Action and localization of neuropeptide Y in the human fallopian tube

Using indirect immunohistochemistry, neuropeptide Y-like immunoreactivity was found in nerve fibers around blood vessels and in the muscle layers of the human fallopian tube. Apart from a network of immunoreactive nerve fibers in connection with the luminary epithelium of the isthmus, the distribution resembled that of adrenergic, tyroxine hydroxylase immunoreactive, nerve fibers. Neuropeptide Y was found to have a dose-dependent inhibitory action on the adrenergic contractile response to field stimulation in the external longitudinal muscle layer of the isthmus. Furthermore, neuropeptide Y inhibited [3H]noradrenaline release from isthmic preparations during field stimulation, suggesting a prejunctional inhibitory action on adrenergic neurotransmission.     

Co-release of neuropeptide Y and noradrenaline from pig spleen in vivo: importance of subcellular storage, nerve impulse frequency and pattern, feedback regulation and resupply by axonal transport

The importance of subcellular storage, nerve impulse rate and pattern, and feedback regulation, as well as resupply by axonal transport for the release of noradrenaline and neuropeptide Y-like immunoreactivity, was studied in the blood perfused pig spleen in vivo. Vasoconstrictor responses were recorded as perfusion pressure changes. Subcellular fractionation experiments using sucrose density gradients showed a bimodal distribution of noradrenaline (peak concentrations at 0.8 and 1.1 M sucrose) while only one main peak of neuropeptide Y was present (at 1.1 M sucrose). Overflow suggesting release of noradrenaline and neuropeptide Y-like immunoreactivity could be detected after 10 s stimulation at 10 Hz. The ratio for the output of noradrenaline and neuropeptide Y upon continuous nerve stimulation in control animals decreased with frequency. After inhibition of noradrenaline reuptake by desipramine the vasoconstrictor response and noradrenaline output were enhanced while the corresponding overflow of neuropeptide Y was reduced by 50% at 0.5 Hz. Stimulation with the irregular or regular bursting patterns at high frequencies caused larger perfusion pressure increase and relative enhancement of neuropeptide Y output compared to noradrenaline than a continuous stimulation both before and after desipramine treatment. A similar fractional release per nerve impulse was calculated both for [3H]noradrenaline (5.6 +/- 1.0 x 10(-5) and neuropeptide Y (7.3 +/- 0.3 x 10(-5). After reserpine treatment combined with preganglionic denervation the vasoconstrictor responses were more long-lasting, neuropeptide Y release was enhanced while noradrenaline content and release were reduced by 99%. The difference in neuropeptide Y overflow between continuous and bursting types of stimulation was smaller after reserpine treatment. After prolonged intermittent stimulation with regular bursts (20 Hz) for 1 h the splenic content of neuropeptide Y was reduced by 58%, while no change was observed for noradrenaline. The maximal perfusion pressure increase upon prolonged nerve stimulation after reserpine was similar in control and reserpine-treated animals, but after reserpine the vasoconstrictor response and neuropeptide Y release were subjected to fatigue. Ligation experiments of the splenic nerves revealed the splenic neuropeptide Y content was resupplied by axonal transport with a calculated total tissue turnover time of 11 days. In contrast, axonal transport contributed only to a marginal extent for the resupply of noradrenaline.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuropeptide Y--a cotransmitter with noradrenaline and adenosine 5'-triphosphate in the sympathetic nerves of the mouse vas deferens? A biochemical, physiological and electropharmacological study

A combination of biochemical, physiological and electropharmacological methods was employed to examine the occurrence of neuropeptide Y and the pre- and postjunctional effects of this peptide on sympathetic neuromuscular transmission in the mouse vas deferens. This tissue had a high content of neuropeptide Y-like immunoreactive material, suggesting a dense innervation by neuropeptide Y-containing nerve fibres. Addition of neuropeptide Y at concentrations from 5 X 10(-9) to 5 X 10(-7) M induced both pre- and postjunctional effects in vitro. Neuropeptide Y per se induced a rise in the resting tension, and "instantly" potentiated the contractile effects of exogenous noradrenaline and of the stable adenosine 5'-triphosphate (ATP) analogue, alpha,beta-methylene ATP. Neuropeptide Y reduced the secretion of [3H]noradrenaline evoked by electrical nerve stimulation, and selectively depressed the stimulus-evoked, but not the spontaneously occurring excitatory junction potentials in smooth muscle cells. Further, neuropeptide Y reduced the amplitudes of the twitch contractions evoked by electrical field stimulation with short stimulus trains at 10 Hz, and also (although to a smaller extent) the delayed contractile response to longer trains of nerve stimuli. The pre- and postjunctional effects of neuropeptide Y were not changed by alpha- or beta-adrenoceptor blocking agents, or by tachyphylaxis to the effects of ATP, or by the calcium channel blocker nifedipine. In conclusion: sympathetic neuromuscular transmission in the mouse vas deferens may be mediated not only by noradrenaline and ATP, but also by neuropeptide Y.(ABSTRACT TRUNCATED AT 250 WORDS)     

