Effect of pituitary adenylate cyclase-activating polypeptide on GH gene expression in rat pituitary cells.
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Analysis of Variance↗
Biomedical subjects
I Wakabayashi
Publications and source records attributed to I Wakabayashi.
Inhibitory effect of neuropeptide Y on growth hormone secretion in rats is mediated by both Y1- and Y2-receptor subtypes and abolished after anterolateral deafferentation of the medial basal hypothalamus.
Neuropeptide Y (NPY) may play a physiological role in the regulation of growth hormone (GH) secretion by acting via somatostatin (SS) in the periventricular nucleus (PeV), as well as via the GH-releasing factor in the arcuate nucleus (ARC) of the medial basal hypothalamus (MBH). The objectives of the present study were to determine the neuron structures and receptor subtypes necessary for mediating the inhibitory effect of NPY on GH secretion in unanesthetized male rats. To eliminate the influence of hypophyseotropic SS, anterolateral deafferentation (ALC) of the hypothalamus was performed. Intracerebroventricular (i.c.v.) administration of 1.17 nmol of NPY decreased the blood level of GH for 3-4 h in sham-operated rats, while the procedure was without effect in ALC rats. The i.c.v. administration of 1.17 nmol of a Y1-receptor agonist ([Leu31, Pro34]-NPY) or a Y2-receptor agonist (NPY 13-36 and NPY 3-36) similarly suppressed the blood GH level. The data support the hypothesis that neuron structures anterolateral to the MBH are required for NPY-induced inhibition of GH secretion that is mediated via Y1- and Y2-receptor subtypes. Combined with data of other investigators, SS is likely the neurohumoral mediator of the effect of NPY on GH secretion.
Afferent Pathways↗
Neuropeptide Y reverses corticotropin-releasing hormone- and psychological stress-caused shortening of sodium pentobarbital-induced sleep in rats.
Intracerebroventricular injection of neuropeptide Y (NPY) prolonged sodium pentobarbital (PhNa)-induced sleep in rats. The prolongation of PbNa-induced sleep by NPY was blocked by naloxone. Both corticotropin-releasing hormone and psychological stress caused shortening of PbNa-induced sleep, and the shortening was reversed by NPY. These results suggest that NPY has a sedative action and that an opioid system in the brain mediates at least in part the action of NPY.
Animals↗
Evidence for a direct inhibitory effect of extracellular H+ on store depletion-activated Ca2+ entry in vascular endothelial cells.
Modulation of store depletion-activated Ca2+ entry by acidosis was investigated in ECV304 endothelial cells. Lowering extracellular pH from 7.4 to 6.9 markedly suppressed Ca2+ entry elicited by direct depletion of Ca2+ stores with thapsigargin (100 nM), but did not significantly affect leak Ca2+ entry. Acidosis diminished thapsigargin-induced Ca2+ entry by 53.7 +/- 7.8% at 2.5 mM extracellular Ca2+. A similar degree of inhibition was observed in cells depolarized by high extracellular K+ (100 mM). Reduction of extracellular pH from 7.4 to 6.9 was associated with a decrease in intracellular pH from 7.23 +/- 0.01 to 7.01 +/- 0.03. Propionate (20 mM) caused a reduction of intracellular pH to 6.97 +/- 0.02, but failed to suppress store depletion-activated Ca2+ entry at 2.5 mM extracellular Ca2+ significantly. Our results suggest that an increase in extracellular proton concentration inhibits store depletion-activated Ca2+ entry through a direct, membrane potential-independent effect on the plasmalemmal Ca2+ channel.
Calcium↗
NH4Cl-induced contraction of porcine coronary artery involves activation of dihydropyridine-sensitive Ca2+ entry.
