Interaction between substance P and gastrin-releasing peptide on thyrotropin secretion by rat pituitary in vitro

Abstract

The effect of substance P (SP) on thyrotropin (TSH) secretion is controversial. In this study we evaluated the effect of SP on TSH secretion by hemipituitaries of 3-month-old Wistar rats in vitro and its interaction with gastrin-releasing peptide (GRP) at equimolar concentrations (1 µM and 10 µM). TSH release was measured under basal conditions and 30 min after incubation in the absence or presence of SP, GRP or both peptides. Pituitary TSH content was also measured in the pituitary homogenate after incubation. SP at both concentrations caused a significant (P<0.05) increase in TSH secretion compared with all other groups, which was approximately 60% (1 µM) and 85% (10 µM) higher than that of the control group (23.3 ± 3.0 ng/ml). GRP at the lower concentration did not produce a statistically significant change in TSH secretion, whereas at the concentration of 10 µM it produced a 50% reduction in TSH. GRP co-incubated with substance P completely blocked the stimulatory effect of SP at both concentrations. Pituitary TSH content decreased in the SP-treated group compared to controls (0.75 ± 0.03 µg/hemipituitary) at the same proportion as the increase in TSH secretion, and this effect was also blocked when GRP and SP were co-incubated. In conclusion, in an in vitro system, SP increased TSH secretion acting directly at the pituitary level and this effect was blocked by GRP, suggesting that GRP is more potent than SP on TSH secretion, and that this inhibitory effect could be the predominant effect in vivo.

Neonatal Low-Protein Diet Changes Deiodinase Activities and Pituitary TSH Response to TRH in Adult Rats

“…Glands were incubated for 30 mins to determine TSH release in response to TRH. Each hemipituitary was homogenized in phosphate-buffered saline (PBS), at pH 7.6, for intrapituitary TSH-content measurement (24,25). TSH levels were measured by murine-specific radioimmunoassay (RIA; National Institutes of Health, Bethesda, MD) and reported in terms of reference preparation (RP3).…”

“…Glands were incubated for 30 mins to determine TSH release in response to TRH. Each hemipituitary was homogenized in phosphate-buffered saline (PBS), at pH 7.6, for intrapituitary TSH-content measurement (24,25).…”

Effects of neuroactive substances on the activity of subcommissural organ cells in dispersed cell and explant cultures

“…In systems other than the SCO, SP has been shown to induce calcium-mediated secretion (Schamgochian and Leeman 1992;Mau et al 1997;Moura et al 1999). This may also hold true for the SCO and may involve the activation of calcium-dependent enzymes (e.g., PKC, Ca 2+ /calmodulin-dependent protein kinase), which stimulate the exocytotic machinery downstream of the [Ca 2+ ] i elevation (for review, see Burgoyne and Morgan 1998;Hilfiker et al 1999).…”

Regulação da síntese e secreção de tireotrofina

“…A tireoidectomia aumenta enquanto o hipertireoidismo diminui o conteúdo hipofisário de SP (49), o contrário do que ocorre com a NB. A SP age diretamente na hipófise estimulando a secreção de TSH por hipófises isoladas (50). Porém, quando injetada in vivo, diminui a concentração sérica de TSH e bloqueia a ação estimulatória do TRH ou do frio (51).…”

“…Portanto, a SP apresenta um efeito inibitório no hipotálamo e estimulatório na hipófise. Há uma interação entre estes peptídeos, visto que o GRP é capaz de bloquear o efeito estimulatório da SP em hipófises isoladas (50).…”