Expression of inhibin alpha, and beta A subunit and activin type II receptor mRNAs in various human pituitary adenomas

Inhibin and activin are known to be involved in the pituitary hormone secretion as well as proliferation of the pituitary. We studied the expression of inhibin alpha, and beta A subunit and activin type II receptor (ACTR 2) mRNAs in human pituitary adenomas to determine the significance of inhibin and activin in pituitary hormone secretion. Tumor tissues were homogenized immediately after resection in guanidinium thiocyanate to extract total RNA. PCR was performed with reversely transcripted cDNA and respective amplification primers. DNA bands obtained for inhibin alpha, beta A and ACTR 2 by agarose gel-electrophoresis were 367, 285, and 389 bp, respectively. Messenger RNAs for inhibin beta A were demonstrated in all of the pituitary tissues studied, namely in 3 GH, 2 ACTH, 6 PRL and 1 FSH producing adenomas and 17 non-functioning adenomas. Inhibin alpha mRNAs were detected in 10 of 12 functioning adenomas and 15 of 17 non-functioning adenomas. ACTR 2 mRNAs were found in 11 out of 17 non-functioning adenomas, but only found in 3 out of 12 functioning adenomas. These results suggested local production of activin, a homodimer of beta-subunits, and inhibin, a heterodimer of alpha and beta subunits, in most of the pituitary adenomas regardless of their hormone secretion. On the other hand, a significantly higher incidence of ACTR 2 in non-functioning adenomas than in functioning adenomas suggested that activin had its main site of action in non-functioning adenomas, which could be potential gonadotropinomas.

The response pattern of noradrenaline release to repeated stress in the hypothalamic paraventricular nucleus differs according to the form of stress in rats

The effect of two repeated forms of stress, manual restraint and tail-pinch, on noradrenaline (NA) release in the hypothalamic paraventricular nucleus of the rat was examined by intracerebral microdialysis. Manual restraint significantly increased NA release, but the stimulatory effect gradually declined when the stress was repeated at intervals of 120 min. High K+ induced a great increase in NA release even when manual restraint produced no significant effect on NA release. In contrast, tail-pinch significantly increased NA release to a greater extent than manual restraint, and the increase in NA release did not change when the stress was repeated three times at intervals of 120 min. These results suggest that desensitization of NA neurons ending in the hypothalamic paraventricular nucleus occurs in response to painless stress, such as manual restraint, whereas no attenuation of NA release is caused by repeated stress accompanied by pain, such as tail-pinch.

Angiotensin converting enzyme inhibitor but not calcium blocker down-regulates gene expression of vascular natriuretic peptide receptor in hypertensive rats

We have recently found that vascular natriuretic peptide (NP)-A receptor mRNA is upregulated in genetically hypertensive (SHR-SP/Izm) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In the present study, we examined the effects of antihypertensive treatments on aortic NP-A receptor mRNA expression in these hypertensive rats using ribonuclease protection assay. Oral administration of an angiotensin converting enzyme inhibitor, derapril, but not a calcium channel blocker, manidipine, produced a significant decrease of the NP-A receptor mRNA level after 4 weeks, while both antihypertensive agents showed similar hypotensive effects. Plasma renin was high in SHR-SP/Izm and low in DOCA-salt rats. These results suggest that the vascular renin-angiotensin system rather than the blood pressure has an important role in the regulation of the vascular NP-A receptor.

Immunoreactive endothelin-1 in the neural lobe of the rat pituitary following hemorrhage and dehydration

Previously we found intragranular colocalization of immunoreactive endothelin-1 and neurohypophysial hormones in the axon terminals of the rat neural lobe. To investigate the function of endothelin-1 in the rat neural lobe, immunoreactive endothelin-1 in plasma and the neural lobe was measured by enzyme immunoassay in rats subjected to hemorrhage and in other rats who were deprived of water for 2 days to induce dehydration. Changes in plasma arginine vasopressin were determined by radioimmunoassay. In addition, morphometric analysis was performed in the neural lobe of rats exposed to these stresses. Plasma concentrations of immunoreactive endothelin-1 were unchanged following hemorrhage or dehydration, whereas those of immunoreactive vasopressin were remarkably increased. In the neural lobe, immunoreactive endothelin-1 content and the number of neurosecretory granules decreased significantly after dehydration. However, immunoreactive endothelin-1 in tissue increased nearly three-fold in hemorrhaged rats, whereas the endothelin-1-immunolabeling in the axon terminals was unchanged. These results suggest that endothelin-1 in the hypothalamo-hypophysial system may be involved in the local modulation of vasopressin secretion when an animal is exposed to hypovolemic and/or osmotic stress.