The role of voltage-dependent, dihydropyridine-sensitive Ca2+ channels in NH4Cl-induced vasoconstriction was investigated in isolated porcine coronary arteries by measuring in parallel isometric tone and 45Ca2+ uptake. NH4Cl (10-80 mM) concentration dependently induced tonic contractions which were preceded by a time lag of several minutes. Contractile responses to high (60 mM) as well as low (25 mM) concentrations of NH4Cl were markedly inhibited by 1 microM nifedipine or removal of extracellular Ca2+. The contractile effect of 25 mM NH4Cl was substantially enhanced by increasing extracellular K+ to 14.7 mM or by pretreatment of coronary arteries with either 5 mM tetraethylammonium chloride or 0.1 microM 1,4-dihydro- 2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyridine carboxylic acid methyl ester (BAY K8644). NH4Cl (60 mM) significantly increased 45Ca2+ uptake with a lag time of more than 5 min. The increase in 45Ca2+ uptake induced by 60 mM NH4Cl was abolished in the presence of 1 microM nifedipine. Although NH4Cl (25 mM) did not detectably stimulate 45Ca2+ uptake in normal K+ solution, it significantly augmented 45Ca2+ uptake when extracellular K+ was increased to 14.7 mM. Furthermore, NH4Cl (20 mM) potentiated histamine-induced contraction of coronary arteries. This potentiating effect of NH4Cl was completely antagonized by nifedipine. Our results suggest an involvement of nifedipine-sensitive Ca2+ channels in NH4Cl-induced vasoconstriction of porcine coronary artery.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
The growth hormone-releasing peptide KP-102 induces c-fos expression in the arcuate nucleus.
Growth hormone-releasing hexapeptide (GHRP) stimulates GH secretion by acting on both the pituitary and the hypothalamus through a poorly understood mechanism. To reveal the hypothalamic action of GHRP, rat brains were processed for in situ hybridization for c-fos mRNA as a marker of neuronal activity after systemic administration of a newly developed GHRP, KP-102. Hypophysectomized adult male Wistar rats were administered KP-102 through an indwelling right atrial cannula. KP-102 treatment was accompanied by transient expression of the c-fos gene selectively in the ventromedial and ventrolateral regions of the arcuate nucleus (ARC). The distribution of c-fos gene-expressing cells overlapped that of GRF mRNA-containing neurons in the ventrolateral region on adjacent sections, whereas few c-fos mRNA signals were detected in the dorsomedial region where somatostatin mRNA signals were localized. To confirm this observations, hypothalamic sections were subjected to double-label in situ hybridization. Twenty-three percent of c-fos mRNA-containing cells were GRF neurons, comprising 20% of the GRF neurons in the ARC. The remaining c-fos mRNA containing cells were unidentified. KP-102 thus appears to act on a subpopulation of GRF neurons and unidentified cells in the ARC to stimulate GH secretion.
Animals↗
Mechanism of the potentiating effect of NH4Cl on vasoconstriction in rat aorta.
1. In medium containing 10 or 20 mM KCl, NH4Cl (10 mM) addition significantly diminished tetraphenylphosphonium bromide (TPP+) uptake in A7r5 vascular smooth muscle cells. 2. Addition of 10 mM NH4Cl significantly potentiated the 45Ca2+ uptake of A7r5 cells in medium containing 20 mM KCl; this increased uptake could be reduced to the basal level by pretreatment with 0.1 microM verapamil. 3. In rat aortic strips, KCl at 10 mM induced a slight contraction, that was greatly potentiated by the simultaneous addition of 10 mM NH4Cl. In this case, also, pretreatment with verapamil (1 microM) completely abolished the NH4Cl-potentiating effect. 4. The results suggest that ammonium ion amplifies the K(+)-induced contraction of rat aorta by facilitating transmembraneous Ca2+ influx through the voltage-dependent calcium channel, which may be due to potentiation of KCl-induced depolarization of the plasma membrane.
Ammonium Chloride↗
ACTH independent Cushing's syndrome occurring in siblings.
Familial Cushing's syndrome due to ACTH independent bilateral macronodular adrenocortical hyperplasia occurring in siblings is reported. The proband was a 69-year-old woman who presented with a typical Cushingoid appearance. The serum cortisol level was elevated, with a loss of diurnal rhythm, and the plasma ACTH level was undetectable. Dynamic testing showed no suppression of urinary 17-OHCS by high dose dexamethasone and no stimulation by metyrapone. An abdominal CT scan showed bilateral adrenal enlargement. The patient died of a subarachnoid haemorrhage, and autopsy revealed a massively thickened adrenal cortex composed of nodules up to 3.5 cm in diameter. A pituitary adenoma was not found. We learned that the patient's elder brother was also diagnosed at 59 years of age with Cushing's syndrome due to bilateral macronodular adrenocortical hyperplasia. His plasma cortisol levels were not suppressed by high dose dexamethasone and the plasma ACTH level was undetectable. Screening of the available family members by administering 1 mg dexamethasone at midnight and performing abdominal CT scan revealed impaired suppressibility of serum cortisol associated with enlarged bilateral adrenal glands in a 64-year-old sister and a 54-year-old brother. The 64-year-old sister was considered as a possible 'affected' case in the early stages of development, because the basal level of ACTH was not suppressed and hyperplasia of the bilateral adrenal glands as revealed by CT scan was less evident.
