Study of the rat TSH-producing cells after met-enkephalin treatment: effects of dopamine antagonists.
The effects of single and repeated doses of met-enkephalin (Met-E) on the ultrastructure and TSH-like immunoreactivity (IR) of pituitary TSH-producing cells, and TSH plasma levels in male rats and the influence of pretreatment with a dopamine antagonist, haloperidol, on these, were evaluated. Both acute and repeated Met-E administration produced changes in TSH cells consisting of: an increase in TSH-like IR, enlargement and dilation of RER and Golgi apparatus, size-increase of secretory granules, and the presence of a variable number of cytoplasmic vacuoles. The ultrastructural changes were more evident in the chronically treated animals, whereas no differences were found in IR-intensity between both Met-E treated groups. Haloperidol alone modifies neither ultrastructure nor TSH-like IR of TSH producing cells, but it prevented the Met-E produced changes. On the other hand, Met-E treatment resulted in a decrease of TSH plasma levels, but being significant only in the acutely injected animals. No variations were produced by haloperidol alone, but it prevented the decrease of TSH plasma levels stimulated by Met-E. Our results suggest that Met-E plays a role in the release of TSH, and that dopamine is implicated in this process. The possible mechanisms through which Met-E influences TSH secretion are discussed.
del Valle-Soto
M E
ME
Departamento de Morfologia y Biologia Celular, University of Oviedo, Spain.
Vega
J A
JA
Calzada
B
B
Hernández
L C
LC
Pérez-Casas
A
A
D000818:Animals; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D006220:Haloperidol / Q000494:pharmacology*; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D010903:Pituitary Gland, Anterior / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains; D013972:Thyrotropin / Q000097:blood*
D004744:Enkephalin, Methionine; D013972:Thyrotropin; D006220:Haloperidol