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.

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.

Tissue-specific expression of isoaspartyl protein carboxyl methyltransferase gene in rat brain and testis

Isoaspartyl protein carboxyl methyltransferase (PIMT) is widely distributed in mammalian tissues. Using a polymerase chain reaction-generated 124-bp DNA fragment from brain cDNA as a probe, four different sizes (approximately 4.0, 2.5, 1.7, and 1.1 kb) of transcripts were detected with northern blot analysis. They were expressed predominantly in rat brain and testis. The major transcripts were 2.5 and 1.7 kb in the brain and 2.5 and 1.1 kb in the testis. One of the major transcripts specific to the testis (1.1 kb) was determined to study the structural difference of major transcripts in the two tissues. This testicular cDNA had neither the 5' (94 nucleotides) nor the 3' (594 nucleotides) end of previously reported brain cDNA corresponding to 1.7 kb. The mRNA levels and enzyme activities of different regions and developmental changes were examined in the brain. The mRNA levels and enzyme activities were concomitantly high in cerebral cortex and hippocampus. Although they increased rapidly approximately 30 days after birth in the testis and decreased in aged rats, they increased gradually after birth and remained high during the aging of the brain. Both structural and developmental studies show that the expression of the PIMT gene in brain and testis is regulated in a tissue-specific manner.

Gene expression of somatostatin receptor subtypes, SSTR1 and SSTR2, in human lung cancer cell lines

Somatostatin (SS) acts as a universal endocrine off-swich, and also inhibits the growth of neuroendocrine tumors through its specific receptors. Small cell lung cancer (SCLC) demonstrates some neuroendocrine characteristics and has been proposed as a candidate for treatment with SS and its analogues. In the present study, we investigated the expression of somatostatin receptor (SSTR) subtype (SSTR1 and SSTR2) mRNA in various human lung cancer cell lines by the sensitive reverse-transcription-PCR method and Southern blotting. The levels of expression of SSTR1 mRNA were higher in both SCLC and squamous cell carcinoma than in adenocarcinoma cell lines. Interestingly, SSTR1 gene expression was independent of that of SSTR2 in each SCLC cell line, although the expression of both genes showed a positive correlation in non-SCLC cells. Membranes from a cell line exhibiting highest expression of SSTR2 gene bound SS and its analogue, octreotide, with moderate affinity. These findings may provide useful information for the future clinical application of SS and its analogues for the treatment of lung cancer.

Acute effects of hypoglycemia and hyperglycemia on hypothalamic growth hormone-releasing hormone and somatostatin gene expression in the rat

Although previous studies have indicated that changes in the plasma glucose concentration alter GH secretion in the rat, the roles of hypothalamic GH-releasing hormone (GRH) and somatostatin (SS) in the glucose modulation of GH secretion have not yet been elucidated. We investigated the acute effects of hypo- and hyperglycemia on hypothalamic GRH and SS mRNA in the rat. Long term atrial catheters were implanted in male rats, and sequential blood sampling was performed in conscious animals. Insulin and 50% glucose were administered iv to induce hypo- and hyperglycemia, respectively. At the end of the experiment, the hypothalamus was removed, and total RNA was extracted for Northern blotting. Hypoglycemia completely inhibited pulsatile GH secretion, whereas hyperglycemia partially inhibited GH secretion. Direct effects of insulin itself on GH secretion in the insulin-induced hypoglycemia were ruled out by glucose clamp studies. Hypothalamic SS mRNA levels were increased dramatically by hypoglycemia (266 +/- 37%) and moderately by hyperglycemia (183 +/- 45%). Hypothalamic GRH mRNA levels were increased only by hyperglycemia (159 +/- 18%). The GH response to GRH was decreased dramatically by hypoglycemia and moderately by hyperglycemia. These results indicated that acute changes in the plasma glucose concentration stimulated hypothalamic SS mRNA in the rat.

Nucleotide sequence of rice dwarf phytoreovirus genome segment 2: completion of sequence analyses of rice dwarf virus

The complete nucleotide sequence of rice dwarf phytoreovirus genome segment 2 (S2) was determined to be 3,512 nucleotides long with one open reading frame initiating at nucleotide 15 and terminating at nucleotide 3363. The encoded polypeptide was predicted to have 1,116 residues with a relative molecular weight of 123 kD. Comparison of S2 of two isolates showed they had identical lengths and 97 and 98.3% nucleotide and amino acid sequence identities, respectively. A search of the Swiss-Prot data base (R 22.0) failed to find any proteins with significant homology to the S2-encoded protein. Determination of the nucleotide sequence of the S2 has completed the sequence determination of the genome of rice dwarf virus. Homology searches made for proteins encoded by each of the genomic segments showed that the polypeptide encoded by S11 has similarity to histone H1 protein and VP6 of blue tongue virus, indicating it might possess nucleic acid binding properties.

