Incubation of ex vivo cultured mature B cells in the presence of nitric oxide or nitric oxide-donor substances delays programmed cell death as determined by the appearance of DNA laddering in agarose gel electrophoresis or by flowcytometry analysis of DNA. Nitric oxide also rescues B cells from antigen-induced apoptosis but fails to provide a costimulatory signal that converts the signal elicited by the antigen into a proliferative response. The protective effects of nitric oxide against programmed cell death can be reproduced by treatment of the cells with permeant analogues of cyclic GMP. Regarding the mechanisms by which nitric oxide prevents apoptosis in B cells, we have observed that nitric oxide release prevents the drop in the expression of the protooncogene bcl-2, both at the mRNA and protein levels, suggesting the existence of an unknown pathway that links nitric oxide signaling with Bcl-2 expression. (J. Clin.

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The induction of hepatic nitric oxide synthase (NOS) and the biosynthesis of nitric oxide (NO) were studied in liver after partial hepatectomy (PH). NOS activity in the liver remnant was observed 4 to 6 hours after PH, and no differences were evidenced between the proximal and distal surgical areas. The form of NOS expressed in liver was independent of calcium and calmodulin, and the messenger RNA levels were first detected 2 hours after hepatectomy using a probe corresponding to the cytokine-induced macrophage NOS. The seric concentration of nitrites remained unchanged after hepatectomy, whereas the content in nitrates and in S-nitrosylated proteins progressively increased in parallel with the NOS activity. The spectra of hemoglobin in the 400-to 460-nm region failed to exhibit the characteristic shift caused by the formation of the nitrosyl-hemoglobin complex, suggesting that NO was rapidly metabolized in liver. Treatment of the animals with substrate analogue NOS inhibitors blocked the pattern of DNA ploidy elicited after hepatectomy, suggesting a role for NO in the regenerative process. Peritoneal resident macrophages were used as an alternative reporter cell system for the assessment of NOS expression. Incubation ex vivo of peritoneal macrophages from animals that underwent hepatectomy induced the expression of NOS in a cytokine-modulated fashion, suggesting that macrophages were primed as a result of the hepatectomy. When peritoneal macrophages from control rats were incubated with the sera of animals that underwent hepatectomy, a time-dependent induction of NOS was observed, with a maximal induction corresponding to sera collected 2 hours after PH. These results indicate that NO might be involved in the control of early responses after PH.

Thyroid hormones play critical roles in differentiation, growth and metabolism, but their participation in immune system regulation has not been completely elucidated. Modulation of in vivo thyroid status was used to carry out an integrative analysis of the role of the hypothalamus-pituitary-thyroid (HPT) axis in T and B lymphocyte activity. The participation of the protein kinase C (PKC) signaling pathway and the release of some cytokines upon antigenic stimulation were analyzed. Lymphocytes from hyperthyroid mice displayed higher Tand B-cell mitogen-induced proliferation, and those from hypothyroid mice displayed lower T-and B-cell mitogeninduced proliferation, compared with euthyroid animals. Reversion of hypothyroid state by triiodothyronine (T3) administration recovered the proliferative responses. No differences were found in lymphoid subset balance. Both total PKC content and mitogen-induced PKC translocation were higher in T and B cells from hyperthyroid mice, and lower in cells from hypothyroid mice, compared with controls. Levels of thyroid-stimulating (TSH) and TSHreleasing (TRH) hormones were not directly related to lymphocyte proliferative responses. After immunization with sheep red blood cells (SRBCs) and re-stimulation, in vitro spleen cells from hyper-or hypothyroid mice showed, respectively, increased or decreased production of interleukin (IL)-2 and interferon (IFN)-cytokines. Additionally, an increase in IL-6 and IFN-levels was found in hyperthyroid cells after in vivo injection and in vitro re-stimulation with lipopolysaccharide (LPS).Our results show for the first time a thyroid hormonemediated regulation of PKC content and of cytokine production in lymphocytes; this regulation could be involved in the altered responsiveness to mitogen-induced proliferation of T and B cells. The results also confirm the important role that these hormones play in regulating lymphocyte reactivity.

