TRH effect on chlordiazepoxide sedation

Low-dose thyrotropin-releasing hormone effects in cognitively impaired alcoholics

The cognitive effects of a low dose of thyrotropin-releasing hormone (TRH) (2.0 mg, IV) were evaluated in 18 chronic alcoholic patients who exhibited memory dysfunction secondary to chronic alcohol abuse. The study used a double-blind crossover design that compared cognitive functions in patients with 2.0 mg of TRH IV as compared with a placebo. TRH was chosen because of its ability to enhance cholinergic transmission. Only minimal effects were seen with TRH. Patients with a shorter duration of alcohol use (mean of 16 years) performed significantly better with TRH as compared with placebo on a test involving verbal learning and memory. Those with a more chronic history of alcohol abuse (mean of 27 years) did not show such a response. All of the subjects showed cardiovascular response to TRH. Factors that may have contributed to the results of our study are discussed. It is our impression that future studies evaluating the cognitive effects of TRH in chronic alcoholics need to include an evaluation of the functional activity of TRH in the brain.

Effects of central and peripheral type benzodiazepine ligands on thyrotropin and prolactin secretion

The cold-stimulated thyrotropin (TSH) levels in the rat were decreased by clonazepam (a central type benzodiazepine agonist), diazepam (a mixed agonist), FG 7142 (an inverse central type agonist) and Ro 5-4864 (a peripheral type agonist), clonazepam being the most potent and Ro 5-4864 the least active. Clonazepam and diazepam also decreased while FG 7142 increased prolactin (PRL) levels. Ro 5-4864 did not have any significant action. Clonazepam (1 and 5 mg/kg) and diazepam (15 mg/kg but not 25 mg/kg) decreased even the TRH-induced PRL levels. Only Ro 5-4864 (25 mg/kg) decreased TRH-induced TSH secretion but not significantly. The actions of central type compounds were antagonized by flumazenil but not by PK 11195. The weak effects of Ro 5-4864 were not antagonized by either antagonists. While the peripheral type benzodiazepine agonist only weakly affected the secretion of anterior pituitary hormones, the central type inhibition of TSH appears to be mediated through the hypothalamic TRH and that of PRL rather through the anterior pituitary gland. The sedating (or agitating in case of FG 7142) effect of high doses of benzodiazepine ligands may contribute to the changes in TSH and PRL levels.

Behavioral and endocrine interactions between thyrotropin-releasing hormone and ethanol in normal human subjects

Thyrotropin-releasing hormone (TRH) has been shown to antagonize the depressant effects of ethanol in animals, but conflicting findings have been reported in humans. To test whether TRH counteracts any of a variety of ethanol-sensitive behavioral measures in normal human subjects and for an effect of ethanol on TRH-induced thyrotropin (TSH) and prolactin (PRL) response, we administered TRH (500 micrograms) or placebo over 1 min intravenously, 30 min after subjects had ingested 0.8 g/kg of ethanol or a placebo drink. Blood samples for TSH and PRL were drawn prior to and 15 and 30 min after injection. Eight male subjects were studied in a balanced, crossover design with each subject receiving placebo-placebo, TRH-placebo, placebo-ethanol, and TRH-ethanol. Whereas ethanol had significant and expected effects on subjective measures, memory, disinhibition, reaction time and time perception, TRH failed to counteract any ethanol effect, except for a small effect in one memory task. Similarly, no effect of ethanol on TRH-induced TSH or PRL response was found. Though the behavioral findings could be interpreted to indicate that TRH does not alter ethanol sensitive behaviors in humans it will be necessary to utilize higher dosages of TRH and/or TRH analogues before firmly drawing this conclusion.

Central and peripheral type benzodiazepine ligands displace [3H][3-ME-HIS2]TRH from its binding sites in the brain and the anterior pituitary and antagonize the effect of TRH in the rat duodenum

The effects of central (clonazepam, an agonist, and FG 7142, an inverse agonist), mixed (diazepam) or peripheral type (Ro 5-4864) benzodiazepine receptor ligands on the action of TRH on the transmurally stimulated rat duodenum and binding of [3H][3-Me-His2] TRH in the rat anterior pituitary, hypothalamus, cortex and brainstem have been studied. TRH dose-dependently inhibited the contractions of transmurally stimulated rate duodenum. Clonazepam (5 x 10(-6) M), diazepam (10(-5) M), Ro 5-4864 (10(-5) M) or FG 7142 (10(-5) M) attenuated the response of TRH in the rat duodenum. The action of these compounds was antagonized neither by the central type benzodiazepine antagonist flumazenil nor by peripheral type antagonist PK 11195 but instead PK 11195 itself counteracted TRH. TRH displaced [3H][3-Me-His2]TRH with Ki-values ranging 0.08 to 0.31 microM. Ki-values for clonazepam diazepam, Ro 5-4864, PK 11195 and FG 7142 ranged 6-117 microM, 3-23 microM, 20-67 microM, 20-40 microM and 260-420 microM, respectively, demonstrating fairly weak affinity to TRH-receptors. In saturation experiments, clonazepam and PK 11195 significantly increased KD but not Bmax of the labelled ligand while Ro 5-4864 increased both KD and Bmax. This indicates that all these compounds competitively inhibit the binding of [3H][3-Me-His2]TRH in the CNS which may also be the mechanism for their antagonism of the effect of TRH in the rat duodenum.