鸟类及鼠类的胸腺、腔上囊及脾脏褪黑素受体的鉴定及意义

应用放射配体结合法检测大鼠、小鼠、仓鼠、鸡、鸭、鸽子及鹌鹑的胸腺、腔上囊及脾脏的[~(125)I]褪黑素(M)特异结合位点。结果显示鸟类及鼠类免疫器官均存在[~(125)I]M特异结合位点,并具低结合容量、高亲和力特点;动力学研究表明具可饱和性及可逆性,符合受体的结合及解离过程;特异性研究显示对M及激动剂有高度特异性,符合特异结合位点的全部条件,亚细胞分布的研究表明以细胞核含量最高,线粒体次之,且该结合位点具年龄依赖性降低。结果证实免疫器官存在根黑素受体(MR),免疫组织是M作用的靶器官,M对免疫系统的调节作用是通过免疫组织上MR直接作用的结果。     

Calcitonin gene-related peptide (CGRP) receptors are linked to cyclic adenosine monophosphate production in SK-N-MC human neuroblastoma cells

Calcitonin gene-related peptide (CGRP) stimulated cyclic adenosine monophosphate (cAMP) levels in SK-N-MC human neuroblastoma cells in a time- and concentration-dependent manner. The efficacy order for CGRPs was human alpha-CGRP = human beta-CGRP = chick CGRP greater than rat CGRP greater than human [Tyr0]CGRP. Calcitonin (CT) failed to influence cAMP production in SK-N-MC cells. [Tyr0]CGRP27-37 which by itself did not affect cAMP levels antagonized CGRP action. Saturation analysis using [125I]CGRP showed a homogeneous population of binding sites. CGRP but not CT, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) inhibited radioligand binding. Our results provide evidence that human neuroblastoma SK-N-MC cells contain highly specific CGRP receptors which are positively coupled to cAMP generation.     

Alpha- and beta-adrenergic receptors of the rat cerebral cortex and cerebral microvessels in aging, and their response to denervation.

We studied the effects of aging and norepinephrine depletion 2 weeks after unilateral locus ceruleus lesion on alpha 1-, alpha 2- and beta-adrenergic receptors by ligand binding methods in the ipsilateral and contralateral cerebral cortex of Fischer-344 rats. We also studied the effects of aging and noradrenergic denervation on beta-adrenergic receptors in isolated cerebral microvessels. We found that specific [125I]HEAT binding to alpha 1-adrenergic receptors was not affected by aging or by norepinephrine depletion. Although aging also had no effect on the density or affinity of [3H]UK-14,304 and [125I]pindolol binding to alpha 2- and beta-adrenergic receptors, the density of receptors increased significantly in all age groups after noradrenergic denervation. beta-Adrenergic receptors of cerebral microvessels also were unaffected by aging, but increased their density after noradrenergic denervation at all ages. In all instances, there were no significant effects on the affinity of ligand binding. We conclude that aging does not affect the density or the affinity of adrenergic receptors in the cerebral cortex of Fischer-344 rats, nor does it affect the response of these receptors to norepinephrine depletion.     

