Biomedical subjects

T Iriuchijima

Publications and source records attributed to T Iriuchijima.

At least 55 records · Page 3Linked to original sources

PubMed1990

A possible direct precursor of thyrotropin-releasing hormone, pGlu-His-Pro-Gly, stimulates prolactin secretion in anorexia nervosa.

TRH is produced from its possible direct precursor, pGlu-His-Pro-Gly (TRH-Gly), by alpha-amidating enzyme. The quantitative response of TRH-Gly-stimulated PRL, TSH, and GH was evaluated in nine patients with anorexia nervosa, six age-matched normal women, eight patients with uremia, five patients with acromegaly, and two patients with prolactinoma. Intravenous injection (500 micrograms) of TRH-Gly caused a 2.6-fold increase in PRL secretion in patients with anorexia nervosa (basal level, 10.0 +/- 1.4 vs. 25.9 +/- 2.5 micrograms/L 15 min after injection; P less than 0.01). In contrast, no significant change was observed in TRH-Gly-stimulated PRL secretion in normal women (basal level, 13.5 +/- 2.3 vs. 15.3 +/- 2.5 micrograms/L 15 min after injection; P greater than 0.05). TRH-Gly did not alter PRL levels in patients with uremia, acromegaly, or prolactinoma. Secretion of TSH, but not GH, was slightly increased by TRH-Gly injection in patients with anorexia nervosa (basal level, 1.41 +/- 0.13 vs. 2.86 +/- 0.22 min/L 30 min after injection; P less than 0.01), whereas no significant secretory response was observed in normal women. These data provide evidence that PRL secretion in anorectic patients is quantitatively different from that in normal persons.

Adult↗

PubMed1990

Inhibition by staurosporine of TRH-induced refractoriness of inositol phospholipid hydrolysis in rat anterior pituitaries.

To clarify the mechanism(s) underlying the TRH-induced refractory state of the anterior pituitary, we evaluated rat pituitary inositol phospholipid hydrolysis in the presence of staurosporine. TRH caused a time- and dose-dependent accumulation of inositol phosphates in rat anterior pituitary slices. Pretreatment with 550 nmol TRH/l completely abolished the subsequent accumulation of inositol phosphates in response to 140 nmol TRH/l. TRH-stimulated accumulation of inositol phosphates did not occur after pretreatment with 0.2 mumol phorbol ester/l. Refractoriness of inositol phospholipid hydrolysis which was produced by pretreatment with TRH and phorbol ester was inhibited by staurosporine. The present data support the hypothesis that protein kinase C plays a profound role in TRH induction of the refractory state of inositol phospholipid hydrolysis in the anterior pituitary.

Alkaloids↗

PubMed1989

[Studies on TRH-binding protein in rat serum].

The possible existence of binding protein for TRH was studied in rat serum. Synthetic TRH was incubated in rat serum and extracted in 90% methanol for measurement of tripeptide by RIA. The amount of TRH in serum at 37 C decreased progressively with incubation time, while that tripeptide, which was incubated in serum at 60 C, significantly decreased 5 min after incubation, but TRH concentration afterward remained unchanged until 60 min. The concentration of TRH, which was incubated in serum at 37 C for 30 min, did not differ from that which was successively incubated at 60 C for 60 min. An elution pattern of TRH incubated in serum on a Sephadex G-25 was similar to that of authentic tripeptide, and this elution profile was not changed by heating at 60 C. An isoelectric focusing analysis of TRH incubated in serum showed a single peak of pI 8.2 which was not distinguished from the authentic peptide and was not changed by heating. These data indicate that TRH-degradation in rat serum is not dependent on its binding protein.

Animals↗

PubMed1989

Regional dissociation of cyclic AMP and inositol phosphate formation in response to thyrotropin-releasing hormone in the rat brain.

The present study was undertaken to define effects of thyrotropin-releasing hormone (TRH) on formation of cyclic AMP (cAMP) and inositol phosphates (IPs) in rat brain regions. The brain of male Wistar rats was dissected into seven discrete regions, and each region was sliced. The slices were incubated in Krebs-Henseleit glucose buffer containing varying doses of TRH. TRH caused a significant and consistent increase in cAMP level, but not in formation of IPs, in the hypothalamus, striatum, and midbrain. TRH stimulated formation of IPs in the cerebellum, where the tripeptide did not change the cAMP level. In contrast, formation of neither cAMP nor IPs was affected by TRH in the cortex, hippocampus, or pons-medulla. These data suggest that TRH possesses two distinct types of brain intracellular signaling systems, which vary with brain regions.

Animals↗

PubMed1989

TRH analog administration increases endogenous TRH levels in the central nervous system.

