Role of nitric oxide in the metabolism of arachidonic acid in the rat anterior pituitary gland

Cadmium as an endocrine disruptor: correlation with anterior pituitary redox and circadian clock mechanisms and prevention by melatonin

To examine the effect of a low dose of cadmium (Cd) as an endocrine disruptor, male Wistar rats received CdCl2 (5ppm Cd) in drinking water or drinking water alone. After 1 month, the rats were euthanized at one of six time intervals around the clock and the 24-h pattern of adenohypophysial prolactin (PRL) synthesis and release, lipid peroxidation, and redox enzyme and metallothionein (MT) gene expression was examined. Cd suppressed 24-h rhythmicity in expression of the PRL gene and in circulating PRL by increasing them at early photophase only, in correlation with an augmented pituitary lipid peroxidation and redox enzyme expression. CdCl2 treatment effectively disrupted the 24-h variation in expression of every pituitary parameter tested except for MT-3. In a second experiment the effect of melatonin (3μg/ml in drinking water) was assessed at early photophase, the time of maximal endocrine-disrupting effect of Cd. Melatonin treatment blunted the effect of Cd on PRL synthesis and release, decreased Cd-induced lipid peroxidation, and counteracted the effect of Cd on expression of most redox enzymes. A third experiment was performed to examine whether melatonin could counteract Cd-induced changes in the 24-h pattern of pituitary circadian clock gene expression and plasma PRL, luteinizing hormone (LH), thyrotropin (TSH), and corticosterone levels. Rats receiving CdCl2 exhibited a suppressed daily rhythm of Clock expression and a significant disruption in daily rhythms of pituitary Bmal1, Per1, Per2, Cry1, and Cry2. The coadministration of melatonin restored rhythmicity in Clock and Bmal1 expression but shifted the maxima in pituitary Per1, Cry1, and Cry2 expression to the scotophase. Melatonin also counteracted the effect of Cd on 24-h rhythmicity of circulating PRL, LH, TSH, and corticosterone. The results highlight the occurrence of a significant endocrine disruptor effect of a low dose of Cd. Generally melatonin counteracted the effects of Cd and ameliorated partially the circadian disruption caused by the pollutant.

24-Hour rhythm in gene expression of nitric oxide synthase and heme-peroxidase in anterior pituitary of ethanol-fed rats

Chronic exposure of rats to ethanol results in significant changes in pituitary hormone secretion. However, identification of the site(s) and mechanism of action of ethanol to induce these effects remains elusive. Free radical damage at the adenohypophyseal level may play a role in the decline in serum gonadotropin levels in ethanol-fed rats. Since 24-h changes in redox state occurred, we analyzed the 24-h changes in pituitary gene expression of the prooxidant enzymes nitric oxide synthase (NOS) 1 and 2, and of heme oxygenase-1 (HO-1) enzyme, and in plasma NO(2)(-) and NO(3)(-) (NO(x)) levels, in ethanol and control rats. Male rats, 35-day-old, received a liquid diet for 4 weeks. The ethanol-fed group received a similar diet to controls except for that maltose was isocalorically replaced by ethanol. Animals were killed at six time intervals during a 24-h cycle. Anterior pituitary mRNA levels encoding NOS1, NOS2 and HO-1 were measured by real-time PCR analysis. Plasma NO(x) concentration was determined by the Griess reaction. Ethanol feeding of prepubertal rats changed significantly the 24-h pattern of expression of NOS1, NOS2 and HO-1 in the adenohypophysis and augmented NOS2 and HO-1 mRNA levels. Peak values for the three enzymes in ethanol-fed rats occurred at the beginning of the scotophase (i.e., at 21:00 h). Ethanol feeding augmented mean values plasma NO(x) levels with a maximum at 13:00 h while in controls a biphasic pattern was observed, with peaks at 09:00 h and 17:00-21:00 h. One of the mechanisms by which ethanol augments oxidative damage in the adenohypophysis may include overproduction of nitric oxide and carbon monoxide.

Atherogenic phospholipids attenuate osteogenic signaling by BMP-2 and parathyroid hormone in osteoblasts

Cardiovascular disease, such as atherosclerosis, has been associated with reduced bone mineral density and fracture risk. A major etiologic factor in atherogenesis is believed to be oxidized phospholipids. We previously found that these phospholipids inhibit spontaneous osteogenic differentiation of marrow stromal cells, suggesting that they may account for the clinical link between atherosclerosis and osteoporosis. Currently, anabolic agents that promote bone formation are increasingly used as a new treatment for osteoporosis. It is not known, however, whether atherogenic phospholipids alter the effects of bone anabolic agents, such as bone morphogenetic protein (BMP)-2 and parathyroid hormone (PTH). Therefore we investigated the effects of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) on osteogenic signaling induced by BMP-2 and PTH in MC3T3-E1 cells. Results showed that ox-PAPC attenuated BMP-2 induction of osteogenic markers alkaline phosphatase and osteocalcin. Ox-PAPC also inhibited both spontaneous and BMP-induced expression of PTH receptor. Consistently, pretreatment of cells with ox-PAPC inhibited PTH-induced cAMP production and expression of immediate early genes Nurr1 and IL-6. Results from immunofluorescence and Western blot analyses showed that inhibitory effects of ox-PAPC on BMP-2 signaling were associated with inhibition of SMAD 1/5/8 but not p38-MAPK activation. These effects appear to be due to ox-PAPC activation of the ERK pathway, as the ERK inhibitor PD98059 reversed ox-PAPC inhibitory effects on BMP-2-induced alkaline phosphatase activity, osteocalcin expression, and SMAD activation. These results suggest that atherogenic lipids inhibit osteogenic signaling induced by BMP-2 and PTH, raising the possibility that hyperlipidemia and atherogenic phospholipids may interfere with anabolic therapy.