Microinjection of norepinephrine into the paraventricular nucleus of the hypothalamus stimulates corticotropin-releasing factor gene expression in conscious rats

To examine the physiological effects of norepinephrine (NE) in the paraventricular nucleus of the hypothalamus (PVH) on CRF gene expression and CRF release, NE was microinjected bilaterally into the PVH of conscious rats, and kinetic studies were performed on the levels of POMC messenger RNA (mRNA) in the anterior pituitary (AP), CRF mRNA in the PVH-containing hypothalamic fragment, and plasma ACTH. Plasma ACTH levels were increased dose dependently by NE (5-50 nmol/side) injection into the PVH. They reached their peaks after 30 min and returned to the basal values after 90 min. The POMC mRNA level in the AP and hypothalamic CRF mRNA level increased significantly 90 min after NE injection and increased further after 120 min. The POMC mRNA level in the AP and hypothalamic CRF mRNA level were increased dose dependently by NE (5-50 nmol/side) after 120 min. Intracerebroventricular pretreatment with prazosin abolished completely the increase in plasma ACTH levels after intrahypothalamic NE injection, whereas pretreatment with propranolol was without significant effect. These results suggest that NE stimulates CRF gene expression in the PVH and CRF secretion into the portal circulation, thus regulating positively the hypothalamic-pituitary-adrenal axis. alpha 1-Adrenergic receptors may mediate the action of NE on CRF neurons.

Basic fibroblast growth factor (FGF-2) in renal cell carcinoma, which is indistinguishable from that in normal kidney, is involved in renal cell carcinoma growth

To investigate the role of basic fibroblast growth factor (FGF) in renal cell carcinoma growth, we have analyzed the expression of mRNA of basic FGF. In 7 of 15 cases, basic FGF mRNA level in renal cell carcinoma tissues was higher than that in corresponding normal tissues. However, the tumor-to-normal ratios of expression levels are chiefly less than 2.0 and, in 5 cases, are even less than 1.0. Furthermore, there was no correlation between the ratio and the clinical stage. In protein analysis, we could not find any difference between basic FGF extracted from renal cell carcinomas and that from normal kidney tissues in bioactivity, immunoreactivity, molecular weight and affinity to heparin. On the other hand, anti-basic FGF monoclonal antibody inhibited the growth of a renal cell carcinoma cell line, VMRC-RCW, and this inhibition was reversed by an extraphysiological amount of exogenous basic FGF (100 ng./ml.). These results suggest that basic FGF itself may have no pivotal role in renal cell carcinoma etiology but is involved in the growth of renal cell carcinomas in an autocrine manner.

Beta 1-adrenergic mechanism is involved in stress-induced increase in arousal

It has been shown that 1 h restraint shortens pentobarbital (PbNa)-induced sleeping time and that brain corticotropin-releasing hormone (CRH) is involved in the mechanism by which restraint shortens. PbNa-induced sleeping time. The present study was designed to further examine the mechanism of the antagonistic effect of 1 h restraint on PbNa in rats. Intracerebroventricular (i.c.v.) administration of propranolol and metoprolol, but not butoxamine reversed the shortening of PbNa-induced sleeping time by 1 h restraint. The i.c.v. administration of phentolamine blocked the shortening of PbNa-induced sleeping time by restraint, while the same dose of phentolamine prolonged the sleeping time in unrestrained rats. Atropine did not affect the PbNa-induced sleeping time in restrained rats. These results suggest that in addition to CRH, the brain beta 1-adrenergic system is involved in the restraint stress-induced increase in arousal.

Addison's disease in Japan: characteristics and changes revealed in a nationwide survey

Patients with Addison's disease, newly diagnosed in the last five years were surveyed nationwide in conjunction with two past surveys. The decreasing incidence, i.e., 168 patients from 1977 to 1981 (survey 1), 108 from 1982 to 1986 (survey 2), and 74 from 1987 to 1991 (the present survey), reflects a decrease in the incidence (n = 28) of tuberculous Addison's disease, but not that (n = 36) of idiopathic Addison's, making the idiopathic form predominant for the first time in the history of the disease in Japan. Because the interval between the preceding tuberculosis and the onset of Addison's averages 32 +/- 15 years, tuberculous Addison's has a relatively late onset. Pigmentation is the most frequent symptom (90%). Other symptoms, abnormal laboratory data, and positive adrenal antibodies are observed less frequently in Japan than in North America or Europe. The types of associated disorders are also distributed differently. Adrenal CT and MRI scans have been the most useful means in differentiating between the two major types of the disease. This report focuses on features distinguishing Japanese sufferers from their western counterparts.