Quantitative and sensitive northern blot hybridization using PCR-generated DNA probes labeled with digoxigenin by nick translation

Northern blot hybridization is one of the most convenient methods of detecting an mRNA. Nonradioactive Northern blotting using digoxigenin (DIG) is becoming widely applied because it is rapid and safe. Previous studies have indicated that DIG-labeled RNA probes are suitable for Northern blot hybridization. Here, the application of PCR-generated double-stranded DNA probes labeled with DIG by nick translation is described. DNA probes were synthesized by PCR, then labeled with DIG by nick translation. Northern blot hybridization was performed using the DIG-labeled DNA probes, and the signals were detected by means of a chemiluminescent reaction. A low amount of DIG-dUTP in the labeling reaction resulted in excellent Northern blots with low background. Densitometric analysis of the blots showed that the mRNA concentrations could be determined by densitometric analysis. The sensitivity of the DIG-Northern system was comparable to Northern blotting using 32P and was sufficiently sensitive to detect low-abundance mRNA.

Identification of galanin-immunoreactive cells in the anterior pituitary of male monkeys (Macaca fascicularis)

The localization of galanin (GAL) was studied in the anterior pituitary of adult male macaque monkeys immunohistochemically. GAL-immunoreactive fiber bundles were noted in the posterior lobe of the pituitary. Cells immunoreactive for GAL were observed in the anterior lobe, and colocalization studies revealed that GAL-like immunoreactivity was present in gonadotrophs and thyrotrophs. The differences among the monkey, human and rat in GAL-immunoreactive localization may indicate that the regulation of GAL in the three species differs.

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.

Nucleotide sequences of serine tRNAs from Bacillus subtilis

Three B. subitilis serine tRNAs were sequenced including modified nucleosides. All the serine tRNAs contained 1-methyl-adenosine in the D-loop. As other characteristic modified nucleosides, 5-methoxyuridine was found in the first letter of the anticodon in the tRNA(UGA).

Stimulatory effects of quinpirole hydrochloride D2-dopamine receptor agonist, at low concentrations on prolactin release in female rats in vitro

Dopamine (DA) has dual actions (inhibitory and stimulatory) in the regulation of prolactin (PRL) release, depending on its concentration. To investigate the stimulatory effects of DA, perifused rat anterior pituitary cells were exposed to the highly-specific DA D2 receptor agonist, quinpirole hydrochloride (LY). Very low concentrations of LY (10(-12)-10(-10) M) stimulated PRL release and potentiated thyrotropin-releasing hormone (TRH)-induced PRL release. Higher concentrations of LY did not stimulate. Pretreatment with pertussis toxin (30 ng/ml, 24 h) completely abolished these effects of LY. The D2 receptor antagonist, metoclopramide, also blocked the potentiation by LY of TRH-induced PRL release. These data indicate that very low concentrations of dopamine stimulate PRL release via an interaction with a D2 receptor connected to a pertussis toxin-sensitive G protein.

A thermostable Gm-methylase recognizes the tertiary structure of tRNA

The efficiency of methylation of tRNA by a thermostable tRNA(guanosine-2')-methyltransferase (Gm-methylase) was examined at various temperatures using several species of tRNA isolated from Escherichia coli, yeast and Bacillus subtilis, each possessing different thermal properties. The optimal temperature for the methylation reaction was ca. 20 degrees C lower than the melting temperature of the tRNA in each case. Arrhenius plots of the methylation reactions with various tRNAs gave straight lines below the optimal temperatures in all cases, with similar activation energies of between 10 and 14 kcal/mol. Above the optimal temperatures, the methyl acceptor activity decreased as the incubation temperature was raised to 80 degrees C, at which point the methylase was still active. A correlation was observed between the remaining methyl acceptor activity and the hyperchromicity of tRNA. These results suggest that Gm-methylase recognizes the tertiary structure of tRNA, and it is not the substrate tRNA but the enzyme which is activated by heat.

Effects of ethanol on methyl mercury toxicity in rats

This study was designed to investigate the effect of different doses of ethanol on the morbidity, mortality, and distribution of mercury in the tissues of groups of rats treated orally once daily with methyl mercury chloride (MMC: 5 mg/kg . d) for 10 consecutive days. Ethanol potentiated the toxicity of methyl mercury in terms of neurological manifestations (hindleg crossings and abnormal gait) and mortality. The magnitude of effect depended on the concentration of ethanol administered. The concentration of mercury in the kidney and brain also increased with the dose of ethanol given. These findings indicate that epidemiologic studies designed to evaluate methyl mercury toxicity must take into account the multiple environmental burdens that can affect the population cumulatively and simultaneously.

Molecular mechanism of codon recognition by tRNA species with modified uridine in the first position of the anticodon

