Neuropeptidergic innervation of equine synovial joints.

Immunocytochemical analysis of equine synovial membranes revealed presence of several neuropeptides, including substance P (SP), neurokinin A, and neuropeptide Y, in nerves of the radiocarpal, middle carpal, and metacarpophalangeal (fetlock) joints. Within the subsynovium, these neuropeptides were located perivascularly, whereas in the fronds, only neuropeptide Y was restricted to the vessels of the synovial membrane. Only SP and neurokinin A were found in the intimal layer. The intimal layer of the metacarpophalangeal joint contained more SP-immunoreactive fibers than were observed in the intimal layer of the radiocarpal joint. Substance P also was detected in the synovial fluid from all 3 joints, but mean +/- SD concentrations were significantly different only between the middle carpal joint (37.56 +/- 5.48 fmol/ml; n = 6) and the metacarpophalangeal joint (55.80 +/- 8.33 fmol/ml; n = 5) and between the middle carpal joint and the radiocarpal joint (52.43 +/- 14.60 fmol/ml; n = 7).

Substance P in the synovial membrane and fluid of the equine middle carpal joint.

This preliminary study was designed to determine whether the neurotransmitter substance P was present in the middle carpal synovial membrane of the normal horse and whether the neuropeptide could be identified in the synovial fluid of normal horses and those with joint diseases. Immunocytochemistry on middle carpal synovial membrane biopsies from fresh cadavers was used to demonstrate substance P-containing neural elements. Substance P was most abundant in the subintimal portion of the membrane, with occasional filaments coursing via synovial fronds to the intimal portion. Radioimmunoassay techniques were used on acidified acetonitrile-preserved synovial fluid samples to measure substance P concentrations. Fluid from 9 joints of 5 normal horses and 6 joints of 4 horses with joint diseases were analysed. Disease conditions included acute and chronic osteoarthritis and osteochondrosis. Synovia from normal horses contained a mean concentration of substance P significantly less than that of horses with joint diseases (P less than 0.05). Elevated concentrations of neurotransmitters in diseased joints suggests a potential contribution to the pathophysiology of joint disorders in horses.

Descending modulation of dorsal horn biogenic amines as determined by in vivo dialysis.

Bipolar concentric stimulating electrodes were placed medially within the nucleus raphe magnus and laterally within the nucleus gigantocellularis. The levels of norepinephrine (NE), serotonin (5-HT), and 5-hydroxyindolacetic acid (5-HIAA) within the dorsal horn of the spinal cord were measured before and after electrical stimulation of these brainstem nuclei using in vivo dialysis coupled with high pressure liquid chromatography and electrochemical detection. Stimulation medially significantly increased the levels of all three amines. While simulation laterally also increased NE, both 5-HT and 5-HIAA were significantly reduced. The relevance of these findings to descending modulation of ascending nociceptive neural activity within the dorsal horn is discussed.

Evoked changes in 5-hydroxytryptamine and norepinephrine release: in vivo dialysis of the rat dorsal horn.

Basal 5-hydroxytryptamine (5HT) and norepinephrine (NE) concentrations were measured in samples collected by in vivo dialysis of the rat dorsal horn. Infusion of KCl, glutamate, and NE by means of the dialysis probe increased NE, but decreased 5HT extracellular concentrations. In contrast, electrical stimulation of the nucleus raphe magnus increased the recovery of both NE and 5HT. These findings suggest differential regulation of noradrenergic and serotonergic nerve terminals modulating nociceptive neurotransmission within the dorsal horn.

Low-calcium diet increases blood pressure and alters peripheral but not central angiotensin II binding sites in rats.