Corticotropin-releasing factor-binding protein concentrations in plasma of patients with hypothalamic-pituitary-adrenal disorders

Immunoreactive corticotropin-releasing factor-binding protein (CRF-BP) concentrations in human plasma were determined by means of radioimmunoassay for human CRF-BP. CRF-BP antiserum to the C-terminal fragment of human CRF-BP (298-322) was produced, and CRF-BP (298-322) was used as the tracer and the standard. Large amounts of human CRF did not affect measurement of plasma CRF-BP with this radioimmunoassay. The basal plasma CRF-BP concentration in normal subjects was 4.19 +/- 0.57 nmol/L (mean +/- SD). The CRF-BP concentration was low in patients with Cushing's syndrome, except those with preclinical Cushing's syndrome, and high in patients with Addison's disease, hypopituitarism and isolated ACTH deficiency. After surgery, the plasma CRF-BP concentration in patients with Cushing's syndrome rose, peaked, and then decreased to the control level. In patients with Addison's disease, the high plasma CRF-BP concentration decreased to the control level after hydrocortisone replacement, the same as plasma ACTH concentration. These findings suggest that the immunoreactive CRF-BP concentration in human plasma was decreased by glucocorticoids, at least under chronic conditions.

Recent advances in endothelin research on cardiovascular and endocrine systems

Recent advances in ET research on the cardiovascular and endocrine systems were reviewed. Considering the potent vasculotropic actions, strategically advantageous localization, and recent findings with the specific receptor antagonist, ET is potentially involved in the regulation of hemodynamic homeostasis and in the pathogenesis of essential and secondary hypertension. The mitogenic action on the vascular smooth muscle cells suggests its more chronic effect on the vascular structure. In addition to the hypertensinogenic aspects, the role of ET in maintaining blood pressure in a hypotensive condition should not be overlooked. The development of specific antagonists which block the action of locally operating ET in vivo will be a powerful tool in elucidating the pathophysiological significance of ET and will provide a new therapeutic approach for hypertension. The roles of ET in the endocrine system are also fascinating. Accumulating evidence supports the notion that ET modulates the secretion of pituitary and adrenal hormones. The mode of action is likely to be paracrine/autocrine rather than endocrine, although a possible role of circulating ET cannot be ruled out. The pathophysiological role of ET in the endocrine tissues remains to be clarified. The diversity of the action of ET on the blood pressure and endocrine functions provides further evidence of the complexity of the homeostatic mechanisms, leaving us an intriguing subject for future study.

Stimulation of interleukin-4 of cell proliferation and mRNA expression of alkaline phosphatase and collagen type I in human osteoblast-like cells of trabecular bone

Interleukin-4 (IL-4) potently inhibits bone resorption by preventing the differentiation of osteoclast precursors to osteoclasts. To elucidate the role of IL-4 in bone formation, we studied the effects of human IL-4 on human osteoblast-like cells obtained from trabecular bone, which showed increased osteocalcin production in response to 1,25-(OH)2D3 in more than 10 passages. IL-4 stimulated the proliferation of osteoblast-like cells in a concentration-dependent manner, showing the minimal and maximal stimulatory effects at 10 pg/ml and 100-1000 pg/ml, respectively. IL-4 also stimulated the expression of alkaline phosphatase mRNA (1.7-fold) and the enzyme activity to the same extent at 10-100 pg/ml. Furthermore, IL-4 stimulated collagen type I mRNA expression in human osteoblast-like cells. The cytokine did not affect osteocalcin production in a short culture period (3 days). These in vitro findings suggest that IL-4, a bone-resorption-inhibitory cytokine produced by activated T cells in bone marrow, may exert an anabolic effect on osteoblast-like cells in trabecular bone through a paracrine mechanism.

