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Biomedical subjects

T Shibasaki

Publications and source records attributed to T Shibasaki.

At least 199 records · Page 11Linked to original sources
PubMed1987

Desensitization of rat pituitary somatotrophs to growth hormone-releasing factor occurs in vitro.

Desensitization of rat pituitary somatotrophs to human growth hormone-releasing factor (hGHRF) was investigated using cultured rat anterior pituitary cells. Growth hormone (GH) release decreased but the production of cAMP was still induced in response to subsequently added 10(-9) M hGHRF from cells pretreated with hGHRF at concentrations ranging from 10(-11) to 10(-7) M for 4 h. Desensitization to 10(-9) M hGHRF was also observed in cells pretreated with 10(-9) M hGHRF for 4 h in the presence of 2 mM EGTA, 10 ng/ml nifedipine or 10(-9) M somatostatin-28, which decreased GH release during pretreatment. Forskolin and A23187, at concentrations of 10(-6) M and 10(-4) M, respectively, stimulated GH release from cells pretreated with hGHRF to the same extent as that from the control cells. These results, therefore, suggest that desensitization to GHRF occurs regardless of the presence of releasable GH pool and that some changes such as uncoupling of GHRF receptors with adenylate cyclase and decreased sensitivity to cAMP of cAMP-dependent protein kinase of the secretory mechanism of GH, in addition to the decrease in releasable GH pool and down regulation of GHRF receptors, may be involved in the desensitization mechanism.

Animals↗
PubMed1986

The antagonistic effect of corticotropin-releasing factor on pentobarbital in rats.

The effects of corticotropin-releasing factor (CRF) on pentobarbital-induced sleeping time and hypothermia in rats were studied. Intraventricular administration of CRF significantly shortened the sleeping time induced by pentobarbital injection (50 mg/kg b.wt.) in a dose-dependent manner. CRF also attenuated the hypothermic effect of pentobarbital. However, peripheral administration of CRF did not affect the action of pentobarbital. alpha-Helical CRF9-41, CRF antagonist, reversed the effects of CRF. These results suggest that CRF antagonizes the effects of pentobarbital within the central nervous system.

Animals↗
PubMed1986

Distribution and efferent projections of corticotropin-releasing factor-like immunoreactivity in the rat amygdaloid complex.

Using cobalt-enhanced immunohistochemistry, the tracing of retrograde transport of horseradish peroxidase (HRP) and experimental manipulations, a widespread localization of corticotropin-releasing factor-like immunoreactive (CRFI) structures in the rat amygdaloid complex, and CRFI-containing pathways from the amygdala to the lower brainstem, bed nucleus of the stria terminalis (bst) and ventromedial nucleus of the hypothalamus (VMH) have been demonstrated. By means of cobalt-enhanced immunohistochemistry, CRFI cells were detected in almost all the regions of the amygdala, including the central amygdaloid nucleus (Ce), basolateral amygdaloid nucleus (B1), intra-amygdaloid bed nucleus of the stria terminalis (Abst), medial amygdaloid nucleus (Me), amygdalohippocampal area (Ahi), posterior cortical amygdaloid nucleus (Aco), lateral amygdaloid nucleus (La), anterior amygdaloid area (AAA) and basomedial amygdaloid nucleus (Bm). Neural processes with CRFI were found in all of the above areas. The greatest density of CRFI fibres was observed in the Ce, the Me and Ahi. Unilateral lesions located in the Ce and adjacent areas caused an ipsilateral decrease in CRFI fibre number in the lateral hypothalamic area (LH), mesencephalic reticular formation (RF), dorsal (Dpb) and ventral (Vpb) parabrachial nuclei, mesencephalic nucleus of the trigeminal nerve (MeV) and in the lateral division of the bst (bstl). In addition, ipsilateral CRFI fibres decreased in number in the core and shell of the VMH after unilateral lesions of the corticomedial amygdala (CoM) and ventral subiculum (S). These findings suggest that the CRFI cells in the Ce and adjacent areas innervate the Dpb, Vpb and MeV through the LH and RF; the CRFI fibres in the bstl are supplied by the Ce and adjacent areas; and the CoM and S give rise to the CRFI fibres to the VMH. The distribution of retrogradely transported HRP has confirmed these projections. Furthermore, combined HRP and immunohistochemical staining has demonstrated double labeled cells in the Ce following HRP injection into the Dpb, Vpb, MeV and bstl. This provides direct evidence for the amygdalofugal CRF-containing projections to the lower brainstem and bstl. Double-labeled cells were not seen in the CoM and S after HRP injection into the VMH.

Amygdala↗
PubMed1986

Atrial natriuretic factor is released from rat hypothalamus in vitro.

In vitro release of atrial natriuretic factor (ANF) from rat hypothalamic fragment during 60 min incubation was studied using a specific and sensitive radioimmunoassay (RIA). The Sephadex G-75 gel filtration profiles of the incubation medium revealed that the majority of released ANF-like immunoreactivity (LI) had a molecular weight same as alpha-atrial natriuretic polypeptide and a small amount of ANF-LI of larger molecular size was also released. The release of ANF was increased by addition of 50 mM KCl and the release by 50 mM KCl was completely suppressed in the presence of 2 mM EGTA, a chelating agent of Ca2+. A23187, a Ca2+ ionophore, at a concentration of 2 X 10(-4) M augmented the release of ANF-LI. These results indicate that hypothalamic ANF is released in a Ca2+-dependent manner like other hypothalamic peptides. This suggests that hypothalamic ANF acts as a neurotransmitter and/or neuromodulator in the hypothalamus and possesses some role in the regulation of pituitary hormone secretion.

Animals↗
PubMed1986

Intragranular colocalization of CRF and Met-Enk-8 in nerve terminals in the rat median eminence.

The ultrastructural localizations of rat corticoliberin (rCRF) and methionine-enkephalin octapeptide (Met-Enk-8) in the external layer of the rat median eminence were examined by double-immunogold labeling with anti-rCRF and anti-Met-Enk-8 sera labeled with small-sized (Gs) and medium-sized (Gm) gold particles, respectively. Two types of immunolabeled terminals were distinguished: one type with small granules (70 nm) labeled with Gs, and the other with large granules (100 nm) labeled with Gm. In both types, however, some granules were labeled with both Gs and Gm.

Animals↗
PubMed1986

Rat atrial natriuretic factor suppresses proopiomelanocortin-derived peptides secretion from both anterior and intermediate lobe cells and growth hormone release from anterior lobe cells of rat pituitary in vitro.

Synthetic rat atrial natriuretic factor (ANF) was found to attenuate, in a dose-dependent manner, basal and corticotropin-releasing factor-induced secretion of proopiomelanocortin-derived peptides from cultured anterior and intermediate lobe cells of rat pituitary. ANF was also found to suppress basal and growth hormone-releasing factor-stimulated secretion of growth hormone from anterior lobe cells of rat pituitary. These results, together with reports of the existence of ANF-positive neurons in the hypothalamus and ANF-positive fibers in the median eminence, suggest that hypothalamic ANF is probably involved in the regulation of pituitary hormone secretion, especially that of proopiomelanocortin-derived peptides and growth hormone.

Adrenocorticotropic Hormone↗
PubMed1986

Ontogeny of gamma-melanocyte-stimulating hormone in the brain and hypophysis of the rat: an immunohistochemical analysis.

The ontogeny of gamma-melanocyte stimulating hormone (gamma-MSH)-like immunoreactive (gamma-MSHI) structures in the brain and hypophysis was investigated in the rat by means of indirect immunofluorescence. gamma-MSHI neurons in the arcuate nucleus appeared at Day 13 of gestation, in the anterior hypophysis at Day 16, in the intermediate lobe at Day 18, and in the nucleus commissuralis after birth. gamma-MSHI fibers first appeared at Day 15 of gestation in the hypothalamic area and extended dorsally to reach the surface of the diencephalon. At Day 16 of gestation, another gamma-MSHI fiber bundle was found that ran laterally along the ventral surface of the diencephalon. At Day 19, immunoreactive fibers first appeared in the forebrain, diencephalon, midbrain and upper pons, and thereafter they increased in number, reaching a maximum at postnatal Day 15. gamma-MSHI fibers in the lower pons and medulla oblongata first appeared after birth. They also increased in number with age and reached a maximum at postnatal Day 15. The present ontogenetical study has demonstrated the different times of first appearance of each of the 3 major gamma-MSHI structures-containing cell groups in the brain, i.e., the arcuate nucleus, hypophysis and nucleus commissuralis. These findings may reflect the different functions of 3 groups of cells.

Animals↗
PubMed1986

In vitro release of growth hormone-releasing factor from rat hypothalamus: effect of insulin-like growth factor-1.

