Behavioral effects of thyrotropin releasing hormone in frontal decorticated rats

A low dose intracerebroventricular injection of thyrotropin releasing hormone (TRH, 100 ng) changed many behavioral responses in the rat. TRH increased locomotion, scratching, body shaking, piloerection, and rearing, but decreased sniffing, and resting. Ablation of frontal neocortex further enhanced the TRH effects on locomotion and resting. A dose effect of TRH (0, 5, 10, 50, 100 ng) to increase general activity was established and the effect was further enhanced by decortication. In our test situations decortication had no effect by itself. Since the TRH effects became much more pronounced without the frontal neocortex it appears that the cortex exerts a powerful inhibitory effect to moderate the TRH effects. The TRH effect does not depend upon the frontal cortex, actually a cortical function is to dampen the TRH effects on various behavioral responses.     

Plasma growth hormone and thyrotropin responses to thyrotropin releasing hormone in freely behaving and urethane anesthetized rats.

Plasma GH and TSH responses to thyrotropin releasing hormone (TRH) were examined in freely behaving and urethane anesthetized rats. The i.v. administration of TRH (200ng/100g b.wt.) resulted in consistent elevations of plasma GH only in urethane anesthetized rats, while significant elevations of plasma TSH were similarly observed in both conditions. Results suggest that urethane influences plasma GH responses to TRH.     

Radioimmunologic determination of the thyrotropin releasing hormone]

We describe the preliminary steps for a radio-immunoassay of Thyrotropin Releasing Hormone (TRH). Rabbit antiserum at dilution 1 : 10 000 is used with radioiodinated TRH (125I). We are able to assay from 5 to 1 000 pg unlabeled TRH with an intraassay reporducibility varying from 7 to 4 % and the lowest detectable amount in this system is 10 pg TRH. TRH mean and standard deviation in normal subjects are 136,9 and 25,3 pg/ml.     

Increased growth hormone responses to growth hormone releasing hormone and thyrotropin releasing hormone in patients with metastatic testicular cancer

In 16 patients with metastatic testicular cancer and 10 age matched male control subjects growth hormone (GH) responses to growth hormone releasing hormone (GHRH; 1 microgram/kg body weight iv.) and thyrotropin releasing hormone (TRH; 200 micrograms iv.) were measured. Basal GH levels and GH levels following stimulation with GHRH or TRH were significantly increased in cancer patients compared to control subjects. 9 patients with testicular cancer were studied both in the stage of metastatic disease and after they had reached a complete remission. In complete remission GH responses to GHRH tended to decrease but the differences did not reach statistical significance. Our data suggest an alteration of hypothalamic and/or pituitary regulation of GH secretion in patients with metastatic testicular cancer.     

Spinal cord thyrotropin releasing hormone receptors of morphine tolerant-dependent and abstinent rats

The effect of chronic administration of morphine and its withdrawal on the binding of 3H-[3-MeHis2]thyrotropin releasing hormone (3H-MeTRH) to membranes of the spinal cord of the rat was determined. Male Sprague-Dawley rats were implanted with either 6 placebo or 6 morphine pellets (each containing 75-mg morphine base) during a 7-day period. Two sets of animals were used. In one, the pellets were left intact at the time of sacrificing (tolerant-dependent) and in the other, the pellets were removed 16 hours prior to sacrificing (abstinent rats). In placebo-pellet-implanted rats, 3H-MeTRH bound to the spinal cord membranes at a single high affinity binding site with a Bmax of 21.3 +/- 1.6 fmol/mg protein, and an apparent dissociation constant Kd of 4.7 +/- 0.8 nM. In morphine tolerant-dependent or abstinent rats, the binding constants of 3H-MeTRH to spinal cord membranes were unaffected. Previous studies from this laboratory indicate that TRH can inhibit morphine tolerance-dependence and abstinence processes without modifying brain TRH receptors. Together with the present results, it appears that the inhibitory effect of TRH on morphine tolerance-dependence and abstinence is probably not mediated via central TRH receptors but may be due to its interaction with other neurotransmitter systems.     

Growth hormone response to thyrotropin releasing hormone in a pellagrin

An abnormal hyperresponse of GH to intravenous injection of TRH in a 66-year-old female pellagra patient with typical 3'D's was reported. Diagnosis of pellagra was mainly based on her clinical course and manifestations, although serum levels of nicotinic acid and serotonin were within the normal range. Serum vitamin A and B2 levels were low. However, these findings did not exclude the diagnosis. The abnormal GH response to TRH observed in this patient was decreased at 2 months and thoroughly disappeared at 10 months after admission. GH response to arginine showed an exaggerated and sustained response on admission, decreased at 2 months and showed an almost normal pattern at 10 months after admission. TSH and prolactin response to TRH were normal throughout the clinical course. LH and FSH response to LH-RH were exaggerated, suggesting post-menopausal hypogonadism. Cortisol response to ACTH showed slightly sustained reactions at both times of the provocation. Oral glucose tolerance test revealed a slight impairment in this patient. These results suggest that pellagra is one of the disorders which exhibit an abnormal hyperresponse of GH to intravenous administration of TRH.     

