Toshihiro Suda

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.

Saireito (a Chinese herbal drug)-stimulated secretion and synthesis of pituitary ACTH are mediated by hypothalamic corticotropin-releasing factor ☆

Administration of Saireito, a Saiko agent (a Chinese herbal drug), via a stomach cannula stimulates ACTH release and proopiomelanocortin, the precursor for ACTH, gene expression in the rat anterior pituitary. To study whether Saireito-stimulated secretion and synthesis of ACTH are mediated by hypothalamic corticotropin-releasing factor (CRF), we examined the effect of passive immunization of endogenous CRF by i.v. administration of CRF antiserum on Saireito-increased plasma ACTH levels and proopiomelanocortin gene expression in the rat anterior pituitary, under pentobarbital anesthesia. CRF antiserum inhibited Saireito-induced plasma ACTH levels and proopiomelanocortin mRNA levels in the anterior pituitary. This result indicates that Saireito stimulates CRF neurons to increase CRF release, which stimulates secretion and synthesis of ACTH.

Stimulatory effect of saireito on proopiomelanocortin gene expression in the rat anterior pituitary gland

The effect of administration of Saireito, a Saiko agent, via a stomach cannula on adrenocorticotropin (ACTH) release and gene expression of proopiomelanocortin (POMC), the precursor for ACTH, in the anterior pituitary, as well as on the corticotropin-releasing factor (CRF) in the hypothalamus, was examined in pentobarbital anesthetized rats. Saireito decreased the hypothalamic CRF level due to an early release of CRF and stimulated ACTH release and POMC gene expression but did not increase CRF gene expression. These results suggest that Saireito does not stimulate CRF gene expression, although it does stimulate CRF release, which in turn stimulates POMC gene expression in the anterior pituitary and ACTH release.

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.

Corticotropin-Releasing Factor Gene Expression

Publisher Summary The corticotropin-releasing factor (CRF) gene expression is positively regulated by the cAMP-dependent pathway and is also stimulated by phorbol ester but is negatively regulated by glucocorticoids. There are at least two methods to determine the change in mRNA levels: (1) Northern blot analysis and (2) in situ hybridization. This chapter presents Northern blot analysis for CRF mRNA in the rat hypothalamus. It presents two methods for analysis: (1) guanidinium thiocyanate–hot phenol method and (2) acid guanidinium thiocyanate–phenol–chloroform method. Poly(A) RNA from the hypothalamus and cerebral cortex enriched by oligo(dT)-cellulose chromatography hybridized with the CRF cRNA probe and exhibited a single band of rat CRF mRNA of approximately 1300 nucleotides. The CRF mRNA level in paraventricular nucleus-hypothalamus (PVN-Hy) increased to 130% of the control level at day 1, 170% at day 3, 210% at day 5, 230% at day 7, and 250% at day 14 after bilateral adrenalectomy. On the other hand, CRF mRNA levels in the cerebral cortex did not change through the experiment. Hypophysectomy caused a marked increase in CRF mRNA levels in PVN-Hy to 140% at day 1, 230% at day 3, 180% at day 5, 320% at day 7, and 340% at day 14 after surgery. There was no significant change in the CRF mRNA level in the cerebral cortex. When the effects of hypophysectomy and adrenalectomy are compared, the trend is toward a greater increase in CRF mRNA levels by hypophysectomy than by adrenalectomy.

Central administration of α-melanocyte-stimulating hormone inhibits corticotropin-releasing factor release in adrenalectomized rats

To determine if there is a short negative feedback effect of hypothalamic ACTH-related peptides on corticotropin-releasing factor (CRF) release in vivo, we examined the effect of cerebroventricular injection of alpha-melanocyte-stimulating hormone (alpha MSH) on ACTH levels in plasma and the anterior pituitary and CRF levels in the median eminence of the hypothalamus in adrenalectomized or sham-operated rats under pentobarbital anesthesia. alpha MSH did not affect basal ACTH or CRF levels in sham operated rats. However, elevated plasma ACTH levels and CRF levels in the median eminence were decreased by central administration of alpha MSH in adrenalectomized rats. These results suggest that there is a short negative feedback effect of alpha MSH on CRF release and it appears only in the absence of a long negative feedback effect of glucocorticoids.