The mechanism by which low-calcium (Ca) diet causes hypertension is unknown. We investigated angiotensin II (Ang II) receptor binding in brain, adrenals and urinary bladders in male Sprague-Dawley rats pair-fed a low-Ca (0.005% Ca; 0.5% P) and normal-Ca (1.4% Ca) diet for 8 weeks beginning at 4 weeks of age. The Ang II receptor sites in hypothalamus-thalamus-septum (HTS), adrenal glands and urinary bladder smooth muscle were measured by saturation isotherm binding using 125I-sarcosine1isoleucine8 Ang II (125I-SI Ang II). Systolic blood pressure was determined at 2-week intervals by tail-cuff method. Serum total Ca, Na+, K+ aldosterone and Ang II and bone density and mineral content were determined at the time of sacrifice. Chronic Ca deficiency in rats raised blood pressure and decreased Ang II receptor density in bladder smooth muscles and tended to increase adrenal Ang II receptors. Serum Ca. bone density and mineral content were significantly lower in the Ca-deficient rats, while serum Na+ was elevated in this group. Serum Ang II and aldosterone were unaltered after the 8-week dietary regimen. Possible mechanisms for the hypertensive actions of reduced dietary Ca intake involving the renin-angiotensin-aldosterone system are discussed.

Metabolism of angiotensins II and III by membrane-bound peptidases from rat brain.

This study examines the metabolism of 125I-angiotensin II (125I-ANG II) and 125I-angiotensin III (applied 125I-ANG III or 125I-ANG IIIapp) by membrane peptidases. The first step in the metabolism of 125I-ANG II was the formation of 125I-ANG III (generated 125I-ANG III or 125I-ANG IIIgen). The ability of both ANG II and ANG III to reduce 125I-ANG IIIgen production without ANG(1-5), ANG(2-5), amastatin or bestatin being similarly effective suggests that this step may be highly substrate-specific. Subsequent metabolism of 125I-ANG IIIgen was similar to that of 125I-ANG IIIapp in that 125I-ANG(2-7) and 125I-ANG(2-4) fragments were produced. The formation of 125I-ANG(2-7) appeared to be a very substrate-specific process because it was only inhibited by ANG II and ANG III. In contrast, the production of 125I-ANG(2-4) was unaffected at the concentration of inhibitors used and is considered to be a relatively nonspecific process. However, despite these similarities sequential N-terminal cleavage leading to the formation of 125I-ANG(3-8), 125I-ANG(4-8) and 125I-Tyrosine appears to be the preferred pathway in the metabolism of 125I-ANG IIIapp. The absence of this pathway in the metabolism of 125I-ANG IIIgen suggests that applied and generated 125I-ANG III may be metabolized in separate degradative compartments. These data demonstrate that 125I-ANG II and 125I-ANG III are metabolized by membrane-bound peptidases in an orderly and sequential manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of 125I-angiotensin III and 125I-angiotensin II binding to rat brain membranes.

The binding of 125I-angiotensin III (125I-ANG III) to rat brain membranes was examined and compared with that of 125I-angiotensin II (125I-ANG II). Degradation of each ligand, as monitored by HPLC, was effectively inhibited using fragments of ANG III and ANG II known to have little affinity for angiotensin binding sites. Three classes of 125I-ANG III-binding sites were observed based on affinity (KD = 0.13, 1.83, and 10.16 nM) and capacity (Bmax = 1.30, 18.41, and 67.2 fmol/mg protein, respectively). Two classes of 125I-ANG II-binding sites of high affinity (KD = 0.11 and 1.76 nM) and low capacity (Bmax = 1.03 and 18.86 fmol/mg protein, respectively) were also identified. Cross-displacement studies confirmed that the two highest-affinity 125I-ANG III-binding sites and the 125I-ANG II-binding sites were the same. On the other hand, the binding of 125I-ANG III to the low-affinity 125I-ANG III-binding site could not be inhibited with ANG II. These data imply that previously measured differences in the biological potency of cerebroventricularly applied ANG III and ANG II probably do not result from differential binding of these peptides to central angiotensin receptors.

Cardiovascular effects in rats following exposure to a high-boiling coal liquid.

