Interleukin-6 stimulates the secretion of adrenocorticotropic hormone in conscious, freely-moving rats

In order to assess the effect of interleukin-6 on the hypothalamo-pituitary-adrenal axis, we administered recombinant human interleukin-6 to conscious, freely-moving rats. The intravenous injection of interleukin-6 significantly increased the plasma level of adrenocorticotropic hormone 30 min after the injection in a dose-related manner. Immunoneutralization of corticotropin-releasing hormone blocked the stimulatory effects of interleukin-6 on adrenocorticotropic hormone secretion. These observations suggest that interleukin-6 stimulates the secretion of adrenocorticotropic hormone through the corticotropin-releasing hormone and is possibly involved in the interaction between the neuroendocrine and immune system.     

Age and the effect of adrenocorticotropic hormone on aldosterone secretion in rats

Age-related changes in functional activity of the glomerular zone were studied in the adrenal cortex of Wistar rats. It was shown that secretion of the basic mineralocorticoid hormone aldosterone was decreased with age. The glomerular zone of old rats showed the reduced sensitivity to the stimulant action of corticotropin, marked by the pronounced reaction to less doses of the hormone administered. At the same time the reactivity and the range of shifts in the course of ACTH dosage build-up decrease with aging.     

Interleukin-1beta deficiency results in reduced NF-kappaB levels in pregnant mice

To determine the role of the renal nerves on renin secretion and expression in the mature ovine fetus, we performed bilateral renal denervation on eight fetuses of time-dated pregnant ewes (126.8 +/- 0.6 days gestation) and compared renin in them to seven fetuses that underwent sham denervation (126.7 +/- 0.6 days gestation). Fetal arterial and venous catheters were implanted, and after 5-7 days of recovery isoproterenol was infused. Plasma active renin was lower in denervated animals than in intact animals under basal conditions and at each dose of isoproterenol. Plasma prorenin levels were lower in denervated fetuses but unaffected by isoproterenol. Denervation did not change renal renin, prorenin, or renin mRNA, but it did block isoproterenol-induced increases in renin mRNA in renocortical cells in vitro. We conclude that the renal nerves are required for renin secretory mechanisms and responsiveness of renin mRNA to beta-adrenergic stimulation but not for the expression of renin in the fetal kidney. We propose that one or more of the factors that maintain renin expression in the perinatal period may be absent or may be replaced by the renal nerves in the adult.     

Interleukin-1 beta induces synthesis and secretion of interleukin-6 in human chondrocytes

Increased concentrations of interleukin-6 (IL-6) have been found in the synovial fluid of patients with osteoarthritis, rheumatoid arthritis and crystal-related joint diseases. It is therefore of great interest to identify the cells responsible for the production of IL-6, and to investigate whether IL-6 plays a role in the pathogenesis of degenerative or inflammatory joint diseases. Here we show that human interleukin-1 beta (IL-1 beta) induces IL-6 synthesis and secretion in differentiated human chondrocytes. In organ cultures resembling closely the in vivo system 10(6) chondrocytes incubated with 100 units of interleukin-1 beta per ml of medium led to the release of 6 X 10(3) units of IL-6 within 24 h. Chondrocytes cultured in agarose or as monolayers similarly incubated with IL-1 beta produced even higher amounts of IL-6: 70 X 10(3) units per 10(6) cells within 24 h. The induction of IL-6 synthesis by IL-1 beta was also shown at the mRNA level. IL-6 secreted by stimulated chondrocytes showed heterogeneity upon Western blot analysis.     

Interleukin-1 beta, tumor necrosis factor and forskolin stimulate the synthesis and secretion of group II phospholipase A2 in rat mesangial cells

Treatment of rat glomerular mesangial cells with interleukin-1 beta, tumor necrosis factor or forskolin resulted in the release of phospholipase A2 activity in the culture medium. Essentially all of this phospholipase A2 activity was bound to immobilized monoclonal antibodies raised against rat liver mitochondrial 14 kDa group II phospholipase A2. Gelfiltration confirmed the absence of higher molecular weight phospholipases A2 in the culture medium. Immunoblot experiments showed the virtual absence of this 14 kDa group II phospholipase A2 in unstimulated mesangial cells. The time-dependent increase of phospholipase A2 activity in both cells and culture medium upon stimulation with interleukin-1 beta plus forskolin is accompanied with elevated 14 kDa phospholipase A2 protein levels. These results indicate that the increased phospholipase A2 activity upon treatment of mesangial cells with these stimulators is due to increased synthesis of group II phospholipase A2. Over 85% of this newly synthesized phospholipase A2 appears to be secreted from the cells.     