Experiments were carried out to increase the endogenous levels of TRH in brain and spinal cord. After 7 days of continuous oral ingestion of TRH analogs (D-pGlu-Leu-ProNH2, pGlu-Leu-Pro, pGlu-Pro-ProNH2, or pGlu-Leu-pyrrolidide), spinal cord and brain levels of TRH were elevated, whereas the content of TRH metabolite, cyclo(His-Pro), was decreased. In addition, the TRH analogs inhibited in vitro metabolism of [3H-Pro]-TRH by brain and spinal cord extracts. Our data show that certain TRH analogs can elevate tissue levels of TRH by inhibiting its metabolism. Furthermore, because these analogs do not affect interaction between TRH and its receptor, the elevated TRH can effectively enhance TRH-related bioactivity.

Animals↗

PubMed1989

Actinomycin D affects thyrotropin-releasing hormone-induced heterogeneous forms of glycosylated thyroid-stimulating hormone in rat anterior pituitary.

Actinomycin D and cycloheximide were used to clarify the tight relationship between protein synthesis and heterogeneous carbohydrate synthesis of rat pituitary thyroid-stimulating hormone (TSH) under thyrotropin-releasing hormone (TRH) stimulation in vitro. Rat anterior pituitaries were incubated with [3H]glucosamine in the presence of TRH, cycloheximide and actinomycin D at 37 degrees C for 3 and 6 h. The TSH fraction of pituitary homogenates was obtained using affinity chromatography coupled with anti-TSH globulin, and was analyzed by isoelectric focusing. Anterior pituitary in the presence of TRH showed heterogeneous components of [3H]glucosamine-labeled TSH with 6 different isoelectric points (components I-VI). Radioactivities of the components increased with the incubation period. Cycloheximide changed these heterogeneous components. Actinomycin D also caused a striking change in the heterogeneity of pituitary [3H]glucosamine-labeled TSH: components I and II decreased and components III and IV increased as compared to the control group after a 6-hour incubation. The present study implies that actinomycin D affects the TRH-induced heterogeneous components of pituitary TSH glycosylation. The data indicate that messenger RNA is essential for the normal processing of carbohydrate synthesis of pituitary TSH.

Animals↗

PubMed1989

Characterization and solubilization of cyclo(His-Pro) binding from rat liver membranes.

We have found cyclo(His-Pro) binding in rat liver plasma membranes. This study focused on the characterization of solubilized binding for cyclo(His-Pro) in rat liver membranes. The cyclo(His-Pro) binding of liver membranes was solubilized by digitonin and octyl-glucopyranoside. The efficiency of solubilization with digitonin was greater. However, cyclo(His-Pro) binding was not solubilized by Triton X-100, CHAPS, or Lubrol. Digitonin-solubilized membranes showed cyclo(His-Pro) binding with a high affinity constant (17 nM) and a low binding capacity (38 fmol/mg protein). Lectins from wheat germ, Bandeiraea simplicifolia II, Dolichos biflorus, Glycine max, and Tetragonolobus purpureas significantly adsorbed [3H]cyclo(His-Pro)-binding complex, but Bandeiraea simplicifolia I, Ricinus communis I, or Lens culinaris did not adsorb the binding complex. An analysis of [3H]cyclo(His-Pro)-associated membranes by high performance gel filtration chromatography showed a radioactive peak of Mr 200,000. These data indicate that cyclo(His-Pro) binding of rat liver membranes is solubilized by digitonin and is a glycoprotein of Mr 200,000.

Animals↗

PubMed1989

An analogue of thyrotropin-releasing hormone, DN1417, decreases naloxone binding in the rat brain.

We explored whether thyrotropin-releasing hormone may affect opioid receptors in the rat brain. Adult male rats were intraperitoneally injected twice a day with varying doses of DN1417, a potent analogue of thyrotropin-releasing hormone, for 2 days, and opioid receptors of the brain (hypothalamus, striatum, hippocampus, midbrain, ponsmedulla, and cortex) homogenates were determined using [3H]naloxone. Intraperitoneal injection of DN1417 in a dose of 0.3 mg/100 g body wt resulted in a significant reduction in naloxone binding of the striatum as compared with the saline-injected group, whereas naloxone binding of other brain regions was not affected by DN1417. DN1417 produced a dose-dependent decrease in naloxone binding of the striatum. The affinity constant of naloxone binding was similar between the saline- and DN1417-injected groups. In vitro addition of DN1417 did not interfere with the brain naloxone binding. The distribution of 3H-labeled DN1417 injected peritoneally did not differ among the brain regions. The present data imply that the opioid antagonistic action of thyrotropin-releasing hormone may be due, at least in part, to the significant decrease in the striatal opioid binding in the rat brain.

Animals↗

PubMed1989

Hypothyroidism enhances carbachol-induced hypothermia in the rat.