In previous work, increased blood pressure was observed in anesthetized rats following a subchronic aerosol exposure to solvent-refined coal heavy distillate (HD). To determine if this increase is a permanent, dose-related response, 11-week-old male rats were exposed by inhalation to 0, 0.24, or 0.70 mg/liter (control, low-exposure, and high-exposure groups, respectively) of HD for 6 hr/day, 5 days/week, for 6 weeks. In addition to blood pressure, select cardiovascular parameters were measured to obtain information on other possible toxic effects of the HD and also to gain some insight into potentially altered regulatory mechanisms that could be affecting the blood pressure. The angiotensin-aldosterone hormonal system, body fluid regulation, cardiac function and regulation, and pulmonary gas-exchange capabilities were examined. Two weeks after the end of exposure, mean blood pressures and heart rates of anesthetized animals in the low-and high-exposure groups were elevated relative to the controls. Plasma angiotensin concentrations decreased with increasing dose, whereas aldosterone concentrations were unaffected. In the high-dose group, blood and plasma volumes were 20 and 28%, respectively, higher than those of controls. Seven weeks after exposure, all measured cardiovascular parameters were similar to control values. Results from this study show that a 6-week exposure to HD resulted in dose-dependent, transient changes in a variety of physiological factors considered important in cardiovascular function.

Improved immunohistochemical staining of angiotensin II in rat brain using affinity purified antibodies.

Recent immunohistochemical studies that have sought to detect angiotensin II/III (AII/AIII) immunoreactive material in the brain have been forced to rely on a small number of antisera because most AII/AIII antibodies have unexplainably proved unsuitable for immunohistochemistry. Although extremely useful tools, these antisera have suffered from high background staining. The purpose of this study was to re-examine and characterize the staining using the most popular AII/AIII antiserum (Denise) before and after purification on an AII CH-sepharose affinity column. The use of crude AII/AIII antiserum resulted in the staining of large varicosities and cell bodies. Fibres were all but invisible owing to extensive background staining. In contrast, the purified antibodies yielded little background staining and produced a discrete staining of AII/AIII fibres with small varicosities in the paraventricular-hypophysial pathway and of cell bodies of large hypothalamic neurones. In addition punctate staining demarcated the perikarya of some neurones and resembled boutons containing immunoreactive AII/AIII. Biochemical and histochemical analysis of the crude antiserum, the affinity purified antibodies and other fractions off the sepharose column demonstrated that a large portion of the total staining (various types of background) seen with crude antiserum and column fractions was not to AII/AIII or several angiotensin-derived fragments. Furthermore, successful preabsorption blanks for the purified antibodies could only be achieved with AII coupled through its N-terminal, suggesting that these purified antibodies reacted best with conjugated angiotensin in the fixed tissue. In total the results of this study indicate that the background staining seen with crude antiserum is not to AII/AIII. The use of affinity purified antibodies greatly enhances resolution, enabling one to visualise even small fibres in rats not treated with colchicine, and should improve our ability to develop accurate maps of central angiotensinergic pathways.

Binding, degradation and pressor activity of angiotensins II and III after aminopeptidase inhibition with amastatin and bestatin.

In the metabolism of angiotensin peptides by tissue angiotensinases, aminopeptidases A, B, M and leucine aminopeptidase have been identified as being particularly effective. Because the inhibitory actions of amastatin (AM) and bestatin (BE) are relatively specific for these aminopeptidases, we have examined the effects of these inhibitors on the binding, degradation and pressor activity of angiotensin II (AII) and angiotensin III (AIII). Within 30 min at 37 degrees C, significant metabolism of 125I-AII and 125I-AIII by homogenates of a block of tissue containing hypothalamus, thalamus, septum and anteroventral third ventricle regions of the brain was observed. A majority of 125I-AIII metabolism was due to soluble peptidases, whereas that of 125I-AII primarily resulted from membrane-bound peptidases. AM, BE and reduced incubation temperatures significantly decreased the metabolism of 125I-AII and 125I-AIII. After appropriate adjustments to reflect the proportion of intact radioligand bound, temperature- or inhibitor-induced decreases in metabolism were matched by corresponding increases in specific binding. Heat-treated bovine serum albumin, as a nonspecific peptidase inhibitor, had no effect on either the metabolism or binding of the ligands used. In accordance with their actions in vitro, i.c.v. administration of AM and BE prolonged the pressor activity of subsequently applied AII and AIII. Unexpectedly, the amplitude of the pressor response to AIII was increased by BE, whereas that to AII was decreased by AM. The results of this study indicate that the metabolism of AII and AIII by aminopeptidases is relatively specific and acts to modulate the actions of these peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevations in plasma angiotensin II with prolonged ethanol treatment in rats.

