Acute changes in the concentrations of prostaglandin F2α (PGF) and cortisol in uterine and ovarian venous blood during PGF-induced luteolysis in cows.

Prostaglandin F2α (PGF) is considered to be the main luteolysin in cattle. We have previously demonstrated that cortisol (Cr) suppresses PGF production in non-pregnant bovine endometrium. This study was carried out to test whether exogenous PGF increases ovarian and/or uterine PGF production and to determine the temporal relationship between PGF and Cr in ovarian and uterine circulations during PGF-induced luteolysis in cows. Catheters were inserted into the ovarian vein (OV), uterine vein (UV) and jugular vein (JV) of 10 cows on Day 9 of the oestrous cycle (Ovulation = Day 0) for frequent blood collection. On Day 10, the cows were divided randomly into two groups and treated with a luteolytic dose of a PGF analogue (cloprostenol) or saline solution. Blood samples were collected at -0.25, 0, 0.25, 0.5, 1 and 2 h and then at 2-h intervals until 12 h after treatment (0 h). The basal concentrations of PGF and Cr in OV and UV plasma were not significantly different. Injection of a PGF analogue induced more than twofold increases in the levels of PGF between 0.25 and 1 h in UV plasma, but not in OV plasma. PGF increased (p < 0.05) the concentrations of Cr in OV, UV and JV plasma between 0.5 and 1 h. The Cr levels in OV, UV and JV plasma were similar. The PGF levels in UV plasma decreased after Cr reached its highest levels. The overall results suggest that the uterus rather than the ovary increases PGF production in response to PGF injection. Based on the temporal changes of PGF and Cr in the ovarian and uterine circulations, Cr may act to reduce uterine PGF production in non-pregnant cows in vivo.

Highly sensitive glucose sensor based on work function changes measured by an EMOSFET.

In this paper, glucose is potentiometrically measured by using a specific field effect transistor, the EMOSFET. In this device, glucose oxidase is immobilized within a bovine serum albumin matrix, using glutaraldehyde. This layer is deposited on the top of an electroactive Os-polyvinylpyridine layer containing horseradish peroxidase, which is used as the gate material of the FET. The basic principle of the sensor is to measure the glucose concentration by means of measuring the change in the work function of the electroactive gate due to its redox reaction with the H2O2, generated by the reaction between glucose and glucose oxidase. The change in the work function can be detected as a change in the threshold voltage of the FET. Moreover, a measuring mode called "constant current potentiometry" has been applied to improve the sensitivity of the sensor. The sensitivity of the sensor working in this mode is found to be much higher than the Nernstian value. The experimental results show that the detection limit of the sensor can be tuned depending on the value of the applied current and the glucose oxidase concentration in the gate.

Activation of cAMP signaling transiently inhibits apoptosis in vascular smooth muscle cells in a site upstream of caspase-3.

Intracellular signaling pathways that are involved in protection of vascular smooth muscle cells (VSMC) from apoptosis remain poorly understood. This study examines the effect of activators of cAMP/cGMP signaling on apoptosis in non-transfected VSMC and in VSMC transfected with c-myc (VSMC-MYC) or with its functional analogue, E1A-adenoviral protein (VSMC-E1A). Serum-deprived VSMC-E1A exhibited the highest apoptosis measured as the content of chromatin and low molecular weight DNA fragments, phosphatidylserine content in the outer surface of plasma membrane and caspase-3 activity (ten-, five-, four- and tenfold increase after 6 h of serum withdrawal, respectively). In VSMC-E1A, the addition of an activator of adenylate cyclase, forskolin, abolished chromatin cleavage, DNA laddering, caspase-3 activation and the appearance of morphologically-defined apoptotic cells triggered by 6 h of serum deprivation. In non-transfected VSMC and in VSMC-MYC, 6 h serum deprivation led to approximately six- and threefold activation of chromatin cleavage, respectively, that was also blocked by forskolin. In VSMC-E1A, inhibition of apoptosis was observed with other activators of cAMP signaling (cholera toxin, isoproterenol, adenosine, 8-Br-cAMP), whereas 6 h incubation with modulators of cGMP signaling (8-Br-cGMP, nitroprusside, atrial natriuretic peptide, L-NAME) did not affect the development of apoptotic machinery. The antiapoptotic effect of forskolin was abolished in 24 h of serum deprivation that was accompanied by normalization of intracellular cAMP content and protein kinase A (PKA) activity. Protection of VSMC-E1A from apoptosis by forskolin was blunted by PKA inhibitors (H-89 and KT5720), whereas transfection of cells with PKA catalytic subunit attenuated apoptosis triggered by serum withdrawal. The protection of VSMC-E1A by forskolin from apoptosis was insensitive to modulators of cytoskeleton assembly (cytochalasin B, colchicine). Neither acute (30 min) nor chronic (24 h) exposure of VSMC to forskolin modified basal and serum-induced phosphorylation of the MAP kinase ERK1/2. Thus, our results show that activation of cAMP signaling delays the development of apoptosis in serum-deprived VSMC at a site upstream of caspase-3 via activation of PKA and independently of cAMP-induced reorganization of the cytoskeleton network and the ERK1/2-terminated MAPK signaling cascade.

