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J W Harding

Publications and source records attributed to J W Harding.

At least 37 records · Page 2Linked to original sources
PubMed1998

Role of nitric oxide in angiotensin IV-induced increases in cerebral blood flow.

The present study investigated the effects of three newly synthesized AngIV analogs (Lysine1-AngIV, Norleucine1-AngIV, and Norleucinal) on cerebral blood flow (CBF) in anesthetized Sprague-Dawley rats utilizing laser-Doppler flowmetry. The results indicate that internal carotid infusions of AngIV, Norleucine1-AngIV, Norleucinal, and Lysine1-AngIV increased CBF above baseline by 25, 32, 33 and 44%, respectively, without changing systemic arterial blood pressure. In a second experiment separate groups of rats were pretreated with nitric oxide (NO) synthase inhibitor, Nw-nitro-L-arginine methyl ester (L-NAME) or saline, followed by AngIV or Norleucinal for the purpose of evaluating the hypothesis that the mechanism of action of these compounds is linked to the release of NO. Pretreatment with saline followed by AngIV and Norleucinal increased CBF by 29 and 39%, respectively, while pretreatment with L-NAME blocked the vasodilatory effects of AngIV and Norleucinal, suggesting that the increment in blood flow induced by these compounds is dependent upon the synthesis and release of NO from vascular endothelial cells.

Angiotensin II↗
PubMed1998

Sex differences in discriminative stimulus and diuretic effects of the kappa opioid agonist U69,593 in the rat.

Female and male rats were trained to discriminate the kappa opioid agonist (5alpha,7alpha,8beta)-(-)-N-methyl-[7-(1-pyrrolidinyl) -1-oxaspiro(4,5)dec-8-yl]benzeneacetamide (U69,593, 0.13 mg/kg SC) from vehicle using a FR-10 schedule of food reinforcement. Female rats took significantly longer than males to acquire the discrimination (66.9 vs. 44.1 sessions, respectively), and the ED50 for U69,593 discrimination was significantly higher in females than in males (0.074 vs. 0.025 mg/kg). The time course of U69,593 discrimination also differed between the sexes: peak and offset occurred earlier in females than in males. The ED50 for bremazocine substitution was significantly higher in females than in males (0.0039 vs. 0.0006 mg/kg), whereas ethylketazocine substituted for U69,593 in all males and five of seven females, with no sex difference in substitution ED50. Morphine and BW373U86 did not substitute for U69,593 in a majority of rats of either sex. U69,593 also produced significantly less urine output/dose in females compared to males (e.g., 5.92 vs. 14.83 ml urine/kg body weight after 1.0 mg/kg U69,593), but was equipotent between the sexes in producing hot-plate antinociception. There was no sex difference in response rate-decreasing effect of any opioid agonist tested, and no sex difference in brain/blood ratio of [3H]U69,593 measured in a separate group of rats, suggesting that sex differences observed in some effects of U69,593 probably are not due to sex differences in U69,593 pharmacokinetics. When retested at the end of the study, U69,593 and bremazocine were no longer differentially potent as discriminative stimuli in females and males, suggesting that factors that change over time (e.g., additional training, age, hormonal status) may contribute to initial sex differences in discriminability of U69,593.

Animals↗
PubMed1998

Autoradiographic identification of kidney angiotensin IV binding sites and angiotensin IV-induced renal cortical blood flow changes in rats.

The present investigation initially determined that specific binding sites for the hexapeptide angiotensin IV (AngIV) are present in the rat kidney cortex and outer medulla but not in the inner medulla, using in vitro autoradiographic techniques. This binding site has been termed AT4, is distinct from the previously characterized AT1 and AT2 sites, and does not bind the specific AT1 receptor antagonist DuP753 or the AT2 receptor antagonist PD123177. Renal artery infusions of AngIV produced a dose-dependent increase in cortical blood flow without altering systemic blood pressure. In contrast, the infusion of angiotensin II (AngII) induced a dramatic decrease in cortical blood flow, accompanied by a significant elevation in systemic blood pressure. The infusion of [D-Val(1)]AngIV, an analog that does not bind at the AT4 receptor site, and the C-terminal truncated analogs AngIV (1-4) and AngIV (1-5) that possess lower affinity for this site, produced no change in cortical blood flow. The infusion of [Nle1]AngIV and [Lys1]AngIV, analogs that bind with high affinity at the AT4 receptor site, produced increases in cortical blood flow with no influence on blood pressure. Pretreatment with a specific AT4 receptor antagonist, Divalinal-AngIV, completely blocked AngIV-induced elevations in blood flow, but failed to influence AngII-induced decreases in blood flow, suggesting that these ligands are acting at different receptor sites. Pretreatment with the nitric oxide synthase inhibitor, NG-Monomethyl-L-Arginine, also blocked subsequent AngIV-induced increases in cortical blood flow. These data support the notion that AngIV exerts a unique influence upon renal hemodynamics via the AT4 receptor subtype, and suggest that AngIV-induced elevations in blood flow may be mediated by nitric oxide.

Amino Acid Sequence↗
PubMed1998

Evaluation and long-term treatment of aberrant behavior displayed by young children with disabilities.

We trained parents to conduct functional analyses and functional communication treatment for 28 young children with developmental disabilities who displayed aberrant behavior. Of this sample, 22 parents conducted treatment for at least 3 months and 11 for 1 year. We conducted single-case analyses of the results of assessment and treatment. The functional analysis identified social functions (positive and negative reinforcement) for 86% (24 of 28) of the children. Treatment resulted in a pre/post decrease in aberrant behavior averaging 87% across the range of children, with the greatest decrease occurring at 3 months. Appropriate social responding increased, on average, by 69% across the range of children. Decreases in aberrant behavior were demonstrated in all children, and all except one child displayed increased social behavior during treatment. On a measure of parent-rated treatment acceptability, ranging from 1 (not at all acceptable) to 7 (very acceptable), the average overall acceptability was 6.35.

Behavior Therapy↗
PubMed1998

Angiotensin IV AT4-receptor system in the rat kidney.

Angiotensin IV, [[des-Asp1,Arg2]ANG II or ANG-(3-8)], has been shown to preferentially bind to a novel angiotensin binding site (AT4 receptor). The cellular location and function of this receptor in the rat kidney is unknown. Autoradiography localized AT4 receptors to the cell body and apical membrane of convoluted and straight proximal tubules in the cortex and outer stripe of the outer medulla. ANG IV (0.1 pM-1 microM) elicited a concentration-dependent decrease in transcellular Na+ transport (as measured by proximal tubule O2 consumption rates) in fresh suspensions of control or nystatin-stimulated (bypasses rate-limiting step of apical Na+ entry) rat proximal tubules. The inhibitory effect of 1 pM ANG IV was unaltered by either 1 microM losartan (AT1-receptor antagonist) or 1 microM PD-123319 (AT2-receptor antagonist) and yet was abolished by 1 microM divalinal-ANG IV (AT4-receptor antagonist) or ouabain pretreatment. These results demonstrate that the kidney AT4-receptor system is localized to the proximal tubule and suggests that one potential biological role of this system is in the regulation of Na+ transport by inhibiting a ouabain-sensitive component of Na(+)-K(+)-adenosinetriphosphatase activity in the rat.

Angiotensin II↗
PubMed1998

Characterization and purification of the bovine adrenal angiotensin IV receptor (AT4) using [125I]benzoylphenylalanine-angiotensin IV as a specific photolabel.

The Ang IV receptor, AT4, has been shown to play important roles in various mammalian tissues. In this study, structural properties of the AT4 receptor from bovine adrenals are described using a novel photoactive analog of Ang IV, [125I]Benzoylphenylalanine-Ang IV (BP-Ang IV), recently developed in our laboratory. [125I]BP-Ang IV is identical to Ang IV with regards to binding specificity and affinity and is easily cross-linked to the AT4 receptor under UV light, thus greatly facilitating the structural analysis of the AT4 receptor by SDS-PAGE. Comparisons between the native, reduced and nonreduced forms of the AT4 receptors by SDS-PAGE revealed that this receptor consists of multiple subunits. The subunit containing the Ang IV binding site (designated as the alpha subunit) has a molecular weight of approximately 165 kDa and contained approximately 20% N-linked carbohydrates. A subunit similar to the adrenal alpha subunit of the AT4 receptor was identified in all of the bovine tissues examined. Hippocampus and aorta contained additional [125I]BP-Ang IV bound protein bands with molecular weights of 150 and 125 kDa, respectively. Further, the alpha subunit was purified to homogeneity using a method that integrates electrofractionation with conventional protein purification techniques.

Adrenal Glands↗
PubMed1997

Important role for angiotensin III and IV in the brain renin-angiotensin system.

Considerable evidence now suggests that the precursors and enzymes necessary for the formation and degradation of biologically active forms of angiotensins are present in brain tissues, accompanied by at least three specific binding sites. It also appears that several forms of angiotensin may serve as signaling agents at these sites. There is accumulating support for the notion that AngII must be converted to AngIII in order to bind at the AT1 and AT2 receptor subtypes, and AngIII must be converted to AngIV in order to activate the AT4 receptor subtype. Further, AngII(1-7) may activate a separate binding site concerned with antidiuresis, however, characterization of this site has not been completed. The AT1 site appears to mediate the classic angiotensin functions concerned with body water balance, maintenance of blood pressure, and cyclicity of reproductive hormones and sexual behaviors. This receptor site also exerts some control over the secretion of pituitary hormones. Less is known about the functional importance of the AT2 site, however, it has been implicated in vascular growth, control of blood flow, and perhaps modulation of NMDA receptors. The AT4 site is heavily distributed in neocortex, hippocampus, cerebellum, and basal ganglia structures, as well as several peripheral tissues. This site appears to mediate memory acquisition and retrieval, the regulation of blood flow, neurite outgrowth, angiogenesis, and kidney function. In addition to the well-studied functions of the brain renin-angiotensin system, additional less well investigated responses are reviewed. These include electrophysiological activation, tachyphylaxis, long term potentiation, learning and memory, and cognitive affect.

Angiotensin II↗
PubMed1997

The AT4 receptor agonist [Nle1]-angiotensin IV reduces mechanically induced immediate-early gene expression in the isolated rabbit heart.

Angiotensin II (ANG II), acting principally at the AT1 receptor, modulates mechanically-induced cardiac growth. The ANG II metabolite Angiotensin IV (ANG IV) has been shown to inhibit ANG II-induced mRNA and protein synthesis in chick cardiomyocytes. This effect did not involve the AT1 receptor, but was likely an action at the AT4 receptor. To determine if ANG IV also modulates a mechanically-induced cardiac growth response, we studied the effects of two AT4 receptor ligands, [Nle1]-ANG IV and [divalinal]-ANG IV, on mechanically-induced immediate-early gene expression (c-fos, egr-1, and c-jun) in the buffer perfused (30 degrees C), ejecting, isolated rabbit heart. Mechanical load alone (high systolic pressure and high end-diastolic volume) induced approximately 23-, 49- and 5-fold increases in c-fos, egr-1 and c-jun mRNA (in comparison to control hearts). Perfusion with [Nle1]-ANG IV (10[-10] mol/l) reduced the mechanically-induced expression of c-/fos and egr-1 by 42% and 48%, respectively (P < 0.05). Mechanically-induced c-jun expression was not significantly reduced. Perfusion with [divalinal]-ANG IV (10[-8] mol/l) had no effect on mechanically-induced immediate-early gene expression. We conclude that AT4 receptor agonism influences mechanical immediate-early gene expression, and propose the hypothesis that AT1 and AT4 receptors initiate opposing effects on mechanically-induced immediate-early gene expression in the isolated rabbit left ventricle.

Angiotensin II↗
PubMed1997

Angiotensin II- and IV-induced changes in cerebral blood flow. Roles of AT1, AT2, and AT4 receptor subtypes.

Our laboratory has previously reported the discovery of a unique angiotensin binding site (termed AT4) specific for angiotensin IV (AngIV) in cultured vascular endothelial and smooth muscle cells. The present investigation employed laser-Doppler flowmetry to examine the effect of angiotensin II (AngII) and AngIV stimulation of these receptors on cerebral microcirculation in anesthetized Sprague-Dawley rats. Internal carotid artery infusion of AngII at a low dose (0.1 pmol min-1) revealed a 23% reduction in cerebral blood flow (CBF), while the infusion of AngIV increased CBF in a dose-dependent fashion with the highest dose (100 pmol min-1) resulting in an elevation of 30%. In a second experiment separate groups of rats were pre-treated with the AT1 receptor subtype antagonist DuP 753 (Losartan), the AT2 receptor subtype antagonist PD123177, or a newly synthesized AT4 receptor subtype antagonist Divalinal-AngIV (Divalinal), followed by AngII or AngIV for the purpose of determining which angiotensin receptor subtype is responsible for mediating these AngII- and AngIV-induced responses. Pre-treatment with Losartan completely blocked subsequent AngII-induced reductions in CBF, while both PD123177 and Divalinal failed to inhibit this response. In contrast, significant increases in CBF were measured due to AngIV stimulation following pre-treatment with Losartan and PD 123177, while Divalinal abolished this AngIV-induced response. These results suggest that AngII and IV play opposite roles in cerebral microcirculation, i.e., the AT1 receptor subtype mediates AngII-induced reductions in CBF, while the AT4 receptor subtype regulates increases in CBF.

Angiotensin II↗
PubMed1997

Solid-phase synthesis of hydroxyethylamine angiotensin analogues.

Three hydroxyethylamine analogues of angiotensins II, III, and IV were prepared by solid-phase methods. The resin-bound peptide was alkylated with the iodomethylketone derivative of the N-terminal amino acid, followed by reduction to the alcohol using sodium borohydride. The iodomethylketones can be made in good yields from commercially available N-protected amino acids. The compounds were evaluated for their ability to displace labeled angiotensins from bovine adrenal membranes, and their metabolic stability tested in kidney homogenates and aminopeptidase M preparations. The hydroxyethylamine amide bond replacement reduced the affinity of the analogues; however, they were substantially more stable to enzymatic degradation.

Adrenal Glands↗
PubMed1996

Characterization of the binding properties and physiological action of divalinal-angiotensin IV, a putative AT4 receptor antagonist.

Divalinal-Ang IV [V psi (CH2-NH2)YV psi (CH2-NH2)HPF] is being employed increasingly as a specific AT4 antagonist. This use, which necessitates a comprehensive physiological and pharmacological evaluation of Divalinal-Ang IV's functional and receptor binding characteristics in order to ensure its efficacy and specificity, was the stimulus for this study using bovine adrenal membranes. [125I]Ang IV and [125I]Divalinal-Ang IV were shown to bind with high affinity to a similar number of binding sites, suggesting that both bound the same receptor. This notion was verified by competition curves using [125I]Ang IV and [125I]Divalinal-Ang IV that indicated identical rank order affinities for several angiotensin-related peptides and 100% cross-displacement by Ang IV and Divalinal-Ang IV. Furthermore, an autoradiographic comparison of [125I]Ang IV and [125I]Divalinal-Ang IV in 20 microns sections of bovine adrenals revealed near identical binding distributions characterized by heavy binding in the glomerulosa layer and the medulla. Physiological studies in which test compounds were injected into the internal carotid of the rat and cerebral blood flor (CBF) was measured by laser Doppler flowmetry indicated that pretreatment with Divalinal-Ang IV, but not DuP 753 or PD123177, blocked the increased flow observed with Ang IV infusion. Conversely, DuP 753, but not Divalinal-Ang IV or PD123177, inhibited the decrease in flow witnessed with Ang II. Metabolic stability studies utilizing rat kidney homogenates as a peptidase source, demonstrated that the structural changes present in Divalinal-Ang IV greatly increased its resistance to metabolism as compared to Ang IV. Together, these studies show that Divalinal-Ang IV is a stable, efficacious and specific inhibitor of AT4 receptors.