Interleukin-1 beta inhibits glucokinase activity in clonal HIT-T15 beta-cells

Interleukin-1 beta (IL-1 beta) has been implicated in the pathogenesis of insulin-dependent diabetes mellitus. In the present study we have investigated the effects of IL-1 beta on glucose metabolism in clonal HIT-T15 beta cells. In the short-term (1 h), 25 U/ml IL-1 beta significantly increased the rates of insulin release and glucose utilisation, but not glucose oxidation. In contrast, after 48 h, IL-1 beta inhibited insulin release and glucose utilisation and oxidation. By assaying enzymes (hexokinase, glucokinase, pyruvate dehydrogenase, glucose 6-phosphatase) and nucleotides (ATP, ADP) associated with the regulation of glycolysis and glucose oxidation, we conclude that the inhibitory effects of IL-1 beta may be due to impaired glucokinase activity.     

Effect of cortisol or adrenocorticotropic hormone on luteinizing hormone secretion by pig pituitary cells in vitro

The effect of cortisol or adrenocorticotropic hormone (ACTH) on basal and gonadotropin-releasing hormone (GnRH)-induced secretion of luteinizing hormone (LH) was studied in vitro using dispersed pig pituitary cells. Pig pituitary cells were dispersed with collagenase and DNAase and then grown in McCoy's 5a medium containing 10% dextran charcoal-pretreated horse serum and 2.5% fetal calf serum for 3 days. Cells were preincubated with cortisol or ACTH before GnRH was added. When pituitary cells were incubated with 400 micrograms cortisol/ml medium for 6 h or longer, increase basal secretion of LH was observed. However, GnRH-induced LH release was reduced by cortisol. The degree of this reduction was dependent on cortisol, and a concentration of cortisol higher than 100 micrograms/ml was needed. Cortisol also inhibited the 17 beta-estradiol-induced increase in GnRH response. ACTH-(1-24), ACTH-(1-39), or porcine ACTH had no influence on GnRH-induced LH secretion. Our results show that cortisol can act directly on pig pituitary to inhibit both normal and estradiol-sensitized LH responsiveness to GnRH.     

Interleukin-1beta and neurogenic control of blood pressure in normal rats and rats with chronic renal failure

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). The rise in central SNS activity is mitigated by increased local expression of neuronal nitric oxide synthase (NOS) mRNA and NO(2)/NO(3) production. Because interleukin (IL)-1beta may activate nitric oxide in the brain, we have tested the hypothesis that IL-1beta may modulate the activity of the SNS via regulation of the local expression of neuronal NOS (nNOS) in the brain of CRF and control rats. To this end, we first found that administration of IL-1beta in the lateral ventricle of control and CRF rats decreased blood pressure and norepinephrine (NE) secretion from the posterior hypothalamus (PH) and increased NOS mRNA expression. Second, we observed that an acute or chronic injection of an IL-1beta-specific antibody in the lateral ventricle raised blood pressure and NE secretion from the PH and decreased NOS mRNA abundance in the PH of control and CRF rats. Finally, we measured the IL-1beta mRNA abundance in the PH, locus coeruleus, and paraventricular nuclei of CRF and control rats by RT-PCR and found it to be greater in CRF rats than in control rats. In conclusion, these studies have shown that IL-1beta modulates the activity of the SNS in the central nervous system and that this modulation is mediated by increased local expression of nNOS mRNA.     

Adrenocortical atrophy of hypophysectomized rats can be reduced by corticotropin-releasing hormone (CRH)

Summary The effects of high dose injections of corticotropin-releasing hormone (CRH) on the adrenal cortex of hypophysectomized rats were studied at the light-and electron-microscopical levels. Adrenocortical atrophy induced by hypophysectomy could be reduced by daily i.p. injection of 10 g (3 nmol) CRH given for 3 days starting at day 5 after the operation. The cortex broadened, mostly because of hypertrophy of the zona fasciculata. Blood vessels were enlarged. Although the adrenocortical cells of hypophysectomized rats showed features of a functionally suppressed state, such as tubular mitochondria, the cells of CRH-treated animals showed characteristics of stimulated cells. The inner membrane of the mitochondria formed the typical densely packed vesicles of adrenocortical cells that are active in steroidogenesis. Lipid droplets were found to be reduced, and the cells developed filopodia at their surface. These morphological observations indicate that CRH influences the adrenal cortex via extrapituitary mechanisms.     

Interleukin-1beta and tumor necrosis factor-alpha mediation of endotoxin action on growth hormone

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1beta or TNF-alpha. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1beta or TNF-alpha did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration of either IL-1beta or TNF-alpha increased plasma concentrations of GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1beta (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14.     

