The Intermediate lactotroph: a morphologically distinct, ghrelin-responsive pituitary cell in the dwarf (dw/dw) rat.

Journal article

Profound 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.

Authors: Huerta-Ocampo, I; Christian, H; Thompson, N; El-Kasti, M; Wells, T

• Publication status: Published
• Journal: Endocrinology
• Volume: 146
• Issue: 11
• Pages: 5012-5023
• Publication date: 2005-11-01
• DOI: 10.1210/en.2005-0335
• EISSN: 1945-7170
• ISSN: 0013-7227
• Language: English
• Keywords: Prolactin; Neurosecretory Systems; Mice, Inbred C57BL; Male; Growth Hormone-Releasing Hormone; Ghrelin; Female; Rats; Microscopy, Electron; Peptide Hormones; Pregnancy; Pituitary Gland, Anterior; Rats, Mutant Strains; Growth Hormone; Mice; Animals; Dwarfism; Aging