Effects of intracerebroventricular injections of thyrotropin releasing hormone on gastrointestinal propulsive motility in rats

The effect of intracerebroventricular (ICV) injections of thyrotropin releasing hormone (TRH) on the propulsive motility of the gastrointestinal tract was examined in rats. The distance travelled by charcoal meal through the small intestine, measured in terms of percentage of its total length, was recorded as the index of propulsive motility. The results were as follows: (1) The propulsive distance of charcoal meal was significantly reduced in a dose-dependent manner after ICV injections of TRH (1 microgram/10 microliters, 5 micrograms/10 microliters or 10 micrograms/10 microliters) (P less than 0.01-0.001) The effects were abolished by injection of atropine (5 micrograms/10 microliters ICV). (2) The gastrointestinal propulsive motility decreased markedly (P less than 0.01) after injection of a larger dose of TRH (50 micrograms/100 g) into the hypodermis. The effects were not completely blocked by subcutaneous injections of propranolol (5 mg/kg). (3) No effects (P greater than 0.05) were found on the inhibition of gastrointestinal propulsive motility after ICV injections of regitine (2.5 mg/kg im, 50 micrograms/50 microliters ICV) or propranolol (5 mg/kg im, 50 micrograms/50 microliters ICV). The results indicate that TRH has an inhibitory effect on the propulsive motility of gastrointestinal tract, which may be mediated via the non-adrenergic inhibitory nerve of the vagal nerves.     

Growth hormone and prolactin response to thyrotropin releasing hormone and growth hormone releasing factor in the immature turkey

Synthetic thyrotropin releasing hormone (TRH) and human pancreatic growth hormone releasing factor (hpGRF) stimulated growth hormone (GH) secretion in 6- to 9-week-old turkeys in a dose-related manner. TRH and hpGRF (1 and 10 micrograms/kg, respectively) each produced a sixfold increase in circulating GH levels 10 min after iv injection. Neither TRH nor hpGRF caused a substantial change in prolactin (PRL) secretion in unrestrained turkeys sampled through intraatrial cannulas. However, some significant increases in PRL levels, possibly related to stress, were noted.     

Antagonism of ethanol narcosis by thyrotropin releasing hormone

Thyrotropin releasing hormone (TRH) reduced the narcosis and hypothermia produced by ethanol in mice. This action of TRH does not appear related to release of thyroid hormone or to the effects of a metabolite of TRH. The ability of TRH to reduce the actions of ethanol after intracisternal injection suggests that the mechanism of the ethanol antagonism is central in origin. The antagonism of ethanol by TRH does not appear to be related to an amphetamine-like stimulant action.     

Spontaneously hypertensive rats exhibit supersensitivity to the hypertensive and hyperthermic effects of thyrotropin releasing hormone

The effect of thyrotropin releasing hormone (TRH) on colonic temperature and systolic blood pressure of age-matched spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. Administration of TRH produced dose-dependent increases in body temperature and systolic blood pressure. TRH-induced changes in both responses were of greater magnitude in SHR rats compared to WKY rats. The results provide the first evidence that SHR rats exhibit supersensitivity to non-neuroendocrinological effects of TRH and that TRH may play a role in the pathophysiology of elevated blood pressure.     

Potentiation of foot shock analgesia by thyrotropin releasing hormone

Thyrotropin releasing hormone (TRH) interacts with both opioid and non-opioid systems in mediating hypothermic, hypoactive, cataleptic, respiratory and analgesic effects. While TRH neither antagonizes opioid analgesia nor alters pain thresholds itself, it blocks neurotensin analgesia. Different forms of pain-inhibition in rats can be activated by selectively altering the parameters of shock: while analgesia induced by 20 inescapable tail-shocks is not reversed by naltrexone, exposure to 60 or 80 shocks does elicit naltrexone-reversible analgesia. The first experiment examined whether intracerebroventricular administration of TRH (0, 10, or 50 micrograms) would alter the elevations in tail-flick latencies in rats induced by 20 or 80 foot shocks and found that TRH significantly lengthened the duration and magnitude of analgesia induced by 20 and 80 foot shocks in a dose-dependent manner. The second experiment extended these findings to the writhing test, a visceral pain test. While the number and duration of writhes of vehicle-treated rats exposed to 80 foot shocks failed to differ from baseline values. TRH (50 micrograms)-treated rats exposed to 80 foot shocks displayed significant decreases in the number and duration of writhes. The third experiment indicated that the differential effects of naltrexone upon analgesia induced by 20 or 80 tail shocks were not apparent when foot shocks were employed, precluding a definitive statement that TRH may be involved in the modulation of both opioid and non-opioid forms of analgesia.     

Opioid modulation of thyrotropin releasing hormone induced prolactin secretion

It is known that opioids stimulate prolactin (PRL) secretion by an action on hypothalamic neurons, but in vitro studies have suggested a direct action on the lactotrophs. The present study was performed on male rats known to have little or no PRL response to TRH. A beta-endorphin (beta EP) injection in the third ventricle stimulated PRL secretion and induced furthermore a PRL secretory reaction to TRH injected intravenously 20 min later. Pretreatment with naloxone 10 min before beta EP injection abolished not only the PRL response to beta EP but also the conjugated effect of beta EP and TRH. Pretreatment with naloxone methyl bromide (Br-naloxone), a quaternary naloxone derivative, which does not cross the blood-brain barrier, had no effect on the PRL response to beta EP but prevented the conjugated effect of beta EP and TRH on PRL secretion. Pretreatment of the animals with -methyl-parathyrosine resulting in a dopamine depletion or with haloperidol, a dopamine antagonist, could not induce lactotroph responsiveness to TRH. These results suggest that beta EP in male rat sensitizes the PRL cell to TRH by a direct effect and not through an inhibition of the dopaminergic tone.