Apoptosis during regression of cardiac hypertrophy in spontaneously hypertensive rats. Temporal regulation and spatial heterogeneity.

We previously reported that increased apoptosis participates in the regression of aortic hypertrophy in spontaneously hypertensive rats. To further document the potential role of apoptosis in cardiovascular therapy, we examined apoptosis during regression of hypertrophy in the heart of spontaneously hypertensive rats receiving the antihypertensive drug enalapril (30 mg. kg(-1). d(-1)), losartan (30 mg. kg(-1). d(-1)), nifedipine (35 mg. kg(-1). d(-1)), hydralazine (40 mg. kg(-1). d(-1)), propranolol (50 mg. kg(-1). d(-1)), or hydrochlorothiazide (75 mg. kg(-1). d(-1)) for 1 to 4 weeks, starting at 10 to 11 weeks of age. Systolic blood pressure and heart rate were measured by the tail-cuff method. Markers of apoptosis included oligonucleosomal DNA fragmentation in extracted cardiac DNA or in situ in ventricular cross sections labeled with terminal deoxynucleotidyl transferase. Cardiac DNA synthesis was evaluated by [(3)H]-thymidine incorporation in vivo. All drugs reduced cardiac workload, defined as the product of blood pressure and heart rate, by >20% at 4 weeks. However, only nifedipine, enalapril, losartan, and propranolol reduced cardiac mass (>19%) within 4 weeks. Regression of cardiac hypertrophy was accompanied by a 50% to 300% increase in DNA fragmentation and a >20% reduction in DNA synthesis, resulting in a >20% reduction in cardiac DNA content after 4 weeks. Apoptosis induction occurred early and was transient within 4 weeks of nifedipine, enalapril, or losartan administration. With all regression-inducing drugs, the increase in DNA fragmentation occurred mainly in the subepicardium. Thus, transient induction of apoptosis in the subepicardium appears to be a characteristic feature of the early response to drug-induced regression of cardiac hypertrophy in spontaneously hypertensive rats.

Altered balance between cell replication and apoptosis in hearts and kidneys of newborn SHR.

Apoptosis is involved in neonatal remodeling of organs of the cardiovascular system. Since we previously reported hyperplasia of these organs at birth in several forms of genetic hypertension, the aim of this study was to determine whether alterations of the apoptotic process could explain our findings. The heart, aorta, and kidneys of newborn Wistar-Kyoto and spontaneously hypertensive rats were harvested 24 hours after an injection of [3H]thymidine. DNA was extracted to measure its specific activity (index of DNA synthesis) and DNA fragmentation as an estimation of apoptosis. All organs studied showed an increased weight to body weight ratio in spontaneously hypertensive rats. Twenty-four hours after birth, DNA synthesis in all organs of spontaneously hypertensive rats was comparable to that in normotensive rats. However, apoptosis was markedly decreased in the heart and kidneys of newborn spontaneously hypertensive rats compared with their normotensive controls. In the aorta, apoptosis was reduced, but not significantly. Calculation of a proliferation index (DNA synthesis/fragmentation) revealed a significant increase of heart proliferation, with a similar trend in the aorta and kidneys. In addition, we found a negative correlation between heart weight and DNA fragmentation. Although other factors may influence hyperplasia of the aorta, we propose that a reduction of apoptotic activity is responsible, at least in part, for heart and kidney hyperplasia in newborn spontaneously hypertensive rats.