Proton NMR analyses have been made to elucidate the conformational characteristics of modified nucleotides as found in the first position of the anticodon of tRNA [derivatives of 5-methyl-2-thiouridine 5'-monophosphate (pxm5s2U) and derivatives of 5-hydroxyuridine 5'-monophosphate (pxo5U)]. In pxm5s2U, the C3'-endo form is extraordinarily more stable than the C2'-endo form for the ribose ring, because of the combined effects of the 2-thiocarbonyl group and the 5-substituent. By contrast, in pxo5U, the C2'-endo form is much more stable than the C3'-endo form, because of the interaction between the 5-substituent and the 5'-phosphate group. The enthalpy differences between the C2'-endo form and the C3'-endo form have been obtained as 1.1, -0.7, and 0.1 kcal/mol (1 cal = 4.184 J) for pxm5s2U, pxo5U, and unmodified uridine 5'-monophosphate, respectively. These findings lead to the conclusion that xm5s2U in the first position of the anticodon exclusively takes the C3'-endo form to recognize adenosine (but not uridine) as the third letter of the codon, whereas xo5U takes the C2'-endo form as well as the C3'-endo form to recognize adenosine, guanosine, and uridine as the third letter of the codon on ribosome. Accordingly, the biological significance of such modifications of uridine to xm5s2U/xo5U is in the regulation of the conformational rigidity/flexibility in the first position of the anticodon so as to guarantee the correct and efficient translation of codons in protein biosynthesis.

The nucleotide sequence of proline tRNAmo5UGG from Bacillus subtilis

The nucleotide sequence of a proline tRNA from Bacillus subtilis W168 was determined to be pC-G-G-G-A-A-G-U-A-G-C-U-C-A-G- C-U-U-G-G-D-A-G-A-G-C-A-C-A-U-G-G-psi-U-mo5U-G-G-m1G-A-C-C-A-U-G-G -G-m7G-U-C-G-C-A-G-G-T-psi-C-G-A-A-U-C-C-U-G-U-C-U-U-C-C-C-G-A-C-C- AOH, by the analysis of the unlabeled preparation and by post-labeling technique. This tRNAPro contained 5-methoxyuridine (mo5U) which is specifically distributed in bacillaceae at the wobble position of the anticodon.

Nucleotide sequence of valine tRNA mo5UAC from bacillus subtilis

A valine tRNA was purified from Bacillus subtilis W168 by a combined use of several column chromatographic systems. The nucleotide sequence was determined to be pG-G-A-G-G-A-U-U-A-G-C-U-C-A-G-C-D-G-G-G-A-G-A-G-C-A-U-C--G-C-C-U-mo5U-A-C-m6-A -A-G-C-A-G-A-G-G-m7G-U-C-G-G-C-G-G-T-psi-C-G-A-G-C-C-C-G-U-C-A-U-C-C-U-C-C-A-C- C-AOH with the main use of of non-labeled tRNA and with the subsidiary use of [32P]-post-labeled sample. This tRNA contains 5-methoxy-uridine (mo5U) at the wobble position of the anticodon. A binding experiment of valyl-tRNA to ribosome revealed that mo5U is recognized by A and G, and fairly well by U.

The nucleotide sequence of 5S rRNA from Mycoplasma capricolum

The nucleotide sequence of 5S rRNA from Mycoplasma capricolum is UUGGUGGUAUAGCAUAGAGGUCACACCUGUUCCCAUGCCGAACACAGAAGUUAAGCUCUAUUACGGUGAAGAUAUUACU GAUGUGAGAAAAUAGCAAGCUGCCAGUUOH. The length is 107 nucleotides long, and the shortest in all the 5S rRNAs so far known. The sequence is more similar to those of the gram-positive bacteria than those of the gram-negative bacteria.

5-(carboxymethylaminomethyl)-2-thiouridine, a new modified nucleoside found at the first letter position of the anticodon

The structure of a modified uridine derivative which was detected at the first letter position of the anticodon of Bacillus subtilis tRNA1Lys was determined to be 5-(carboxymethylaminomethyl)-2-thiouridine. The determination was mainly based in this ultraviolet absorption spectra and mass spectrometric analysis of the trimethylsilyl derivative.

The nucleotide sequence of 5S ribosomal RNA from Micrococcus lysodeikticus

The nucleotide sequence of ribosomal 5S RNA from Micrococcus lysodeikticus is pGUUACGGCGGCUAUAGCGUGGGGGAAACGCCCGGCCGUAUAUCGAACCCGGAAGCUAAGCCCCAUAGCGCCGAUGGUUACUGUAACCGGGAGGUUGUGGGAGAGUAGGUCGCCGCCGUGAOH. When compared to other 5S RNAs, the sequence homology is greatest with Thermus aquaticus, and these two 5S RNAs reveal several features intermediate between those of typical gram-positive bacteria and gram-negative bacteria.

On the biosynthesis of 5-methoxyuridine and uridine-5-oxyacetic acid in specific procaryotic transfer RNAs

The uridine-5-0-derivatives, 5-methoxyuridine (mo5U) and uridine-5-oxyacetic acid (cmo5U) occupy the first position of anticondons in certain tRNA species of B. subtilis and E. coli, respectively. Here we present experimental evidence showing that both modifications are derived from a common precursor, 5-hydroxyuridine. Incompletely modified tRNASer and tRNAVal from E. coli met- rel-. All five tRNAs accepted methyl groups from S-adenosylmethionine with B. subtilis extracts in vitro and mo5U was formed. In B. subtilis tRNAs the mo5U was proved to be at the specific site; in E. coli tRNAVal the mo5U was demonstrated to be present in the oligonucleotide that comprises the anticodon. In submethylated E. coli tRNAVal,5-hydroxyuridine was detected whereas considerable amounts of cmo5U were lacking.