1,25-Dihydroxyvitamin D3 reduces the number of alpha 1-adrenergic receptors in FRTL-5 rat thyroid cells.
Noradrenaline and ATP evokes a transient increase in the intracellular calcium concentration ([Ca2+]i) in FRTL-5 cells. In a previous study, we showed that 1,25-dihydroxyvitamin-D3 (1,25(OH)2-D3) increases the ATP evoked changes in [Ca2+]i. In the present paper, we found that pre-incubating the cells with 10 nM 1,25(OH)2-D3 for 48 h did not affect the noradrenaline-evoked increase in [Ca2+]i. We subsequently examined if this could be due to an effect of 1,25(OH)2-D3 on alpha 1-adrenergic receptor number, or receptor affinity. Pretreatment with 10 nM 1,25(OH)2-D3 for 48 h decreased the binding of the alpha 1-adrenergic specific antagonist [3H]prazosin by 55% (Bmax for 1,25(OH)2-D3 treated = 27.6 +/- 5.0 fmol/mg protein, untreated = 61.7 +/- 5.4 fmol/mg protein). No effect of 1,25(OH)2-D3 on the affinity for [3H]prazosin was observed. The effect of 1,25(OH)2-D3 on the [3H]prazosin binding was both time- and dose-dependent and could first be seen after 8-12 h of 1,25(OH)2-D3 treatment, indicating a genomic effect. The effect of 1,25(OH)2-D3 could be abolished with the protein synthesis inhibitor cycloheximide. No effect on the [3H]prazosin binding could be seen after a 48 h preincubation with 100 nM of either 24,25-dihydroxyvitamin D3 and 25-dihydroxyvitamin D3, indicating that the effect of 1,25(OH)2-D3 was specific. The cellular cAMP concentration was decreased after 48 h treatment with 10 nM 1,25(OH)2-D3. When TSH was replaced with dibutyryl cAMP or forskolin the [3H]prazosin binding increased. 1,25(OH)2-D3 also reduced the dibutyryl cAMP and forskolin stimulated [3H]prazosin binding.(ABSTRACT TRUNCATED AT 250 WORDS)
Ahlström
M
M
Calcium Research Unit, Minerva Foundation Institute for Medical Research, Helsinki, Finland.
Törnquist
K
K
Lamberg-Allardt
C
C
D015650:24,25-Dihydroxyvitamin D 3 / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology; D013997:Time Factors
D011942:Receptors, Adrenergic, alpha; D005576:Colforsin; D015650:24,25-Dihydroxyvitamin D 3; D000255:Adenosine Triphosphate; D013972:Thyrotropin; D003513:Cycloheximide; D000242:Cyclic AMP; D002117:Calcitriol; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin