Nobuo Horiba

Serotonin stimulates corticotropin-releasing factor gene expression in the hypothalamic paraventricular nucleus of conscious rats

To examine the direct effects of serotonin (5-HT) on the release and synthesis of corticotropin-releasing factor (CRF) in the hypothalamic paraventricular nucleus (PVN), 5-HT was microinjected just onto the bilateral PVN of conscious rats. Plasma adrenocorticotropic hormone (ACTH) levels peaked at 30 min and returned to the basal levels in 90 min. Northern blot analysis revealed that the CRF messenger RNA (mRNA) level in the PVN as well as the proopiomelanocortin mRNA level in the anterior pituitary significantly increased 120 min after the 5-HT injections (50-250 nmol/side). Pretreatment with intracerebroventricular (i.c.v.) injection of pindobind 5-HT1A (5 nmol) or LY-278584 (500 nmol) completely abolished the 5-HT-induced ACTH response, whereas LY-53857 (100 nmol) was without effect. These results suggest that 5-HT stimulates CRF release, which has interactions with 5-HT1A and 5-HT3 receptors on CRF neurons in the PVN, and activates CRF synthesis in conscious rats.

The genomic organization of the human corticotropin-releasing factor type-1 receptor.

We determined the genomic organization of human CRF type-1 receptor (hCRF-R1). The gene coding for hCRF-R1 consists of at least 14 exons and spans over 20 kilobases. hCRF-R1s three reported isoforms originate from the same gene by alternative splicing. The first hCRF-R1, which binds to CRF with the highest affinity and transduces the most sensitive cAMP accumulation in response to CRF, is encoded in a total of 13 exons, the only one excluded being exon 6. The second isoform contains an additional 29-amino acid sequence which corresponds to exon 6. Unlike the first isoform, the third lacks a 40-amino acid sequence, corresponding to exon 3. Exon-intron boundaries are the same as that of the consensus sequence. Locations of introns in the coding sequence are similar to human CRF-R1, rat CRF-R1, human CRF-R2alpha and others belonging to the human glucagon receptor family.

Corticotropin-releasing hormone, proopiomelanocortin, and glucocorticoid receptor gene expression in adrenocorticotropin-producing tumors in vitro.

To differentiate between ectopic ACTH syndrome and Cushings disease, gene expression of corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), and glucocorticoid receptor was examined in 10 pituitary adenomas (Cushings disease) and in 10 ectopic ACTH-producing tumors. CRH increased plasma ACTH levels in all patients with Cushings disease and in five patients with ectopic ACTH syndrome whose tumors contained CRH and CRH mRNA. In five CRH nonresponders, CRH was not detected in tumors that contained no CRH mRNA or that contained only long-size CRH mRNA. Dexamethasone (Dex) decreased plasma ACTH levels in all patients with Cushings disease and in three patients with ectopic ACTH-producing bronchial carcinoid. These tumors contained glucocorticoid receptor mRNA. CRH increased and Dex decreased ACTH release and POMC mRNA levels in pituitary adenoma and bronchial carcinoid cells. PMA increased POMC mRNA levels only in carcinoid cells. These results reveal characteristics of ectopic ACTH-producing tumors: long-size CRH mRNA and PMA-induced POMC gene expression. In addition, there are two ectopic ACTH syndrome subtypes: tumors containing ACTH with CRH (CRH responder) and tumors without CRH. Dex decreases ACTH release and POMC mRNA levels in some bronchial carcinoids. Therefore, CRH and Dex tests have limited usefulness in differentiating between Cushings disease and ectopic ACTH syndrome.

Involvement of cAMP-response element binding protein in corticotropin-releasing factor (CRF)-induced down regulation of CRF receptor 1 gene expression in rat anterior pituitary cells

Corticotropin‐releasing factor (CRF) is a major secretagogue of adrenocorticotopic hormone from the anterior pituitary and a key activator of the hypothalamic‐pituitary‐adrenal axis. We previously reported that CRF down‐regulates expression of the CRF type‐1 receptor (CRF‐R1) mRNA in cultured rat anterior pituitary cells. The present study was conducted to clarify the signal transduction systems involved in CRF‐induced down‐regulation of CRF‐R1 gene expression in the anterior pituitary. Northern blot analysis revealed that, under serum‐free conditions, 10 nM CRF decreased CRF‐R1 mRNA levels in cultured rat anterior pituitary cells as we reported previously. Treatment with 5 mM 8‐Br‐cAMP reduced CRF‐R1 mRNA levels within 2 h. The mRNA level fell to 37±3% of the basal level at 2 h and remained low for 16 h after treatment. This CRF‐induced reduction of CRF‐R1 mRNA expression was inhibited completely by pretreatment with protein kinase A (PKA) inhibitor (1 µM H‐89). Further examination revealed that after pretreatment with 10 µM of antisense oligodeoxynucleotide for cyclic AMP‐response element binding protein (CREB), the CRF‐induced inhibition of CRF‐R1 mRNA was partially decreased to 79±4% of the control level 2 h after administration of CRF. These findings indicate that CRF may down‐regulate CRF‐R1 mRNA expression via a cAMP‐PKA‐mediated mechanism in rat anterior pituitary cells, and that CREB may mediate at least a portion of this inhibitory effect.

Effect of D-glucose on nitric oxide release from glomerular endothelial cells

Altered glomerular production of nitric oxide (NO) may be involved in hyperfiltration in early diabetic nephropathy. However little is known as to the role of glomerular endothelial cells (GECs) in diabetic hyperfiltration and their ability to release NO in response to hyperglycemia.

