The Intermediate lactotroph: a morphologically distinct, ghrelin-responsive pituitary cell in the dwarf (dw/dw) rat.
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.
Huerta-Ocampo
Icnelia
I
School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, United Kingdom.
Christian
Helen C
HC
Thompson
Nichola M
NM
El-Kasti
Muna M
MM
Wells
Timothy
T
D000375:Aging; D000818:Animals; D004392:Dwarfism / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology*; D005260:Female; D054439:Ghrelin; D013006:Growth Hormone / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D009490:Neurosecretory Systems / Q000503:physiopathology; D036361:Peptide Hormones / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011922:Rats, Mutant Strains
D054439:Ghrelin; D036361:Peptide Hormones; D011388:Prolactin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone