Vascular responses to neuropeptide Y in the rat: effect of age

Neuropeptide Y Y2 antagonist treated ovariectomized mice exhibit greater bone mineral density

Osteoporosis, a disease characterized by progressive bone loss and increased risk of fracture, often results from menopausal loss of estrogen in women. Neuropeptide Y has been shown to negatively regulate bone formation, with amygdala specific deletion of the Y2 receptor resulting in increased bone mass in mice. In this study, ovariectomized (OVX) mice were injected once daily with JNJ-31020028, a brain penetrant Y2 receptor small molecule antagonist to determine the effects on bone formation. Antagonist treated mice had reduced weight and showed increased whole-body bone mineral density compared to vehicle-injected mice. Micro computerized tomography (micro-CT) demonstrated increased vertebral trabecular bone volume, connectivity density and trabecular thickness. Femoral micro-CT analysis revealed increased bone volume within trabecular regions and greater trabecular number, without significant difference in other parameters or within cortical regions. A decrease was seen in serum P1NP, a measure used to confirm positive treatment outcomes in bisphosphonate treated patients. C-terminal telopeptide 1 (CTX-1), a blood biomarker of bone resorption, was decreased in treated animals. The higher bone mineral density observed following Y2 antagonist treatment, as determined by whole-body DEXA scanning, is indicative of either enhanced mineralization or reduced bone loss. Additionally, our findings that ex vivo treatment of bone marrow cells with the Y2 antagonist did not affect osteoblast and osteoclast formation suggests the inhibitor is not affecting these cells directly, and suggests a central role for compound action in this system. Our results support the involvement of Y2R signalling in bone metabolism and give credence to the hypothesis that selective pharmacological manipulation of Y2R may provide anabolic benefits for treating osteoporosis.

The localization of calcitonin gene-related peptide in the human trigeminal ganglion and masseter muscle

The localization of calcitonin gene-related peptide (CGRP) is similar to that of a neurotransmitter which indicates masticatory muscle pain in the area of the masseter fascia. CGRP is released from the trigeminal ganglion (TG). The aim of this study was to analyze the distribution of CGRP in the fascia of the masseter muscle (FMM) and TG in a morphometric manner, with respect to the location and density of CGRP-immunopositive reaction fiber (CGRP-IRF). A higher number of the CGRP-IRF were mainly found located around elongated blood vessels and small nerves on the origin side of the middle zone FMM in the O group (presented with occlusion). In the sectional histochemical analysis of the O group, the CGRP-IRF were clearly detected in oval vessels, large elongated vessels and large nerves in contrast with that of the Non-O group (presented with no occlusion) samples. The number of CGRP-immunopositive ganglion cells (CGRP-IPGCs) in the O group mandibular nerve division was higher than that of other divisions. A reduction of the CGRP-IRF numbers were found in the no-loading groups. The characterization of these locations of CGRP-IPGCs can also provide useful data for the understanding of myofascial pain syndrome of the masseter muscle (MM).

Neuropeptide Y overflow and metabolism in skeletal muscle arterioles

The purpose of this study was to characterize neuropeptide Y (NPY) overflow and metabolism from isolated skeletal muscle arterioles of female rats. Gastrocnemius first-order arterioles were removed from young (2 months), young adult (6 months) and middle-aged (12 months) F344 female rats. Arterioles were isolated, cannulated and pressurized in a microvessel bath with field stimulation electrodes. NPY overflow from isolated arterioles was assessed at 0 s and 30 s post-field stimulation. Dipeptidyl peptidase IV (DPPIV) activity was quantified via fluorometric assay of whole vessel homogenate. In young adult and middle-aged rats, NPY overflow increased 0 s and 30 s following field stimulation. In young adult rats, DPPIV inhibition resulted in an increase in NPY overflow at 30 s, while middle-aged rats had no increase in NPY overflow with DPPIV inhibition (P <0.05). DPPIV activity was influenced by factors such as age, vessel type, and endothelium (P <0.05). The present data suggest that DPPIV plays a significant role in modulating the actions of NPY in arterioles of young adult females; however, this role appears to diminish with age.

Melatonin receptors mediate potentiation of contractile responses to adrenergic nerve stimulation in rat caudal artery

The hormone melatonin potentiated contractile responses to adrenergic nerve stimulation in isolated ring segments of rat caudal artery. This effect was inhibited by the melatonin receptor antagonist luzindole but not by the serotonin 5-HT2 receptor antagonist ketanserin. Melatonin had no direct effects on vascular tone. Melatonin agonists potentiated contractile responses with a relative order of potency (2-iodomelatonin, EC50 = 0.6 nM; melatonin, EC50 = 4.7 nM; N-acetylserotonin, EC50 = 1.5 microM) that is consistent with the melatonin ML1 receptor subtype. Melatonin also potentiated contractions elicited by exogenous norepinephrine and produced its effects in the absence of an intact endothelium. These data suggest that melatonin acts on receptors in the smooth muscle. The caudal artery provides a useful functional assay for pharmacological analysis of melatonin receptors. Physiologically, melatonin may activate its receptors at night to influence thermoregulation in the rat by enhancing the effects of sympathetic input to the caudal artery.

Cocaine promotes an apparent direct vasoconstrictor effect of neuropeptide Y in the rat tail artery

Neuropeptide Y is a powerful vasoconstrictor in vivo; however, in vitro it shows weak constrictor effects. This discrepancy may have led to conflicting reports concerning the contractile effects of neuropeptide Y on isolated blood vessels. Using isolated rat tail and femoral artery segments neuropeptide Y (0.1-100 nM) did not induce any contractile response. However, if the catecholamine neuronal uptake blocker cocaine was added to the tissue bath, neuropeptide Y induced a contraction which could be fully blocked by prazosin (1000 nM). Furthermore, an age-dependent increase in the contraction to neuropeptide Y plus cocaine was observed. In conclusion, in the rat tail artery an apparent direct vasoconstrictor effect of neuropeptide Y occurs only in the presence of cocaine. Since this contraction can be fully blocked by prazosin, spontaneously released norepinephrine is an important component of the contraction. The discrepancy between in vivo and in vitro effects of neuropeptide Y may be explained in part by the presence of circulating vasoconstrictors.