Chronic alcohol consumption frequently leads to hypertension in humans. While previous reports have implicated the renin-angiotensin system as a potential mediator of this effect, plasma angiotensin II (AII) levels were either not measured or yielded negative results. The present investigation noted significant elevations in circulating AII in rats intubated daily with ethanol (4 g/kg) for 50 days. Animals administered ethanol only once evidenced AII concentrations equivalent with water intubated controls. Radioligand binding assay data indicated no differences in the number or affinity of Sar1,Ile8-AII binding sites in the thalamus, septum-anterior ventral third ventrical region or adrenal gland comparing those groups chronically treated with ethanol to water intubated controls. These results may support a role for the vasoconstrictive hormone AII in the etiology of alcohol-induced hypertension.

High-performance liquid chromatographic analysis of 'specifically bound' label after [125I]angiotensin II binding to rat brain membranes.

The combined hypothalamus-thalamus-septum and anteroventral third ventricular region (HTSA) of the rat was examined for [125I]angiotensin II ([125I]AII) binding using two protocols: one that preserved synaptosomal structure and a second that did not. Although maximum binding (Bmax) and dissociation constants (Kd) were similar in both preparations, high-performance liquid chromatographic analyses revealed that [125I]AII made up the majority of specifically bound label in the synaptosome preserved preparation while [125I]tyrosine ([125I]Tyr) represented most of the specifically bound label in the disrupted preparation. These results indicate that [125I]Tyr accumulation occurred subsequent to binding and degradation of [125I]AII and are consistent with the notion that rapid internalization of the receptor-[125I]AII complex occurs in those preparations where the synaptosomal structure remains intact.

Pressor action and dipsogenicity induced by angiotensin II and III in rats.

The primary brain sites responsible for angiotensin-induced pressor action and dipsogenicity in the laboratory rat appear to be located in forebrain circumventricular organs (CVO). Because CVOs have a reduced blood-brain barrier, intracarotid infusion of angiotensin via a brachial arterial catheter results in direct stimulation of these sites. This investigation determined that brachial arterial infusion of angiotensin II (ANG II) into alert free-moving rats resulted in pressor and dipsogenic responses greater than those observed with equivalent doses of angiotensin III (ANG III). However, intracerebroventricular (ICV) injections of ANG II and ANG III yielded equivalent pressor and drinking responses. ICV pretreatment with the specific angiotensin receptor antagonist [Sar1, Ile8]-ANG II significantly reduced ANG II- and ANG III-induced pressor and drinking responses. This inhibition lasted approximately 20 min with recovery at 60-70 min. The results indicate that ICV-administered ANG III is a much more potent ligand than previously determined if the stickiness due to electrical charge of this compound is prevented by appropriate treatment of glassware. The receptor antagonist results encourage the possibility that ANG II and ANG III activate a common central receptor site.

Characterization of angiotensin binding in the African green monkey.

The observation that there are differences in the characteristics and distribution of angiotensin receptors in the central nervous system of mammalian species led to the analysis of angiotensin binding in a primate model, the African Green monkey. Initial studies using [125I]angiotensin II ([125I]AII) as the radioligand showed binding in peripheral tissues but little binding in the central nervous system. Conversely, binding studies using [125I]AIII as the radioligand indicated more central nervous binding with diminished peripheral binding. Specific binding of [125I]AIII is evident throughout the brain with high binding in the circumventricular organs, striatum, caudate nucleus, olfactory bulb and localized areas of the thalamus and cerebral cortex. This binding was found to possess many of the properties commonly associated with binding to membrane-bound receptors. The specifically bound radioligand extracted from incubations of [125I]AIII and central nervous tissue appears to be a product of the metabolism of [125I]AIII rather than the peptide itself. Binding of [125I]AII does occur in peripheral tissues and to a limited extent in the cerebellum, but to a different receptor from that characterized using [125I]AIII. These results are similar to those seen in the gerbil and raise questions concerning the utilization of the rat as the primary model for studying the biochemistry of the brain-angiotensin system in humans.

