Adrenergic stimulation decreases osteoblast oxytocin synthesis

Oxytocin effects on osteoblastic differentiation of Bone Marrow Mesenchymal Stem Cells from adult and aging female Wistar rats

Recently, it has been suggested that oxytocin (OT) might play a role in the control of bone remodeling and in bone health of young and adult females. The purpose of this study was to evaluate the effect of osteogenic medium (OM) plus OT (OM + OT; 100 nmol/L) on osteoblastic differentiation of bone marrow mesenchymal stem cells (BMMSCs) from cyclic adult (12 months old) and acyclic aging (24 months old) female Wistar rats. After 14 days, OM + OT increased the oxytocin and oxytocin receptor in the BMMSCs from animals of both age groups relative to OM controls. Alkaline phosphatase activity was higher in the OM + OT than OM group in BMMSCs from 24-month-old female rats. OM + OT improved osteogenic differentiation, observed by anticipated mineralization and increased gene expression of bone morphogenetic protein 2, bone sialoprotein, osteopontin and osteocalcin in both aged relative to OM controls. These findings suggest a role for OT as an adjuvant to induce osteoblastic differentiation of BMMSCs from aged female rat.

Effects of fenoterol on the skeletal system depend on the androgen level

BACKGROUND

The role of sympathetic nervous system in the osseous tissue remodeling is not clear enough.

METHODS

The effects of fenoterol, a selective β₂-adrenomimetic drug, on the skeletal system of normal and androgen deficient (orchidectomized) rats were studied in vivo. Osteoclastogenesis and mRNA expression in osteoblasts were investigated in vitro in mouse cell cultures.

RESULTS

Fenoterol administered to animals with physiological androgen level unfavorably affected the skeletal system, damaging the bone microarchitecture. Androgen deficiency induced osteoporotic changes, and fenoterol protected the osseous tissue from consequences of androgen deficiency. The results of in vitro studies correlated with the in vivo observations. A significantly increased number of osteoclasts in bone marrow cell cultures to which testosterone and fenoterol were added simultaneously was demonstrated. In cultures without the addition of testosterone, fenoterol significantly inhibited osteoclastogenesis in comparison with control cultures.

CONCLUSIONS

The results indicate the favorable action of fenoterol in conditions of testosterone deficiency, and its destructive influence upon the skeleton in the presence of androgens. The results confirm the key role of sympathetic nervous system in the regulation of bone remodeling.

Extracellular norepinephrine clearance by the norepinephrine transporter is required for skeletal homeostasis

Changes in bone remodeling induced by pharmacological and genetic manipulation of β-adrenergic receptor (βAR) signaling in osteoblasts support a role of sympathetic nerves in the regulation of bone remodeling. However, the contribution of endogenous sympathetic outflow and nerve-derived norepinephrine (NE) to bone remodeling under pathophysiological conditions remains unclear. We show here that differentiated osteoblasts, like neurons, express the norepinephrine transporter (NET), exhibit specific NE uptake activity via NET and can catabolize, but not generate, NE. Pharmacological blockade of NE transport by reboxetine induced bone loss in WT mice. Similarly, lack of NE reuptake in norepinephrine transporter (Net)-deficient mice led to reduced bone formation and increased bone resorption, resulting in suboptimal peak bone mass and mechanical properties associated with low sympathetic outflow and high plasma NE levels. Last, daily sympathetic activation induced by mild chronic stress was unable to induce bone loss, unless NET activity was blocked. These findings indicate that the control of endogenous NE release and reuptake by presynaptic neurons and osteoblasts is an important component of the complex homeostatic machinery by which the sympathetic nervous system controls bone remodeling. These findings also suggest that drugs antagonizing NET activity, used for the treatment of hyperactivity disorders, may have deleterious effects on bone accrual.

Nocturnal oxytocin secretion is lower in amenorrheic athletes than nonathletes and associated with bone microarchitecture and finite element analysis parameters

OBJECTIVE

Preclinical data indicate that oxytocin, a hormone produced in the hypothalamus and secreted into the peripheral circulation, is anabolic to bone. Oxytocin knockout mice have severe osteoporosis, and administration of oxytocin improves bone microarchitecture in these mice. Data suggest that exercise may modify oxytocin secretion, but this has not been studied in athletes in relation to bone. We therefore investigated oxytocin secretion and its association with bone microarchitecture and strength in young female athletes.

DESIGN

Cross-sectional study of 45 females, 14-21 years (15 amenorrheic athletes (AA), 15 eumenorrheic athletes (EA), and 15 nonathletes (NA)), of comparable bone age and BMI.

METHODS

We used high-resolution peripheral quantitative CT to assess bone microarchitecture and finite element analysis to estimate bone strength at the weight-bearing distal tibia and non-weight-bearing ultradistal radius. Serum samples were obtained every 60  min, 2300-0700  h, and pooled for an integrated measure of nocturnal oxytocin secretion. Midnight and 0700  h samples were used to assess diurnal variation of oxytocin.

RESULTS

Nocturnal oxytocin levels were lower in AA and EA than in NA. After controlling for estradiol, the difference in nocturnal oxytocin between AA and NA remained significant. Midnight and 0700  h oxytocin levels did not differ between groups. At the tibia and radius, AA had impaired microarchitecture compared with NA. In AA, nocturnal oxytocin correlated strongly with trabecular and cortical microarchitecture, particularly at the non-weight-bearing radius. In regression models that include known predictors of microarchitecture in AA, oxytocin accounted for a substantial portion of the variability in microarchitectural and strength parameters.

CONCLUSIONS

Nocturnal oxytocin secretion is low in AA compared with NA and associated with site-dependent microarchitectural parameters. Oxytocin may contribute to hypoestrogenemic bone loss in AA.