EFFECTS OF ACUTE ETHANOL ADMINISTRATION AND COLD-EXPOSURE ON THE HYPOTHALAMIC-PITUITARY-THYROID AXIS

A single dose of ethanol increases cellular levels of the mRNA encodin g thyrotropin-releasing hormone (TRH) in neurons of the paraventricula r nucleus (PVN), but blocks the cold-induced increase in the levels of this mRNA. Because the thyrotropic response to cold is dependent upon TRH secretion, we hypothesized that ethanol uncouples the stimulus-in duced regulation of TRH secretion from the stimulus-induced regulation of TRH expression. We employed two complementary strategies to test t his hypothesis. The first was to determine whether ethanol alters pitu itary sensitivity to TRH. Animals given a single intraperitoneal injec tion of ethanol (3 g/kg) that produced a blood alcohol concentration o f nearly 300 mg/100 mL exhibited the same increase in circulating leve ls of TSH following an intravenous infusion of TRH. Thus, ethanol does not appear to alter pituitary sensitivity to TRH. Second, we tested w hether ethanol blocks the cold induction of c-fos expression in TRH ne urons of the PVN. Both cold exposure and ethanol induced the expressio n of c-fos in the PVN and in TRH neurons; the effects of cold and etha nol on c-fos expression were additive. Thus, ethanol clearly does not block the cold activation of TRH neurons.