Gender differences and the effect of different endocrine situations on the NOS expression pattern in the anterior pituitary gland

Nitric Oxide Plays a Key Role in Ovariectomy-Induced Apoptosis in Anterior Pituitary: Interplay between Nitric Oxide Pathway and Estrogen

Changes in the estrogenic status produce deep changes in pituitary physiology, mainly because estrogens (E2) are one of the main regulators of pituitary cell population. Also, E2 negatively regulate pituitary neuronal nitric oxide synthase (nNOS) activity and expression and may thereby modulate the production of nitric oxide (NO), an important regulator of cell death and survival. Little is known about how ovary ablation affects anterior pituitary cell remodelling and molecular mechanisms that regulate this process have not yet been elucidated. In this work we used freshly dispersed anterior pituitaries as well as cell cultures from ovariectomized female rats in order to study whether E2 deficiency induces apoptosis in the anterior pituitary cells, the role of NO in this process and effects of E2 on the NO pathway. Our results showed that cell activity gradually decreases after ovariectomy (OVX) as a consequence of cell death, which is completely prevented by a pan-caspase inhibitor. Furthermore, there is an increase of fragmented nuclei and DNA cleavage thereby presenting the first direct evidence of the existence of apoptosis in the anterior pituitary gland after OVX. NO production and soluble guanylyl cyclase (sGC) expression in anterior pituitary cells increased concomitantly to the apoptosis. Inhibition of both, NO synthase (NOS) and sGC activities prevented the drop of cell viability after OVX, showing for the first time that increased NO levels and sGC activity observed post-OVX play a key role in the induction of apoptosis. Conversely, E2 and prolactin treatments decreased nNOS expression and activity in pituitary cells from OVX rats in a time- and E2 receptor-dependent manner, thus suggesting interplay between NO and E2 pathways in anterior pituitary.

Methylmercury inhibits prolactin release in a cell line of pituitary origin

Heavy metals, such as methylmercury, are key environmental pollutants that easily reach human beings by bioaccumulation through the food chain. Several reports have demonstrated that endocrine organs, and especially the pituitary gland, are potential targets for mercury accumulation; however, the effects on the regulation of hormonal release are unclear. It has been suggested that serum prolactin could represent a biomarker of heavy metal exposure. The aim of this study was to evaluate the effect of methylmercury on prolactin release and the role of the nitrergic system using prolactin secretory cells (the mammosomatotroph cell line, GH3B6). Exposure to methylmercury (0-100 μM) was cytotoxic in a time- and concentration-dependent manner, with an LC₅₀ higher than described for cells of neuronal origin, suggesting GH3B6 cells have a relative resistance. Methylmercury (at exposures as low as 1 μM for 2 h) also decreased prolactin release. Interestingly, inhibition of nitric oxide synthase by N-nitro-L-arginine completely prevented the decrease in prolactin release without acute neurotoxic effects of methylmercury. These data indicate that the decrease in prolactin production occurs via activation of the nitrergic system and is an early effect of methylmercury in cells of pituitary origin.

Endocrine cells and blood vessels work in tandem to generate hormone pulses

Hormones are dynamically collected by fenestrated capillaries to generate pulses, which are then decoded by target tissues to mount a biological response. To generate hormone pulses, endocrine systems have evolved mechanisms to tightly regulate blood perfusion and oxygenation, coordinate endocrine cell responses to secretory stimuli, and regulate hormone uptake from the perivascular space into the bloodstream. Based on recent findings, we review here the mechanisms that exist in endocrine systems to regulate blood flow, and facilitate coordinated cell activity and output under both normal physiological and pathological conditions in the pituitary gland and pancreas.

Functional importance of blood flow dynamics and partial oxygen pressure in the anterior pituitary

The pulsatile release of hormone is obligatory for the control of a range of important body homeostatic functions. To generate these pulses, endocrine organs have developed finely regulated mechanisms to modulate blood flow both to meet the metabolic demand associated with intense endocrine cell activity and to ensure the temporally precise uptake of secreted hormone into the bloodstream. With a particular focus on the pituitary gland as a model system, we review here the importance of the interplay between blood flow regulation and oxygen tensions in the functioning of endocrine systems, and the known regulatory signals involved in the modification of flow patterns under both normal physiological and pathological conditions.