Regulation of the natriuretic peptide system in rat uterus during the estrous cycle.

Uterine natriuretic peptides may be involved in the alterations that occur in the uterus during the estrous cycle through its role in hydromineral balance. The following studies were performed to determine whether uterine natriuretic peptides and receptors follow a cyclic pattern during the estrous cycle. The results obtained show that atrial natriuretic peptide (ANP) content in rat uterine tissue was low in proestrus (8.5 +/- 2.6 pg/g) and significantly increased (P < 0.001) in estrus (71.5 +/- 16.6 pg/g), metestrus (82.6 +/- 19.7 pg/g) and diestrus (91.0 +/- 19.4 pg/g), whereas plasma ANP was not altered during the cycle. Similarly, measurement of uterine ANP mRNA by reverse transcribed polymerase chain reaction (RT-PCR) indicated lowest levels of ANP mRNA at proestrus. Measurement of C-type natriuretic peptide (CNP) by a specific and sensitive radioimmunoassay revealed that uterine CNP also varies with the estrous cycle. Uterine CNP was low in diestrus (143.2 +/- 22.4 pg/mg protein) as compared with proestrus, estrus and metestrus (305.3 +/- 51.5, 267.5 +/- 44.9, 291 +/- 41.2 pg/mg protein respectively, P < 0.05). Autoradiography performed on uterine tissue slices localized natriuretic peptide receptors to myometrial smooth muscle layers and to endometrial uterine glands. High binding of 125I-ANP was observed in proestrus and estrus with 60-75% decreases during metestrus and diestrus. Binding of 125I-tyr0CNP to uterine slices was also high during proestrus, but declined by 35% at estrus, metestrus and diestrus. The alterations in the receptors were also observed at the level of synthesis. RT-PCR detection of guanylyl cyclase A (GC-A) receptor mRNA and guanylyl cyclase B (GC-B) mRNA showed high signals at proestrus but 4- and 2-fold reductions respectively at metestrus and diestrus. In conclusion, variations in uterine ANP and CNP and their receptors during the rat estrous cycle imply the involvement of the natriuretic peptides in uterine hydromineral balance and myometrial motor activity.

C-type natriuretic peptide and the guanylyl cyclase receptors in the rat ovary are modulated by the estrous cycle.

We have previously shown that rat ovaries synthesize atrial natriuretic peptide (ANP) and express the cognate guanylyl cyclase (GC-A and GC-B) receptors for ANP. Since another natriuretic peptide, termed the C-type natriuretic peptide (CNP), can also interact with these receptors, we have investigated whether rat ovaries express CNP and if so, whether the concentration of this natriuretic peptide and the guanylyl-cyclase receptors are influenced by the estrous cycle. CNP mRNA was detected in rat ovaries using a reverse transcription (RT) polymerase chain reaction (PCR) strategy. RIA of ovarian extracts, obtained at the individual days of the estrous cycle, revealed the presence of immunoreactive CNP. The highest levels of CNP were detected at proestrus and were approximately 4-fold higher than the levels seen at any other stage of the cycle. GC-A and GC-B receptors were detected using quantitative autoradiography after application of either [125I]ANP or [125I]-tyr0CNP to sections of frozen ovaries. The highest specific binding of each radiolabeled ligand was seen in ovaries from proestrous animals. The GC-B receptors were localized to the membrana granulosa of developing ovarian follicles. Using quantitative PCR, we determined that levels of GC-A and GC-B mRNAs were highest in the ovaries of proestrous animals and were approximately 2- to 3-fold higher than the levels seen at diestrus. These findings demonstrate that a natriuretic peptide system, consisting of ligands and receptors, is present in the rat ovary. Since CNP and the GC receptors show coordinate estrous cycle-dependent variation with maximal expression at proestrus, we speculate that the natriuretic peptides may play an important role in either the development of ovulatory follicles or in the ovulatory process.

The time window of apoptosis: a new component in the therapeutic strategy for cardiovascular remodeling.

APOPTOSIS AND EXPERIMENTAL HYPERTROPHY: Apoptosis (programmed cell death) is a physiological counterpart of cell replication with shared as well as specific pathways. Our initial studies have demonstrated increased apoptosis in the heart, kidney and brain of spontaneously hypertensive rats (SHR) and mice, persisting in cultured vascular smooth muscle cells. In these target organs of hypertension, programmed cell death paralleled the well known hypertrophy/hyperplasia. We also observed that the two processes can be dissociated in time, as in experimental hypertrophy of the heart induced by pressure overload. In this context, only a short-lived apoptotic window precedes the overt development of cardiac hypertrophy. EFFECTS IN HYPERTENSION: We now propose that a more prolonged apoptotic window is present in hypertension. Apoptosis seems to be significantly reduced during the first weeks of life in SHR, possibly contributing to the early cardiac hyperplasia. However, increased apoptosis is clearly evident thereafter throughout the development of hypertension and fades below the levels observed in normotensive animals after the age of 24 weeks. ANTIHYPERTENSIVE THERAPY AND APOPTOSIS: In addition to the apoptotic windows that suggest a dynamic regulation of this process in disease states, antihypertensive therapy with angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists and calcium channel blockers can also modify the contribution of apoptosis, independently of the blood pressure fall. We propose that the presence of apoptotic windows and the involvement of this biological process as a primary or secondary event in cardiovascular remodeling should be taken into account when designing innovative therapeutic approaches.

Apoptosis and vascular wall remodeling in hypertension.

Vascular structure plays a key role in the pathogenesis of hypertension. Because it is less readily reversible than protein accumulation, DNA accumulation in the arterial wall may be considered as a record of past episodes of vascular growth, contributing to the persistence of the vascular disease. Apoptosis, a ubiquitous and highly regulated form of programmed cell death that is involved in tissue morphogenesis and homeostasis as the essential counterpart of cell replication, is potentially involved in the regulation of vascular structure, via the deletion of cells in the vessel wall. We discuss how the current knowledge on apoptosis may provide insights into the pathogenesis of vascular wall remodeling, with an emphasis on the biology of vascular smooth muscle cells. Evidence suggests that heightened cell replication rates are often associated with increased apoptosis, as for smooth muscle cells in genetic hypertension or in arterial repair after injury. However, apoptotic cell death may also be regulated independently of cell growth. The triggering of apoptosis depends on a balance of environmental cues that are not specific to apoptosis. However, there is a common set of key biochemical events mediating apoptosis (i.e., committing the cell to die), thus providing a basis for the design of novel pharmacological strategies specifically targeting apoptotic cell death. The identification of biochemical markers of apoptosis and other methodological advances will ultimately help in understanding the role of apoptotic cell death in vascular remodeling and hypertensive end-organ damage.

Apoptosis in vascular smooth muscle cells: role of cell shrinkage.

Cell volume decrease is known to be one of the earliest steps of apoptosis in immune system cells. In this study, we compared the kinetics of apoptosis and cell volume adjustment in cultured vascular smooth muscle cells (VSMC) from the aorta of normotensive Brown-Norway (BN.1x) as well as spontaneously hypertensive (SHR) rats and in Mardin-Darby canine kidney (MDCK) cells. The transfer of VSMC to serum-deprived medium led to a transient cell volume decrease and to increased apoptosis. Both the cell volume decrease and apoptosis displayed faster kinetics in SHR than in BN.1x VSMC. Increased tonicity of serum-deprived medium by the addition of 200 mM mannitol augmented apoptosis in VSMC by 2.5- to 3-fold. In contrast to VSMC, neither apoptosis nor the cell volume of MDCK cells was affected by serum deprivation. Apoptosis in MDCK cells was also insensitive to tonicity of serum-deprived medium. There results demonstrate an initial volume decrease in VSMC undergoing apoptosis and suggest that this phenomenon is involved in triggering the apoptotic process.

