Vascular alpha1-adrenoceptors in isolated perfused rat kidney: influence of ageing.

1. The present study identifies alpha1-adrenoceptor subtype(s) involved in constrictor responses of the kidney and how ageing influences it. 2. The study was conducted on kidneys from F344BNF1 rats, which unlike F344 or Wistar rats used by many previous investigators do not exhibit glomerulonephritis at advanced age. 3. Noradrenaline (NA) and phenylephrine (PHE) (non-selective alpha1) and A61063 (selective alpha(1A)) adrenoceptor agonists elicited constriction of perfused kidneys of young and old rats. The pD2 values (index of renovascular reactivity) were significantly higher for A61603 than for either PHE or NA, and significantly decrease across age groups. 4. BMY 7378 or RS 100329, alpha(1D)- or alpha(1A)-adrenoceptor antagonists, respectively antagonized the constrictor responses and suppressed the maximal responses to all agonists in young adult rat kidneys. However, antagonism of PHE or A61063 by BMY 7378 in old rat kidneys was surmountable. 5. This study suggests that: (i) alpha(1A) and alpha(1D)-adrenoceptor subtypes mediate vasoconstriction of perfused rat kidney; (ii) alpha(1A)-adrenoceptor subtype appears to predominate in renal vasculature based on agonist relative potencies. (iii) Ageing significantly decreases alpha1-adrenoceptor-mediated vasoconstriction of rat kidney.

Acrolein induces vasodilatation of rodent mesenteric bed via an EDHF-dependent mechanism.

Acrolein is generated endogenously during lipid peroxidation and inflammation and is an environmental pollutant. Protein adducts of acrolein are detected in atherosclerotic plaques and neurons of patients with Alzheimer's disease. To understand vascular effects of acrolein exposure, we studied acrolein vasoreactivity in perfused rodent mesenteric bed. Acrolein induced endothelium-dependent vasodilatation that was more robust and more sensitive than dilation induced by 4-hydroxy-trans-2-nonenal, trans-2-hexenal, or propionaldehyde. Acrolein-induced vasodilatation was mediated by K(+)-sensitive components, e.g., it was abolished in 0 [K(+)](o) buffer or in 3 mM tetrabutylammonium, inhibited 75% in 50 microM ouabain, and inhibited 64% in 20 mM K(+) buffer. Moreover, combined treatment with the Ca(2+)-activated K(+) channel inhibitors 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34, 100 nM) and apamin (5 microM) significantly reduced vasodilatation without altering sensitivity to acrolein. However, acrolein-induced % dilation was unaffected by l-NAME or indomethacin pretreatment indicating mechanistic independence of NO and prostaglandins. Moreover, acrolein induced vasodilatation in cirazoline-precontracted mesenteric bed of eNOS-null mice confirming eNOS independence. Pretreatment with 6-(2-propargyloxyphenyl) hexanoic acid (PPOH 50 microM), an epoxygenase inhibitor, or the superoxide dismutase mimetic Tempol (100 microM) significantly attenuated acrolein-induced vasodilatation. Collectively, these data indicate that acrolein stimulates mesenteric bed vasodilatation due to endothelium-derived signal(s) that is K(+)-, ouabain-, PPOH-, and Tempol-sensitive, and thus, a likely endothelium-derived hyperpolarizing factor (EDHF). These data indicate that low level acrolein exposure associated with vascular oxidative stress or inflammation stimulates vasodilatation via EDHF release in medium-sized arteries--a novel function.

Evaluation of valuation of toxicity profile of an alkaloidal fraction of the stem bark of Picralima nitida (fam. Apocynacaes).

Dermal and acute toxicity evaluation of the basic alkaloidal fraction of the stem bark of Picralima nitida, which has been shown to have pronounced activity against causative organisms of dermatomycosis in man, was carried out in animals. Acute intraperitoneal toxicity tests showed a dose-dependent toxicity. There was inflammation and necrosis of liver hepatocytes accompanied by reduction in neutrophilic count and a corresponding increase in lymphocytic count. There was no sign of reddening or irritation when applied into the eye conjunctiva. Dermal tests also showed that the fraction caused no sensitization, inflammation or death in the animal models used.

Potentiation of sympathetic neurotransmission in bovine isolated irides by isoprostanes.

Isoprostanes (IsoP) are formed by free radical catalyzed peroxidation of arachidonic acid independent of the cyclooxygenase enzyme. In the present study, we examined the effect of IsoP on norepinephrine (NE) release from the bovine isolated iris. Furthermore, we studied the role of IsoP's in hydrogen peroxide (H2O2)-induced enhancement of NE release from this tissue. Isolated bovine irides were prepared for studies of [3H]NE release using the superfusion method. Release of [3H]NE was induced via electrical field stimulation. Both 8-iso-prostaglandin E2 (E2-IsoP) and 8-iso-prostaglandin F2 alpha (F2-IsoP) produced a concentration-related enhancement of field-stimulated [3H]NE release from isolated bovine irides, an effect that was mimicked by the thromboxane (Tx) receptor agonist, U46619 and by H2O2. The Tx-receptor antagonist, SQ 29548 inhibited responses to E2-IsoP (10 microM) with an IC50 of 370 +/- 50 nM. SQ 29548 (10 microM) also blocked the enhancement of electrically-evoked [3H]NE release induced by U46619 (10 microM) but not that caused by H2O2 (300 microM). The Tx synthetase inhibitor, carboxyheptylimidazole (10 microM) prevented the stimulatory effect of E2-IsoP on evoked [3H]NE release without affecting responses induced by H2O2. We conclude that IsoP's can enhance sympathetic neurotransmission in the bovine isolated iris, an effect that can be blocked by a Tx-receptor antagonist. Furthermore, endogenously produced Tx's mediate the stimulatory effect of IsoP's on NE release. However, endogenously generated IsoP's or Tx's are not involved in H2O2-induced potentiation of sympathetic neurotransmission.