Inhibition of rat peritoneal mast cell histamine secretion by protoporphyrin and incandescent light.

Rat peritoneal mast cells (RPMC) exposed to protoporphyrin (PP) and incandescent light (IL) become refractory to the stimulatory effects of compound 48/80. Once initiated, this refractory state continues to develop even after removal of the light source and is essentially complete within 30 min. While this state of unresponsiveness appears to be relatively permanent in the dark, prolonged incubation in the light (greater than 80 min) induces cell lysis. We have shown that the resistant state is not specific for the mast cell stimulator compound 48/80. Mast cells passively sensitized with IgE and illuminated for 30 min in the presence of 100 ng/ml PP also fail to release histamine upon stimulation by anti-rat IgE, anti-rat F(ab')2, concanavalin-A (Con-A), and the calcium ionophore A23187. The inability to respond to immunological stimuli could not be ascribed to the reversible loss of membrane-bound IgE from its receptor. While the binding of either the inducer to IgE or IgE to its receptor may actually be impaired in refractory cells, the significance of such impairments on the development of the resistant state in these cells is precluded by the inability of A23187 to either increase intracellular 45Ca2+ levels or induce histamine release. The data suggest that the RPMC refractory state develops as a result of covalent inter- and/or intramolecular cross-linking of membrane proteins. Furthermore, this cross-linking may involve sulfhydryl or amino groups essential to either stimulus transduction, or the histamine secretory process itself.

Characterization of angiotensin binding to gerbil brain membranes using [125I]angiotensin III as the radioligand.

The observation that an Angiotensin II (AII)-sensitive species, the gerbil, exhibited little or no [125I]AII binding to brain membranes led to the hypothesis that AII's central action may be mediated by smaller and/or modified fragments of AII. This possibility was assessed, in part, by examining the ability of gerbil brain membranes to specifically bind [125I]desAsp1 AII (AIII), a heptapeptide fragment of AII. Specific binding was evident throughout the gerbil brain with highest binding in the septum (containing the subfornical organ), anterior ventral third ventricular region, hypothalamus (containing the median eminence), and striatum. This binding was found to possess many of the properties commonly associated with binding to membrane bound receptors. The binding within the circumventricular organs had characteristics that set them apart from the other central nervous tissues examined. Both the olfactory bulb and adrenal gland appeared to have two different angiotensin binding sites. It appears that the binding sites within the brain interact with a product of the metabolism of AIII or AII rather than the peptides themselves. The results suggest that [125I]AIII appears to be a better ligand than [125I]AII in the binding assay because it is more readily degraded to another substance.

Decreased osmotic fragility in heritable canine myopathy.

Osmotic fragility was examined in red blood cells from dogs with a heritable muscle disorder that clinically resembles a muscular dystrophy. Several erythrocyte abnormalities have been reported in patients with certain forms of muscular dystrophy and it is thought that these changes reflect genetically induced alterations in the plasma membrane. It is believed that the examination of erythrocytes may eventually lead to the understanding of membrane involvement in muscle disorders. In this study, the mean osmotic fragility was found to be significantly lower in affected cells than in normal cells. These differences were maintained regardless of changes in incubation temperature (5 degrees, 20 degrees, or 35 degrees C) and pH (6.5, 7.0, 7.5, or 8.0). Quantitative analysis of glycolytic metabolites and adenine nucleotide concentrations revealed little variance between erythrocytes from normal and affected animals. Similarly, the pattern of membrane protein phosphorylation in intact erythrocytes from affected animals did not differ from that observed when erythrocytes from normal animals were examined. Of the red cell indices measured, the erythrocyte count in affected animals was moderately increased, but both the mean corpuscular volume and mean corpuscular hemoglobin content were significantly reduced. From these data it is concluded that the decrease in osmotic fragility cannot be explained by differences in cell metabolism or energy production. However, the decrease in affected cell mean corpuscular volume and mean corpuscular hemoglobin content may be correlated with the decrease in osmotic fragility in a manner similar to that observed in the hemolytic disorder of beta-thalassemia.