Renal atrial natriuretic factor receptors in hamster cardiomyopathy.

Hamsters with cardiomyopathy (CMO), an experimental model of congestive heart failure, display stimulated renin-angiotensin-aldosterone and enhanced sympathetic nervous activity, all factors that lead to sodium retention, volume expansion and subsequent elevation of plasma atrial natriuretic factor (ANF) by the cardiac atria. However, sodium and water retention persist in CMO, indicating hyporesponsiveness to endogenous ANF. These studies were undertaken to fully characterize renal ANF receptor subtypes in normal hamsters and to evaluate whether alterations in renal ANF receptors may contribute to renal resistance to ANF in cardiomyopathy. Transcripts of the guanylyl cyclase-A (GC-A) and guanylyl cyclase B (GC-B) receptors were detected by quantitative polymerase chain reaction (PCR) in renal cortex, and outer and inner medullas. Compared to normal controls, the cardiomyopathic hamster's GC-A mRNA was similar in cortex but significantly increased in outer and inner medulla. Levels of GC-B mRNA were not altered by the disease. On the other hand, competitive binding studies, autoradiography, and affinity cross-linking demonstrated the absence of functional GC-B receptors in the kidney glomeruli and inner medulla. Also, C-type natriuretic peptide (CNP), the natural ligand for the GC-B receptors, failed to stimulate glomerular production of its second messenger cGMP. In CMO, sodium and water excretion were significantly reduced despite elevated plasma ANF (50.5 +/- 11.1 vs. 309.4 +/- 32.6 pg/ml, P < 0.001). Competitive binding studies of renal glomerular ANF receptors revealed no change in total receptor density, Bmax (369.6 +/- 27.4 vs. 282.8 +/- 26.2 fmol/mg protein), nor in dissociation constant, Kd (647.4 +/- 79.4 vs. 648.5 +/- 22.9 pM). Also, ANF-C receptor density (254.3 +/- 24.8 vs. 233.8 +/- 23.5 fmol/mg protein), nor affinity were affected by heart failure. Inner medullary receptors were exclusively of the GC-A subtype with Bmax (153.2 +/- 26.4 vs. 134.5 +/- 21.2 fmol/mg protein) and Kd (395.7 +/- 148.0 vs. 285.8 +/- 45.0 pM) not altered by cardiomyopathy. The increase in ANF-stimulated glomerular cGMP production was similar in normal and CMO hamsters (94- vs. 75-fold). These results demonstrate that renal ANF receptors do not contribute to the attenuated renal responses to ANF in hamster cardiomyopathy.

Characterization and distribution of natriuretic peptide receptors in the rat uterus.

Atrial natriuretic peptide (ANP) receptors were characterized in rat uterus. The binding of [125I]ANP to uterine membranes was completely competed for by increasing concentrations of unlabeled ANP (Kd = 0.39 nM) and brain natriuretic peptide (Kd = 1.24 nM) and partially by C-type natriuretic peptide (CNP; Kd = 80.4 nM), but not by C-ANF. Also, [125I]Tyr-CNP bound to uterine membranes was completely competed by unlabeled CNP (Kd = 1.12 nM). Cross-linking of [125I]ANP to uterine membranes revealed the presence of one band of 130 kilodaltons, corresponding to the guanylyl cyclase (GC-A and/or GC-B) subtypes of natriuretic peptide receptors. The presence of messenger RNA coding for genes of both GC-A and GC-B receptors was shown by quantitative reverse transcriptase polymerase chain reaction. Furthermore, ANP and, to a lesser degree, CNP stimulated the production of cGMP in rat uterus. Autoradiographic studies localized the highest binding of [125I]ANP in the endometrium, whereas [125I]Tyr-CNP binding was distributed in the endometrium as well as in the myometrium. These results demonstrate that rat uterine ANP receptors are of the guanylyl cyclase-coupled subtypes. The uterus is a target of natriuretic peptides where ANP induces its biological effects through the production of cGMP.

