enkephalin--ala(2)-mephe(4)-gly(5)- and Hypothyroidism

The effects of a mild hypothyroidism condition on benzodiazepine (BDZ) and mu opioid receptor levels was investigated. Female Wistar rats were randomly divided into two groups: 1) hypothyroid rats (n=7), which received methimazole (60 mg/kg per day) in drinking water for four weeks, and 2) euthyroid rats (n=8), which drank only tap water. Animals were sacrificed and their brains were used for autoradiography experiments. When compared to the euthyroid group, the hypothyroid group presented reduced benzodiazepine receptor binding in medial amygdala (24%) and high mu-receptor levels in frontal (25%), sensorimotor (65%) and temporal (29%) cortices, basolateral amygdala (50%) and ventroposterior thalamic nucleus (49%). The present data suggest that alterations in BDZ and mu-receptor binding could be associated with the higher excitability observed in animals with triiodothyronine (T(3)) deficiency.

Topics: Animals; Antithyroid Agents; Autoradiography; Binding, Competitive; Brain; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Female; Flunitrazepam; GABA Agonists; GABA-A Receptor Agonists; Hypothyroidism; Methimazole; Radioligand Assay; Random Allocation; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, Opioid, mu; Thyroxine; Triiodothyronine

The effect of chronic administration of methimazole (0.05% w/v) in drinking water for 32 days to male Sprague-Dawley rats on the binding of opioid ligands, 3H-Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO, mu-receptors), 3H-Tyr-D-Ser-Gly-Phe-Leu-Thr (DSTLE, delta-receptors) and 3H-ethylketocyclazocine (EKC, kappa-receptors) to membranes of brain regions was determined. Chronic administration of methimazole to rats decreased their rate of body weight gain, colonic temperature, systolic blood pressure and heart rate in comparison to vehicle-treated rats. Administration of methimazole also decreased the serum concentration of triiodothyronine (total T3) and T4 when compared to vehicle-treated rats. The binding of 3H-DAGO to membranes of amygdala, pons and medulla, striatum, midbrain and cortex of methimazole-treated rats was greater than vehicle-treated rats, however, the binding to membranes of hypothalamus in the two treatment groups did not differ. The binding of 3H-DSTLE in amygdala and hypothalamus of methimazole-treated rats did not differ but it was significantly greater in pons and medulla, midbrain, cortex and striatum of methimazole-treated rats than vehicle-treated rats. The binding of 3H-EKC to membranes of pons and medulla was lower and of striatum and cortex of methimazole-treated rats was significantly greater than vehicle-treated rats, but the binding to membranes of amygdala, hypothalamus, and midbrain of the two treatment groups did not differ. The results indicate that brain, mu-, delta- and kappa-opioid receptors are differentially altered in hypothyroidism.

Topics: Animals; Body Temperature; Body Weight; Brain Chemistry; Cyclazocine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Ethylketocyclazocine; Heart Rate; Hypothyroidism; Male; Methimazole; Oligopeptides; Rats; Rats, Inbred Strains; Receptors, Opioid; Triiodothyronine