Dynamics and Regulation of TSH Secretion by Superfused Anterior Pituitary Cells

Connors, John M.; Wright, Kenneth C.; Judd, Allan M.; Liu, Chengming; Hedge, George A.

doi:10.1159/000179352

Cited by 25 publications

(11 citation statements)

References 14 publications

(19 reference statements)

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“…In contrast to an earlier report [4], the TRH concentration was the only determinant of the amplitude of the acute phase. A 60-fold variation of TRH exposure duration was without obvious effect on the amplitude or duration of the acute phase.…”

Section: Discussioncontrasting

confidence: 99%

“…Prior reports have not used this or other comparable strategy. We believe that an earlier report [4], which found that an increase in stimulus duration resulted in an increase in secretory response, was probably complicated by chang ing baselines and other longitudinal biases.…”

Section: Discussionmentioning

confidence: 86%

“…Decreases in secretory responsiveness during prolonged in vitro stimulation with TRH have been reported previ ously [4,10,14]. This is most simply attributed to depletion of readily releasable hormone.…”

Section: Discussionmentioning

confidence: 99%

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Dynamics of Thyrotropin-Releasing Hormone-Induced Thyrotropin and Prolactin Secretion by Acutely Dispersed Rat Adenohypophyseal Cells

Ld¹,

Tam²,

Ikeda³

et al. 1986

Neuroendocrinology

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We have examined the dynamics of thyrotropin-releasing hormone (TRH)-stimulated secretion of prolactin (PRL) and thyrotropin-stimulating hormone (TSH) using enzymatically dispersed rat adenohypophyseal cells suspended in a perifusion chamber with a volume of 0.2 ml to minimize mixing and dilution. One-min exposure to 3–300 nMTRH, the effective dose range, elicited immediate pulses of PRL and TSH secretion with dose-dependent amplitudes. At all TRH concentrations, following a brief burst of secretion lasting < 1 min, release of both hormones declined precipitously. Increasing the duration of stimulation up to 30 min with half-maximal TRH concentrations did not alter the dynamics of the initial response and was ineffective in maintaining the initial amplitude of secretion. This phenomenon could not be attributed to exhaustion of readily releasable intracellular PRL and TSH, since an increment in TRH concentration elicited a second pulse of hormone secretion with temporal response characteristics identical to the first. The amplitude of the second pulse was dependent on both the initial concentration of TRH and the magnitude of the increment in TRH concentration. With a stepwise increase in TRH concentration during continuous perifusion, the sum of PRL or TSH secreted from all bursts of secretory activity approximated that achieved with a single exposure to the highest concentration of TRH employed. The high-amplitude secretory response to a given concentration of TRH was restored after an 8-min perifusion with medium alone. The data indicate that: (1) multiple pools of immediately secretable hormone, differing with respect to their TRH stimulation thresholds, exist for both PRL and TSH: each pool or ‘secretory unit’ has an individual threshold of response to TRH and is refractory to further stimulation by TRH after discharging its readily releasable hormone; (2) secretion of both PRL and TSH rapidly becomes refractory to continuous TRH stimulation, but is maintained by pulsatile TRH stimulation, and (3) the dynamics of PRL and TSH secretion by dispersed perifused rat adenohypophyseal cells are indistinguishable.

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 86%

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Dynamics of Thyrotropin-Releasing Hormone-Induced Thyrotropin and Prolactin Secretion by Acutely Dispersed Rat Adenohypophyseal Cells

Ld¹,

Tam²,

Ikeda³

et al. 1986

Neuroendocrinology

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“…Our data confirm earlier reports [2,3] that it takes > 60 min for Tj to inhibit TRH-induced TSH secretion in vitro. The time required to induce suppression of TRH-induced TSH se cretion was not detectably different between T4 and Ti.…”

Section: Discussionsupporting

confidence: 93%

“…To date, only Tj has been shown to inhibit the secretion of TSH induced by TRH in perifused isolated rat pituitary fragments [2,3]. The present study was undertaken to compare the temporal and quantitative ef fects of T4 and Tj on the TSH response to TRH in this sys tem.…”

mentioning

confidence: 97%

Comparison of the Ability of Thyroxine and Triiodothyronine to Suppress TRH-Induced TSH Secretion by Perifused Rat Anterior Pituitary Fragments

1985

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Adenohypophyseal fragments from 8 rats were perifused in small 0.2-ml chambers with medium alone or with medium containing 0.2 or 2 µg/dl T3 or 20 µg/dl T4. The TSH secretion in response to 1-min perifusion with 3 × 10^–8M TRH was measured before and at 20- to 40-min intervals after beginning T4 or T3 perifusions. A similar temporal course of inhibition of TRH-induced TSH secretion was produced by both iodothyronines, suggesting but not proving that T4 may inhibit the TSH secretion by a direct effect not dependent on its prior intra- or extrapituitary conversion to T3.