The release of growth hormone-releasing factor (GHRF) from rat hypothalamus was investigated in vitro. After 60 min preincubation the released GHRF from sliced rat hypothalamic fragments during 60 min incubation was detected by a highly specific and sensitive radioimmunoassay for rat GHRF. The release of GHRF was Ca2+-dependent and enhanced by high concentration of K+. Insulin-like growth factor-1 (IGF-1) significantly decreased GHRF release to 65% and 84% of the control at concentrations of 10(-8) M and 10(-7) M, respectively. These results suggest that this in vitro system is useful for the investigation of the mechanism of GHRF release from the hypothalamus and that IGF-1 is probably involved in the feedback inhibition of growth hormone secretion by attenuating GHRF release from the hypothalamus besides countering the effect of GHRF on the pituitary.

Animals↗
PubMed1986

A divergence of plasma growth hormone response between growth hormone-releasing factor and insulin-induced hypoglycaemia among middle-aged healthy male subjects.

The capability of the anterior pituitary gland to secrete GH in response to an intravenous injection of growth hormone-releasing factor (GRF) and insulin-induced hypoglycaemia was evaluated in 9 healthy male subjects ranging in age between 37 and 52 years old. Plasma GH response to 100 micrograms human GRF showed considerable intersubject variation and the increment of the peak value from the basal did not exceed 5 ng/ml in four out of 9 subjects. In contrast, insulin-induced hypoglycaemia resulted in a consistent stimulation of GH that exceeded 21 ng/ml in all subjects. The mean peak GH response after insulin-induced hypoglycaemia was significantly higher than that after GRF (27.4 +/- 1.6 vs 10.6 +/- 1.9 ng/ml). These results demonstrate that a significant divergence exists in plasma GH responses between the two provocative tests in the middle-aged subjects and suggest that the stimulation of GH following insulin-induced hypoglycaemia is not mediated solely by endogenous GRF.

Adult↗
PubMed1986

Concentrations of glycine and serine in cerebrospinal fluid during disturbed consciousness; a study of the therapeutic effect of thyrotropin-releasing hormone on the consciousness level.

The concentrations of aliphatic amino acids (glycine, serine, valine, threonine, alanine, leucine, isoleucine) in lumbar cerebrospinal fluid from patients with consciousness disturbances and normal controls were measured. Thyrotropin-releasing hormone (TRH) was administered to patients and the changes of levels of consciousness and amino acid concentrations were followed before and after TRH administration. The concentrations of glycine and serine from patients were significantly higher than those from controls; they returned to the control values with improvement of consciousness disturbances. The influence of TRH upon these amino acid concentrations was not observed. These results suggest that within the central nervous system, an alteration of the level of consciousness is associated with a distortion of glycine and serine metabolism and that TRH itself has no influence upon these amino acid concentrations.

Adolescent↗
PubMed1986

The effect of glucose and free fatty acids on growth hormone (GH)-releasing factor-mediated GH secretion in rats.

We have examined the effect of glucose and FFA on GH-releasing factor (GHRF)-mediated GH secretion in rats under pentobarbital anesthesia. Hyperglycemia did not affect GH secretion induced by administration of 20, 100, and 200 ng GHRF/100 g body weight. In contrast, GH response to 50 ng GHRF/100 g body weight in lipid heparin-treated rats, which showed high plasma FFA levels, was significantly suppressed compared with the control group (plasma peak GH: control, 1526 +/- 263 ng/ml; lipid-heparin group, 377 +/- 69 ng/ml P less than 0.05, mean +/- SEM). This suppressive effect of FFA on GH secretion was abolished by pretreatment with antisomatostatin serum (ASS) (GH level at 4 min after GHRF administration: ASS-saline group, 1606 +/- 210 ng/ml; ASS-lipid-heparin group, 1531 +/- 174 ng/ml; mean +/- SEM). These results suggest that hyperglycemia does not change the GH response to GHRF and that elevation of plasma FFA suppresses GHRF-induced GH secretion by the stimulation of somatostatin secretion in rats.

Animals↗
PubMed1986

The responses of plasma adrenocorticotropin and cortisol to corticotropin-releasing hormone (CRH) and cerebrospinal fluid immunoreactive CRH in anorexia nervosa patients.

