Search PubMed⌕ Search

Biomedical subjects

M Niimi

Publications and source records attributed to M Niimi.

At least 127 records · Page 7Linked to original sources
PubMed1995

Nucleotide sequence and the molecular evolution of a new A2 gene in the DQ subregion of the bovine major histocompatibility complex.

cDNA clones encoding the bovine major histocompatibility complex (MHC) class II DQ alpha chain were isolated. One clone, MQ9, encoded a primary translated product of 255 amino acids, with a signal peptide of 23 amino acids and a mature polypeptide of 232 amino acids. A new A2 gene in the DQ subregion of the bovine genome was identified from a comparison of amino acid sequences encoded by class II A genes among several species and the construction of a phylogenetic tree. It was revealed that MQ9 is most closely related to the ovine DQA2 genes among sequences from various mammalian species. By contrast, the BoLA-DQA genes previously isolated are more closely related to ovine DQA1 than to the BoLA-DQA2 gene, and they represent BoLA-DQA1 genes. Thus, the presence of two BoLA A genes, which may be expressed and functional in the bovine, as well as in sheep was confirmed. A large number of amino acids unique to products of DQA2 genes of bovine and ovine origin were identified when the predicted amino acid sequences for both species were compared, and most of the DQA2-specific residues were located in the alpha 1 domain and were conserved with respect to products of DQA1 genes of ruminants. Thus, several characteristics of the bovine DQA genes were found to differ from those of human and rodent genes, despite similarities in gene structure and in nucleotide sequence.

Amino Acid Sequence↗
PubMed1995

Identification of a new bovine MHC class II DRB allele by nucleotide sequencing and an analysis of phylogenetic relationships.

Three overlapping cDNA clones coding for the bovine major histocompatibility complex (MHC) class II DR beta chain were isolated. A clone NR1 encoded a primary translated product of 266 amino acids, 29 of which were deduced to form a signal peptide and 237 to form the mature polypeptide. The protein predicted from this cDNA appeared to have all the features expected of an expressed MHC class II molecule. Comparison of the sequences and construction of a phylogenetic tree revealed that NR1 represents a BoLA-DRB3 gene and not a BoLA-DRB1 or BoLA-DRB2 pseudogene. NR1 and ovine sequences exhibited the greatest overall similarity among sequences from various mammalian species, followed by the equivalent human sequences. Indeed, the bovine allele was more closely related to certain ovine alleles than to other bovine alleles. A large number of replacement substitutions were identified when beta 1 domains encoded by NR1 and each of the 36 distinct BoLA-DRB3 alleles were compared, and most of the allelic variations were found in regions that are commonly polymorphic in DRB sequences from different species and correspond to the predicted antigen-recognition site. Thus, the predicted structure of the unique NR1 allele for BoLA-DRB3 further confirms the overall conservation of the product of this locus, as previously established from studies in rodent and man.

Alleles↗
PubMed1995

Induction of Fos protein in the rat hypothalamus elicited by insulin-induced hypoglycemia.

To evaluate the responses to insulin-induced hypoglycemia of neurons in vivo, we studied Fos protein induction in the brain by means of immunohistochemistry. The induction of Fos protein was maximum after the first injection of insulin for 3 h. This induction was found in the parvocellular division of paraventricular nucleus (PVN), the periventricular, dorsomedial and arcuate nuclei and the lateral hypothalamic area of the hypothalamus. These findings show the activation of specific subsets of neurons in areas of the hypothalamus following hypoglycemic stimulation.

Animals↗
PubMed1995

Central glucopenia induced by 2-deoxy-D-glucose stimulates somatostatin secretion in the rat.

The mechanisms involved in 2-deoxy-D-glucose (2-DG)-induced growth hormone (GH) suppression in the rat were examined. Conscious male rats were given 2-DG by intracerebroventricular (icv) injection and the pulsatile GH secretion was monitored for 6 h. The single icv injection of 2-DG (8 mg/rat) eliminated pulsatile GH secretion in conscious rats. Pretreatment with somatostatin (SS) antiserum completely restored the suppressed GH secretion in the 2-DG treated rats. Hypothalamic GH-releasing hormone (GRH) and SS mRNA levels were not altered by single and multiple icv injections of 2-DG. These findings suggest that 2-DG-induced GH suppression is primarily due to hypersecretion of SS without a significant change at the transcription level in the rat.