New perspectives on the mechanisms through which nitric oxide may affect learning and memory processes

Nitric oxide (NO) has been well established as a molecule necessary for memory consolidation. Interestingly, the majority of research has focused on only a single mechanism through which NO acts, namely the up-regulation of guanylate cyclase (GC). However, since NO and NO-derived reactive nitrogen species are capable of interacting with a broad array of enzymes, ion channels and receptors, a singular focus on GC appears short-sighted. Although NO inhibits the action of a number of molecules there are four, in addition to GC, which are up-regulated by the direct presence of NO, or NO-derived radicals, and implicated in memory processing. They are: cyclic nucleotide-gated channels; large conductance calcium-activated potassium channels; ryanodine receptor calcium release (RyR) channels; and the enzyme mono(ADP-ribosyl) transferase. This review presents evidence that not only are these four molecules worthy of investigation as GC-independent mechanisms through which NO may act, but that behavioural evidence already exists suggesting a relationship between NO and the RyR channel.

In vivo protective effect of melatonin on cadmium-induced changes in redox balance and gene expression in rat hypothalamus and anterior pituitary

Cadmium (Cd) is widely used in industrial applications and is an important side contaminant of agricultural products. As an endocrine disruptor, Cd modifies pituitary hormone release. It has been shown that this metal causes oxidative stress in primary cultures of anterior pituitary cells. To examine whether Cd induces redox damage in the hypothalamic-pituitary axis in vivo and to evaluate the efficacy of the antioxidant molecule melatonin to prevent Cd activity, rats were exposed to Cd (5 p.p.m. in drinking water) with or without melatonin (3 microg/mL drinking water) for 1 month. In the anterior pituitary, Cd increased lipid peroxidation and mRNA levels for heme oxygenase-1 (HO-1) at both time intervals tested (09:00 and 01:00 hr, beginning of rest span and middle of activity span, respectively). Melatonin administration prevented the Cd-induced increase in both parameters. In the hypothalamus, Cd affected the levels of mRNA for HO-1 by decreasing it in the evening. Melatonin reduced hypothalamic HO-1 gene expression. Cd treatment augmented gene expression of nitric oxide synthase (NOS)1 and NOS2 in the pituitary whereas melatonin decreased it, impairing the activity of Cd. Exposure to Cd increased the levels of hypothalamic NOS1 mRNA at 09:00 hr and decreased the levels of NOS2 mRNA at 01:00 hr, with melatonin treatment preventing Cd effects. Cd treatment decreased plasma thyroid-stimulating hormone levels at both examined times, while melatonin reversed the effect of Cd at 09:00 hr and partially counteracted the effect at 01:00 hr. There were important variations between day and night in the expression of all the genes tested in both tissues. Melatonin treatment was effective reducing all examined effects of Cd, documenting its effectiveness to protect the rat hypothalamic-pituitary axis from the toxic metal effects.

Current concepts in the use of antioxidants for the treatment of preeclampsia

Preeclampsia is a leading cause of maternal and neonatal mortality and morbidity. It is a complex syndrome of undetermined etiologic origin, usually diagnosed during the second half of pregnancy, with clinical features of hypertension, proteinuria, and edema. No cure for preeclampsia exists, except premature delivery. There is increasing evidence that oxidative stress is an important contributing factor to the pathogenesis of preeclampsia. Oxidative stress is defined as an imbalance between reactive oxygen species (ROS), such as nitric oxide (NO*), superoxide anion (O2*-), and hydrogen peroxide (H2O2), and antioxidants, favouring an overabundance of ROS. The consequence of an overproduction of ROS can be observed as increased levels of markers of oxidative stress, such as lipid peroxides. Pregnant women affected by preeclampsia may have abnormal ROS production, particularly NO* and O2*-, abnormal levels of antioxidant defences, and increased placental lipid peroxidation. Several observations suggest that decreased bioavailability of endothelium-derived NO*, due to oxidative destruction of NO* by ROS, might contribute to the impaired endothelium-dependent vasodilatory responses and multisystemic pathology of preeclampsia, a phenomenon in which antioxidant vitamins may play a beneficial role. This review focuses on the rationale for vitamins C and E supplementation toward prevention of preeclampsia, with an emphasis on the limit of our scientific knowledge concerning the deleterious oxidative events taking place in this pathology.