Angiotensin II↗
PubMed1996

Angiotensin IV inhibits neurite outgrowth in cultured embryonic chicken sympathetic neurones.

Angiotensin IV (Val-Tyr-Ile-His-Pro-Phe) is reported to enhance apomorphine induced stereotypy and to improve memory recall through actions on specific binding sites in the central nervous system. In the present study, 10 nM angiotensin IV or angiotensin II inhibited neurite outgrowth from cultured E11 chicken paravertebral sympathetic neurones by 25%. The effects of both peptides were inhibited by a 1 microM concentration of the angiotensin IV analogues. WSU 4042, Nle1-Y-I-amide or Nle1-AIV, but not by the avian angiotensin II antagonists, [Sar1,Ile8]Ang II or CGP 42112, suggesting that the inhibition of neurite outgrowth by both peptides is mediated by the angiotensin IV binding site. These results suggest that angiotensin IV may be involved in neurite modelling and may therefore have an important role in neuronal development.

Angiotensin II↗
PubMed1996

Effects of LY231617 and angiotensin IV on ischemia-induced deficits in circular water maze and passive avoidance performance in rats.

The antioxidant LY231617 has previously been shown to offer significant protection against postischemic cell death in the hippocampus and corpus striatum of rats. The present results extend this observation by demonstrating a concomitant protection against the spatial memory deficits that accompany damage to the hippocampus, as measured by the circular water maze task. These animals were further tested for changes in associative memory by employing a passive avoidance conditioning task. No deficits in passive avoidance conditioning were measured among the 4-vessel occlusion animals treated with LY231617 or vehicle. However, the intracerebroventricular injection of angiotensin IV (Ang IV) immediately prior to foot-shock conditioning improved retention of the conditioned response during the subsequent 2-day period. These results suggest that LY231617 can offer considerable protection against global ischemia-induced cell death in the hippocampus with resulting preservation of spatial memory abilities. In addition, untreated animals that suffered cell losses in the hippocampus remained capable of responding to the facilitory effect of centrally administered Ang IV on a non-spatial memory task. The hypothesized mechanisms of the protection characteristics of LY231617, and the nootropic effect of Ang IV, are discussed.

Angiotensin II↗
PubMed1996

Effects of discrete kainic acid-induced hippocampal lesions on spatial and contextual learning and memory in rats.

Substantial information is available concerning the influence of global hippocampal lesions on spatial learning and memory, however the contributions of discrete subregions within the hippocampus to these functions is less well understood. The present investigation utilized kainic acid to bilaterally lesion specific areas of the rat hippocampus. These animals were subsequently tested on a spatial orientation task using a circular water maze, and on an associative/contextual task using passive avoidance conditioning. The results indicate that both the dorsal CA1 and the ventral CA3 subregions play important roles in learning. Specifically, CA1 lesions produced a deficit in the acquisition of the water maze task and a significant memory impairment on the passive avoidance task. CA3 lesions also caused learning deficits in the acquisition of the water maze task, and produced even greater impairments in performance on the passive avoidance task. We conclude that CA1 and CA3 hippocampal subregions each play significant roles in the overall integration of information concerning spatial and associative learning.

Animals↗
PubMed1996

Neuropathology of synthetic beta-amyloid peptide analogs in vivo.

Considerable evidence exists demonstrating that beta-amyloid protein and its fragments 1-40 and 25-35 (beta (25-35)) are neurotoxic to cells in the rat hippocampus both in culture and in vivo. This neurotoxicity has been correlated to the aggregational state of the peptides. Previously we have shown that beta (25-35) produces a cavitational lesion in rat hippocampus and also reduces the enzyme or transmitter expressions in two subcortical structures whose axons project to the hippocampus: the locus coeruleus (LC) and the medial septum. In the present study, we further investigated the amino acid sequence that might be responsible for these effects. A series of synthetic peptide analogs of beta (25-35) with glycine substituted for serine, asparagine, lysine and methionine at positions 26, 27, 28 and 35, respectively, were injected at a 3 nmol dosage into the rat hippocampus once a week for 2 weeks. The damage to the hippocampus and immunohistochemistry of the LC and medial septum were examined 1 week following the second treatment. All of the synthetic peptides with glycine substitution produced damage to the hippocampal tissue. This damage was similar to that seen with beta (25-35). However, the reduction of enzyme expressions in the LC and medial septum was less from these substituted peptides than from that of beta (25-35). While beta (25-35) application resulted in a similar reduction of tyrosine hydroxylase (TH) and glutamate (Glu) immunoreactivities in the LC, only TH was significantly reduced in the substituted peptide groups. The least reduction of TH and Glu immunoreactivities in the LC was observed in rats treated with peptides in which glycine replaced either lysine or methionine. In the basal forebrain medial septum, the application of beta (25-35) resulted in a marked decrease in choline acetyltransferase (ChAT) immunoreactivity. This reduction was found to be less by each of the synthetic peptides. These results suggest that the biological activity of beta (25-35) is sensitive to changes in the primary structure of the peptide. Among the 4 amino acid residues examined, lysine and methionine at positions 28 and 35 appear to play more important roles in determining the action of beta (25-35).

Amino Acid Sequence↗
PubMed1996

Microinfusion of aminopeptidase M into the paraventricular nucleus of the hypothalamus in normotensive and hypertensive rats.

Normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) received aminopeptidase M (AmM) delivered into the paraventricular nucleus of the hypothalamus (PVN). Resulting changes in blood pressure were recorded in both anesthetized and alert animals. The findings indicate significant dose-determined decreases in blood pressure in members of both strains with SHR more responsive than WKY rats. The respective drops in blood pressure for members within each strain were equivalent for the anesthetized and alert conditions. Pretreatment with the specific angiotensin receptor antagonist, sarthran, [Sar1, Thr2] Angll, into the PVN greatly diminished these responses, suggesting the involvement of the brain angiotensin system. Additionally, a sympathetic nervous system blocker, hexamethonium, and the arginine vasopressin antagonist, Pmp1, O-Me-Tyr2-[Arg] vasopressin, were peripherally administered to assess the potential contributions of these systems to cardiovascular regulation by the brain angiotensin system. The use of these blockers, individually and combined, attenuated responsiveness to infusion of AmM into the PVN. We conclude that AmM can act as a hypotensive agent in both SHR and WKY rats, and that this decrease in blood pressure is at least partially mediated via the brain angiotensin system although other systems may play a role.

Aminopeptidases↗
PubMed1996

Angiotensin III and IV activation of the brain AT1 receptor subtype in cardiovascular function.

The present investigation determined that native angiotensins II and III (ANG II and III) were equipotent as pressor agents when ICV infused in alert rats, whereas native angiotensin IV (ANG IV) was less potent. An analogue of each of these angiotensins was prepared with a hydroxyethylamine (HEA) amide bond replacement at the N-terminus, yielding additional resistance to degradation. These three angiotensin analogues, HEA-ANG II, HEA-ANG III, and HEA-ANG IV, were equivalent with respect to maximum elevation in pressor responses when ICV infused; and each evidenced significantly extended durations of effect compared with their respective native angiotensin. Comparing analogues, HEA-ANG II had a significantly longer effect compared with HEA-ANG III, and HEA-ANG IV, whereas the latter were equivalent. Pretreatment with the AT1 receptor subtype antagonist, Losartan (DuP753), blocked subsequent pressor responses to each of these analogues, suggesting that these responses were mediated by the AT1 receptor subtype. Pretreatment with the specific AT4 receptor subtype antagonist, Divalinal (HED 1291), failed to influence pressor responses induced by the subsequent infusion of these analogues. These results suggest an important role for Ang III, and perhaps ANG IV, in brain angiotensin pressor responses mediated by the AT1 receptor subtype.

Amino Acid Sequence↗