Animals↗
PubMed1995

Resistance of growth hormone secretion to hypoglycemia in the mouse.

Although previous studies have demonstrated that acute hypoglycemia inhibits growth hormone (GH) secretion due to stimulation of hypothalamic somatostatin (SS) neurones in the rat, the effect of hypoglycemia on GH secretion has not yet been elucidated in the mouse. In this study, the effects of insulin-induced hypoglycemia on mouse GH secretion, hypothalamic c-fos expression, GH-releasing hormone (GRH) and SS mRNA levels were investigated in conscious male mice. Seven days after implantation of chronic atrial catheters, blood samples were taken every 20 min from 1200-1600 h under unrestrained conditions. Insulin was administered iv every 20 min from 1200-1240 h to induce moderate hypoglycemia (MH) and severe hypoglycemia (SH), respectively. Expression of hypothalamic c-fos protein was examined 30 min and 60 min after induction of hypoglycemia by immunohistochemistry. Hypothalamic GRH and SS mRNA levels were examined 1 h and 3 h after induction of hypoglycemia by Northern blot analysis. The lowest mean plasma glucose levels after insulin injections were 49.1 +/- 4.1 mg/dl and 34.2 +/- 5.6 mg/dl in conscious mice, respectively. However, pulsatile GH secretion was not significantly altered in either group. Although both MH and SH markedly stimulated c-fos expression in specific hypothalamic nuclei including the paraventricular nucleus, they did not induce c-fos protein in the periventricular nucleus. Neither MH nor SH altered hypothalamic GRH or SS mRNA levels. These results suggest that hypoglycemia does not activate SS neurons which inhibit GH secretion in the mouse.

Animals↗
PubMed1995

Suppression of episodic growth hormone secretion in streptozotocin-induced diabetic mice: time-course studies on the hypothalamic pituitary axis.

To elucidate the roles of the hypothalamic peptides, GH-releasing hormone (GRH) and somatostatin (SRIH), potentially responsible for altered GH dynamics in diabetes, we studied the time courses of their changes in level associated with altered GH secretion in streptozotocin (STZ)-induced diabetic mice. Diabetic mice were used at 4, 7, and 14 days after STZ injection for analyses of 1) GH secretion in vivo, 2) hypothalamic GRH and SRIH messenger RNA (mRNA) levels, 3) pituitary GH mRNA and protein contents, and 4) pituitary GH response to GRH in vitro. GH secretion was completely suppressed 7 and 14 days after STZ injection. The hypothalamic GRH mRNA level was reduced to 59.8%, 61.2%, and 48.5% of control values at 4, 7, and 14 days, respectively. In contrast, the hypothalamic SRIH mRNA level was not altered at all of these time points. Pituitary GH mRNA and protein contents were significantly reduced to 70.2% and 61.5% of those in controls, respectively, only at 14 days. Pituitary GH responses to GRH at three doses (10, 50, and 250 nM) in vitro were remarkably increased at 4, 7, and 14 days. These findings indicate that the diabetic state rapidly and primarily inhibits hypothalamic GRH gene expression without affecting SRIH. A persistent decrease in hypothalamic GRH tone has been suggested to result in inhibition of GH synthesis in the pituitary. Enhancement of GH responsiveness to GRH may be due to the up-regulation of GRH receptors in the pituitary.

Animals↗
PubMed1995

Inhibitory effects of interleukin-1 on growth hormone secretion in conscious male rats.

