Sympathetic thyroidal vasoconstriction is not blocked by a neuropeptide Y antagonist or antiserum

Increased blood pressure responses in neuropeptide Y transgenic rats

Considering the coexistence of neuropeptide Y (NPY) and norepinephrine in perivascular sympathetic nerves and the known vasoconstrictor cooperation of NPY with norepinephrine, we investigated the involvement of NPY in long-term control of cardiovascular functions using NPY transgenic (NPY-tg) rats. These rats were developed by injection of the rat (Sprague-Dawley) pronuclei with a 14.5-kb clone of the rat structural NPY gene. When compared with nontransgenic littermates, NPY concentrations were significantly increased in a number of cardiovascular tissues of NPY-tg hemizygotes. Direct basal mean arterial pressure and heart rate were not changed, but calculated total vascular resistance was significantly increased in NPY-tg subjects. Arterial pressure increases, in response to norepinephrine injection, were greater in the NPY-tg rats. Also, the hypotension and bradycardia in response to hemorrhage were significantly reduced in NPY-tg subjects. These results indicate that NPY, when expressed in increased amounts, potentiates the pressor effects of norepinephrine and contributes to maintaining blood pressure during hemorrhage, but it does not alter resting blood pressure. These transgenic rats will facilitate studies of the role of NPY signaling in cardiovascular regulation, particularly regarding its functional cooperation with norepinephrine.

The neuropeptides, VIP and NPY, that are present in the thyroid nerves are not released into the thyroid vein

In the present study, we tested the hypothesis that the neuropeptides, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), which are present in the thyroid nerves, act as physiological neurotransmitters involved in the regulation of thyroid hormone secretion and thyroid blood flow. Specifically, we examined whether these neuropeptides can be released into thyroid blood vessels by electrical stimulation of the major thyroid nerves or whether their expression is altered by changes in iodine intake. Sprague-Dawley rats were used in this study. The cervical sympathetic trunk or the superior laryngeal nerve was stimulated by bipolar electrodes in anesthetized rats. During nerve stimulation, blood samples were withdrawn from the thyroid vein. Thyroid blood flow was monitored by laser Doppler blood flowmetry. Sympathetic stimulation caused a marked decrease in thyroid blood flow, which was associated with a significant increase in release of norepinephrine. However, these effects were not accompanied by any change in NPY release into the thyroid vein. Stimulation of the superior laryngeal nerve was not associated with changes in thyroid blood flow or VIP release into the thyroid vein. In a separate experiment, rats were fed a diet containing low-, high-, or normal iodine concentrations. Triiodothyronine (T3) and thyroxine (T4) levels in thyroid venous plasma were significantly reduced in rats fed a low-iodine diet but not in a separate group of rats fed a high iodine diet. However, these treatments had no effect on VIP or NPY concentrations in thyroid venous plasma or in thyroid ganglia. Thus, our results indicate that VIP and NPY, which are present in the thyroid nerves, may not be directly involved in the regulation of thyroid function.

D-myo inositol 1,2,6, triphosphate (alpha-trinositol, pp56): selective antagonist at neuropeptide Y (NPY) Y-receptors or selective inhibitor of phosphatidylinositol cell signaling?

1. D-myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, D-myo inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes anti-inflammatory and analgesic effects and antagonism of neuropeptide Y (NPY)-mediated cellular responses. 2. However, not all responses elicited by this neuropeptide are sensitive to antagonism by pp56. Evidence is emerging, at least in certain tissues, that other receptor populations, in addition to those for NPY, are also sensitive to inhibition by pp56. 3. A direct or allosteric interaction of pp56 at receptors for NPY is now considered unlikely and it is more probable that pp56 might interfere at some point in the phosphatidylinositol signaling pathway, possibly at the level of the plasmalemmal inositol 1,3,4,5, tetrakisphosphate receptor. 4. Full realization of the therapeutic potential of this novel compound, however, must await a thorough characterization of the cellular mechanism(s) associated with the various pharmacological effects of pp56.

Neuropeptide Y in the human thyroid gland

Autonomic nerve fibers immunoreactive to Neuropeptide Y (ir-NPY) were counted in tissue samples from human thyroid glands. Samples were taken from the non-pathological parts of gland material removed surgically from nine female patients suffering from struma nodosa or solitary adenoma. The ir-NPY fiber population was subdivided into fibers associated with blood vessels (perivascular innervation) and fibers either attached to the wall epithelium of the follicles or coursing within the gland's connective tissue (extravascular innervation). Most perivascular fibers were found in arterioles (20-40 microns diam.). Capillaries (< 10 microns diam.) were not innervated. These fibers surrounded the vessels. They formed a characteristic reticular or coil-like pattern close to the tunica adventitia. Sometimes a second, smaller fiber layer was found between the tunica adventitia and media. Ir-NPY fibers were unmyelinated and less than 2 microns in diameter. Based on counts of the gland's arterial supply, it was calculated that about 23% of all arterial vessels (< 80 microns diameter) were innervated. On average, one innervated arteriole was found per 0.2 mm2 of thyroid tissue. Extravascular fibers were less frequent. In ca. 3 mm2 of thyroid tissue at least two ir-NPY fibers were found outside the vessels close to the follicular epithelium or within the connective tissue. No follicles with a dense ir-NPY innervation were found. Extravascular fibers were less arborized. They appear to be either smaller or less intensively stained than perivascular fibers, although some extravascular fibers were collaterals of the perivascular fibers.

Use of D-myo inositol 1,2,6 trisphosphate to inhibit contractile activity in rat ventricular cardiomyocytes induced by neuropeptide Y and other cardioactive peptides through phospholipase C

1. D-Myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes antagonism of a number of neuropeptide Y (NPY)-mediated cellular processes. The ability of pp56 to inhibit selectively the myocardial contraction mediated by NPY in relation to the responses to other cardioactive peptides, including endothelin-1, calcitonin gene-related peptide (CGRP), secretin and vasoactive intestinal peptide (VIP), was assessed. In order to investigate the possible interaction of pp56 with mechanisms of inositol phosphate signalling generated in heart muscle cells by activation of the beta-isoenzyme of phospholipase C (PLC beta), noradrenaline was used as a positive control, and isoprenaline and forskolin were included as negative controls. 2. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM). The concentrations of agonists used were in the region of their maximally effective concentrations for myocyte contraction and the concentration of pp56 was in the range of 1-100 microM. Contractile activity was monitored by video microscopy and maximum shortening determined by image analysis. 3. In the absence of agonist, contractile amplitudes following 20 min preincubation with pp56 were not different from that observed in the absence of pp56. Pp56 (1-100 microM) inhibited significantly the positive contractile response to noradrenaline (5 microM) in the presence of propranolol (500 nM), such that the response was almost completely attenuated at the highest concentration of the inhibitor. Pp56 did not inhibit the positive contractile responses to forskolin (40 microM) or isoprenaline (100 nM). 4. NPY alone does not influence the basal level of contraction of cardiomyocytes, but can attenuate isoprenaline-stimulated contraction and can increase contractile amplitude from basal when the transient outward current is blocked with 4-aminopyridine. In the presence of isoprenaline (100 nM), the negative response to NPY (100 nM) was attenuated significantly by pp56 (1-100 microM). With 4-aminopyridine, the positive contractile response to NPY (200 nM) was decreased by pp56, although this was not statistically significant. 5. Pp56 inhibited the positive contractile responses to CGRP (1 nM) and endothelin-1 (20 nM) completely, but did not affect the responses to secretin (20 nM) or VIP (20 nM). 6. In conclusion, these data challenge the previously obtained selectivity of pp56 as an antagonist of NPY-mediated cellular processes, since responses to CGRP and endothelin-1 were at least equally sensitive. Furthermore, as pp56 discriminated clearly in its inhibition of responses to alpha-adrenoceptor by comparison with beta-adrenoceptor/adenylate cyclase stimulation, it appears that pp56 may be a useful pharmacological agent with which to distinguish between PLC beta-dependent and PLC beta-independent coupling mechanisms. On this basis, further evidence has been obtained that, in rat cardiomyocytes, the contractile responses to NPY, CGRP and endothelin-1 are attributable to the activation of PLC beta-dependent pathways, whereas the responses to secretin and VIP are mediated by PLC beta-independent pathways.

