17 beta-estradiol increases calcium content in fetal mouse parietal bones cultured in serum-free medium only at physiological concentrations

Using a bone organ culture system that shows mineralization in vitro, we investigated whether 17 beta-estradiol dose-dependently increases calcium content in cultured calvarial bones in serum-free medium. Fetal mouse parietal bones (3 x 3 mm) were cultured in phenol red-free BGJ medium containing phosphate (3-4 mmol/L), calcium (1-1.25 mmol/L), insulin (6 micrograms/ML), and transferrin (6 micrograms/mL) for 4-5 days. Under these culture conditions, the calcium content of the cultured bones (at dissection 34.0 +/- 4.6 micrograms/bone [mean +/- SD], n = 50) increased by 15-20 micrograms during 4-5 days of culture. 17 beta-Estradiol increased the calcium content significantly at 10(-12) to 10(-11) mol/L, but not at lower (10(113) mol/L) or higher (10(-10) to 10(-9) mol/L) concentrations. 17 alpha-Estradiol had no effect. The stimulatory effect of 17 beta-estradiol was completely inhibited by the antiestrogen agent ICI-182,780. The anabolic effect of 17 beta-estradiol was elicited not only in bones from females but also in those from males. 17 beta-Estradiol had no significant effect on 45Ca release from prelabeled parietal bones. Furthermore, light- and electron-microscopic examinations revealed that bone mineralization proceeded through formation of matrix vesicles, without any metastatic or dystrophic calcification. These in vitro findings suggest that 17 beta-estradiol elicits small, but reproducible, direct effects on calcium content in the parietal bones not only in female but also in male fetal mice at physiological-free E2 concentrations (10(-12)-10(-11) mol/L), which is attainable in serum of normal human subjects. In contrast to in vivo studies, pharmacological doses of 17 beta-estradiol had no anabolic effect on parietal bones. The mechanism of such a biphasic effect of estrogens remains to be elucidated.

Demonstration of activin in normal pituitary and in various human pituitary adenomas by immunohistochemistry

Inhibins and activins have been known to modify the secretion of various pituitary hormones. To study whether inhibins and activins are present in human pituitary tissues, immunohistochemical studies with antisera to activin A and inhibin alpha subunit were performed on 9 human pituitary adenoma tissue specimens and one sample of normal pituitary tissue adjacent to one adenoma. Activin immunoreactivities were demonstrated in the cytoplasms of one GH and one PRL and two non-functioning adenomas and one normal pituitary tissue, but they were negative in one PRL, one ACTH, one FSH and two non-functioning adenomas. Thus, the presence and absence of activin in the same type of adenoma in regard to hormone production, suggested that the difference in immunostaining simply reflected the difference in the activin concentration. In contrast to this, inhibin alpha subunit immunoreactivity was not found in any of the tissues studied. These data suggested a local synthesis of activin in the normal pituitary as well as various kinds of pituitary adenoma tissues and its local role in the human pituitary gland.

Inhibin alpha, beta A and beta B subunit messenger ribonucleic acid levels in cultured rat pituitary: studies by a quantitative RT-PCR

Recent studies have demonstrated that inhibins and activins both play not only endocrine roles but also local regulatory roles in gonadotoropin secretion. There has been controversy as to the subtype of rat pituitary inhibin/activin. We studied the levels of inhibin alpha, beta A and beta B subunit mRNAs by a quantitative reverse transcription-polymerase chain reaction (RT-PCR) and the changes in their levels by adding inhibin alpha, beta A and beta B mRNA antisense oligonucleotides and inhibin A, activin A or GnRH to cultured rat anterior pituitary cells. This study demonstrated the level of 3 mRNAs to be 1.6 x 10(-2), 0.75 and 3.4 x 10(-2) molecules/cell with a molar ratio of 1:50:2. A stimulatory role for activin B in FSH secretion was suggested as beta B mRNA antisense oligonucleotide decreased FSH secretion. The beta B mRNA level tended to be decreased by the addition of activin A, but the decrease was not statistically significant. GnRH did not affect alpha and beta B mRNA levels when administered singly. The level of beta A mRNA was not changed by any of the above treatments. In conclusion, the presence of inhibin alpha, beta A and beta B subunit mRNAs in the rat anterior pituitary with the greatest abundance of beta A was demonstrated by using RT-PCR. Activin B or activin AB may play important roles in FSH secretion in an autocrine or a paracrine fashion, and activin A may play an indirect role in FSH secretion.