Adrenal Cortex↗
Intracerebroventricular administration of the growth hormone-releasing peptide KP-102 increases food intake in free-feeding rats.
Recent evidence suggests that growth hormone-releasing peptides (GHRPs) mimic an unidentified native GH-releasing hormone (GHRH)-amplifying hormone. GHRH has been shown to stimulate food intake acting on the central nervous system. The present studies were conducted to test the hypothesis that GHRPs may also potentiate the central effect of GHRH on feeding in free-feeding rats. Intracerebroventricular (ICV) administration of picomole doses of a newly developed GHRP, KP-102, or human GHRH stimulated feeding, but the phenomenon was not reproduced by systemic injection. A prior ICV injection of a GHRH antagonist completely prevented the increase of food intake evoked by GHRH, but this pretreatment did not influence the increase in food intake induced by KP-102. When maximally effective doses of GHRH and KP-102 were co-administered ICV, the amount of food intake increased significantly compared with after ICV injection of a maximum dose of either peptide alone. These findings suggest that GHRPs stimulate food intake via a specific receptor for GHRPs in the central nervous system and amplify the central effect of GHRH on feeding.
Animals↗
Growth hormone receptor gene is expressed in neuropeptide Y neurons in hypothalamic arcuate nucleus of rats.
GH feeds back on the hypothalamus and regulates its own secretion. We have previously shown that systemic administration of GH induces expression of the c-fos gene, a marker of neuronal activity, on the hypothalamic neuropeptide Y(NPY) and somatostatin neurons in rats. We argued that if GH were to act directly on NPY neurons, NPY neurons should express the GH receptor (GHR) gene. To test this hypothesis, coronal sections of the medial basal hypothalamus from adult male Wistar rats were processed by double label in situ hybridization using a 35S-labeled NPY complementary RNA probe and a digoxigenin-labeled GHR complementary RNA probe. In the medial basal hypothalamus, NPY messenger RNA (mRNA) was observed in the arcuate nucleus (ARC) and the dorsomedial nucleus. The majority (95%) of NPY mRNA-containing cells in the ARC expressed the GHR gene, whereas no NPY mRNA-containing cells in the dorsomedial nucleus expressed the GHR gene. These findings suggest that NPY neurons in the ARC mediate the feedback effect of GH on the hypothalamus.
Animals↗
Evaluation of semiquantitative reverse transcriptase-polymerase chain reaction assay of PML/retinoic acid receptor alpha mRNA and in vitro differentiation assay as prognostic prediction in acute promyelocytic leukemia treated with all-trans retinoic acid.
We studied the quantitative changes in PML/retinoic acid receptor alpha (PML/RAR alpha) fusion mRNA using the reverse transcriptase-polymerase chain reaction (RT-PCR) and the in vitro differentiation of leukemic cells from eight acute promyelocytic leukemia (APL) patients during treatment with all-trans retinoic acid (ATRA). In three patients, the intensity of the chimeric PML/RAR alpha bands decreased rapidly after the start of ATRA therapy. However, these three patients required variable periods of time to obtain complete remission (CR) (24, 29 and 100 days). In the five other patients, the chimeric bands decreased slowly, and the time until CR also varied (22, 28, 30, 39 and 67 days). As for the in vitro assay, leukemic cells from the three patients who achieved CR in a short period of time (22, 28 and 30 days) showed marked differentiation in response to 1 mumol/L ATRA, and leukemic cells from the four patients with slow or delayed clinical responses to ATRA did not show morphological differentiation in vitro. These findings suggest that the clinical response of APL patients to ATRA is predicted from the results of the in vitro differentiation assay, but not by RT-PCR analysis of the PML/RAR alpha fusion mRNA.
Adolescent↗
Effects of hyper- and hypoglycemia on blood growth hormone level in free-feeding rats with anterolateral deafferentation of the medial basal hypothalamus.
In rats with anterolateral deafferentation of the medial basal hypothalamus, the growth hormone (GH) level in the blood showed irregular and small fluctuations instead of the usual high bursts and low trough level, and the baseline GH level was higher than that in sham-operated rats. Continuous infusion of a glucose solution to operated rats increased the baseline level, GH pulse and pulse amplitude. I.v. bolus injection of the glucose solution resulted in a significant but transient increase in GH level. Insulin-induced hypoglycemia decreased the blood GH level in operated rats more effectively than in sham-operated ones and that was prevented by simultaneous infusion of glucose. Since SS influence on GH secretion had been largely eliminated in rats with anterolateral deafferentation of the medial basal hypothalamus, it is highly unlikely that the effects of hyperglycemia or hypoglycemia on GH secretion were the consequence of altered SS secretion.
