HYPOTHALAMIC NEUROHORMONES REGULATE ANTERIOR PITUITARY NEUROMEDIN B EXPRESSION* * Supported by CAPES, CNPq, FAPERJ, FUJB, NIH. E-mail: taniaort@biof.ufrj.br
TÂNIA MARIA ORTIGA-CARVALHO, KAREN DE JESUS OLIVEIRA AND CARMEN C. PAZOS-MOURA
Lab. Fisiologia Endócrina, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, RJ, Brazil. LENY A. CAVALCANTE
Hypothalamic neurohormones, TRH (thyrotropin-releasing hormone) and somatostatin regulate pituitary thyroid-stimulating hormone (TSH). TRH is the most important stimulator of TSH release, and somatostatin inhibits TSH release, as well as, thyroid hormones. We had shown before that neuromedin B (NB), a bombesin-like peptide, highly concentrated in the pituitary gland, due to its local synthesis, has an inhibitory action on TSH release, acting as an autocrine regulator. Anterior pituitary (AP) NB expression is positively regulated by thyroid hormones and probably also somatostatin, since we had demonstrated that octreotide, long-acting somatostatin analogue, increased NB content in the AP. Here we investigated, in rats, regulation of AP NB expression by acute administration of TRH, acute cold exposure as well as by leptin administration. NB mRNA was determined by RPA. AP NB was measured by specific RIA, as well as serum TSH, T4 and T3. A single injection of TRH (
g/rat) decreased the content of NB mRNA and peptide within 15 minutes (NB mRNA-C: 1.0, 15min: 0.28 NB/bactin DO; NB:C: 
, 15 min: 
fmol/mg ptn, 
), in concomitance with an increase in serum TSH. Acute cold exposure, which increased TSH release within 30 minutes (C: 
and 30 min: 
ng/ml), was associated with a progressive decrease in NB pituitary content, which was statistically significant after 2h (C: 
; 15 min: 
; 30 min: 
; 1 h: 
and 2 h: 
fmol/mg ptn, ). We suggest that the decrease of NB expression can be one of the mechanisms by which TRH increases TSH release. Leptin, a protein that was first found in adipose tissue but that now has been found in central nervous system, may be involved. After 2 hours of leptin administration into normal rats (
g/100 g B.W.), pituitary NB content decreased (C:
and 2h: 
fmol/mg ptn, ) and serum TSH increased. Therefore, data support the concept that regulation of pituitary NB expression and of TSH release are closely related in time in a manner that favours the hypothesis that NB exerts an important role in the local regulation of TSH release and that NB can be one intermediary of the effects of neurohormones that regulate TSH release. ( June 27, 2000 )
Publication Dates
-
Publication in this collection
05 Oct 2000 -
Date of issue
Sept 2000