We studied cholinergic regulation of body temperature in hypothyroid rats. Thyroidectomy caused a progressive decrease in core temperature. Intraventricular injection of carbachol in a dose of 10 nmol did not change core temperature of the normal rat, whereas the same dose of carbachol significantly decreased the temperature of thyroidectomized rats. One hundred nmol carbachol decreased to a greater extent core temperature of the thyroidectomized rats than that of normal rats. Intraventricular injection of atropine significantly increased core temperature of thyroidectomized rats. The present data indicate that brain cholinergic mechanisms participate in controlling temperature in the hypothyroid status and thyroid hormones play a significant role in the brain cholinergic regulation of body temperature.

Animals↗

PubMed1988

[Influences of protein synthesis inhibitors on TRH-stimulated secretion of glycosylated TSH].

The significant influence of protein synthesis inhibitors on TRH-stimulated secretion of glycosylated TSH was investigated in the rat anterior pituitary in vitro. TRH stimulated secretion of (3H)glucosamine-labeled TSH but did not change incorporation of its labeled precursor into the pituitary TSH. Addition of cycloheximide significantly inhibited both incorporation of (14C)alanine into the pituitary protein and of (3H)glucosamine into the pituitary TSH even 3 hours after incubation, while it did not cause a significant change in secretion of glucosamine-labeled TSH. Apparent inhibition of (14C)alanine incorporation into the pituitary protein was produced by addition of actinomycin D in the 3 and 6 hour-incubation, but the same drug did not cause the significant change in the amount of (3H)-glucosamine-labeled TSH in the anterior pituitary and medium. It is concluded from the present study that TRH plays a potential role in regulating carbohydrate synthesis of TSH prior to secretion, and messenger RNA is not essential for its role in the glycosylation of TSH.

Animals↗

PubMed1988

Food deprivation decreases the blood TRH concentration in the rat.

Adult male rats were deprived of food for 1-6 days and the hypothalamo-pituitary axis in these rats was evaluated. Food deprivation caused a progressive decrease in TRH concentration in the peripheral blood with a concomitant reduction in the blood TSH level. No significant change was observed in the hypothalamic, extrahypothalamic or pancreatic TRH concentration between the control and starved groups. Starvation did not cause a significant change in the pituitary TRH receptors or the in vitro responsiveness of TSH to TRH. These data imply that the reduction in the blood TRH level may contribute in part to the decrease in the blood TSH level after food deprivation, but the origin of the blood TRH has remained to be determined.

Animals↗

PubMed1988

Water deprivation changes naloxone binding in the rat brain.

The significant relationship of drinking to brain opioid receptors was determined using naloxone, a preferential antagonist of opioid mu receptor, in water-deprived rats. Whereas 48-hour food deprivation did not affect naloxone binding in any brain regions, 48-hour water deprivation caused a significant decrease in naloxone binding in the striatum, but not in the other brain regions. The striatal naloxone binding was found to progressively decrease with a period (0-48 h) of water deprivation. No significant change in naloxone binding in the hypothalamus or midbrain was observed during water deprivation. Water deprivation did not change the affinity constant of naloxone binding in the striatum. These observations indicate that the change in the striatal opioid receptors was specifically associated with thirsty sensation in the rat.

Animals↗

PubMed1988

Cyclo(His-Pro) concentration. Changes in brain striatum of hyperglycemic rat.

We scrutinized whether the hyperglycemic status changed the concentration of prototype neuropeptides cyclo(His-Pro) and thyrotropin-releasing hormone (TRH) in the rat brain. Streptozocin-induced hyperglycemia caused a significant increase in cyclo(His-Pro) concentration in the striatum but not in the other brain regions, whereas TRH concentration in any brain region did not differ between control and hyperglycemic groups. Insulin injection normalized blood glucose level and prevented an increase in cyclo(His-Pro) concentration after hyperglycemia. These data indicate that hyperglycemia causes a profound alteration in cyclo(His-Pro) concentration in the rat brain striatum.

Animals↗

PubMed1987

Thyrotropin-releasing hormone and cyclo (His-Pro)-like immunoreactivities in the cerebrospinal fluids of 'normal' infants and adults, and patients with various neuropsychiatric and neurologic disorders.