Regulation of renal atrial natriuretic peptide receptors in pregnant sheep.

These studies were designed to characterize the atrial natriuretic peptide (ANF) receptor subtypes (guanylyl cyclase GC-A and GC-B and ANF-C) in normal sheep kidneys and to evaluate alterations in receptor kinetics during pregnancy. Kidneys were obtained from 12 nonpregnant and 12 pregnant sheep during late gestation and maintained on a 100 mmol/day salt intake. Competition binding receptor assays using [125I]human ANF showed that inner medullary membranes are exclusively of the GC-A subtype. The maximum binding capacity (Bmax, 109 +/- 12 vs. 89 +/- 18 fmol/mg protein) and dissociation constant (Kd, 240 +/- 70 vs. 324 +/- 99 pM) are not altered by pregnancy. Specific binding of glomerular membranes to [125I]Tyr-C-type natriuretic peptide, which shows the highest affinity toward GC-B receptors, was observed, but this binding was abolished when ANF-C receptors were saturated with excess C-ANF-(101-121), suggesting that [125I]Tyr-C-type natriuretic peptide binding was mediated by ANF-C receptors. Binding of [125I]human ANF to glomerular membranes revealed that glomerular ANF receptor number was reduced during pregnancy (1040 +/- 212 vs. 335 +/- 42 fmol/mg protein; P = 0.001), but binding affinity was not changed. The reduced number was mainly due to a decrease in ANF-C receptor density (832 +/- 213 vs. 260 +/- 31 fmol/mg protein; P = 0.005). Autoradiography of whole kidney frozen sections produced similar findings. These studies demonstrate that GC-B receptors are absent from renal glomeruli and inner medulla, and that ANF receptor subtypes are differentially regulated in the pregnant sheep kidney, suggesting a role for ANF in the altered volume and pressure homeostasis of pregnancy.

Apoptosis in target organs of hypertension.

Apoptosis or programmed cell death frequently parallels abnormalities in cell proliferation and differentiation. As hypertrophy/hyperplasia or remodeling occurs in organs affected by hypertension, we evaluated the degree of apoptosis in the heart, kidney, and brain in situ in genetically hypertensive mice and rats as well as in cultured vascular smooth muscle cells. Apoptosis was characterized by morphological features, DNA fragmentation, and laddering as well as by terminal deoxynucleotidyl transferase labeling of the 3' OH ends of both extracted DNA and tissue sections. The present report provides the first evidence of increased apoptosis in whole organs of genetically hypertensive rat and mouse strains: in the heart of spontaneously hypertensive rats (SHR) and in the heart (ventricular cardiomyocytes), kidney (inner cortex and medulla), and brain (cortex, striatum, hippocampus, and thalamus) of spontaneously hypertensive mice, with a higher effect of apoptotic inducers in cultured aortic smooth muscle cells derived from SHR. Both types of known apoptotic processes, oligonucleosomal cleavage and large DNA fragmentation, were observed in vascular smooth muscle cells, but only the former appeared to be increased in SHR. This study underlines the importance of cell death dysregulation in hypertension, reveals a new route for investigation of the pathogenesis of hypertension, and suggests novel targets of therapeutic intervention.

Effects of dorsal rhizotomy on neurokinin receptor sub-types in the rat spinal cord: a quantitative autoradiographic study.