Central administration of saikosaponin-d increases corticotropin-releasing factor mRNA levels in the rat hypothalamus ☆

Saiko agents, Chinese herbal drugs, stimulate corticotropin-releasing factor (CRF) release from the hypothalamus, adrenocorticotropin (ACTH) secretion and proopiomelanocortin (the precursor for ACTH) gene expression in the anterior pituitary. In the present study, the effect of intracerebroventricular injection of saikosaponin (SS)-a and -d, two of the main components of saiko agents, on hypothalamic CRF gene expression was examined in pentobarbital-anesthetized rats. Administration of SS-d, 0.2-2.0 micrograms/kg body wt, increased plasma ACTH levels, proopiomelanocortin mRNA levels in the anterior pituitary and the CRF mRNA level in the hypothalamus in a dose-dependent manner, whereas SS-a failed to have an affect on these levels. These findings indicate that SS-d stimulates both CRF gene expression and CRF release, which in turn increases ACTH release and proopiomelanocortin gene expression in the anterior pituitary. Therefore, SS-d is believed to have an important role both in saiko agent-induced CRF release and CRF gene expression in the hypothalamus.

Involvement of phosphorylation of β-subunit in cAMP-dependent activation of L-type Ca2+ channel in aortic smooth muscle-derived A7r5 cells

We investigated the effect of intracellular cAMP on the gating kinetics of L-type Ca2+ channel in an A7r5 smooth muscle-derived cell line using the whole-cell patch-clamp technique. Application of dibutyryl cyclic AMP (db-cAMP) to the cell increased the magnitude of Ca2+ currents through L-type Ca2+ channels (I(Ca)), and shifted the current-voltage relationship (I-V curve) for I(Ca) to the left. The magnitudes of maximum I(Ca) were 14.1 +/- 0.7 before and 16.0 +/- 1.1 pA/pF after application of 1 mM db-cAMP (P < 0.05). The values of the half-activation potential (V(1/2)) of I(Ca), estimated from activation curves, were -7.0 +/- 0.8 mV before and -10.8 +/- 1.0 mV after application of db-cAMP (P < 0.05). In cells pretreated with 10 microM Rp-cAMPS (a specific inhibitor of PKA), db-cAMP affected neither the I-V curve nor the activation curve for I(Ca). In cells pretreated with the antisense oligonucleotide for the beta-subunit of L-type Ca2+ channel, db-cAMP failed to enhance I(Ca) or alter the activation curve. On the other hand, in the cells pretreated with the nonsense oligonucleotide, application of db-cAMP caused an increase in magnitude of I(Ca) and shifted the activation curve to the left. Western blot analysis revealed that the pretreatment of cells with antisense oligonucleotide but nonsense oligonucleotide reduced the expression of the beta-subunit of the L-type Ca2+ channel. We conclude that the cAMP-dependent phosphorylation of the beta-subunit potentiates the voltage dependency of the activation kinetics of the L-type Ca2+ channel in A7r5 cells.

Rat atrial natriuretic polypeptide stimulation of adrenal zona glomerulosa cell growth

Rat atrial natriuretic polypeptide (rANP) was found to stimulate [3H] thymidine incorporation into the DNA of bovine adrenal glomerulosa cells in a primary culture in a dose-dependent manner. The minimum effective dose was a very low concentration (10(-12) M of ANP), suggesting that ANP had a physiological effect. These findings are the first indication that ANP possesses growth-stimulating activity with regard to adrenal zona glomerulosa cells.

Regulation of Corticotropin Releasing Hormone Receptor (CRH-R) in the Rat Anterior Pituitary as Assessed by Radioimmunoassay

Since the cloning of corticotropin releasing hormone receptor type 1 (CRH-R1), an essential component of the hypothalamo-pituitary-adrenal (HPA) axis, numerous studies have been conducted to monitor its changes in transcription levels under various conditions. However, the precise dynamics at the protein levels are yet to be elucidated. In the present study we aimed at establishing an RIA system for CRH-R1 protein, with an antiserum against the C-terminal fragment of human/rat CRH-R1. The generated antiserum showed a moderate cross-reactivity with CRH-R2. We examined the in vivo effect of adrenalectomy (ADX) on immunoreactive CRH-R (irCRH-R) levels in the rat AP, and the in vitro profile of irCRH-R levels in cultured rat AP cells after administration of CRH. The irCRH-R in the AP membrane of intact rats was 51.8 ± 6.8 fmol/mg protein, which is comparable to those reported in binding studies. ADX elicited a significant decrease of irCRH-R to approximately 50% of the control level one day after ADX, which returned to the baseline level the following day. Addition of CRH to cultured AP cells resulted in a significant decrease of irCRH-R in the membrane fraction to 18% of the control level at 4 h, and it returned rapidly to 70% at 8 h. These experiments together with our previous study implicate that irCRH-R makes a different profile, with an earlier recovery than that of mRNA. Although this system cannot precisely discriminate between CRH-R1 and CRH-R2, our findings may serve to demonstrate differing CRH receptor regulations at the synthesis level and at the protein level in the rat AP.

Renotropic activity of lutropin: direct stimulation of DNA synthesis of cultured rat renal cortical cells

Two differently purified ovine lutropin (LH) preparations were studied to see if they stimulated [3H] thymidine incorporation into cultured rat renal cortical cells. Both preparations showed a dose-dependent (0.11-1 ng/ml), time-dependent (peaking at 18 h), serum-dependent (7.5% of fetal calf serum or 10% castrated-hypo-physectomized rat serum) renotropic effect. Ovine TSH and FSH failed to mimic this specific, renotropic effect. We concluded that LH directly stimulates renal DNA synthesis in cooperation with other serum factors.