Ethanol inhibition of pituitary-thyroid axis: an effect secondary to nutritional deficiency

Hypothalamic-pituitary-thyroid (HPT) axis in chronic alcoholism. I. HPT axis in chronic alcoholics during withdrawal and after 3 weeks of abstinence

Thyroxine (T4), free T4 (fT4), triiodothyronine (T3), free T3 (fT3), reverse T3 (rT3), thyrotropin (TSH), thyroxine binding globulin (TBG), and T3 uptake were measured in 14 chronic alcoholics during withdrawal and after 21 days of abstinence. Results were compared with those of 16 healthy volunteers. During withdrawal, the fT4 and fT3 concentrations were subnormal, whereas the respective protein-bound fractions were normal. T4, T3, and TBG increased during the abstinence period, T3 and TBG being significantly higher than in normals at the second measuring time. T3 uptake values fell, but remained well within the normal range at both measuring times. During abstinence, the fT3 levels remained significantly lower than in healthy subjects. rT3 concentrations decreased, but not significantly. The TSH values were normal throughout. These results showed numerous abnormalities in the hypothalamic-pituitary-thyroid axis in alcoholics, the reasons for which are as yet unclear. The following possible interpretations are suggested: 1. The abnormally low serum fT3 and fT4 levels during withdrawal might reflect an increase in tissue uptake. 2. The increases in T4--and partly those in T3--during abstinence seem to reflect increased binding by TBG, the level of which rose markedly for reasons as yet unknown. 3. If increases in TBG during abstinence are taken into account, the decreases in rT3 concentrations may reach the level of statistical significance. These falls in rT3 concentrations may reflect an increase in rT3 metabolization (deiodination) in various tissues, including the CNS, leading to a reduction in serum rT3 bioavailability. 4. Factors such as liver disease, protein caloric malnutrition, and "psychological stress" do not fully explain all these abnormalities. A direct effect of ethanol on intracellular thyroid hormone metabolism and/or function seems conceivable.

Effect of ethanol exposure on circulating levels of insulin-like growth factor I and II, and insulin-like growth factor binding proteins in fetal rats

Maternal ethanol (ETOH) exposure is associated with impaired fetal growth. Because insulin-like growth factors (IGFs) are thought to be important in the regulation of fetal somatic growth, we examined the influence of maternal ETOH exposure on fetal growth and plasma levels of IGF-I, IGF-II, and IGF binding proteins (IGFBPs) in the rat model. Control (A) dams were fed a standard rat chow ad libitum. ETOH (E) consuming dams were fed a 36% ETOH diet, and pair-fed (P) dams were fed isocaloric amounts of a control liquid diet. All animals were killed on day 20 of gestation. Plasma concentrations of IGF-I and -II were determined by radioimmunoassay after formic acid-acetone extraction and heat inactivation of IGFBPs. Levels of IGFBPs in fetal plasma were estimated by Western ligand blotting after protein separation by SDS-PAGE and electrotransfer to nitrocellulose. Membranes were probed with [125I]IGF-I, and IGFBPs were identified by autoradiography, quantified by scanning densitometry and results expressed relative to corresponding IGFBPs in control fetal plasma. Maternal weight gain from conception to 20 days of pregnancy was reduced for E compared to P and A dams (p < 0.05 E vs. P or A). The same pattern was reflected in fetal weight that tended to be lower in P compared with A pups, and was significantly reduced in E pups compared with both groups (p < 0.0001 E vs. P or A). Thus, fetal growth was more retarded in E animals despite equal caloric and protein intake by E and P dams.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of thyroid state on preference for and sensitivity to ethanol in Fischer-344 rats

1. It has been reported by several groups that thyroid status can alter ethanol preference in rats. However, results using different methods and different strains of rats have not been consistent. 2. In this study, thyroidectomy or T4 augmentation was used to produce hypothyroidism or hyperthyroidism, respectively, in adult male Fischer-344 rats. 3. Preference for weak solutions (4 or 5%) of ethanol or tap water and ethanol-induced sedation and hypothermia were compared in hypothyroid, hyperthyroid and euthyroid rats. 4. No significant differences in preference indices (the ratios of ethanol to total liquid consumed) among the three groups were observed; however, for ethanol to contribute a greater portion of total calories ingested by hypothyroid rats than by euthyroid or hyperthyroid rats. 5. The duration of sleep resulting from a single i.p. injection of 2.5 mg/kg ethanol was increased (by 34%) in hyperthyroid rats and decreased (by 16%) in hypothyroid rats compared to euthyroid controls. Only the effect of hyperthyroidism was significant at the 0.05 level. 6. Colonic temperatures differed with thyroid state (hyperthyroid > euthyroid > hypothyroid) but the decrease produced by ethanol did not differ by thyroid state. 7. Observed differences in ethanol-induced sedation are consistent with differences in brain TRH levels and effects on neurotransmitter systems associated with different thyroid states.

Effects of ethanol and control liquid diets on the hypothalamic-pituitary-thyroid axis of male Fischer-344 rats

The effects of a high dextrose liquid diet containing ethanol and two different control liquid diets on serum and brain thyroid axis hormones and liver and brain deiodinase activities were studied in groups of adult male Fischer-344 (F-344) rats. Rats received either lab chow, ad libitum; a nutritionally complete 10% (w/v) ethanol liquid diet, ad libitum; a volume of either a high carbohydrate (HC) or a high fat (HF) isocaloric control liquid diet equal to the volume of diet consumed by rats given the ethanol diet; or the HC control diet, ad libitum. Consumption of liquid diets was measured daily and body weights recorded every other day throughout the study. Hormones were measured after 2, 4, or 8 weeks and deiodinase activities after 4 or 8 weeks. Also, groups of rats were given the 10% ethanol diet, ad libitum, or pair-fed the HC control diet intermittently for 8 weeks, and thyroid hormones and thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) were determined. Within 2 weeks rats became accustomed to all diets and thereafter weight gain was comparable in all groups. Small differences between serum thyroid hormones of rats fed the ethanol diet and pair-fed HC or HF controls may have been caused by lower T4 secretion in ethanol-fed rats. Marked differences in free and total T4 and T3 between F-344 rats fed liquid diets for 4 or 8 weeks and rats fed lab chow probably resulted from higher liver 5'-deiodinase activity in rats fed liquid diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic alcohol ingestion decreases pituitary-thyroid axis measures in Fischer-344 rats

In a chronic feeding study adult male Fischer-344 rats (n = 12) were fed a nutritionally complete liquid diet containing 10% (w/v) ethanol for 40 days while control animals (n = 12) were pair fed a nutritionally complete isocaloric diet in which dextrose was substituted for ethanol. Treated animals were gradually introduced to and withdrawn from the 10% diet. At the end of the study and at sacrifice ethanol-fed rats had gained slightly more weight than pair-fed controls. They also showed a significant decrease in total thyroxine, free thyroxine, L-triiodothyronine, reverse L-triiodothyronine, and basal thyroid-stimulating hormone. These differences did not appear to result from caloric deprivation alone. Possible explanations for some of these thyroidal changes are discussed.