Noradrenergic and peptidergic sympathetic regulation of cutaneous microcirculation in the rat

Cutaneous microcirculatory changes were measured by laser-Doppler flowmetry in response to electrical stimulation of sympathetic efferent fibres of the rat's saphenous nerve. After perineural capsaicin (2%) pretreatment, electrical stimulation of the peripheral stump of the cut saphenous nerve evoked a reduction in blood flow (vasoconstriction) followed by a minimal enhancement. This late vasodilatation was further reduced by resiniferatoxin (1 microg/kg i.v.), and vasoconstriction was abolished by guanethidine (8 mg/kg i.v.), indicating the involvement of sensory and sympathetic fibres in the respective responses. The vasoconstrictor response was analysed after blockade of antidromic vasodilatation by combined capsaicin-resiniferatoxin pretreatment. alpha-Adrenoceptor antagonists (1 mg/kg phentolamine, 0.5 mg/kg prazosin and 1 mg/kg GYKI-12743 (RS-2-(3)N-(2-benzo;1,4i-dioxanyl)-methylamino(propyl)-3(2H) -piridazinone hydrochloride) inhibited, but did not eliminate the blood flow reduction evoked by 3 Hz stimulation. At 10 Hz stimulation significant inhibition was obtained only with GYKI-12743. No inhibition was observed with propranolol (10 microg/kg) on any occasion. A functional neuropeptide Y antagonist, alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56; 50 mg/kg i.v.), markedly diminished the vasocontrictor response remaining after treatments with the alpha-adrenoceptor blocking agents. Inhibition was more pronounced at 10 Hz. Since 3 Hz corresponds to an average, and 10 Hz approaches the maximal firing rate of the sympathetic efferents, these results emphasise the significant role of neuropeptide Y in regulation of the cutaneous microcirculation by sympathetic fibres under physiological circumstances, particularly during high activity.

Contribution of alpha- and beta- adrenoceptors and neuropeptide-Y to autonomic dysreflexia

Modest increases in urinary bladder pressure result in acute hypertensive episodes in humans with spinal cord lesions above T5. The underlying mechanisms of this condition, referred to as autonomic dysreflexia, are not well understood. The aim of this study was to characterize the contribution of alpha- and beta-adrenoceptors as well as circulating neuropeptide-Y (NPY) to the pressor response to bladder distension in conscious cervical spinal rats. Rats were chronically instrumented with arterial and venous catheters. After 2-3 days, a complete spinal transection (C7) was performed, and the urinary bladder was catheterized: 24 h later, mean arterial pressure (MAP) responses to 5 min bladder distensions (+40) were measured under control conditions and after administration of specific autonomic antagonists. To assess the contribution of alpha and beta adrenergic mechanisms the alpha antagonist prazosin (0.45 mg/kg i.v.) and beta antagonist, propranolol (4 mg/kg i.v.), were administered individually or together. Blood samples were taken before, during and after bladder distension for determination of plasma NPY by radioimmunoassay. The pressor response to bladder distension was approximately 30 mmHg under control conditions. The response was attenuated (-38%), but not abolished, by prazosin. A similar attenuation (-41%) was observed with propranolol. There were no changes in plasma NPY in response to bladder distension. Finally, the pressor response was completely abolished by combined alpha- and beta-adrenergic blockade. These results suggest that autonomic dysreflexia is mediated exclusively by adrenergic receptors in the spinal rat. Moreover, both alpha and beta adrenergic receptors contribute to the pressor response induced by bladder distension in the conscious cervical spinal rat.

Neuropeptide Y in sympathetic co-transmission: recent advances in the search for neuropeptide Y antagonists

Since the discovery of neuropeptide Y which is co-stored and co-operate with noradrenaline (NA) in sympathetic nerve fibers, several scientific groups have searched for structures with neuropeptide Y antagonistic properties. Research has mainly focused on various peptide fragments which originate from or are related to the neuropeptide Y sequence. Some non-peptide antagonists have been proposed but they are mostly of low potency and non-selective. Our recent observations that alpha-trinositol (D-myo-inositol 1.2.6-trisphosphate) is an inhibitor of neuropeptide Y effects will hopefully lead to the development of useful non-peptide neuropeptide Y inhibitors. As a novel approach the highly selective approach of down-regulating neuropeptide Y receptors with antisense oligodeoxynucleotides is also discussed. Neuropeptide Y antagonistic agents would help us to understand the physiological role of neuropeptide Y and may serve as useful medication in circulation disorders.