Although various pathophysiological effects of interleukin (IL) on the CRF-ACTH-adrenal axis and gonadotropin secretion have been studied extensively, the effects of IL on GH secretion still remain to be elucidated. We investigated the possible effects of IL on GH secretion in six groups of conscious rats. In four groups, IL was administered by continuous iv infusion and in the other two, by intracerebroventricular injection. Saline-treated rats served as controls for these groups. Sequential blood sampling was performed every 20 min in all groups, and the plasma GH concentration was determined by RIA. The expression of hypothalamic c-fos protein in a separate group was examined by immunohistochemistry. Continuous infusion of both IL-1 alpha and IL-1 beta (10 ng/min) significantly inhibited GH surges. The plasma IL-1 level was elevated to 2-3 ng/ml. Continuous iv infusion of IL-2 and IL-6 had no effect on GH secretion. The intracerebroventricular injection of both IL-1 alpha and IL-1 beta significantly inhibited GH surges, and the inhibitory effect was much greater for IL-1 beta than for IL-1 alpha. Continuous iv infusion of IL-1 beta markedly stimulated c-fos expression in specific hypothalamic nuclei, particularly in the paraventricular nucleus. These findings suggest that, in the rat, IL-1 inhibits GH secretion through its peripheral and central actions.

Animals↗
PubMed1995

Differential gene expression of growth hormone (GH)-releasing hormone (GRH) and GRH receptor in various rat tissues.

Growth hormone (GH)-releasing hormone (GRH) acts on specific receptors in the anterior pituitary to stimulate the synthesis and release of GH. Recent reports suggest that GRH is also synthesized in extrahypothalamic tissues. To evaluate the potential roles of extrahypothalamic GRH, we studied the gene expression of GRH and GRH receptors in various rat tissues by reverse transcribed (RT)-polymerase chain reaction (PCR). Total RNA was extracted from twenty-three rat organs and RT-PCR was performed with GRH and GRH receptor primers. Highly-sensitive RT-PCR-Southern blotting showed that GRH and GRH receptor mRNA coexist in the widespread tissues (14 of 25 tissues). GRH mRNA was relatively abundant in the cerebral cortex, brain stem, testis, and placenta, while GRH receptor mRNA was abundant in renal medulla and renal pelvis. Northern blot hybridization using poly A+ RNA indicated that the transcript of GRH receptor gene found in the renal medulla was similar to the longer transcript (about 4 Kb) of pituitary GRH receptor in the size. These results suggest that GRH plays a potential role not only in the neuroendocrine axis, but also in the autocrine and paracrine systems in extrahypothalamic tissues.

Animals↗
PubMed1995

Gene expression of hypothalamic growth hormone (GH)-releasing hormone and somatostatin does not correlate with pulsatile secretion of GH in the adult mouse.

The secretion of growth hormone (GH) shows a pulsatile pattern in many mammalian species, and depends on the interaction of two hypothalamic hormones, GH-releasing hormone (GHRH) and somatostatin (SRIH). A surge of GHRH secretion into the hypophysial portal blood induces peak secretion of GH from the anterior pituitary. To study whether the rhythmic and reciprocal oscillation in secretion of GHRH and SRIH are associated with changes in synthesis of these peptides, we examined the expression of hypothalamic GHRH and SRIH mRNA by Northern blotting during trough and peak phases of GH secretion in male mice. Hypothalamic GHRH and SRIH mRNA levels did not differ between trough and peak phases of GH secretion. This result suggests that changes in GHRH and SRIH secretion have little association with changes in the synthesis of these peptides at the hypothalamus in the male mouse.

Animals↗
PubMed1994

Interleukin-1 beta induces histamine release in the rat hypothalamus in vivo.

We have previously demonstrated the increase of histidine decarboxylase activity and histamine content in the murine hypothalamus after intracerebroventricular injection of lipopolysaccharide possibly due to inducible interleukin-1 beta (IL-1 beta). Therefore, we investigated the effects of IL-1 beta on brain histamine dynamics by directly injecting it into the tuberomammillary nucleus of the rat hypothalamus (TM) using an in vivo microdialysis method. Injection of artificial cerebrospinal fluid or recombinant murine IL-1 beta at 0.1 ng into the TM did not evoke a significant change in core temperature, however, a significant monophasic febrile response was observed following injection of IL-beta at more than 1 ng per animal. Histamine release in the anterior hypothalamic area in vivo was significantly augmented from 140 min to 360 min following injection of IL-1 beta at 10 ng dose. These results suggest the possibility that interrelationship between histamine and IL-1 beta may modulate the acute phase reaction in the central nervous system.

Animals↗
PubMed1994

Effects of long-term infusion of growth hormone (GH)-releasing factor on pulsatile GH secretion in the male rat.