Frequency- and reserpine-dependent chemical coding of sympathetic transmission: differential release of noradrenaline and neuropeptide Y from pig spleen

The importance of impulse pattern and stimulation frequency for the release of noradrenaline (NA) and the coexisting peptide neuropeptide Y (NPY) in relation to vasoconstriction (perfusion-pressure increase) was studied in the blood-perfused pig spleen in vivo. Splenic nerve stimulation with intermittent bursts at high frequency (20 Hz) caused a several-fold larger release of NPY-like immunoreactivity (-LI) in relation to NA than a continuous stimulation at a low frequency (2 Hz), giving the same total number of impulses. alpha-Adrenoceptor blockade by phentolamine enhanced markedly both NA and NPY release, especially at low stimulation frequency, suggesting prejunctional adrenergic inhibition of release. Addition of propranolol unmasked a large remaining perfusion-pressure response to nerve stimulation. Reserpine treatment reduced the NA content of the spleen as well as the stimulation-evoked NA release by greater than 90%. However, the perfusion-pressure increase in response to nerve stimulation was well maintained. A marked increase in the stimulation-evoked release of NPY-LI occurred after reserpine. Adrenoceptor blockade after reserpine treatment reduced only slightly the perfusion-pressure response in parallel with a decline in NPY output. NPY caused an adrenoceptor-resistant perfusion-pressure increase at plasma concentrations that were in the same range as the maximal increase during nerve stimulations. In conclusion, the present data suggest a frequency-dependent, chemical coding of sympathetic transmission with preferential release of the classical transmitter NA at low, continuous frequencies and release of NPY, mainly at high frequencies. Reserpine treatment enhances markedly NPY release, which may explain why the functional response is largely intact in spite of adrenoceptor blockade and marked NA depletion.     

Neuropeptide Y and catecholamine synthesizing enzymes and their mRNAs in rat sympathetic neurons and adrenal glands: studies on expression, synthesis and axonal transport after pharmacological and experimental manipulations using hybridization techniques and radioimmunoassay.

The effects of reserpine treatment (10 mg/kg, i.p.) on the content of neuropeptide Y-like immunoreactivity and catecholamines were compared with the levels of mRNA coding for neuropeptide Y, tyrosine hydroxylase and phenylethanolamine N-methyltransferase in rat sympathetic neurons and adrenal gland. A reversible depletion of neuropeptide Y-like immunoreactivity was observed in the right atrium of the heart, kidney and masseter muscle, while the immunoreactive neuropeptide Y content in the stellate and lumbar sympathetic ganglia and its axonal transport in the sciatic nerve increased following reserpine. The increase in the stellate ganglion was maximal at 48 h and absent 9 days after reserpine treatment. The expression of neuropeptide Y mRNA and tyrosine hydroxylase mRNA in both the stellate and the superior cervical ganglion increased earlier than the neuropeptide Y content, with a clear cut two-fold elevation at 24 h after reserpine. The increase in both mRNAs in the superior cervical ganglion and the depletion of neuropeptide Y, but not of noradrenaline, in terminal areas was prevented after pretreatment both with a nicotinic receptor antagonist (chlorisondamine) and with surgical preganglionic denervation. A marked (75-90%) depletion of neuropeptide Y-like immunoreactivity and adrenaline in the adrenal gland, concomitant with 3-4-fold increases in neuropeptide Y mRNA and tyrosine hydroxylase mRNA expression, was present at 24 h after reserpine treatment. Also in the adrenal gland, there was a reversal of the reserpine-induced increase in neuropeptide Y mRNA and tyrosine hydroxylase mRNA and depletion of neuropeptide Y and adrenaline following splanchnic denervation. Pharmacological, ganglionic blockade prevented the depletion of neuropeptide Y and the increased expression of neuropeptide Y mRNA, but not fully, the tyrosine hydroxylase mRNA elevation. In addition, a marked decrease in phenylethanolamine N-methyltransferase mRNA levels was noted after reserpine. This decrease was reversed by denervation and by ganglionic blockade. Denervation alone led to a small but significant decrease in all mRNAs examined both in the superior cervical ganglion and the adrenal medulla. The present data suggest that the depletion of neuropeptide Y-like immunoreactivity in sympathetic nerves and in the adrenal gland after reserpine is associated with a compensatory increase in neuropeptide Y synthesis and axonal transport, most likely due to increased nicotinic receptor stimulation. Whereas the reserpine depletion of neuropeptide Y in both sympathetic nerves and adrenal gland is related to neuronal activation, adrenal but not nerve terminal depletion of catecholamines can be prevented by the ganglionic blocker chlorisondamine.4+e difference in effect of pharmacological ganglionic     

Differential changes in messenger RNA expressions and binding sites of neuropeptide Y Y1, Y2 and Y5 receptors in the hippocampus of an epileptic mutant rat: Noda epileptic rat