Interaction of endothelin-1 with porcine thyroid cells in culture: a possible autocrine factor regulating iodine metabolism

Although endothelins were originally discovered as peptides with vasoconstrictor activity, recent studies have indicated a number of endothelin (ET)-induced hormonal functions in various tissues. We have studied the interaction of endothelins with porcine thyroid cells in culture. Specific binding of 125I-labelled ET-1 was demonstrated in porcine thyroid cells. The binding was displaced equally by unlabelled ET-1 and ET-2, but receptor affinity for ET-3 was lower than that for ET-1 and -2. Scatchard analysis of the data revealed a single class of high-affinity ET-1 receptors with a Kd of 0.45 nmol/l and a binding capacity of 2100 sites/cell. SDS-PAGE and autoradiography of 125I-labelled ET-1 cross-linked with thyroid cell membranes demonstrated ET-1 binding sites with an apparent molecular weight of 50 kDa. These results indicated that ET-1 receptors in thyroid cells are type A ET receptors. In association with the presence of ET-1 receptors, porcine thyroid cells responded to ET-1 and ET-2 with an increase in c-fos mRNA expression. Although ET-1 did not affect DNA synthesis stimulated by either EGF or IGF-I, it dose-dependently inhibited TSH-induced iodide uptake and also inhibited iodide uptake stimulated by forskolin and 8-bromo-cAMP. ET-1 had no effect on TSH-stimulated cAMP production. Thus, ET-1 inhibited TSH-induced iodine metabolism by acting at the steps distal to cAMP production. In agreement with a recent report, immunoreactive ET-1 was detected in medium conditioned by porcine thyroid cells. Antibody to ET-1 was found to increase TSH-induced iodide uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Progressively increased serum 1,25-dihydroxyvitamin D2 concentration in a hypoparathyroid patient with protracted hypercalcemia due to vitamin D2 intoxication

A 76-year-old female patient who had been taking vitamin D2 100,000 U/day for more than 14 years due to hypoparathyroidism following total throidectomy was admitted because of protracted hypercalcemia. On admission, the levels of serum vitamin D2 (99.8 ng/ml) and 25-OHD2 (356 ng/ml) were very high, and 1,25-(OH)2D2 was low (4.0-18.7 pg/ml). Serum D3' 25-OHD3 and 1,25-(OH)2D3 were below the normal range. Despite intensive hydration with saline, intravenous hyperalimentation with phosphate- and calcium-free nutrients, and administration of glucocorticoid and calcitonin, the hypercalcemia persisted, accompanied by hypoproteinemia, edema, pleural effusion and congestive heart failure. The serum D2 and 25-OHD2 concentrations remained high and were accompanied by a gradual increase in 1,25-(OH)2D2 (121 pg/ml), which further increased after the administration of bisphosphonate (pamidronate) to 183 pg/ml. Seventeen months later, serum calcium and 1,25-(OH)2D2 were normalized but serum D2 and 25-OHD2 remained high. The serum 24,25-(OH)2D2/25-OHD2 ratio was relatively constant throughout her clinical course, whereas the low serum 1,25-(OH)2D2/25-OHD2 ratio at admission gradually increased during admission, suggesting that the increase in serum 1,25-(OH)2D2 is due to increased production rather than decreased degradation. The administration of pamidronate further increased serum 1,25-(OH)2D2. These features of the clinical course demonstrate that the 1,25-dihydroxyvitamin D concentration in hypercalcemic patients with protracted vitamin D intoxication may be decreased, normal or increased. Possible factors responsible for a protracted increase in serum 1,25-(OH)2D2 are body weight loss, hypoproteinemia, and phosphate depletion. In addition, some bisphosphonates would certainly promote PTH-independent production of 1,25-(OH)2D2.

[Clinical significance of nitric oxide in hypertension]