The effects of long-term infusion of GRF on pulsatile GH secretion were investigated in conscious, freely-moving male rats. GH-releasing factor (GRF) was intravenously administered for 14 days using an osmotic minipump. Six-hour iv infusion of 0.5 microgram/h GRF significantly increased mean GH concentration in the conscious rats. In contrast, 14-day iv infusion of 0.5 microgram/h GRF significantly inhibited pulsatile GH secretion. The pituitary GH content was significantly increased by the 14-day treatment. The GH response to bolus injection of 1 microgram GRF under urethane anesthesia was enhanced by the 14-day infusion of GRF. Pretreatment with somatostatin (SS) antiserum did not restore the inhibited GH secretion in rats treated with 14-day infusion of GRF. These results suggest that neither pituitary GH depletion nor high somatostatin tone is involved in the GRF-induced GH inhibition.

Animals↗
PubMed1994

Analysis of growth hormone release from rat anterior pituitary cells by reverse hemolytic plaque assay: influence of interleukin-1.

Interleukin-1 (IL-1) has been suggested to directly affect pituitary growth hormone (GH) release, although other investigators have failed to observe this effect. We examined the effects of IL-1 beta on GH secretion from single somatotrophs by means of reverse hemolytic plaque assay (RHPA). Anterior pituitary cells of adult male rats were enzymatically dispersed and subjected to RHPA. IL-1 beta at 100 pM and 1 nM, increased both the mean plaque area and the fraction of somatotrophs forming large plaques. IL-1 beta did not increase the mean plaque area in the presence of the IL-1 receptor antagonist (IL-1ra). IL-1 beta (1 nM) added together with GH-releasing hormone (GHRH; 10 nM), showed no additive effect on GHRH-induced GH release. The stimulatory action of IL-1 beta on the release of GH was suppressed by somatostatin. In conclusion, our data show that IL-1 beta stimulates GH-secretion through direct action on the pituitary.

Animals↗
PubMed1994

Evidence for conformational change of fatty acid-binding protein accompanying binding of hydrophobic ligands.

Conformational change of rat liver fatty acid-binding protein was investigated by making use of change of protease-susceptibility in the presence or absence of bound oleic acid and clofibrate. Delipidated fatty acid-binding protein was rapidly digested by Achromobacter lysyl endopeptidase, bovine alpha-chymotrypsin, and Staphylococcal V8 protease, while protein recombined with oleic acid was strongly refractory to proteolysis. This observation indicates that a striking change in the conformational state of the protein occurred upon lipid binding, and seems to support the recent hypothesis that the large segment homologous to fatty acid-binding proteins found in a fatty acid-regulated ion channel constitutes a regulatory domain of the channel [Petrou, S., Ordway, R.W., Singer, J.J., and Walsh, J.V., Jr. (1993) Trends Biochem. Sci. 18, 41-42]. Clofibrate, which is a potent peroxisome proliferator and structurally unrelated to oleic acid, also conferred similar protease resistance upon the protein. A possible physiological aspect of the present observation is that the cellular level of free fatty acids, which have metabolic importance and cytotoxicity as well, regulates the turnover rate of fatty acid-binding proteins by modulating the protease susceptibility of the protein.

Animals↗
PubMed1994

Effect of excitatory amino acid receptor agonists on secretion of growth hormone as assessed by the reverse hemolytic plaque assay.

Recent findings indicate that excitatory amino acids (EAAs) can modulate growth hormone (GH) secretion in several mammalian species in vivo and in vitro. In this study, we examined the effects of EAA receptor antagonists [N-methyl-D,L-aspartate (NMDA), kainic acid, L-glutamate] on GH secretion by the reverse hemolytic plaque assay (RHPA). Anterior pituitary cells of adult male Sprague-Dawley rats were enzymatically dispersed and subjected to RHPA. EAA receptor agonists increased the mean plaque area in a dose-dependent manner: the maximal increase was observed at 10 microM and increased the fraction of somatotrophs forming large plaques. NMDA (10 microM) did not increase the mean plaque area in the presence of the NMDA receptor antagonists 10 microM AP-7 and 10 microM MK-801. Coincubation of kainic acid with the non-NMDA receptor antagonist CNQX blocked the kainic-acid-stimulated increase in GH secretion. The addition of MK-801, AP-7 or CNQX to glutamate caused a partial reduction of the mean plaque area. Ten micromoles per liter glutamate with 10 nM GH-releasing hormone (GHRH) produced an additive effect on GHRH-induced GH release. Somatostatin suppressed the stimulatory action of glutamate. We speculate that glutamate plays a role in the regulation of GH secretion.

