Mechanisms involved in the effects of TRH on GHRH-stimulated growth hormone release from ovine and bovine pituitary cells

Hart, Gillian; Ray, Keith P.; Wallis, Michael

doi:10.1016/0303-7207(88)90008-1

Cited by 9 publications

(6 citation statements)

References 34 publications

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“…In mammals and birds, several reports have suggested the involvement of a cAMP-independent, calcium-dependent mechanism underlying the stimulatory effects of TRH on GH secretion (Hart et al 1988;Hall et al 1985). Present results demonstrated that the mechanism of TRH action on in vitro GH release in common carp is Ca 2 + dependent, and the GH responses to TRH are somewhat reduced by a high concentration of Ca 2 + (6.25 mM).…”

Section: Discussionsupporting

confidence: 58%

“…Present results demonstrated that the mechanism of TRH action on in vitro GH release in common carp is Ca 2 + dependent, and the GH responses to TRH are somewhat reduced by a high concentration of Ca 2 + (6.25 mM). Inhibition of neuropeptide-induced GH secretion by a supraphysiological dose of Ca 2 + was also reported for TRH in chicken (Hall et al 1985) and for GHRH in mammals (Hart et al 1988), but the mechanism for this inhibition remains to be determined. The present results also showed that basal GH release is dependent on extracellular Ca 2 +, consistent with the idea that extracellular Ca 2 + plays an important role in mediating basal , I _ _e_ _ · GH secretion in the goldfish (Chang and De Leeuw 1990) and in other vertebrates (Hall et al 1985;Stojilkovic et al 1988).…”

Section: Discussionmentioning

confidence: 99%

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The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro

Lin

Peter

1993

Fish Physiol Biochem

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The effects of thyrotropin-releasing hormone (TRH) on growth hormone (GH) and gonadotropin (GtH) release, and the influences of somatostatin (SRIF), the dopamine agonist apomorphine (APO) and extracellular calcium on basal and TRH-induced GH release were examined using an in vitro perifusion system for pituitary fragments of common carp (Cyprinus carpio). Five minute pulses of different dosages of TRH stimulated a rapid and dose-dependent increase in GH release from the perifused pituitary fragments with an ED50 of 9.7 ± 2.3 nM. TRH was ineffective on GtH release. SRIF significantly inhibited basal and TRH-induced GH release from the perifused pituitary fragments, and the effects of SRIF were dose-dependent. APO induced a dose-dependent increase in basal and TRH-stimulated GH release from the perifused pituitary fragments. Increasing the concentrations of extracellular calcium from 0 mM to 1.25 mM resulted in an increase in basal and TRH-induced GH release. The high dose of calcium (6.25 mM) caused a slight decrease in basal and TRH-induced GH release compared with those at a concentration of 1.25 mM.

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Section: Discussionsupporting

confidence: 58%

Section: Discussionmentioning

confidence: 99%

The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro

Lin

Peter

1993

Fish Physiol Biochem

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“…The very different results obtained by Fumagalli & Zanini (1985) in cows suggest that in that species at least, secretion of GH and/or prolactin by somatomammotrophs may be important in regulating circulating levels of these hormones. In this respect it is interesting that responses to some secretagogues are very different for ovine and bovine pituitary cells (Hart, Ray & Wallis, 1988 Sheep pituitary tissue minimally fixed and embedded in LR Gold resin at 4°C and double immunogold labelled for pro¬ lactin (20 nm gold particles) and GH (10 nm gold particles). Fig.…”

Section: Discussionmentioning

confidence: 99%

Occurrence of rare somatomammotrophs in ovine anterior pituitary tissue studied by immunogold labelling and electron microscopy

Thorpe

Ray²,

Wallis³

1990

Journal of Endocrinology

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Prolactin and GH are distinct hormones that have been conventionally thought to be produced and secreted by separate cells in the anterior pituitary gland. Recently it has been suggested that some cells (somatomammotrophs) may secrete both hormones. We have examined the occurrence of somatomammotrophs in sheep anterior pituitary tissue using immunogold labelling. Of a number of procedures used, double labelling using first antibodies raised in different species proved the least susceptible to apparent co-localization of hormones due to artifacts. Using this approach it was shown that a large proportion of the cells in the sheep anterior pituitary glands examined were mammotrophs or somatotrophs, showing no significant co-localization of GH and prolactin. Of 1800 cells examined, only two were somatomammotrophs. One of these, from a female animal, contained GH and prolactin in different granules within the same cell. The other, from a male animal, showed co-localization of these two hormones within the same granules.

