Huerta-Ocampo, I.Christian, H.Thompson, N.El-Kasti, M.Wells, T.2011-06-202011-06-202005Endocrinology, 2005; 146(11):5012-50230013-72270013-7227http://hdl.handle.net/2440/64695Profound somatotroph hypoplasia in the dwarf (dw/dw) rat is accompanied by an estrogen-dependent induction of prolactin secretion by the GH secretagogue, GHRP-6. Using electron microscopy, we demonstrated that the reduction in the somatotroph population in the dw/dw pituitary is accompanied by the presence of a morphologically distinct lactotroph subpopulation. In these cells, which did not coexpress GH, the size, shape, and number of the secretory granules were between those of the type I and type II lactotrophs. We therefore called these cells intermediate lactotrophs. The intermediate lactotrophs accounted for up to 30% of the total prolactin-positive cell population in dw/dw males and up to 12% in females. Using tannic acid to quantify the fusion of secretory granules, we have shown that the intermediate lactotrophs are unresponsive to either GH-releasing factor (GRF) or TRH but exhibit a sexually dimorphic secretory response to acute ghrelin treatment, granular fusions being 4-fold higher in females. No cell matching the morphology of the novel lactotroph subpopulation was observed in the pituitary of the GRF-insensitive lit/lit mouse. However, ablation of GRF neurons with neonatal monosodium glutamate treatment had no effect on the population of intermediate lactotrophs in the dw/dw rat. Thus, the presence of the intermediate lactotrophs in the dw/dw pituitary appears to be independent of the function of the GRF neurons.enCopyright © 2005 by The Endocrine SocietyPituitary Gland, AnteriorNeurosecretory SystemsAnimalsMice, Inbred C57BLMiceRatsRats, Mutant StrainsDwarfismProlactinPeptide HormonesGrowth HormoneMicroscopy, ElectronAgingPregnancyFemaleMaleGrowth Hormone-Releasing HormoneGhrelinJournal article002010789110.1210/en.2005-03350002325852000502-s2.0-2684454671330034Thompson, N. [0000-0003-0378-2581]