It has previously been shown that alcohol can suppress reproduction in humans, monkeys, and small rodents by inhibiting release of luteinizing hormone (LH). The principal action is via suppression of the release of LH-releasing hormone (LHRH) both in vivo and in vitro. The present experiments were designed to determine the mechanism by which alcohol inhibits LHRH release. Previous research has indicated that the release of LHRH is controlled by nitric oxide (NO). The Alcohol suppresses reproductive function in humans, monkeys, and small rodents, such as the rat (1-4). In the rat,The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 3416 chronic administration of alcohol not only inhibits the estrous cycle but it can also delay onset of puberty (4, 5). In conscious animals, administration of alcohol via an indwelling gastric cannula in doses that produce mild intoxication inhibits pulsatile release of luteinizing hormone (LH), but not folliclestimulating hormone, within a few minutes (4). In this situation, the responsiveness of the pituitary gland to acute injection of LH-releasing hormone (LHRH) is unaffected, which shows that the mechanism of this effect is via suppression of the pulsatile LHRH release into the hypophyseal portal vessels that triggers release of LH from the gonadotropes of the adenohypophysis. The interference with estrous cycles and the delayed onset of puberty in the female rat is likely brought about by this suppression by ethanol of LHRH release (5). Secretion of LH is required to stimulate the ovary to produce ovarian steroids responsible for the estrous cycle, and the onset of puberty is consequently delayed.We have recently shown that nitric oxide (NO) controls the release of LHRH both in vivo and in vitro (6). On the basis of in vitro experiments employing incubation of medial basal hypothalamic (MBH) explants in a static incubation system, it has been determined that norepinephrine activates constitutive NO synthase (NOS) in neurons in this region (NOergic neurons) (6, 7). The NO released from these neurons diffuses to LHRH terminals, where it induces the release of LHRH, probably by activating cyclooxygenase 1. The activated cyclooxygenase then converts arachidonate into prostaglandin E2 (PGE2) (8). PGE2 activates adenylate cyclase, causing generation of cAMP, which acts via protein kinase A to evoke exocytosis of LHRH granules into the hypophyseal portal vessels for its delivery to the anterior pituitary gland (9, 10). The LHRH acts on the gonadotropes and causes a pulse of LH release. Support for this theoretical pathway stems from the ability of inhibitors of NOS, such as NG-monomethyl-Larginine, to inhibit LHRH release, whereas releasers of NO, such as sodium nitroprusside (NP), induce LHRH release both in vitro and in vivo (6-9).We have identified the site of inhibitory action of interleukin 1 (IL-1) on LHRH release...

Autoimmune thyroid diseases (AITD) are the most common organ-specific autoimmune disorders affecting approximately 5% of the overall population. An aberrant interaction between abnormal thyrocytes, abnormal antigen-presenting cells and abnormal T cells forms the basis for the atypical autoimmune reaction targeting thyroid antigens. It was proposed that nongenetic (environmental and hormonal) factors play a crucial etiological role in AITD development, through altering immune-endocrine interactions. The most outstanding fact is that in genetically predisposed individuals, the disruption of these neuroendocrine-immune interactions by environmental factors results in thyroid autoimmune dysfunction. These interactions are able to incline the balance between Th1-Th2 immune response toward one side, resulting in a Th1-cell-mediated autoimmune reaction with thyrocyte destruction and hypothyroidism in Hashimoto’s thyroiditis but to a hyperreactive Th2-mediated humoral response against TSH receptor with stimulatory antibodies leading to Graves’ disease hyperthyroidism. In this review the main mechanisms involved are summarized. In this sense, the participation of stress-mediated activation of the sympathoadrenal system and hypothalamic-pituitary-adrenal axis, the hormonal changes occurring during pregnancy and postpartum acting on antigen-presenting cells and influencing, in this way, the balance of the immune status are shown to participate in AITD etiology. The possibility that altered levels of thyroid hormones during the course of the AITD may alter immune function is also discussed.

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Incubation of peritoneal macrophages with /3-phorbol 12,13-dibutyrate promotes a time-dependent release of NO to the incubation medium. This effect was antagonized by LPS, a well known inducer of nitric oxide synthase (NOS) expression in macrophages, and was inhibited by .V"-methylt_-arginine and N"-nitro-L-arginine. An increase in intracellular cGMP and NOS activity was observed in parallel with NO release. The induction of NOS was accompanied by a stimulation of arginine influx within the cell. These results suggest that activation of protein kinase C by phorbol esters is sufficient to promote NOS induction in macrophages.Nitric oxide; Phorbol ester; Protein kinase C; Macrophage