Although abundant evidence suggests a major role for substance P (SP) and other neurokinins (NK) in the transmission of nociceptive information, it is not known whether the various NK receptor classes are differentially located in the substantia gelatinosa of the spinal cord where primary afferent fibres mostly terminate. In order to investigate this issue, we studied the effects of unilateral dorsal rhizotomy on binding of 125I-Bolton-Hunter-SP, (2-[125I]iodohistidyl1)-neurokinin A, and 125I-Bolton-Hunter-eledoisin as respective radioligands for the NK-1, NK-2 and NK-3 receptor sub-types. Seven, 14, 21 and 28 days following unilateral lumbosacral dorsal horn deafferentiation, NK receptor binding parameters were evaluated using quantitative receptor autoradiography. Rhizotomy produced an increase in the densities of NK-1, NK-2 and NK-3 binding sites in the superficial laminae of the dorsal horn. Increases were maximal at 14 days, post-operatively, for both NK-1 and NK-2 sites; slight recovery being observed thereafter. For NK-3 sites, unilateral rhizotomy induced a progressive increase in binding without evidence of recovery over time, at least up to 28 days post-lesion. NK-1 receptor binding parameters around the central canal and in the ventral horn were not affected by the dorsal rhizotomy. These data suggest that all 3 NK receptor classes are located post-synaptically to afferent fiber terminals in laminae I, II and X of the dorsal horn of the spinal cord.

Autoradiographic distribution of brain neurokinin-1/substance P receptors using a highly selective ligand [3H]-[Sar9,Met(O2)11]-substance P.

The autoradiographic distribution of neurokinin (NK)-1 receptors was visualized in the rat brain using the highly selective ligand, [3H]-[Sar9,Met(O2)11]-substance P. This ligand apparently binds to a single class of high affinity (Kd = 1.4 +/- 0.5 nM), low capacity (Bmax = 160 +/- 3.0 fmol/mg protein) sites in rat brain membrane preparations. The ligand selectivity profile reveals that substance P (SP) and unlabeled [Sar9,Met(O2)11]-SP are potent competitors of [3H]-[Sar9,Met(O2)11]-SP binding while NK-2 and NK-3 analogues are virtually inactive demonstrating the selectivity of this radioligand for the NK-1 receptor class. Autoradiographic data show that [3H]-[Sar9,Met(O2)11]-SP binding sites are broadly but discretely distributed in rat brain, the highest densities of sites being located in the external plexiform layer of the olfactory bulb, striatum, olfactory tubercule, amygdala-hippocampal area, endopiriform and entorhinal cortices, superior colliculus, locus coeruleus and substantia gelatinosa of the spinal cord. This distribution is similar, but not identical, to that previously reported for NK-1 sites using less selective ligands such as [125I]Bolton-Hunter SP. For example, some difference in labelling patterns are observed in the hippocampal formation. This could be explained by the existence of NK-1 receptor subtypes, only one of them being recognized by [3H]-[Sar9,Met(O2)11]-SP or by the greater selectivity of this radioligand for NK-1 over NK-2 and NK-3 receptor classes.

Quantitative autoradiographic distribution of multiple neurokinin binding sites in rat spinal cord.

As a means of evaluating the role of neurokinins (NKs) in spinal function, the present study examines the quantitative autoradiographic distribution in the rat spinal cord of [125I]Bolton-Hunter-substance P, (2-[125I]iodohistidyl1)-neurokinin A and [125I]Bolton-Hunter-eledoisin as respective radioligands for NK-1, NK-2 and NK-3 receptors. These putative NK receptor sub-types are clearly differentially distributed at the various levels of the spinal cord. NK-1 sites represent the most abundant population of spinal NK receptors. They are most concentrated in the dorsal and ventromedial borders of the dorsal horn, the intermediolateral nucleus of the thoracic cord and the phrenic motor nucleus in the cervical ventral horn. NK-2 and NK-3 sites are also present in the spinal cord, although in much lower quantities than NK-1 sites. NK-2 sites are mostly found along the dorsal and ventromedial borders of the dorsal horn, in a narrow band connecting the two lateral horns of the thoracic cord, around the central canal of the lumbar and sacral segments and lamina IX of the cervical ventral horn. NK-3 sites are most dense in the dorsal border of the dorsal horn, with moderate amounts in the lateral horn of the thoracic cord and around the central canal of lumbar and sacral segments. The differential distribution of these 3 classes of NK sites in the spinal cord suggests that each NK receptor sub-type could mediate specific sensory, autonomic and/or motor functions at the spinal level.