The anti-convulsive effects of neuropeptide Y have been suggested in several animal models of epilepsy. We have found the sustained increase of neuropeptide Y contents and the seizure-induced elevation of hippocampal messenger RNA in a novel spontaneous epileptic mutant rat: Noda epileptic rat. In the present study, we investigated the change of neuropeptide Y Y1 and Y2 receptor messenger RNA expressions and binding sites in the hippocampus following a spontaneous generalized tonic-clonic seizure of Noda epileptic rat. Furthermore, the binding sites of a more recently isolated receptor subtype, neuropeptide Y Y5 receptors, were also evaluated by receptor autoradiography. A marked elevation of neuropeptide Y immunoreactivity in the mossy fiber, and Y2-receptor up-regulation in the dentate gyrus were observed in the hippocampus of Noda epileptic rat, which coincided with the previous results of the other epileptic models. In contrast, Y1-receptor down-regulation was not found after a spontaneous seizure of Noda epileptic rat while this occurs in kindling and after kainic acid-induced seizures. [125I][Leu31, Pro34]peptide YY/BIBP 3226-insensitive (Y5 receptor) binding sites in CA1 stratum radiatum were significantly decreased following a spontaneous seizure of Noda epileptic rat. The present results suggest that a spontaneous seizure of Noda epileptic rat induces significant changes in neuropeptide Y-mediated transmission in the hippocampus via Y2 and Y5 receptors, but not Y1 receptors. Therefore, specific subset of neuropeptide Y receptor subtypes might be involved in the epileptogenesis of Noda epileptic rat.     

Release of neuropeptide Y upon haemorrhagic hypovolaemia in relation to vasoconstrictor effects in the pig

Neuropeptide Y is co-stored with noradrenaline in peripheral sympathetic nerves, but is not present in the adrenal chromaffin cells in the pig. Plasma levels of neuropeptide Y-like immunoreactivity and catecholamines were studied upon haemorrhagic shock in the anaesthetized pig. The animals were bled in two successive steps (30 and 10 ml kg^–), resulting in a reduction of the mean arterial blood pressure by 44% and 53 %, respectively. Plasma levels of noradrenaline increased abruptly after the first bleeding from 1.21 ± 0.27 to 26.5 ± 6.3 nmol 1^-1. Plasma neuropeptide Y showed a progressive increase from 62 ± 8 pmol 1^–1 in the basal state to 365 ± 98 pmol 1^–1 at 60 min after the first bleeding. After the second bleeding plasma neuropeptide Y and noradrenaline showed a largely parallel increase and finally reached levels of 2524 ± 580 pmol 1^–1 and 316 ± 117 nmol 1^–1, respectively. A veno-arterial gradient of neuropeptide Y and noradrenaline indicating local release was present over the spleen after both bleeding steps. The overflow of neuropeptide Y was delayed about 15 min compared to noradrenaline after the initial bleeding. Depletion of the neuropeptide Y content after shock in the heart and skeletal muscle supported local release also from these organs. Infusions of neuropeptide Y to obtain similar plasma concentrations as during shock (nM range) caused reduction in blood flow as determined by the radionuclide-labelled microsphere technique in several organs including spleen and skeletal muscle (threshold response at 319 ± 22 pmol 1^–1) but not in heart and brain. In conclusion, both neuropeptide Y and noradrenaline were markedly elevated in plasma upon haemorrhagic shock, suggesting release from sympathetic nerve terminals. Neuropeptide Y could therefore have a role as a sympathetic neurotransmitter, and during severe stress, circulating plasma levels are in the range where vasoconstriction is evoked by exogenous NPY.     

125I]iodomelatonin binding sites in spleens of birds and mammals.

The specific binding of [125I]iodomelatonin to duck spleen membrane preparations was studied in detail. These binding sites were stable, saturable, reversible and of high affinity. Scatchard analysis of the binding revealed a equilibrium binding constant (Kd) of 73.1 +/- 5.4 pM and a total number of binding sites (Bmax) of 3.64 +/- 1.38 fmol/mg protein. Studies on the relative binding capacities of [125I]iodomelatonin to the spleen in different species showed the following order: duck greater than chicken greater than guinea pig greater than pigeon greater than mouse. No binding site was detected in the rat spleen. The presence of [125I]iodomelatonin binding sites in the spleen of birds and mammals suggested a direct action of pineal melatonin on the immune system.     

