Effects of TRH on blood flow and the microcirculation

Thyrotropin-Releasing Hormone Is Induced in the Left Ventricle of Rats With Heart Failure and Can Provide Inotropic Support to the Failing Heart

Background— We reported previously that left ventricular gene expression for thyrotropin-releasing hormone (TRH) precursor was increased in rats with heart failure 8 weeks after myocardial infarction (MI) and that early ACE inhibition tended to cause further myocardial induction of this gene.

Methods and Results— Here, we show that after MI, the expression of pro-TRH is induced in the heart coordinately with the protease PC1, an important enzyme in TRH biosynthesis. Pro-TRH gene expression was induced in cardiac interstitial cells after MI, and this effect was restricted to the heart, because no increase in TRH mRNA abundance was observed in the hypothalamus, kidney, or lung. Transcript abundance of pro-TRH can be increased in cultured cardiac fibroblasts by several adrenergic agonists, indicating that the adrenergic axis may play a regulatory role in cardiac TRH production. Acute intravenous administration of TRH to rats with ischemic cardiomyopathy caused a significant increase in heart rate, mean arterial pressure, cardiac output, stroke volume, and cardiac contractility.

Conclusions— Taken together, these results indicate that TRH is specifically induced in the heart after MI and that it can increase cardiac performance in rats with ischemic cardiomyopathy. Thus, in addition to catecholamine and angiotensin II, pro-TRH/TRH may be another important axis that affects hemodynamics and cardiac function in heart failure.

Beneficial effect of thyrotropin-releasing hormone on neuropathy in diabetic rats

Thyrotropin releasing hormone (TRH) is therapeutically effective in experimental and clinical spinal injury. The effects of TRH on diabetic neuropathy are not known. The aim of the present study was to investigate the electrophysiological effects of TRH in the streptozotocin diabetic rats. Three groups of rats were studied, non-diabetic control (n = 10), diabetic controls (n = 8), and TRH treated diabetic rats (n = 9). Administration of TRH or saline and electrophysiological measurements were performed 4 weeks after induction of diabetes. TRH was given intraperitoneally in a dose of 600 microg (3 ml). Nerve conduction velocity (NCV), measured in caudal nerve, and N1 latency of somatosensory evoked potentials (SEP) were measured 75 min after injection of TRH or serum saline. SEP latencies were 28.1 +/- 0.6, 29.4 +/- 0.8, 27.8 +/- 1.1 ms, in normal, diabetic and diabetic TRH-treated groups, and NCV values were 28.1 +/- 0.8, 23.8 +/- 0.4, and 27.9 +/- 0.7 m/s respectively. NCV was significantly reduced in the diabetic group compared to normals (P < 0.05). but then improved by TRH treatment (P < 0.05). Our findings suggest that TRH has an acute effect on peripheral neuropathy in experimental streptozotocin diabetes in the rat.

The protective effect of 5-HT3 receptor antagonist in thyrotropin releasing hormone-induced gastric lesions

The present study examined 1) oxidative stress and gastric lesions induced by thyrotropin releasing hormone (TRH) 2) The effect of a 5-hydroxytryptamine3 (5-HT3) receptor antagonist, ICS 205930 on protective effect of calcitonin on gastric lesions produced by TRH. Calcitonin (5 micrograms/10 microliter) was injected i.c.v. 10 min before TRH (10 micrograms/10 microliter, i.c.v.) injection or ICS 0.5 mg/kg, (i.p.) was given 60 min prior to calcitonin or TRH to rats. Ulcer index, lipid peroxidation (LP) and glutathione (GSH) levels were quantified 3 h after TRH injection in the stomach, liver and brain. TRH caused mucosal lesions (UI: 10.0 +/- 2.0 mm) without changing gastric GSH and LP. JCS did not alter the protective effect of calcitonin against TRH-induced lesions but attenuated. TRH-induced lesion formation. The oxidative effects of calcitonin or ICS were similar to TRH but both drugs attenuated gastric lesion formation. Hence, oxidative changes in tissues studied are not directly involved in TRH-induced lesions.

Association between chronic widespread musculoskeletal complaints and thyroid autoimmunity. Results from a community survey

OBJECTIVE

To test a hypothesis derived from observations in general practice that thyroid antibodies were associated with chronic widespread musculoskeletal complaints.

DESIGN

Cross-sectional study of 40-42 year old men and women based on a self-administered questionnaire and on results of blood tests.

SETTING

Sarpsborg municipality, Norway.

PARTICIPANTS

737 men and 771 women who attended the National Health Screening Service's mobile unit in 1989 and answered the questionnaire.

MAIN OUTCOME MEASURES

Prevalence of detectable microsomal thyroid antibodies in persons with and without chronic widespread musculoskeletal complaints.

RESULTS

The prevalence of thyroid microsomal antibodies was significantly higher in persons with than without chronic widespread musculoskeletal complaints (16.0% versus 7.3%, p < 0.01). The increase was restricted to women (20.4% versus 11.6%, p = 0.02). Thyroid function tests did not differ significantly between the two groups.

CONCLUSION

The association between chronic widespread musculoskeletal pain complaints and thyroid antibodies in women may reflect a subgroup of patients in which thyroid autoimmunity, rather than thyroid function, is important. A possible relationship to fibromyalgia is discussed as well as a hypothetical role for thyrotropin releasing hormone.