Levels of thyrotropin-releasing hormone (TRH) - and cyclo(His-Pro) (CHP)-like immunoreactivities and the activity of enzyme Pyroglutamate aminopeptidase (PAPase) were measured in cerebrospinal fluid (CSF) of over 100 normal adults (NA) and infants, and adult patients with various neurologic and neuropsychiatric disorders (NNDA). Levels of TRH and CHP in CSF of over 70% of the NA group were below 50 and 500 pg/ml respectively. The TRH- and CHP-like immunoreactivities in the remainder of the 30% of NA specimens exhibiting higher peptide concentrations were enzymatically and chromatographically characterized and were found to behave like authentic peptides. The levels of both of these peptides were significantly elevated in the CSF of most of the NNDA patients. An elevation in the CSF level of CHP was significantly correlated with the level of TRH, but not PAPase. Results from this study suggest that CSF elevation of TRH level may be due to a nonspecific response to stress that may be associated with hospitalization, myelogram procedure, and/or the neurologic and neuropsychiatric diseases for which the patients were admitted.

Adult↗

PubMed1987

[Disappearance rate of TRH: change in the status of TSH refractoriness in vitro].

We studied on the potential change in TRH disappearance rate in the status of TSH refractoriness in vitro. TSH secretion from the rat anterior pituitaries progressively increased in the presence of TRH in doses between 0.2-20 ng/ml. In contrast, administration of TRH in a dose of 200 ng/ml decreased TSH secretion as compared to TRH in a dose of 20 ng/ml. Disappearance rate of 2 ng/ml TRH in incubation media increased as compared to that of 20 ng/ml TRH, but it was statistically similar between 20 and 200 ng/ml of TRH. Incubated TRH was indistinguishable from the authentic tripeptide on a HPLC. These data indicate that in vitro refractoriness of TSH response to TRH did not depend on the significant change in TRH disappearance rate.

Animals↗

PubMed1987

[TRH and cyclo (His-Pro) concentrations in the young rat brain are altered by a liquid protein diet].

Effects of liquid protein diet (LPD), that is known to be poor in protein quality, on brain TRH and cyclo (His-Pro) concentrations were explored in young male rats. At day 23 of weaning, the animals were fed either a 20% casein diet ad libitum or a 20% LPD, or were pair-fed with a 20% casein diet. They were decapitated at day 35 or day 48. The body weight of those in the LPD group decreased significantly, and the loss was sustained in comparison with those in the pair-fed and ad libitum groups. The extrahypothalamic cyclo (His-Pro) concentrations were significantly greater in the LPD group than in the pair-fed and ad libitum groups throughout the experimental period, whereas these concentrations were similar in the pair-fed and ad libitum groups. At day 48, TRH concentrations in the hypothalamus and extrahypothalamus also increased in the LPD group in comparison with the concentrations in ad libitum group. These data indicate that quality of the protein component in the diet has a potential effect on alteration in the neuropeptides, TRH and cyclo (His-Pro), in the young rat brain.

Animals↗

PubMed1987

[Changes in TRH and cyclo (His-Pro) concentrations in the rat brain after cold exposure].

Intraventricular administration of TRH and cyclo (His-Pro) has been investigated to cause the respectively, increase and decrease, in body temperature. We scrutinized whether cold exposure (4 degrees C) may change TRH and cyclo (His-Pro) concentrations in the rat brain. While the blood TSH level rose after cold exposure, the rectal temperature was not significantly changed by the same exposure. Cyclo (His-Pro) concentrations in the hypothalamus increased significantly 15 and 30 min after cold exposure and returned to the basal level after 60 min. The extrahypothalamic concentrations of cyclo (His-Pro) decreased 60 min after cold exposure. No significant changes were observed in either the hypothalamic or extrahypothalamic concentrations of TRH under the cold status. It is postulated from the present data that the cold exposure-induced increase in cyclo (His-Pro) concentrations in the hypothalamus may be a potent hypothermic signal to elicit the counter regulatory mechanism(s) for the decrease in body temperature.

Analysis of Variance↗

PubMed1987

Thyrotropin-releasing hormone and histidyl-proline diketopiperazine: stimulation of secretion from hypothalamic fragments in vitro by depolarizing agents.

The influence of depolarizing agents on the release of TRH and histidyl-proline diketopiperazine [C(HP)] from rat hypothalami was examined in vitro. Thin hypothalamic fragments from two separate animals were incubated in Krebs-Ringer bicarbonate media. Immunoreactive TRH and C(HP) released into medium were determined by specific RIAs. Potassium and ouabain, a Na+/K+-ATPase inhibitor, stimulated TRH and C(HP) secretion in a graded fashion, but the magnitudes of C(HP) secretory responses were less than those of TRH. The stimulation by KCl and ouabain was inhibited by the addition of verapamil, a Ca2+ channel blocker, or omission of Ca2+ from medium in the presence of EGTA. Veratridine, a Na+ channel activator, also stimulated TRH and C(HP) release from rat hypothalami, and this stimulation was completely blocked by tetrodotoxin, a Na+ channel blocker. The results of this study indicate that TRH and C(HP) release from rat hypothalami are stimulated by membrane depolarization in vitro and depend on Na+ and Ca2+ influx.

Animals↗