Vascular endothelial cells produce various biologically active factors regulating blood pressure, coagulation, and possibly cell growth of the vascular wall. Of the factors, nitric oxide (NO) has been the object of attention because of its quite simple molecular structure and variety of biological functions. In the present review, we focused on the physiologic and pathologic aspects of NO in hypertension. In experimental animals, both acute and chronic inhibition of NO synthase (NOS) with arginine derivatives produce a significant rise in blood pressure, indicating that tonic production of NO regulates basal vascular tonus. The chronic hypertension caused by NOS inhibitor is associated with cardiac hypertrophy and renal insufficiency. Sodium retention, though transient, and the plasma and tissue renin/angiotensin system in addition to the reduced production of NO have been implicated in the development of hypertension. Hypertension and the associated target organ failure can be reversed by co-administration of L-arginine or blockades of the renin/angiotensin system. Studies in which L-arginine as the substrate of NO or NOS inhibitor was administered demonstrated an important role of NO in the regulation of tonic vascular tonus also in normal subjects. In hypertensive subjects, however, endothelium-dependent vasorelaxation and production of NO are impaired, possibly due to a deficiency of L-arginine and/or a disorder of its utilization. Recent advances in the methods of detecting NO enabled us to demonstrate its diminished production from endothelial cells of hypertensive rats in vitro, although no definite biochemical evidence has been obtained in hypertensive subjects. The endothelial dysfunction, however, is not a primary cause of hypertension but a secondary result since it is commonly observed in various types of hypertension and can be reversed by correcting the blood pressure. Other common diseases including atherosclerosis and diabetes mellitus are also associated with similar abnormalities of the endothelium. NO has anti-atherogenic actions: inhibition of platelet functions and proliferation of vascular smooth muscle cells. Therefore, potentiation of endogenous NO and/or supplement of exogenous NO donors could be novel therapeutic approaches for the treatment of hypertension and atherosclerosis, while potential adverse effects of NO including cytotoxicity, immunosuppressibility, and hypotensive shock should be taken into account.

[Stress and hormone]

The history of the studies on stress and hormones is briefly reviewed. The two main stress transmission systems are the endocrine (CRH-ACTH-Cortisol) and the neural (Sympatho-adreno-medullary) systems. The junction of the two systems resides in the hypothalamus. It has been clarified that CRH has central suppressive effects on eating, sleeping and sexual behavior. The relationships between emotions such as fear, anger and neurotransmitters (noradrenaline or serotonin) are discussed. Recent studies have revealed that various kinds of cytokines secreted from leukocytes stimulate the secretions of CRH and ACTH. Thus the cooperative mechanisms and actions of the endocrine, neural and immune systems against stress to keep homeostasis are elucidated.

Reduction of telomeric length and c-erbB-2 gene amplification in human breast cancer, fibroadenoma, and gynecomastia. Relationship to histologic grade and clinical parameters

BACKGROUND

Telomeric deletions contribute to genetic instability and may represent an important mechanism of carcinogenesis. Amplification of the c-erbB-2 gene has been demonstrated in breast carcinoma. The clinical significance of telomeric deletions and c-erbB-2 gene amplification therefore was studied in patients with breast disorders.

METHODS

The Southern blot analysis was used to measure telomeric length as well as the c-erbB-2 gene amplification of breast carcinomas, adjacent normal breast tissues, fibroadenomas, and cases of gynecomastia.

RESULTS

Significant reductions in telomeric length and concentration were observed in all breast tissues when compared to placental DNA. Mean telomeric lengths were lowest in carcinomas and fibroadenomas. There were no significant differences, however, in the telomeric lengths among tissues from patients with breast carcinomas, fibroadenomas, or gynecomastia. The degree of telomeric deletion correlated significantly with histologic grade and was most notable in Grade 3 (scirrhous) breast carcinoma. The extent of telomeric deletion reflects the histologic aggressiveness of breast carcinoma, and telomeric reduction already can be seen in the adjacent normal breast tissues from patients with breast cancer. c-erbB-2 gene amplification was observed in 26.8% of the patients with breast carcinoma. c-erbB-2 gene amplification was not observed, however, in patients with fibroadenomas or gynecomastia. The degree of telomeric deletion did not correlate with c-erbB-2 gene amplification, tumor size, clinical stage, steroid receptors, or prognosis. Telomeric length was shorter in lymph node-negative tumors than in lymph node-positive tumors.

CONCLUSIONS

These findings indicate that a shorter telomere length reflects growth advantage in breast cancer tissue, and telomeric reduction may promote cancer progression.

Central administration of alpha-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.

Effects of cysteamine, a somatostatin depleter, on the renin-angiotensin-aldosterone axis and glomerulosa cell growth in rats

Cysteamine, a specific somatostatin depleter, was given to male rats to clarify its role in relation to the renin-angiotensin-aldosterone (RAA) axis and glomerulosa cell growth. Rats received seven daily sc injections of cysteamine at doses of 50 or 150 mg/kg body weight (BW). Their adrenal weights and whole cortical thickness increased, but zona glomerulosa thickness decreased dose-responsively. Plasma renin activity (PRA) and aldosterone concentration (PAC) decreased. Similar results were observed in rats on a low or high salt diet and receiving daily doses of 150 mg/kg BW of cysteamine. In hypophysectomized rats, however, cysteamine given for seven days at daily doses of 100 mg/kg BW did not change either PRA or PAC. Adrenal weight did not change either too. Our results indicate that cysteamine suppresses the RAA axis and glomerulosa cell growth, probably through pituitary factors.