Regulation of pituitary growth hormone-releasing factor (GRF) receptor gene expression by GRF

We examined how growth hormone-releasing factor (GRF) regulated pituitary GRF receptor gene expression in the conscious rat. GRF receptor mRNA levels were significantly increased by immunoneutralization of endogenous GRF with its specific antiserum. This effect was dose dependent and the maximum level was 3.8-fold higher than that in control rats. A similar rise in GRF receptor gene expression was obtained by the depletion of noradrenaline, a neurotransmitter thought to stimulate GRF release, and was reversed by 87% by the repeated administration of synthetic GRF. These results indicate that pituitary GRF receptor gene expression was up- or down-regulated in vivo in the absence or presence of GRF, respectively.

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.

Reversible, extremely severe hypothyroidism in a patient with chronic hepatitis C treated with interferon-alpha

A 55-year-old patient with chronic hepatitis C received interferon-alpha (IFN-alpha) therapy in March-August 1992. After a few months of treatment, easy fatigability, general malaise, nonpitting edema, and facial edema developed. After treatment for 22 weeks, the patient, with typical clinical features of myxedema, was referred to our outpatient clinic with undetectable serum levels of T4 (< 1.0 microgram/dL) and T3 (< 25 ng/dL) and a markedly elevated TSH level (217 microU/mL). The serum thyroglobulin concentration was also undetectable (less than 5 ng/mL), suggesting that thyroid function was completely abolished. Following supplementation therapy with L-thyroxine, all the symptoms gradually disappeared. The patient remained euthyroid for nearly 2 years at a daily oral dose of 100 micrograms L-thyroxine. To clarify whether the IFN-alpha-induced hypothyroidism was reversible, L-thyroxine was discontinued after obtaining informed consent. The patient thereafter remained in a euthyroid state, without any significant symptoms, for more than 11 months. The present case indicates that hypothyroidism induced by IFN-alpha treatment may be reversible, even if it has developed over a prolonged period and become severe, resulting in undetectable serum levels of T3, T4, and thyroglobulin.

Inhibin alpha and beta A subunit messenger ribonucleic acids expression in human pituitary adenomas: studies by quantitative reverse transcription-polymerase chain reaction

Inhibin alpha and beta A subunit messenger ribonucleic acid (mRNA) levels were measured quantitatively by reverse transcription-polymerase chain reaction (RT-PCR) in human pituitary adenomas. The inhibin alpha subunit mRNA levels were undetectably low in cultured adenoma tissues, but beta A mRNA were 0.383 +/- 0.074 in 3 GH adenomas, 0.672 +/- 0.140 in 3 prolactinomas and 0.957 +/- 0.414 molecules/cell in 3 non-functioning adenomas. The addition of 10(-8) M activin A decreased the beta A mRNA levels within 4 h in 1 of 3 GH adenomas, 2 of 3 prolactinomas and 2 of 3 non-functioning adenomas, though the decreases were not statistically significant. The results showed an abundance of beta A subunit mRNA compared with alpha subunit mRNA in all human pituitary adenomas and a local role for activin in its own production through inhibin beta A mRNA subunit expression.

Major role of 3',5'-cyclic adenosine monophosphate-dependent protein kinase A pathway in corticotropin-releasing factor gene expression in the rat hypothalamus in vivo

To assess whether the cAMP-dependent protein kinase-A and/or the diacylglycerol-dependent protein kinase C (PKC) pathways play important roles in the activation of CRF neurons in vivo under physiological conditions, we tested the effect of microinjection of 8-bromo-cAMP (8-Br-cAMP) or 12-O-tetradecanoyl phorbol 13-acetate (TPA) into both paraventricular nuclei (PVN) of the hypothalamus in conscious rats. Both 8-Br-cAMP and TPA increased plasma ACTH concentrations and the POMC messenger RNA (mRNA) concentrations in the anterior pituitary. While injection of 8-Br-cAMP also increased CRF mRNA concentrations in hypothalamic tissue containing the PVN, TPA injection had no effect on CRF mRNA concentrations there. During insulin-induced hypoglycemia, which stimulates CRF gene expression and release, c-fos and c-jun mRNA increases in the hypothalamic tissue preceded the increase in the CRF mRNA level after insulin-induced hypoglycemia. Antisense oligodeoxyribonucleotides (oligos) directed against c-fos, c-jun, or the cAMP response element binding protein (CREB) mRNA were injected into both PVN before insulin-induced hypoglycemia to assess whether activator protein-1 or CREB mediates transcriptional activation of CRF during hypoglycemia. Only antisense oligo against CREB mRNA reduced the CRF mRNA level after insulin-induced hypoglycemia. These results suggest that protein kinase A may transduce intracellular signals in CRF neurons under physiological conditions and raises the possibility that CREB may be involved in stress-induced CRF gene expression.