Treatment with thyrotropin-releasing hormone (TRH) in patients with traumatic spinal cord injuries

Numerous preclinical studies have demonstrated that posttraumatic treatment of spinal cord injury (SCI) with thyrotropin-releasing hormone (TRH) or TRH analogs improves long-term behavioral recovery. The purpose of the present study is to provide preliminary data regarding the safety and potential efficacy of TRH in patients with acute SCI. A total of 20 patients with SCI were classified by clinical examination into complete and incomplete injury groups within 12 h of trauma and randomly assigned in double-blinded fashion to treatment with either TRH (0.2 mg/kg intravenous bolus followed by 0.2 mg/kg/h infusion over 6 h) or vehicle (equal volume physiological saline) placebo. A variety of physiological variables were followed during treatment. Clinical examination included motor and sensory testing, as well as assigning a Sunnybrook score based upon level of function. Patients were examined at 24 h, 72 h, 1 week, 1 month, 4 months, and 12 months after injury. TRH infusions were well tolerated. There appeared to be no discernible treatment effect in patients with complete injuries although data were available from only six such patients at 4 months. For the incomplete injury group, a total of 6 treated and 5 placebo patients had 4-month evaluations. TRH treatment was associated with significantly higher motor, sensory, and Sunnybrook scores than placebo treatment. Because of patients lost to subsequent follow-up, 12-month data were not highly informative. These observations must be interpreted with considerable caution because of the small patient numbers, but together with extensive animal studies they support the need for a larger multicenter clinical trial of TRH.

The influence of muscarinic and prostaglandic mechanisms on regional cerebral and peripheral blood flows and on the vascular effects of thyrotropin releasing hormone (TRH)

TRH has pronounced vascular effects. The final transmitter mechanisms of these effects are not fully understood. The present study was conducted in order to elucidate whether these effects are mediated by prostaglandic or muscarinic mechanisms. Muscarinic blockade augmented the vasoconstricting- and pressor effect of TRH; vasodilation in the brain was attenuated only in the caudate nucleus. Indomethacin provoked a decrease in regional cerebral blood flow and in the gastric mucosal blood flow. No effect of indomethacin was observed on the vascular effects of TRH. It is concluded that the cerebral vasodilating and peripheral vasoconstricting effects of TRH are not mediated by prostaglandins. Muscarinic mechanisms are involved in the vasodilating effect of TRH only in the caudate nucleus.

Imidazole-substituted analogues of TRH limit behavioral deficits after experimental brain trauma

Treatment with thyrotropin releasing hormone (TRH) or TRH analogues improves outcome after experimental brain or spinal cord trauma. TRH analogues with modifications at the N-terminal position of the tripeptide are effective, whereas analogues with modifications of the C-terminal residue are not. Imidazole-substituted TRH analogues, which modify the middle amino acid (histidine) of the tripeptide, have more recently been developed but have not been evaluated in models of central nervous system (CNS) trauma. In the present studies two imidazole-substituted analogues--4(5)-NO2(Im)TRH and 2,4 diiodo(Im)TRH--are shown to improve behavioral recovery following fluid percussion-induced traumatic brain injury (TBI) in rats. Because 4(5)-NO2(Im)TRH has little endocrine activity and 2,4 diiodo(Im)TRH has minimal cardiovascular effects, these experiments support the hypothesis that the neuroprotective actions of TRH analogues are independent of their endocrine or autonomic actions.

Comparison of single and combination drug treatment strategies in experimental brain trauma

Effects of single-drug and combination drug treatments were examined in a model of lateral fluid percussion-induced traumatic brain injury (TBI) in rats. Treatments included the opioid receptor antagonist nalmefene, the thyrotropin releasing hormone (TRH) analog YM14673, the noncompetitive N-methyl-D-aspartate (NMDA) antagonist dextrorphan, nalmefene + dextrorphan, YM14673 + nalmefene, YM14673 + dextrorphan, and equal volume saline. Single-dose treatment with nalmefene, YM14673, or dextrorphan at 30 min after trauma each significantly improved behavioral recovery at two weeks as compared with vehicle-treated controls, confirming earlier studies with these agents. No combination treatment was superior to treatment with the most effective individual drug alone. Combination treatment with the TRH analog and the NMDA antagonist resulted in significantly less effectiveness than treatment with either drug alone. These findings indicate the need for preclinical studies to examine potential drug-drug interactions in the treatment of central nervous system (CNS) trauma.

Naloxone and TRH affect regional blood flows in the anesthetized rabbit

The cardiovascular effects of IV naloxone and a subsequent administration of TRH IV were studied in the rabbit. Naloxone caused a vasodilation in the myocardium and adrenal glands. Naloxone elicited an increment in cerebral blood flow in several regions which attenuated the cerebrovasodilating effect of TRH in a few regions. The blockade of endogenous opioids with naloxone did not modify the peripheral vasoconstricting effect of TRH or affect the vascular effects of TRH mediated by the peripheral sympathetic nerves. The results indicate that naloxone has a vasodilating effect in the myocardium and CNS in anesthetized rabbits. The major part of the cardiovascular effect of TRH is not dependent on mechanisms sensitive to naloxone.

Baroreflex-governed sympathetic outflow to muscle vasculature is increased in hypothyroidism

Microelectrode recording of muscle nerve sympathetic activity (MSA), which is baroreflex-governed and involved in cardiovascular homeostasis, was made in five patients with hypothyroidism and in seven patients with hyperthyroidism prior to treatment and after recovery to euthyroidism. Patients with hypothyroidism had a higher level of MSA when hypothyroid than after recovery (mean +/- SEM 39.3 +/- 7.1 and 26.8 +/- 7.9 bursts/min, respectively, P less than 0.05), whereas hyperthyroidism was not accompanied by a change in the number of sympathetic bursts/min. The response of MSA to manouvres known to influence the neural outflow via baroreceptors and other receptor inputs was not changed with altered thyroid function. The findings provide direct evidence of an increased sympathetic activity in hypothyroidism, but suggest that other physiological properties of MSA are intact in thyroid disease.