Restraint changes pentobarbital-induced sleeping time in rats: evidence that arousal is modulated by brain corticotropin-releasing hormone and opioid in stress

The effect of restraint of different duration on sodium pentobarbital (PbNa)-induced sleeping time was examined in rats. 1 h-restraint significantly shortened PbNa (50 mg/kg b.wt., administered i.p. immediately after restraint)-induced sleeping time as reported previously, whereas 2 h-restraint significantly prolonged the sleeping time. Naloxone (1 mg/kg b.wt.) administered i.p. 15 min before the start of restraint further exaggerated the 1 h-restraint-caused shortening of PbNa-induced sleeping time, and it blocked the 2 h-restraint-caused prolongation of the sleeping time. SDZ202-250 (0.1 pmol and 0.5 pmol), a selective mu agonist, but not [D-Pen2-D-Pen5]enkephalin (0.1 pmol-1.0 nmol), a selective delta agonist, or U50488H (0.1 pmol-1.0 nmol), a selective kappa agonist, administered i.c.v. 15 min before the i.p. injection of PbNa significantly prolonged PbNa-induced sleeping time; its prolongation was blocked by naloxone. These results suggest that a mu receptor-binding opioid prolongs PbNa-induced sleeping time in stress. The 2 h-restraint-caused prolongation of PbNa-induced sleeping time was also blocked by alpha-helical CRH(9-41) (26 nmol), a corticotropin-releasing hormone (CRH) receptor antagonist, administered i.c.v. 15 min before the start of restraint. In conjunction with our previous findings that the i.c.v. administration of CRH shortens PbNa-induced sleeping time and the 1 h restraint-caused shortening of PbNa-induced sleeping time is blocked by the CRH receptor antagonist, the present results suggest that CRH may stimulate an opioid-specific sedative mechanism, thus causing the prolongation of PbNa-induced sleeping time in 2 h-restraint.(ABSTRACT TRUNCATED AT 250 WORDS)

[Radioimmunoassay of synthetic steroid hormones]

The problem and recent progress of radioimmunoassay for various kinds of synthetic steroid hormones are reviewed. The specificity and sensitivity depend mostly on the position of synthetic antigen (hemisuccinate or oxime). Using good antibodies, a direct radioimmunoassay without extraction procedures of samples is available. A simplified method is required for the monitoring of synthetic steroids to know the effects and side effects.

Characterization and localization of mouse hypothalamic growth hormone-releasing factor and effect of gold thioglucose-induced hypothalamic lesions

Hypothalamic growth hormone-releasing factor (GRF) in higher mammals, including human GRF, is a 44 amino acid residue peptide and is highly homologous in structure. By contrast, mouse GRF (mGRF) recently deduced by cDNA cloning consists of only 42 residues and shows relatively low homology to the GRFs of higher mammals and the same rodent species, rat. To characterize and localize the predicted mature mGRF peptide in the hypothalamus, we have generated its antiserum and developed a homologous radioimmunoassay. Immunoreactive mGRF in the acid hypothalamic extract was eluted as a single peak at a position identical to that of synthetic peptide on both gel filtration chromatography and reverse-phase high-performance liquid chromatography (HPLC). Secretion of immunoreactive mGRF from incubated hypothalami increased several fold in response to 50 mM K+, and this rise was abolished in the absence of medium Ca2+. Only a single peak of immunoreactive mGRF that coeluted with synthetic replicate was observed after the K(+)-stimulated medium was extracted on Bond Elut C18 cartridges and applied on reverse-phase HPLC. Immunohistochemistry identified many mGRF-positive cell bodies in the arcuate nucleus and dense bundles of immunoreactive fibers in the median eminence. Treatment of mice with gold thioglucose (GTG), a chemical agent known to cause hypothalamic lesions, markedly depleted both content and in vitro secretion of immunoreactive mGRF. The decline in mGRF secretion was greater in GTG obese than in nonobese mice, whereas somatostatin secretion was not affected by GTG treatment.(ABSTRACT TRUNCATED AT 250 WORDS)