Adrenergic receptors in bovine retinal microvessels: presence of alpha 2- and beta- but not alpha 1-receptors

In bovine retinal microvessels, alpha 1, alpha 2- and beta-adrenergic receptors were characterized by binding assay, using [3H]prazosin, [3H]para-aminoclonidine and [125I]iodocyanopindolol as radioligands, respectively. The microvessels were purified from bovine eyes by differential centrifugation through a high concentration of bovine serum albumin followed by use of a glass bead filtration technique. In the preparation, specific binding sites for [3H]para-aminoclonidine and [125I]iodocyanopindolol were observed, whereas [3H]prazosin binding was not detected. The [3H]para-aminoclonidine binding sites localized to the microvessels were characterized by high affinity and saturability (KD: 173 +/- 9 pM; Bmax: 394 +/- 11 fmol/mg protein) as well as the [125I]iodocyanopindolol binding sites (KD: 20 +/- 3 pM; Bmax: 43 +/- 4 fmol/mg protein). Furthermore, the specificity of both binding sites was pharmacologically evaluated by measuring the inhibitory effects of various adrenergic reagents on binding. The existence of alpha 2- and beta-adrenergic receptors which were characterized by high affinity, saturability and stereospecificity, leads to the hypothesis that the retinal microcirculation is under neuronal control.     

Autoradiographic distribution of tachykinin NK2 binding sites in the rat brain: comparison with NK1 and NK3 binding sites

The autoradiographic distribution of tachykinin NK(2) binding sites was determined in the adult rat brain using [(125)I]neurokinin A in the presence of either senktide (NK(3) agonist) and [Pro(9)]substance P (NK(1) agonist) or senktide and SR 140333 (NK(1) antagonist). Indeed, this radioligand labels two subtypes of NK(1) binding sites (which present a high affinity not only for SP but also for neurokinin A, neuropeptide K and neuropeptide gamma) as well as NK(3) binding sites. The distribution of NK(2) binding sites was also compared with those of NK(1) and NK(3) binding sites, these sites being labeled with [(125)I]Bolton and Hunter substance P and [(125)I]Bolton and Hunter eledoisin, respectively. In agreement with our results obtained with membranes from various brain structures, NK(2)-sensitive [(125)I]neurokinin A labeling was mainly observed in few structures including the dorsal and ventral hippocampus, the septum, the thalamus and the prefrontal cortex. The density of NK(2) binding sites was weak when compared with those of NK(1) and NK(3) binding sites. Marked differences were observed in the distributions of NK(1), NK(2) and NK(3) binding sites. These results are discussed taking into consideration differences or similarities between the distributions of NK(2)-sensitive [(125)I]neurokinin A binding sites and of their endogenous ligands (neurokinin A, neuropeptide K and neuropeptide gamma) but also local NK(2) agonist responses blocked by NK(2) antagonists. Insights on the roles of endogenous tachykinins in several brain functions are also discussed on the basis of the respective distributions of different neurokinin binding sites.     

Different regulations of dopaminergic (D1) receptors and neurotensinergic binding sites in the rat prefrontal cortex

The effects of the destruction of mixed dopamine/neurotensin (DA/NT) meso-cortical neurons were investigated by studying the development of denervation supersensitivity of DA (D1) and NT cortical post-synaptic binding sites using respectively [3H]SCH 23390 and [125I]NT as ligands. These neurons were destroyed bilaterally either by injection of 6-hydroxydopamine (6-OHDA) or by an electrolytic coagulation made in the ventral tegmental area (VTA). Five weeks later, both [3H]SCH 23390 and [125I]NT bindings were analysed by quantitative autoradiography on each lesioned animal and on corresponding controls. The chemical lesions of the VTA induced an increase in the density of the cortical NT binding sites but did not affect D1 binding sites. On the contrary, electrolytic lesions induced an increase in D1 binding sites and no change in NT binding sites. One possible explanation of these differences may be that, since chemical lesions of the VTA destroy noradrenergic (NA) ascending pathways while electrolytic lesions spare the cortical NA innervation, the observed modifications of D1 and NT cortical binding sites following their presynaptic denervation are dependent on the presence (increase in D1 receptors) or the absence (increase in NT binding sites) of the cortical NA innervation.     

