did not stimulate exocytosis from gonadotrophs or cause LH release. In conclusion, we report for the first time a rapid, nongenomic effect of T on PRL secretion.

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