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Thyroid status influences in vitro thyrotropin and growth hormone responses to thyrotropin‐releasing hormone by pituitary glands of hatchling slider turtles (Pseudemys scripta elegans)

Denver

Licht

1988

J. Exp. Zool.

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The effects of thyroidal feedback on thyrotropin (TSH), growth hormone (GH) and prolactin (PRL) secretion by pituitary glands, and on TSH responsiveness of thyroids in hatchling turtles, Pseudemys scripta elegans, were investigated by in vitro techniques. Pituitaries were stimulated in culture with 0,1,10, or 100 ng/ml thyrotropin-releasing hormone (TRH) at intervals up to 36 hr; hormones were estimated by RIA. TSH release was elevated by all doses of TRH during the first 2 hr of stimulation (1.8 to 3.6-fold) and secretion rates increased further during the following 4 hr, with a dose response between 1 and 10 ng/ml TRH. TSH release then returned to initial basal levels and showed the same response to TRH on the second day. GH secretion was also elevated by all doses of TRH tested. A progressive increase in basal GH secretion over time in vitro suggested that GH might normally be under inhibitory control. Medium concentrations of PRL were nondetectable at all times and thus were not measured in subsequent experiments. In vitro thyroxine (T4) secretion by thyroids from these same turtles showed a dose response when stimulated with 5-20 ng/ml purified sea turtle TSH for 8 or 20 hr.Treatment of turtles in vivo with 0.5 pg T4 at 2 hr or daily for up to 2 wk prior to sacrifice greatly reduced in vitro basal TSH secretion and the response to 10 ngiml TRH. In contrast, several of the T4 treatments significantly elevated basal GH secretion. Plasma TSH was markedly elevated after 4 wk treatment with a goitrogen, methimazole, and this was accompanied by increased basal TSH secretion and responsiveness to TRH by pituitaries in vitro; basal GH secretion was reduced but the response of GH to TRH was unaffected. The response of in vitro thyroidal T4 output to TSH was augmented in hyperthyroid animals ( 3 1 wk T4) and was abolished by methimazole treatment.These data demonstrate a clear thyroidal feedback in the regulation of chelonian TSH secretion and are consistent with an involvement of TRH in the control of pituitary TSH and GH. While the site(s) of the inhibitory actions of T4 are unknown, changes in the functional properties of the pituitary thyrotropes are involved; the somatotropes appear to be less dependent on Tq.In both classes of endothermic vertebrates, mam-hypothalamo-pituitary-thyroid axis in "lower" vermals and birds, pituitary thyrotropin (TSH) secre-tebrates hinders evaluation of this hypothesis. tion is stimulated by the tripeptide amide, thyro-Increased thyroid weight following hypothatropin-releasing hormone (TRH) (mammals: re-lamic lesions suggested that thyrotropes were unviewed in Morley, '81; birds: Bolton et al., '74; der hypothalamic inhibition in a lizard (Callard Kamis and Robinson, '78; Klandorf et al., '78). and Chester Jones, '71). The only in vivo study of Although TRH has been localized in the hypothal-TRH action in reptiles suggested that this peptide amus of representatives of all vertebrate classes may lack significant TSH-stimulating activity; (Jackson and Reichlin, ' 741, attempt...

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Dynamics and Regulation of TSH Secretion by Superfused Anterior Pituitary Cells

Cited by 25 publications

References 14 publications

Dynamics of Thyrotropin-Releasing Hormone-Induced Thyrotropin and Prolactin Secretion by Acutely Dispersed Rat Adenohypophyseal Cells

Dynamics of Thyrotropin-Releasing Hormone-Induced Thyrotropin and Prolactin Secretion by Acutely Dispersed Rat Adenohypophyseal Cells

Comparison of the Ability of Thyroxine and Triiodothyronine to Suppress TRH-Induced TSH Secretion by Perifused Rat Anterior Pituitary Fragments

Thyroid status influences in vitro thyrotropin and growth hormone responses to thyrotropin‐releasing hormone by pituitary glands of hatchling slider turtles (Pseudemys scripta elegans)

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