Animals↗
Inhibitory effects of cadmium ion on extracellular Ca(2+)-independent contraction of rat aorta.
In vitro effects of cadmium ion on vasoconstriction, particularly on vasoconstriction independent of extracellular Ca2+, were investigated using isolated rat aorta. Aorta incubation with CdCl2 (0.01, 0.1 mM) significantly attenuated contractile responses to KCl and phenylephrine in the medium containing normal Ca2+ (2.5 mM). The contractile response to phenylephrine in the presence of calcium channel antagonists, nifedipine (1 microM) or verapamil (1 microM), was markedly inhibited by CdCl2 (0.1 mM). In the medium without Ca2+, phenylephrine (10 microM) induced a phasic contraction, which was markedly inhibited by CdCl2 (0.1 mM). In the medium without Ca2+, phorbol 12-myristate 13-acetate (1 microM) and okadaic acid (10 microM) caused tonic contractile responses, which were strongly attenuated by CdCl2 (0.1 mM) pretreatment. Contractile response to sodium fluoride (5 approximately 15 mM) in the absence of extracellular Ca2+ was strongly attenuated by CdCl2 (0.1 mM) pretreatment. These results suggest that cadmium ion depresses an extracellular Ca(2+)-independent component of agonist-induced vasoconstriction by hindering an intracellular contractile mechanism(s).
Animals↗
Endothelium-dependent relaxation resistant to NG-nitro-L-arginine in rat aorta.
Experiments were designed to determine whether cyclic GMP-independent relaxation is involved in the endothelium-dependent vascular relaxation response of rat aortic strip to acetylcholine. The relaxation response to acetylcholine in the presence of 3 x 10(-4) M NG-nitro-L-arginine was apparent when the precontraction was induced by norepinephrine at 5 x 10(-9) M or 10(-8) M. The relaxation response to acetylcholine resistant to NG-nitro-L-arginine was abolished by 10(-6) M atropine, 10 mM tetraethylammonium, or endothelium removal, but was not inhibited by 10(-5) M indomethacin, 3 x 10(-6) M oxyhemoglobin or 10(-5) M glibenclamide. The response was virtually abolished when the vascular strips had been preconstricted with 20 mM KCl. The increase in vascular cyclic GMP levels induced by 10(-5) M acetylcholine was completely abolished by 3 x 10(-4) M NG-nitro-L-arginine. These results suggest that acetylcholine-induced endothelium-dependent relaxation resistant to NG-nitro-L-arginine in rat aorta is unmasked when the precontractile force is caused by lower concentrations of norepinephrine and the relaxation is mediated by a cyclic GMP-independent mechanism, possibly an endothelium-derived hyperpolarizing factor.
Acetylcholine↗
Central glucoprivation evoked by administration of 2-deoxy-D-glucose induces expression of the c-fos gene in a subpopulation of neuropeptide Y neurons in the rat hypothalamus.
Central glucoprivation evoked by the intracerebroventricular administration of 2-deoxy-D-glucose (2DG) induces eating and suppresses growth hormone (GH) secretion in rats. To elucidate the hypothalamic mechanism of these phenomena, the induction of c-fos gene expression was examined by in situ hybridization using rats with centrally administered 2DG. Autoradiography on X-ray film showed that c-fos gene expression was transiently induced in discrete hypothalamic regions; namely the paraventricular nucleus, arcuate nucleus (ARC), the surrounding regions of the third ventricle dorsal to the ARC, and the periventricular nucleus (PeV). The time course of the expression was different in these nuclei. Double-label in situ hybridization for c-fos mRNA and neuropeptide Y (NPY) or somatostatin mRNAs revealed that 20% of the NPY neurons in the ARC expressed the c-fos gene, while a small population of somatostatin neurons (6.1% in the ARC and 2.6% in the PeV) expressed the c-fos gene following 2DG administration. Since NPY is an orexigenic neuropeptide and has an inhibitory effect on GH secretion, the data suggest that the activation of a subpopulation of NPY neurons in the ARC contributes, in part, to the increased food intake and suppression of GH secretion after central glucoprivation evoked by 2DG.