Clinical implications of renal cyst in primary aldosteronism

The present study surveyed 69 patients with aldosteronoma to study the clinical implications of renal cysts demonstrated in computed tomography. Patients who had cysts (n = 16, 23.2%) were older and had a longer duration of hypertension and more severe hypokalemia than those without cysts (n = 53). Patients with cysts therefore had longer-term, more severe hypokalemia than those without cysts. Endogeneous creatinine clearance (Ccr), measured in 61 patients, was significantly lower in patients with cysts (58.4 +/- 7.1 ml/min, n = 16) than in those without cysts (77.3 +/- 7.1 ml/min, n = 45, P = 0.0039). This significant difference was observed even after adjusting for covariables (age, duration of hypertension, and serum potassium) between the two groups by analysis of covariance (ANCOVA). No significant difference was observed in gender, blood pressure, serum creatinine, plasma aldosterone, or PRA. Age, serum potassium levels, and systolic and diastolic blood pressure were the significant determinants in predicting Ccr in a backward stepwise multiple regression analysis (r = 0.505, n = 61, P = 0.0025). Cysts were graded into four classes on the basis of number and size. Cyst grading correlated negatively with Ccr at a Spearman rank correlation (rho = -0.33, n = 61, P = 0.0103). The incidence of chronic renal failure was significantly higher in patients with cysts (18.8%) than in patients without (0%) in a Fischer's exact probability test (P = 0.0107). Thus, both renal cysts and dysfunction arose and/or developed from common roots, i.e., the duration and severity of hypokalemia, in primary aldosteronism. In addition, we surveyed 27 patients with pheochromocytoma. Patients with renal cysts (n = 8) had a significantly longer duration of hypertension than those without cysts. No significant difference was observed in Ccr between patients with and those without cysts. Thus, a significant link between renal cysts and Ccr was a specific feature of primary aldosteronism, but not of pheochromocytoma. In summary, the renal cysts in primary aldosteronism should be recognized as a significant complication representing the extent of renal injury and dysfunction.

Regulation of corticotropin-releasing factor receptor messenger ribonucleic acid in rat anterior pituitary

Adrenalectomy (ADX) leads to a decrease in the number of CRF-binding sites in the rat anterior pituitary (AP). However, the molecular mechanisms of CRF receptor (CRF-R) regulation are unknown. In the present study, we analyzed the effects of ADX on pituitary CRF-R1 messenger RNA (mRNA) levels in vivo and the direct effects of CRF, arginine vasopressin (AVP), and glucocorticoid, the levels of which are altered by ADX, on CRF-R1 mRNA levels in vitro. The mRNA level was determined by Northern blot analysis using a rat brain CRF-R1 complementary RNA probe. The CRF-R1 level in AP fell to 20% of the sham level 1 day after ADX and returned to the sham level after 14 days. In cultured rat AP cells, treatment with CRF, AVP, and dexamethasone led to significant reductions in CRF-R1 mRNA, with maximal inhibition to 32%, 22%, and 37% of control levels, respectively. The time course of CRF-R1 mRNA reduction varied depending on the drug, with effects detectable as early as 1 h after treatment. These findings indicate that elevated portal CRF and AVP levels may contribute to the decrease in CRF-R1 mRNA soon after ADX. A decrease in mRNA levels, in turn, may lead to a decrease in CRF-R1 protein on corticotrophs.

Corticotropin-releasing factor up-regulates its own receptor mRNA in the paraventricular nucleus of the hypothalamus

We investigated the role of CRF in regulating receptor expression in the paraventricular nucleus (PVN). First, to clarify the effect of exogenously administered CRF, 1 microgram of ovine CRF was injected into rat lateral ventricle and changes in concentration of the CRF type 1 receptor (CRF1-R) and CRF mRNA in the PVN were semiquantified after in situ hybridization. Second, we determined the effect of stress, as a stimulant of endogenous CRF secretion, on mRNA accumulation. While CRF1-R mRNA expression was low to be undetectable in the PVN of controls, both intracerebroventricular administration of CRF and restraint significantly increased CRF1-R and CRF signals in the parvocellular PVN. Thus CRF may modulate CRF production and release from the PVN, by regulating CRF1-R expression.