Amino Acids↗
PubMed1994

Relationship between thyroid functions and urinary growth hormone secretion in patients with hyper- and hypothyroidism.

Thyroid hormone plays an important role in growth hormone (GH) synthesis and secretion. To study the relationship between thyroid function and urinary GH secretion in the hyperthyroid and hypothyroid states, we measured thyroid hormones, simultaneously with serum and urinary GH levels, in 54 patients with thyroid diseases. GH-releasing hormone (GRH) test was performed in 18 patients in order to evaluate serum and urinary GH responses to GRH in hyper- and hypothyroid states. Serum thyroid hormone levels were strongly correlated with the urinary GH levels in the patients, and the correlation was greater than that between serum thyroid hormone and serum GH levels. Urinary GH levels were significantly higher in the hyperthyroid patients than in the euthyroid and hypothyroid patients, although serum GH levels were not significantly different among these three groups. Serum GH response to GRH was significantly decreased in hyperthyroid patients as compared to euthyroid patients. However, urinary GH levels after GRH administration were not decreased in the hyperthyroid patients. These results suggest that hyperthyroid states increase GH in urine and may accelerate the urinary clearance of GH.

Adult↗
PubMed1994

[Effect of aging on the aerobic capacity measured by a step-test].

The purpose of this study was to develop a step-test in order to evaluate age-related change in aerobic capacity. A total of 149 healthy men of age through 18 to 83 yrs ascended and descended a single step of 0.2 m height in time to a metronome. The step rate increased step-wise through three stages, each of 3 min duration; 15, 20 and 25 (step/min) for subjects aged 59 or less, and 10, 15, and 20 (step/min) for those age 60 and over. Using the linear relationship between load and heart rate, physical work capacity (PWC, watt/kg) was estimated as the work load with maximum heart rate predicted by age (220-age). In the elderly group (n = 34), heart rate at the end of the last stage was within 60-80% of the maximum heart rate for 25 subjects, and more than 80% for the other 9 subjects. No risky arrhythmia or significant ST change on ECG appeared in any subject. A retest of the step-test for 16 elderly subjects showed its repeatability and a linear relationship between heart rate and oxygen consumption. The results suggested that the step-test was applicable to the elderly in regard to appropriate work load and safety. The PWC significantly declined with aging (r = 0.52, p < 0.001). Relative aerobic capacity, taking that at age 20 as 100%, was 60% and 53% for subjects aged 60 and 70, respectively, which was in good agreement with available reports which measured oxygen consumption directly.

Adolescent↗
PubMed1993

The stimulatory and inhibitory effects of quinpirole hydrochloride, D2-dopamine receptor agonist, on secretion of prolactin as assessed by the reverse hemolytic plaque assay.

Recent findings indicate that low concentrations of dopamine (DA) stimulate the secretion of prolactin (PRL) in vitro. In this study, we found that low concentrations of the highly-specific DA D2 receptor agonist, quinpirole hydrochloride (LY) stimulate PRL secretion in female rats, assessed by reverse hemolytic plaque assay. Low concentrations of LY (10(-12), 10(-10) M) increased the mean plaque area and increased the fraction of lactotrophs forming large plaques. On the other hand, higher concentrations of LY (10(-8), 10(-6) M) reduced the mean plaque size. Treatment of cells with 10(-6) M LY produced a unimodal distribution of small plaques. Low concentrations of LY (10(-12), 10(-10) M) with TRH (10(-7) M) produced an additive effect on TRH-induced PRL release. Pretreatment of anterior pituitary cells with pertussis toxin (30 ng/ml, 24 h) inhibited the LY-stimulated increase in plaque area. These findings indicate that very low concentrations of DA agonist stimulate the secretion of PRL per cell, and that the stimulatory effects of DA agonist on PRL secretion may be mediated by a pertussis toxin-sensitive G protein.

Analysis of Variance↗