Influence of prolonged fasting and thyroid hormone on the alpha 2-adrenergic response in isolated epididymal adipocytes of Wistar rats.
Fasting and thyroid hormone have been reported to modulate the beta-adrenergic pathway of lipolysis in rat, but their effects on the alpha 2-adrenergic response are not well known. The purpose of the present study was to investigate this point. Male Wistar rats, 3 weeks old, were thyroidectomized surgically, kept for 1 month at 25 degrees C and then fasted or not fasted for 3 days with or without daily intraperitoneal injection of 3,5,3'-tri-iodo-L-thyronine (T3; 4.6 nmol/100 g body weight). Age-matched, sham-operated, fed and fasted euthyroid rats were used as controls. The experiments were carried out using isolated epididymal adipocytes. The alpha 2-adrenergic agonist UK 14304 (UK) inhibited the stimulated lipolysis more in fed than in fasted euthyroid rats whereas it had no effect in hypothyroid or T3-treated hypothyroid rats. The alpha 2-adrenergic antagonist idazoxan reversed the antilipolytic effect of UK more in fasted than in fed euthyroid rats. The alpha 2-adrenergic antagonist RX 821002 (RX) did so, but at lower concentrations than those of idazoxan. Idazoxan slightly increased the glycerol release in hypothyroid and especially T3-treated hypothyroid rats. RX had practically no effect on the production of glycerol in these animals. The findings suggest that (a) fasting and probably hypothyroidism decrease the alpha 2-adrenergic response in adipocytes from rats, (b) T3 treatment of hypothyroid rats has no effect on the alpha 2 response, and (c) thyroid hormone does not directly modulate the alpha 2-adrenergic response in rat adipocytes.
Ben Cheikh
R
R
Laboratoire de Chimie Analytique, UFR des Sciences Pharmaceutiques et Biologiques, Dijon, France.
Chomard
P
P
Beltramo
J L
JL
Autissier
N
N
Dumas
P
P
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000273:Adipose Tissue / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002469:Cell Separation; D004822:Epididymis; D005215:Fasting; D019329:Idazoxan / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism*; D013997:Time Factors; D014284:Triiodothyronine / Q000494:pharmacology*
D000317:Adrenergic alpha-Antagonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D014284:Triiodothyronine; D000068438:Brimonidine Tartrate; C058525:2-methoxyidazoxan; D019329:Idazoxan