A very small juxtaglomerular cell tumor preoperatively identified by magnetic resonance imaging

We describe a 31-year-old man. Although the plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were elevated, computed tomography and rapid sequence pyelography disclosed no abnormality. However, based on the findings of the small tumor (8 x 8 mm) in the kidney visualized by magnetic resonance imaging (MRI) and excessive PRA in the right renal vein, tumor resection was performed. The positive immunohistochemical staining of renin and the visualization of renin mRNA by in situ hybridization provided evidence supporting the diagnosis of juxtaglomerular cell tumor. Blood pressure, PRA, and PAC were normalized after the surgery. The observations suggest that MRI is a powerful diagnostic procedure in small juxtaglomerular cell tumor.

Increase of vascular endothelial growth factor mRNA expression by 1,25-dihydroxyvitamin D3 in human osteoblast-like cells

Vascular endothelial growth factor (VEGF), a secreted endothelial cell-specific mitogen, is produced in endocrine organs and regulated by trophic hormones. Because angiogenesis and osteogenesis are closely regulated, we studied whether human osteoblast-like cells produce VEGF, and if so, what factors regulate VEGF mRNA expression. Human osteoblast-like cells (HObLC) derived from trabecular bone explants were cultured in alpha-MEM supplemented with 10% fetal calf serum. Northern blot analysis revealed that HObLC expressed VEGF mRNA, as did several human osteosarcoma cells. 1,25-(OH)2D3 increased the steady-state levels of VEGF mRNA in a time- and concentration-dependent manner in HObLC and one of the osteosarcoma cell lines, SaOS-2, accompanied by an increase in the concentration of immunoreactive VEGF in the conditioned medium. PTH and IGF-I also increased the level of VEGF mRNA in HObLC and SaOS-2 cells. Furthermore, 12-O-tetradecanoylphorbol ester stimulated VEGF mRNA in a time-and concentration-dependent manner. The VEGF mRNA expression induced by 1,25-(OH)2D3 was completely inhibited by H-7, but only partially by staurosporine. We have demonstrated that PTH, IGF-I, and most potently 1,25-(OH)2D3 stimulate the mRNA expression and secretion of VEGF in human osteoblast-like cells, suggesting that one of the anabolic effects of 1,25-(OH)2D3 on skeletal tissue may be mediated by VEGF produced by osteoblasts.

[Pseudohypoaldosteronism]

Mineralocorticoid resistance results from inability of aldosterone to exert its effect on its target tissues. The syndrome is associated with salt loss, hypotension and hyperkalemic acidosis. We have cloned and sequenced the cDNA of the mineralocorticoid receptor of five sporadic cases with this syndrome but have found no mutations of pathophysiological significance, which would explain the resistance of these patients to aldosterone. In all of these patients, we also examined 0.9 kb of the 5' regulatory region and the first untranslated exon of the mineralocorticoid receptor gene, without detecting any abnormalities. We are now studying the subunits of the amiloride-sensitive sodium channel (ENaC), which are in the postreceptor pathway of aldosterone action, in this disease.

Angiotensin II-dependent down-regulation of vascular natriuretic peptide type C receptor gene expression in hypertensive rats

Biological actions of natriuretic peptide (NP) are determined by the condition of the receptor as well as that of the hormone. Although we previously demonstrated in hypertensive rats the up-regulation of NP-A receptor that mediates various biological actions of NPs, the pathophysiologic significance of NP-C receptor, another subtype thought to be related to clearance of NPs and possibly to biological actions, remains unknown. In the present study, we determined NP-C receptor messenger RNA (mRNA) level in the aortic tissue of stroke-prone spontaneously hypertensive rats (SHR-SP/Izm) and in cultured aortic smooth muscle cells by ribonuclease protection assay. The aortic NP-C receptor mRNA level in SHR-SP/Izm was significantly lower than that in the control WKY/Izm. Oral administration of an angiotensin (Ang) II receptor (AT1) antagonist, TCV-116, but not a calcium channel blocker, manidipine, reversed the down-regulated NP-C receptor mRNA in SHR-SP/Izm to the level in WKY/Izm, whereas the latter was more potent in decreasing the blood pressure. In cultured aortic smooth muscle cells, the NP-C receptor was the predominant subtype. Ang II decreased the NP-C receptor mRNA level in a dose-dependent manner, but this effect was reversed by an AT1 antagonist, CV-11974. Neither the NP-A nor NP-B receptor mRNA level was altered by Ang II. These findings indicate that vascular NP-C receptor is down- regulated via Ang-II-mediated mechanism in SHR-SP/Izm. The phenomenon, together with the up-regulation of the NP-A receptor, may play an important role in counteracting hypertension by enhancing the action of NPs.

