Prolactin and Thyrotropin in Thyroid Diseases: Lack of Evidence for a Physiological Role of Thyrotropin-Releasing Hormone in the Regulation of Prolactin Secretion

Abstract. The mechanism by which 30% medium hyposmolarity induces PRL secretion by GH4C1 cells was compared with that induced by 100 nmol/l TRH or 30 mmol/l K+. Removing medium Ca2+, blocking Ca2+ channels with 50 μmol/l verapamil, or inhibiting calmodulin activation with 20 μmol/l trifluoperazine, 10 μmol/l chlorpromazine or 10 μmol/l pimozide almost completely blocked hyposmolarity-induced secretion. The smooth muscle relaxant, W-7, which is believed relatively specific in inhibiting the Ca2+-calmodulin interaction, depressed hyposmolarity-induced PRL secretion in a dose-dependent manner (r = −0.991, p<0.01 ). The above drugs also blocked or decreased high K+-induced secretion, but had much less effect on TRH-induced secretion. Secretion induced by TRH, hyposmolarity, or high K+ was optimal at pH 7.3-7.65 and was significantly depressed at pH 6.0 or 8.0, indicating that release of hormone induced by all 3 stimuli is due to an active cell process requiring a physiologic extracellular pH and is not produced by nonspecific cell toxicity. The data suggest hyposmolarity and high K+ may share some similarities in their mechanism of stimulating secretion, which is different from that of TRH.

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Possible role of Ca2+-independent protein kinase C isozyme, nPKCɛ, in thyrotropin- releasing hormone-stimulated signal transduction: Differential down-regulation of nPKCɛ in GH4C1 cells

Biochemical and Biophysical Research Communications ◽

10.1016/s0006-291x(05)80191-3 ◽

1990 ◽

Vol 172 (1) ◽

pp. 184-189 ◽

Cited By ~ 50

Author(s):

Yoshiko Akita ◽

Shigeo Ohno ◽

Yukiko Yajima ◽

Koichi Suzuki

Keyword(s):

Signal Transduction ◽

Protein Kinase C ◽

Protein Kinase ◽

Thyrotropin Releasing Hormone ◽

Down Regulation ◽

Releasing Hormone ◽

Kinase C ◽

Independent Protein

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The Hypothalamic-Pituitary Thyroid Axis : Studies on the Regulatory Role of Thyrotropin Releasing Hormone (TRH)

Folia Endocrinologica Japonica ◽

10.1507/endocrine1927.52.9_908 ◽

1976 ◽

Vol 52 (9) ◽

pp. 908-925

Author(s):

Yoshifumi HIROOKA

Keyword(s):

Thyrotropin Releasing Hormone ◽

Regulatory Role ◽

Releasing Hormone ◽

Pituitary Thyroid Axis ◽

Thyroid Axis

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Anorexia-Cachexia in Type 2 Diabetic (T2D) Goto-Kakizaki (GK) Rats: Role of Impaired Brainstem Thyrotropin-Releasing Hormone (TRH) Regulation of Vagal Function.

10.1210/endo-meetings.2010.part1.p10.p1-483 ◽

2010 ◽

pp. P1-483-P1-483

Author(s):

Ai Chen ◽

Myungsoo Ko ◽

Vay Liang W Go ◽

Moon K Song ◽

Kaitlyn Liu ◽

...

Keyword(s):

Thyrotropin Releasing Hormone ◽

Releasing Hormone ◽

Gk Rats ◽

Type 2 Diabetic ◽

Vagal Function

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Physiological role of galanin in the regulation of anterior pituitary function in humans

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1994.266.1.e57 ◽

1994 ◽

Vol 266 (1) ◽

pp. E57-E61 ◽

Cited By ~ 4

Author(s):

A. Giustina ◽

M. Licini ◽

M. Schettino ◽

M. Doga ◽

G. Pizzocolo ◽

...

Keyword(s):

Anterior Pituitary ◽

Physiological Role ◽

Thyroid Stimulating Hormone ◽

Pituitary Function ◽

Slight Reduction ◽

Baseline Serum ◽

Releasing Hormone ◽

Anterior Pituitary Function ◽

Stimulating Hormone

The aim of our study was to elucidate the physiological role of the neuropeptide galanin in the regulation of anterior pituitary function in human subjects. Six healthy men (age range 26-35 yr, body mass index range 20-24 kg/m2) underwent in random order 1) an intravenous bolus injection of growth hormone-releasing hormone (GHRH)-(1-29)-NH2 (100 micrograms) + thyrotropin-releasing hormone (TRH, 200 micrograms) + luteinizing hormone-releasing hormone (LHRH, 100 micrograms) + corticotropin-releasing hormone (CRH, 100 micrograms), and 2) intravenous saline (100 ml) at time 0 plus either human galanin (500 micrograms) in saline (100 ml) or saline (100 ml) from -15 to +30 min. Human galanin determined a significant increase in serum GH (GH peak: 11.3 +/- 2.2 micrograms/l) from both baseline and placebo levels. No significant differences were observed between GH values after galanin and those after GHRH alone (24.3 +/- 5.2 micrograms/l). Human galanin significantly enhanced the GH response to GHRH (peak 49.5 +/- 10 micrograms/l) with respect to either GHRH or galanin alone. Human galanin caused a slight decrease in baseline serum adrenocorticotropic hormone (ACTH; 16.3 +/- 2.4 pg/ml) and cortisol levels (8 +/- 1.5 micrograms/dl). Galanin also determined a slight reduction in both the ACTH (peak 27 +/- 8 pg/ml) and cortisol (peak 13.8 +/- 1.3 micrograms/dl) responses to CRH. Baseline and releasing hormone-stimulated secretions of prolactin, thyroid-stimulating hormone, LH, and follicle-stimulating hormone were not altered by galanin. Our data suggest a physiological role for the neuropeptide galanin in the regulation of GH secretion in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

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