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  • Title: Alpha 1-adrenoreceptors and alpha 1-adrenoreceptor-mediated thyrotropin release in cultures of euthyroid and hypothyroid rat anterior pituitary cells.
    Author: Dieguez C, Foord SM, Peters JR, Hall R, Scanlon MF.
    Journal: Endocrinology; 1985 Aug; 117(2):624-30. PubMed ID: 2990855.
    Abstract:
    TSH responses to adrenergic agonists have been measured in 3-day monolayer cultures of euthyroid and hypothyroid male rat anterior pituitary (AP) cells. Responses were qualitatively similar in that (-)epinephrine and (-)norepinephrine had the same ED50 in each culture (ED50 = approximately 6 and 16 nM, respectively) and demonstrated the same alpha 1-adrenergic specificity. Hypothyroid cultures secreted approximately twice as much TSH per cell as euthyroid cultures over the 2-h experimental period. (-)Epinephrine produced a 95 +/- 8% (mean +/- SE) release of TSH relative to basal secretion in euthyroid cultures and only 62 +/- 7% release in the hypothyroid cultures (P less than 0.01). The comparable figures for (-)norepinephrine were 62 +/- 7% and 38 +/- 5%, respectively (P less than 0.05). In absolute terms, adrenergic agonists released the same amount of TSH from euthyroid and hypothyroid cultures. In contrast, TRH (and the Ca+2 channel ionophore A23187) released twice as much TSH from the hypothyroid cells as in the euthyroid cultures. Epinephrine-induced TSH release was significantly impaired (P less than 0.001) when either euthyroid or hypothyroid cells were cultured without thyroid hormones. In contrast, TRH-induced TSH release was enhanced (P less than 0.001) in the euthyroid cultures. [3H]Dihydroergocryptine [( 3H]DHE) was used to quantify alpha 1-adrenoreceptors on the same cell preparations as those used to derive the functional data (see above). Prazosin (1 microM) was used to define nonspecific binding of [3H]DHE. Specific binding to euthyroid cells had a Kd of 5.8 +/- 4 nM and a maximum binding capacity of 2.2 +/- 0.4 fmol/10(5) cells (n = 5). In parallel cultures of hypothyroid cells, the Kd (6.2 +/- 5 nM) was not significantly different, whereas the maximum binding capacity (1.4 +/- 0.3 fmol/10(5) cells) was significantly reduced (P less than 0.05). Adrenergic compounds showed a rank order of potency of prazosin greater than (-)epinephrine greater than or equal to (-)norepinephrine greater than or equal to yohimbine greater than clonidine against the binding of 5 nM [3H]DHE to euthyroid and hypothyroid cells. The amount of [3H]DHE binding per cell that each adrenergic compound was able to displace at saturating concentrations was less in hypothyroid cells than in euthyroid cells. There was no change in the ED50 values of these compounds in the same experiments.(ABSTRACT TRUNCATED AT 400 WORDS)
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