Interleukin-6 and Nitric Oxide Synthase Expression in the Vasopressin and Corticotrophin-releasing Factor Systems of the Rat Hypothalamus

Nitric oxide synthase (NOS) and interleukin-6 (IL-6) are constitutively expressed in hypothalamic cells. However, phenotypic and functional aspects of these cells remain unknown. We have studied the expression pattern of these two molecules in hypothalamic cells expressing corticotropin-releasing factor (CRF) and arginin-vasopressin (AVP), two major regulatory peptides in the hypothalamus-pituitary system, using immunofluorescence, intracerebroventricular injection of colchicine, and the study in parallel of the labeling pattern of axons in the median eminence. Within AVP cells, we distinguished two different populations: large, intensely stained AVP cells coexpressing IL-6; and large, intensely stained AVP cells coexpressing IL-6 and NOS. Within the CRF cells, we distinguished three different populations: large, intensely stained CRF cells immunonegative for AVP, NOS, and IL-6; large cells weakly stained for CRF and AVP, immunopositive for NOS and immunonegative for IL-6; and small cells intensely stained for CRF and AVP and immunonegative for IL-6 and NOS. In addition, we also found AVP cells containing IL-6 in the suprachiasmatic nucleus. These results suggest that neuronal NOS and IL-6 may be involved in different modulatory processes in hypophysiotropic and non-hypophysiotropic cells.

Changes in renal hemodynamics and structure in the aging kidney; sexual dimorphism and the nitric oxide system

With advancing age the kidney shows both functional declines (falls in GFR) and development of structural damage. In most individuals this occurs slowly and does not lead to severe renal impairment unless additional insults are superimposed. There is a pronounced sexual dimorphism with females protected, due both to beneficial effects of the estrogens and damaging effects of androgens, some of which act directly on the glomerular mesangial cell to regulate growth and extracellular matrix production. Nitric oxide is a major factor in regulation of vascular tone and growth and becomes deficient with advancing age, as endothelial dysfunction develops. Although the abundance of the substrate, L-arginine, is well maintained during aging, there are increases in the concentration of circulating endogenous nitric oxide synthase (nNOS) inhibitors, which will contribute, to the endothelial dysfunction. There is a clear sexual dimorphism in the NO system, with pre-menopausal females producing more NO than men. Within the kidney, declines in the abundance and activity of the neuronal form of the nitric oxide synthase (nNOS) correlate with development of disease. In the male rat where injury and dysfunction occurs, nNOS abundance declines markedly, whereas in the protected female, renal nNOS abundance is maintained. Taken together, it is likely that age-dependent declines in NO generation contribute to age-dependent kidney damage.

Roles of estrogen receptor alpha and androgen receptor in the regulation of neuronal nitric oxide synthase

In brain and peripheral tissues, steroid hormones regulate nitric oxide synthase (nNOS). We asked whether estrogen receptor-alpha (ERalpha) and/or androgen receptor (AR) regulated nNOS immunoreactivity in mouse brain. First, we quantified cells singly labeled for nNOS immunoreactivity or labeled dually with ERalpha-immunoreactive (-ir) or AR-ir cells in the nucleus accumbens (Acb), preoptic area (POA), bed nucleus of the stria terminalis (BNST), posterior dorsal and posterior ventral regions of the medial amygdala (MePD and MePV, respectively), and paraventricular nucleus (PVN). The POA and MePD contained the greatest number of double-labeled cells. More nNOS-ir cells were colabeled with ERalpha immunoreactivity compared with AR immunoreactivity. Next, by using a double mutant mouse in which males lacked functional ERalpha, AR, or both, we investigated the roles of these steroid receptors in nNOS-ir cell numbers and immunoreactive area staining under testosterone (T) and estradiol (E2) conditions. Our data show that functional ERalpha is correlated with more nNOS-ir cells under T conditions and more immunoreactive area staining in the POA under both T and E2 conditions. However, ERalpha decreases nNOS-ir cell number in the BNST under E2 treatment. In summary, the data suggest that AR has organizational actions on nNOS-ir cell numbers in the MePV, that interactions between ERalpha and AR genes occur in PVN, and that sex differences in nNOS-ir area staining are limited to the POA. Thus, we show that ERalpha and AR interact to regulate nNOS in male and female brain in a site-specific manner.