Functional autoradiography of neuropeptide Y Y1 and Y2 receptor subtypes in rat brain using agonist stimulated [35S]GTPgammaS binding

Neuropeptide Y, one of the most abundant brain peptides, has been found to modulate several important biological functions via a family of G-protein coupled receptors. To investigate the localization of functional NPY receptor subtypes in the rat brain, we performed agonist-induced [35S]GTPgammaS autoradiography. The Y1/Y4/Y5 agonist Leu(31), Pro(34)-NPY increased [35S]GTPgammaS binding in several brain areas with a regional distribution consistent with that produced when labeling adjacent sections with [125I]-Leu(31), Pro(34)-PYY. The Y1 selective antagonist BIBP3226 antagonized the Leu(31), Pro(34)-NPY stimulated increase in [35S]GTPgammaS binding in all areas examined. The Y2 agonist C2-NPY stimulated [35S]GTPgamma binding in numerous brain areas with a regional distribution similar to the binding observed with [125I]-PYY 3-36. No increase in [35S]GTPgammaS binding above basal was observed in any brain area evaluated using Y4 and Y5 selective agonists. This study demonstrates abundant Y1 and Y2 receptor activation in the rat brain, while evidence for functional Y4 and Y5 receptors was not observed.     

Receptor-selective analogs demonstrate NPY/PYY receptor heterogeneity in rat brain.

Neuropeptide Y (NPY) receptors are heterogeneous, consisting of at least two subclasses, Y1 and Y2. We sought evidence for differential expression of NPY receptor subtypes in the rat brain. Tissue was incubated with 125I-peptide YY (PYY) which labels NPY and PYY binding sites. The Y1-selective agonist, p[Pro34]NPY, and the Y2-selective agonist, pNPY 13-36, were used as displacing ligands. Autoradiographic analyses of regional receptor binding demonstrated heterogeneity across brain regions. We conclude that Y1- and Y2-receptors may be independently expressed in the brain. While the predominate NPY/PYY receptor subtype in the brain is Y2, there are also Y1-receptors in some brain regions such as the superficial layers of the parietal cortex.     

Effects of cerebral lesions on binding sites for calcitonin and calcitonin gene-related peptide in the rat nucleus accumbens and ventral tegmental area.

Binding site densities of [125I]-labelled salmon calcitonin and human calcitonin gene-related peptide were investigated in the rat nucleus accumbens and ventral tegmental area by means of quantitative autoradiography following selective brain lesions. [125I]salmon calcitonin and [125I]human calcitonin gene-related peptide binding sites were highly concentrated in the accumbens, whereas the ventral tegmental area only contained [125I]salmon calcitonin binding sites. Unilateral injection of 6-hydroxydopamine into the ventral tegmental area did not alter [125I]salmon calcitonin and [125I]human calcitonin gene-related peptide binding site densities in the ipsilateral accumbens, while it produced a significant decrease in [125I]salmon calcitonin binding sites in the lesioned ventral tegmental area (-50%). In contrast, following unilateral injection of quinolinic acid into the accumbens, the densities of [125I]salmon calcitonin and [125I]human calcitonin gene-related peptide binding sites were significantly decreased in the lesioned accumbens (-57% and -56%, respectively), while [125I]salmon calcitonin binding site densities were not modified in the ipsilateral ventral tegmental area. The present study clearly suggests that [125I]salmon calcitonin and [125I]human calcitonin gene-related peptide binding sites are located on intrinsic neurons but not on the dopaminergic nerve terminals in the accumbens. Moreover, a certain proportion of [125I]salmon calcitonin binding sites could be present on dopaminergic cell bodies in the ventral tegmental area.     

Differential distribution of somatostatin receptor subtypes in rat brain revealed by newly developed somatostatin analogs.

Somatostatin receptor subtypes were labeled with the somatostatin analogs [125I]CGP 23996 and [125I]MK 678 and the distribution of these receptors in rat brain was investigated using quantitative autoradiographic techniques. [125I]CGP 23996 and [125I]MK 678 specifically label different populations of somatostatin receptors in rat brain. In a number of brain regions striking differences in the distribution of the somatostatin receptor subtypes labeled by each peptide were observed. High levels of binding sites for both [125I]CGP 23996 and [125I]MK 678 were present in the cerebral cortex, CA1 region and subiculum of the hippocampus. In contrast, high levels of [125I]MK 678 binding were found in the dentate gyrus of the hippocampus while few [125I]CGP 23996 binding sites were observed in this brain region. [125I]CGP 23996 binding was detected in the central region of the interpeduncular nucleus whereas the dorsal and lateral subnuclei of this brain area expressed mainly somatostatin receptors with high affinity for MK 678. The locus coeruleus and regions of the superior colliculus and hypothalamus selectively express [125I]MK 678-sensitive somatostatin receptors. Furthermore, limbic structures such as the lateral septum, the nucleus accumbens and ventromedial striatum had much higher levels of [125I]MK 678 binding sites than [125I]CGP 23996 binding sites. Differences in the expression of the somatostatin receptor subtypes were also detected in the substantia nigra. [125I]CGP 23996 binding was present in the pars reticulata but not the pars compacta whereas the reverse distribution for [125I]MK 678 binding sites was observed. The differential distribution of [125I]CGP 23996 and [125I]MK 678 binding sites in rat brain supports the hypothesis that these peptides selectively label different somatostatin receptor subtypes in the central nervous system.     