LH and testosterone modulate mercuric chloride-induced acute renal failure in male rats: the implication of stress-induced hypogonadism

The significance of stress-induced hypogonadism remains unclear. Since plasma testosterone and LH have renotropic activity that is other than reproductive, we hypothesize that stress-induced hypogonadism is an adaptive response to protect the kidney. To examine this hypothesis, we prepared hypogonadal male rats with different levels of LH and testosterone through orchiectomy (castration), through chronic treatment with a slowly secreted form of gonadotropin-releasing hormone agonist (GnRHA; GnRHA pretreatment), or through both treatments concomitantly (castration with GnRHA pretreatment). Castrated rats had undetectable plasma testosterone and high plasma LH. GnRHA-pretreated rats had low plasma testosterone and normal plasma LH. Castrated rats with GnRHA pretreatment had undetectable plasma testosterone and normal plasma LH. We compared their sensitivity to HgCl2 nephrotoxicity and found that, when a low dose of HgCl2 (1.5 mg/kg body weight (BW)) was injected s.c. to induce acute renal failure, endogenous creatinine clearance (Ccr) decreased from 390 +/- 30 to 94 +/- 17 ml/h per kg BW in intact (unpretreated) rats. Such a decrease in Ccr was completely prevented in castrated rats (388 +/- 30 ml/h per kg BW) and partially prevented in GnRHA-pretreated rats (216 +/- 40 ml/h per kg BW). When a high dose of HgCl2 (2.25 mg/kg BW) was injected, half of the eight intact rats died but castrated rats and GnRHA-pretreated rats survived (P < 0.05). The elevated resistance in castrated rats was reduced when plasma LH was reduced with GnRHA pretreatment, but was restored by additional pretreatment with ovine LH (40 micrograms/day), as evidenced by changes in Ccr. Elevated resistance in castrated rats was also reduced by the administration of testosterone propionate. In conclusion, hypogonadism activated the preventive and defensive mechanisms that protect the kidney through both decreased plasma testosterone and high or even normal plasma LH.

An allel-specific abnormal transcript of the heat shock protein 70 gene in patients with major depression

Stress-inducible 72-kDa heat shock proteins (HSP70) were encoded on genes in multiple chromosomes. The expression of mRNA transcribed from the gene (HSP70-1) on chromosome 6 was studied using reverse transcript polymerase chain reaction in peripheral blood mononuclear cells of patients with different diseases. The deletion of 29 bp occurred in 5' noncoding and subsequent 133 bp in coding sequences of HSP70 mRNA in patients with major depression (n = 18), while normal subjects (n = 10) and patients with schizophrenia (n = 5), essential hypertension (n = 3), rheumatoid arthritis (n = 7), and Graves' disease (n = 3) had normal mRNA. No such deletion occurred in genomic DNA and no protein was translated from deleted mRNA. The allel-specific abnormal transcript of the HSP70 gene on chromosome 6 thus may underlie the altered stress and/or immune response in major depression.

Intracerebroventricular administration of beta-endorphin increases the expression of c-fos and of corticotropin-releasing factor messenger ribonucleic acid in the paraventricular nucleus of the rat

We evaluated the effects of intracerebroventricular (i.c.v.) administration of beta-endorphin and naloxone, an opioid antagonist, on the induction of c-fos and corticotropin-releasing factor (CRF) mRNA to clarify the effects of beta-endorphin on cellular activity and CRF gene expression in the paraventricular nucleus (PVN) of the rat using in situ hybridization. A significant induction of c-fos mRNA was noted in the PVN after i.c.v. injection of beta-endorphin, compared to control. This induction was inhibited by the administration of naloxone. A significant increase in CRF mRNA levels in the PVN was observed 120 min after the i.c.v. injection of beta-endorphin. This increase was partially, but significantly, inhibited by naloxone administration. In addition, i.c.v. administration of beta-endorphin increased plasma ACTH concentration in freely moving rats, which was inhibited by intravenous injection of CRF antiserum. These results suggest that the i.c.v. injection of beta-endorphin increases the neuronal activity and the biosynthesis of CRF in the PVN, and stimulates the secretion of ACTH by increasing CRF secretion. This effect on the PVN was mediated, at least in part, via the opioid receptor.