Pituitary-adrenocortical responses to the iv injection of 100 micrograms synthetic ovine corticotropin-releasing hormone (CRH) were studied in 13 patients with anorexia nervosa, and the concentrations of immunoreactive CRH in cerebrospinal fluid were measured in 7 of them. Mean basal levels of plasma ACTH and cortisol were 32 +/- 5 pg/ml (+/- SEM) and 21.1 +/- 1.5 micrograms/dl, respectively. The latter value was significantly higher than that in age-matched normal women (P less than 0.005). The mean increments of plasma ACTH and cortisol in response to CRH injection in those 13 patients were 21 +/- 5 pg/ml and 5.3 +/- 1.7 micrograms/dl, respectively, significantly lower than those in normal women (58 +/- 6 pg/ml and 15.3 +/- 7.7 micrograms/dl, respectively; P less than 0.005). When 4 patients were reexamined after weight gains of between 3 and 22 kg, their responses to the CRH injection increased. The mean concentration of immunoreactive CRH in the cerebrospinal fluid of seven patients was 30.8 +/- 3.9 pg/ml (+/- SEM), which was higher than the value of 18.4 +/- 1.1 pg/ml (P less than 0.005) in control subjects with cervical spondylosis. These findings suggest the possibility that hypersecretion of CRH may occur in patients with anorexia nervosa.

Adolescent↗
PubMed1986

Studies on the response of growth hormone (GH) secretion to GH-releasing hormone, thyrotropin-releasing hormone, gonadotropin-releasing hormone, and somatostatin in acromegaly.

The plasma GH response to GH-releasing hormone (GHRH), TRH, or GnRH administration was examined in 25 acromegalic patients. Plasma GH levels increased in 21 patients after GHRH, in 19 after TRH, and in 4 after GnRH. The four GHRH nonresponders had had acromegaly longer than had the GHRH responders. No specific combination of GH responsiveness to these 3 releasing hormones was found among the patients. Infusion of 1 mg GHRH for 150 min gradually increased plasma GH levels, with some fluctuations, from the beginning to the end of infusion in normal subjects and in 7 patients who were GHRH responders, but a bolus injection of 100 micrograms GHRH at the end of the infusion did not further elevate plasma GH levels. These results suggest that desensitization to GHRH occurred in the normal subjects and acromegalic patients. However, in 5 acromegalic patients who responded to both GHRH and TRH, a bolus injection of 500 micrograms TRH given at the end of the 150-min infusion of 1 mg GHRH evoked a further plasma GH rise. In 5 normal subjects and 2 patients who were responders to GHRH but not TRH, a bolus injection of 500 micrograms TRH did not cause plasma GH elevation at the end of 150-min infusion of 1 mg GHRH. These results imply that TRH and GnRH stimulate GH secretion from the adenoma cells in vivo through receptors different from those for GHRH. In vitro studies using cultured pituitary adenoma cells from 2 patients revealed that the responses of GH secretion to GHRH were similar to those in vivo. These data, therefore, suggest that the responsiveness of GH secretion to stimuli is determined by the specificity of the receptors on adenoma cells. The action of somatostatin-28 was more potent than that of somatostatin-14 in the suppression of GH secretion from adenoma cells.

Acromegaly↗
PubMed1986

Effect of a single administration of somatostatin analogue (SMS 201-995) on GH, TSH and insulin secretion in patients with acromegaly.

The effect of a long-acting somatostatin analogue SMS 201-995 on GH secretion was investigated. Eleven acromegalic patients received a single dose of 50 micrograms SMS 201-995 administered subcutaneously, and plasma GH, IGF-I, GRF, TSH, IRI and blood glucose were determined at regular intervals. Nine of 11 patients had elevated basal plasma GH levels above 5 ng/ml. In all patients, plasma GH levels fell immediately from 39.5 +/- 17.3 ng/ml (mean +/- SEM) to 4.3 +/- 1.6 ng/ml (P less than 0.05) with a maximal inhibition of 82.9 +/- 3.3% of the basal levels and the suppression persisted for about 6 h of the observation period. IGF-I and GRF levels were not apparently altered. TSH and IRI levels also rapidly fell. Blood glucose levels fell slightly by 0.5 h. Ten of 11 patients had pain at injection sites. Except for this, no side effects were observed. Our results show that the new somatostatin analogue SMS 201-995 may inhibit GH hypersecretion in acromegalic patients for significant periods, suggesting that this agent can be a useful clinical tool for the treatment of acromegaly.

Acromegaly↗