Growth hormone-releasing peptide-2 stimulates secretion and synthesis of adrenocorticotropic hormone in mouse pituitary

Growth hormone (GH)-releasing peptides (GHRPs) are synthetic peptides which induce strong GH release in both animals and humans. Among them, GHRP-2 is known to stimulate GH release by acting at both hypothalamic and pituitary sites, but also induces adrenocorticotropic hormone (ACTH) release in healthy subjects. GHRP-2 may stimulate ACTH release directly via GHRP receptor type 1a in ACTH-producing tumors. GHRP-2 increases ACTH secretion in rat in vivo, but not ACTH release from rat primary pituitary cells. In the present study, in order to elucidate the mechanism underlying ACTH secretion by GHRPs, mouse pituitary cells were stimulated by GHRP-2. GHRP receptor mRNA was expressed in the mouse pituitary, and GHRP-2 directly stimulated secretion and synthesis of ACTH in the mouse anterior pituitary cells. GHRP-2 increased intracellular cyclic AMP production. H89, a potent protein kinase A (PKA) inhibitor, and bisindolylmaleimide I, a selective protein kinase C (PKC) inhibitor, inhibited the GHRP-2-induced ACTH release, and that H89, but not bisindolylmaleimide I, inhibited the GHRP-2-induced proopiomelanocortin mRNA levels. Together, the GHRP-2-induced ACTH release was regulated via both PKA and PKC pathways in the mouse pituitary cells, while ACTH was synthesized by GHRP-2 only via the PKA pathway.     

The effects of thyrotropin-releasing hormone, metabolites and analogues on locomotor activity in rats

Thyrotropin-releasing hormone (TRH) has generally been reported to increase locomotor activity in rats; however there are also some negative reports. In order to identify the possible causes for this discrepancy, the effects of intra-cerebroventricular injection of TRH, its metabolites 'acid TRH' (TRH-OH) and His-Pro-diketopiperazine (DKP), and two analogues 3-methyl-His-TRH and RX 77368 (3,3-dimethyl-Pro-TRH), were assessed using photocell activity cages. All compounds were tested in groups of eight rats in the afternoon (1300-1700 h), but in addition TRH and DKP were tested in two further groups of rats during the morning (0900-1230 h). TRH and DKP failed to induce a significant rise in activity during the morning test period, but TRH did have a significant effect when tested in the afternoon. Both TRH and TRH-OH caused dose dependent increases in locomotor activity, whereas DKP and the two analogues had no effect. This stimulation of activity was shown to be at least partly mediated by dopamine since locomotor enhancement was blocked in a second experiment using the dopamine antagonist alpha-Flupenthixol. The results are discussed in terms of actions on the mesolimbic dopamine system, and the importance of circadian variations within this system to the expression of peptide effects in general.     

The role of adrenocorticotropic hormone in inhibition of pain reaction in awake rats

The effect of hormones of hypothalamic-pituitary-adrenocortical system on pain sensitivity were studied in experiments on awake Sprague-Dawley males rats. Pain sensitivity was tested by tail flick reaction induced by thermal stimuli. Systemic glucocorticoids and ACTH injection increased the tail flick latency. The ACTH-induced analgesic effect was unaffected by deficiency of glucocorticoids production in pretreatment with pharmacological dose of cortisol but was fully eliminated by pretreatment with opiate antagonist naltrexone. These findings suggest that ACTH-induced analgesic effect is mediated by opiate receptors but not by glucocorticoids released in response to ACTH injection.     

A mutant protein of human interleukin-1 beta with immunostimulatory but not pyrogenic potency

Interleukin-1 (IL-1) mediates a variety of immune and inflammatory responses. In order to understand the mechanisms involved in multiple biological functions, it is important to define the active sites of IL-1. Using the technique for site-specific mutagenesis, we tested whether the arginine residue at the 4th position in human IL-1 beta is essential for multiple biological activities. In our experiments, the fourth position is replaced by a non-basic amino acid--either glycine or aspartic acid. The resulting mutant protein shows both immunostimulatory activity and the ability to induce hematopoietic growth factors similar to native IL-1 beta, but has a markedly reduced pyrogenic potency. Therefore, the mutant protein of IL-1 beta may represent a good candidate for use in vivo as an adjuvant for poor immunogenic vaccines.     

Interleukin-1 inhibits the secretion of gastric acid in rats: possible involvement of prostaglandin

To examine the hypothesis that interleukin-1 may inhibit the secretion of gastric acid, the present study was carried out using pylorusligated rats. Based upon three lines of evidence, we report here that interleukin-1, both endogenously released and exogenously administered, suppresses gastric acid secretion and that the interleukin-1-induced inhibition of acid output is possibly mediated by prostaglandin. First, lipopolysaccharide, a potent stimulant of the release and production of endogenous interleukin-1, caused the suppression of gastric acid, and this response was dose-related. Second, the intraperitoneal injection of interleukin-1 resulted in a dose-related inhibition of gastric acid output. Third, the administration of indomethacin completely blocked the suppression of gastric acid secretion induced by interleukin-1. These results demonstrated for the first time that IL-1 might be involved in the regulation of gastric secretion.