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“…It is known that the cyclic AMP system is involved in the secretory process of growth hormone (GH) in response to GRH (Brazeau, Ling, Esch, Bohlen, Maugin & Guillemin, 1982;Bilezikjian & Vale, 1983;Labrie, Gagne & Lefevre, 1983;Schettinni, Cronin, Hewlett, Thorner & Macleod, 1984). The involvement of the cyclic AMP pathway in the GRH response is also known in cultured ovine and bovine pituitary cells (Law, Ray & Wallis, 1984;Hart, Ray & Wallis, 1988). These cells respond to GRH in a dose-dependent manner (1 pM-100 nM) to produce a rise in GH release and also in the intracellular level of cyclic AMP (Law et al 1984;Hart et al 1988).…”

mentioning

confidence: 99%

“…The involvement of the cyclic AMP pathway in the GRH response is also known in cultured ovine and bovine pituitary cells (Law, Ray & Wallis, 1984;Hart, Ray & Wallis, 1988). These cells respond to GRH in a dose-dependent manner (1 pM-100 nM) to produce a rise in GH release and also in the intracellular level of cyclic AMP (Law et al 1984;Hart et al 1988). A role for cyclic AMP is also supported by the evidence showing that phosphodiesterase inhibitors, cyclic AMP derivatives and activators of adenylate cyclase can cause stimulation of the GH release .…”

mentioning

confidence: 99%

A potassium current evoked by growth hormone‐releasing hormone in follicular oocytes of Xenopus laevis.

Yoshida

Plant

1991

The Journal of Physiology

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SUMMARY1. Electrophysiological properties of the growth hormone-releasing hormone (GRH) receptor were studied in Xenopus oocytes with an intact follicle cell layer (i.e. follicular oocytes) by measuring whole-cell current using the two-electrode voltageclamp method.2. A slow transient outward current was elicited in oocytes, clamped at -60 mV, by the application of rat GRH but not bovine, porcine, or human GRH.3. The response to GRH was not suppressed by blockers known to inhibit other endogenous receptors present in follicular Xenopus oocytes; blockers used were timolol (2,UM; ,1-adrenergic blocker), theophylline (0-1 mM; purinergic blocker) and atropine (100 nM; muscarinic blocker).4. The current response evoked by rat GRH occurred in a dose-dependent manner. The concentrations of GRH for threshold and maximum responses were 1 and 100 nm respectively and the estimated EC50 (half-maximal effective concentration) was approximately 7 nM. The amplitude and conductance of the response became larger and the latency, time-to-peak and half-decay time were shortened when the concentration of GRH was increased.5. The GRH response was reversibly inhibited by a K+ channel blocker, tetraethylammonium+ (TEA+; 20 mM). The reversal potential for the GRH response was around -100 mV and was compatible with the reported value for a K+ current in Xenopus oocytes. Furthermore, a depolarizing shift of 40 mV in the reversal potential was observed when the external K+ concentration was increased from 2 to 10 mm, agreeing with the Nernst equation. In contrast, no significant shift in the reversal potential was observed by changing the external concentration of Na+ or Cl-.6. The GRH response was not suppressed in oocytes treated with an acetoxy-* Present address:

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Mechanisms involved in the effects of TRH on GHRH-stimulated growth hormone release from ovine and bovine pituitary cells

Cited by 9 publications

References 34 publications

The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro

The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro

Occurrence of rare somatomammotrophs in ovine anterior pituitary tissue studied by immunogold labelling and electron microscopy

A potassium current evoked by growth hormone‐releasing hormone in follicular oocytes of Xenopus laevis.

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