Influence of renal sympathectomy, sodium depletion and prostaglandin synthetase inhibition on prostaglandin production and [3H]PGE2 binding characteristics in rat kidney

The effects of renal sympathectomy (unilateral, renal microsurgical denervation), sodium depletion (hypovolaemia) and prostaglandin synthetase inhibition on the rate of prostaglandin synthesis and [3H]PGE2 binding characteristics were studied in the rat kidney. The intrarenal rate of prostaglandin synthesis was measured by monitoring the urinary excretion of 6-keto-PGF1 alpha, the stable hydration product of prostacyclin. Dietary sodium restriction was associated with a 99% decrease in urinary sodium excretion (P less than 0.001) and a 17% decrease of urine volume (n.s.). Renal denervation or sodium deprivation changed neither the rate of excretion of 6-keto-PGF1 alpha nor the density or affinity of [3H]PGE2 binding sites as compared to control. However, in sodium-depleted rats, prostaglandin synthesis inhibition, induced by naproxen, decreased the urinary excretion of 6-keto-PGF1 alpha by 40% (P = 0.011) and increased the number of [3H]PGE2 binding sites by almost 30% (P = 0.031) with no change in binding affinities as compared with sodium-depleted controls. In contrast, sulindac was not able to suppress the renal synthesis and excretion of 6-keto-PGF1 alpha, and did not modulate the [3H]PGE2 binding characteristics. The lack of effect on the excretion of 6-keto-PGF1 alpha and on the [3H]PGE2 binding characteristics supports the view that sulindac spares renal prostaglandin synthesis.     

Inhibition of neuropeptide Y-induced augmentation of noradrenaline-induced vasoconstriction by D-myo-inositol 1,2,6-trisphosphate in the rat mesenteric arterial bed

The effect of the neuropeptide Y antagonist D-myo-inositol-l,2,6-trisphosphate (α-trinositol) was tested against modulatory actions mediated by neuropeptide Y in the isolated rat mesenteric arterial bed. Neuropeptide Y (1 and 10 nM) had no direct postjunctional effects, but augmented vasoconstrictor responses to noradrenaline and to sympathetic nerve stimulation to an extent which was greater with the higher concentration of neuropeptide Y. The augmenting effect of neuropeptide Y at 1 nM on vasoconstriction induced by lower doses of noradrenaline was antagonized by α-trinositol (1 μM), producing a shift to the right of the dose-response curve. A lower concentration of α-trinositol (0.1 μM) had no inhibitory effect on responses to noradrenaline. Augmentation by the higher concentration of neuropeptide Y (10 nM) of noradrenaline-induced vasoconstriction was not affected by α-trinositol at concentrations of up to 10μM. α-Trinositol did not significantly antagonize neuropeptide Y-induced augmentation of vasoconstrictor responses to sympathetic nerve stimulation, α-Trinositol alone did not affect vasoconstrictor responses to noradrenaline, potassium, or to sympathetic nerve stimulation. In the raised-tone preparation (tone raised with methoxamine) in the presence of guanethidine (5 μM) to block sympathetic neurotransmission, perivascular nerve stimulation caused vasodilatation due to activation of sensory-motor nerves. Neuropeptide Y inhibited sensory-motor nerve induced vasodilatation in a concentration-dependent manner but this was not affected by α-trinositol (1 μM). These results suggest that α-trinositol can be a useful functional antagonist of neuropeptide Y-induced augmentation of vasoconstrictor responses to noradrenaline in the rat mesenteric arterial bed. Antagonistic effects of α-trinositol on neuropeptide Y-mediated pre-junctional inhibition of sensory-motor neurotransmission were not evident.