Animals↗
Caloric intake stimulates growth hormone secretion in food-deprived rats with anterolateral deafferentation of the medial basal hypothalamus or administered antiserum to somatostatin.
In rats, food deprivation inhibits episodic growth hormone (GH) secretion. On the basis of previous studies, we hypothesized that during a recovery from prolonged fasting, caloric intake stimulates the release of GH-releasing factor (GRF) and this process does not depend on the specific macronutrients in the meal, while protein in the meal acts to restore characteristic ultradian rhythmicity of GH secretion. To test this hypothesis, the effect of caloric intake on GH secretion was examined in fasted adult male Wistar rats devoid of somatostatin (SS) influence on GH secretion either by anterolateral deafferentation (ALC) of the medial basal hypothalamus (MBH) or administration of anti-SS goat serum (ASS). Rats were provided with an indwelling right atrial cannula and were deprived of food for 72 h. ALC was performed 2 weeks prior to the study. ASS was given i.v. 8 h and 7 h prior to refeeding, respectively. Serial blood specimens were collected every 10 min. In rats with ALC (ALC rats) or rats given ASS (ASS rats), the blood GH level revealed irregularly occurring small fluctuations, instead of the usual high bursts and low trough level. The baseline GH level and the mean GH level of fasted ALC rats or fasted ASS rats were significantly lower than those of fed ALC rats or fed ASS rats. Feeding the isocaloric mixed meal, the protein meal or the protein-deficient meal increased the GH pulse frequency, the pulse amplitude, the baseline GH level and the mean GH level in 72-h fasted ALC rats. These changes in GH secretory pattern persisted during the period of observation and were independent of the type of meal ingested. Following feeding the mixed meal, similar changes in the GH secretory pattern demonstrated in 72-h fasted ALC rats were also observed in 72-h fasted ASS rats, suggesting that the stimulation of GH secretion following caloric intake is not limited to ALC rats. Since the influence of SS on GH secretion has been largely eliminated in ALC or ASS rats, it is highly unlikely that the augmentation of GH secretion following feeding after prolonged food deprivation was the consequence of inhibition of SS secretion. Although GRF measurement was not performed, it is conceivable that the signal of caloric intake is conveyed to the MBH and acts to stimulate GRF release.
Animals↗
Mechanisms in inhibitory action of aclarubicin on contractility of rat aorta.
The effects of aclarubicin on vasocontractile response and 45Ca2+ influx were investigated using rat isolated aorta. KCl-induced contractile force in medium containing 2 center dot 5 mM calcium and calcium-induced contractile force in high K+ (60 mM)-depolarized aorta were both markedly attenuated by aclarubicin (70 microM) pretreatment. 45Ca2+ influx stimulated by 60 mM KCl was significantly lower in the aclarubicin (70 microM)-pretreated aorta compared with the control. Aclarubicin pretreatment attenuated phorbol 12, 13-dibutyrate (1 microM)-induced contraction both in the presence and absence of calcium in the medium. Aclarubicin pretreatment also attenuated caffeine (20 mM)-induced transient contraction. These results suggest that aclarubicin attenuates vasoconstriction by inhibiting both Ca2+ entry through the voltage-dependent calcium channel and the intracellular contractile pathway after elevation of intracellular free calcium in vascular smooth muscle, in addition to the known mechanism of inhibition of phosphoinositides hydrolysis.
Aclarubicin↗
Effect of D-Ala-D-beta Nal-Ala-Trp-D-Phe-Lys-NH2 (KP-102) on GH secretion in urethan-anesthetized rats.
The effect of a newly developed growth hormone (GH)-releasing hexapeptide (KP-102) on GH secretion was studied in urethan-anesthetized adult male rats. Although KP-102 alone exerted a small influence on GH secretion, it produced a large plasma GH response in the presence of exogenous GH-releasing factor (GRF). During the continuous infusion of GRF, the somatotropes became refractory to a large bolus dose of GRF, but KP-102 induced a marked increase of plasma GH. The GH response to KP-102 alone or KP-102 with GRF was significantly augmented when antiserum to somatostatin (ASS) was previously administered. Although KP-102 and GRF acted synergistically on GH secretion in control animals, they acted additively in ASS-administered rats. The KP-102 effect on plasma GH was significantly attenuated in control animals and ASS-administered rats by prior i.v. injection of antiserum to GRF. Taken together, KP-102 stimulates GH secretion dependent on GRF and appears to act synergistically with GRF by antagonizing the SS effect.
Animals↗