In situ identification of messenger RNA of endothelial type nitric oxide synthase in rat cardiac myocytes

The endothelial type nitric oxide synthase (NOS) termed as NOS-III has been demonstrated in various nonendothelial cells. Although NOS-III was recently found in the cardiac tissues, identification of the cells expressing NOS-III gene in the heart remains unknown. In this study, we compared the expression of NOS-III mRNA in various tissues of rats by Northern blot analysis using a homologous cDNA probe and identified the cell type by in situ hybridization histochemistry with a cRNA probe. NOS-III mRNA was found more abundantly in atria and ventricle than in other various tissues examined. NOS-III mRNA was intensely and specifically visualized in the cardiac myocytes as well as in the endothelial cells of the heart. No staining was seen with a sense cRNA probe. These results provide the first in vivo evidence for NOS-III mRNA in the cardiac myocytes and suggest its role in the regulation of cardiac functions.

Angiotensin converting enzyme inhibitor normalizes vascular natriuretic peptide type A receptor gene expression via bradykinin-dependent mechanism in hypertensive rats

We previously demonstrated that angiotensin converting enzyme (ACE) inhibitor normalizes the up-regulated gene expression of vascular natriuretic peptide type A (NP-A) receptor in hypertensive rats. To elucidate the mechanism, we examined the effect of angiotensin II receptor (AT1) antagonist (TCV-116) and bradykinin receptor (B2) antagonist (Hoe 140) on the NP-A receptor mRNA level in the aorta of genetically hypertensive rats (SHR-SP/Izm) using ribonuclease protection assay. The effect of ACE inhibitor on the NP-A receptor mRNA level was completely abolished by a concomitant administration of Hoe 140, while TCV-116 did not show any significant effect on the NP-A receptor mRNA level. These results suggest that bradykinin plays an important role in the regulation of the vascular NP-A receptor gene expression.

C-type natriuretic peptide as a possible local modulator of aldosterone secretion in bovine adrenal zona glomerulosa

Although atrial and brain natriuretic peptides are well known to be involved in the regulation of cardiovascular and endocrine functions as circulating hormones, the roles of the C-type natriuretic peptide (CNP) remain unknown. We examined the effects of CNP on the secretion of aldosterone and cyclic nucleotides from bovine adrenal zona glomerulosa cells in culture. CNP produced a dose-dependent increase in the basal secretion of cGMP, with an EC50 of 3.8 x 10(-10)M. CNP significantly inhibited the ACTH-induced increase in aldosterone and cAMP in a dose-related manner, with an IC50 of 3.6 x 10(-10)M. Although ACTH itself did not increase cGMP secretion, the addition of CNP elicited a significant increase in cGMP secretion. The effects of CNP on the basal secretion of cGMP and the ACTH-induced secretion of aldosterone were significantly reversed by a nonpeptide natriuretic peptide receptor antagonist, HS-142-1. CNP immunoreactivity was localized in the zona glomerulosa by immunohistochemical staining. In addition, expression of CNP messenger RNA and natriuretic peptide B receptor messenger RNA was demonstrated by RT-PCR in the zona glomerulosa tissue and cells in culture. These findings suggest that CNP is a local factor regulating ACTH-induced aldosterone secretion through a guanylyl cyclase-cGMP pathway.

Thyroid hormone regulation of gene expression of the pituitary growth hormone-releasing factor receptor

To examine thyroid hormone regulation of the pituitary receptor for hypothalamic growth hormone (GH)-releasing factor (GRF), we studied effects of hypothyroidism on the pituitary GRF receptor (GRF-R) mRNA and its related parameters in rats. Thyroidectomy (Tx) induced a 61-65% reduction in GRF-R mRNA levels, which was significantly reversed with thyroxine (T4) replacement for 5 days at a dose of 1 microgram/100 g/day. Pituitary GH contents changed parallel to GRF-R mRNA levels following the Tx and T4 replacement. In contrast, Tx enhanced GRF release > 2 fold, which was not reversed with the regime of T4 replacement. These results indicate that thyroid hormone promotes pituitary GRF-R gene expression, not by modulating GRF secretion, but by acting on the pituitary directly. The decline in GRF receptor expression would contribute to somatotroph failure by rendering the pituitary refractory to the increased GRF signal in hypothyroidism.