[(3)H]-serotonin release from bovine iris-ciliary body: pharmacology of prejunctional serotonin (5-HT(7)) autoreceptors.

In the present study, we investigated the pharmacological characteristics of electrically stimulated [(3)H]-serotonin release from mammalian iris-ciliary bodies. Isolated bovine and human iris-ciliary bodies were loaded with [(3)H]-serotonin, superfused with Krebs buffer solution and then stimulated with trains of 300 direct current (d.c.) pulses to initiate the release of the transmitter. The modification of this [(3)H]-serotonin release process by various serotonergic agonists and antagonists was studied in order to define the pharmacology of serotonin receptor(s) present in the iris-ciliary body. In bovine iris-ciliary body, electrically-evoked [(3)H]-serotonin release was calcium-dependent, tetrodotoxin-sensitive and was enhanced by serotonin (EC(50) = 200 n M) and 5-carboxmidotryptamine (EC(50) = 4 n M). The rank order of potency of agonists in enhancing field-stimulated [(3)H]-serotonin release was: 5-carboamidotryptamine > m-chlorophenylbiguanide > 2-methyl-5-hydroxytryptamine = 5-methoxy-dimethyltryptamine > serotonin > 5-methoxy-tryptamine > L-694,247 = alpha-methyl-5-hydroxytryptamine > CGS 12066A = 8-hydroxy-2-(di- n -propylamino)tetraline. Serotonin and m-chlorophenylbiguanide also enhanced electrically-evoked [(3)H]-serotonin release from human iris-ciliary bodies with EC(50)s of 3 microM and 30 n M, respectively. The pharmacological profile displayed by serotonin receptor agonists was supported by the potent antagonism of the serotonin-induced enhancement of [(3)H]-serotonin release by 5HT(7)receptor antagonists SB-258718 (IC(50) = 18.6 +/- 1.2 nM; n = 4) and mesulergine (IC(50) = 0.26 +/- 0.05 nM; n = 4). However, antagonists at 5HT(6)and 5HT(3)receptors exhibited a relatively weak blockade of serotonin induced enhancement of field-stimulated [(3)H]-serotonin release. These studies have shown the presence of functionally active prejunctional 5HT(7)autoreceptors regulating the release of [(3)H]-serotonin from bovine iris-ciliary bodies. Excitatory prejunctional 5-HT autoreceptors also exist in human iris-ciliary bodies. It is possible that these serotonin autoreceptors may have relevance to the regulation of aqueous humor dynamics in the anterior uvea.

Effect of hydroxycitric acid on serotonin release from isolated rat brain cortex.

There is evidence that hydroxycitric acid (HCA), an extract of dried fruit rind of South Asian trees of the genus Garcinia cambogia, can reduce food intake in experimental animals. In the present study, we investigated the effect of HCA on basal and potassium-depolarization evoked increase in radiolabeled serotonin ([3H]-5-HT) release from rat brain cortex slices in vitro. HCA (10 microM-1 mM) altered the baseline of spontaneous tritium efflux but had no significant effect on potassium-evoked release of [3H]-5-HT. When applied on its own, HCA (10 microM-1 mM) elicited a concentration-dependent increase in efflux of [3H]-5-HT reaching a maximum at 300 microM. We conclude that HCA can increase the release of radiolabeled 5-HT from the isolated rat brain cortex.

Role of catalase in pre- and postjunctional responses of mammalian irides to hydrogen peroxide.

In the present study, we examined the effect of inhibition of catalase with 3-aminotriazole (3-AT) on hydrogen peroxide (H2O2)-induced enhancement of sympathetic neurotransmission in bovine irides and on the inhibitory effect of this oxidant on norepinephrine (NE) release from human irides, in vitro. Furthermore, we investigated the effect of 3-AT on H2O2-induced attenuation of contractile responses to carbachol in the bovine isolated irides. Isolated mammalian irides were prepared for studies of [3H]NE release using the superfusion method and for contractile studies using isolated organ baths. At concentrations less than 100 microM, H2O2 had no significant effect on field-stimulated [3H]NE release from bovine or human irides. In bovine irides, 3-AT caused significant (P < 0.001) leftward shifts of concentration-response curves to H2O2 (10-300 microM). 3-AT also increased H2O2-induced attenuation of evoked [3H]NE release from human isolated irides. Low concentrations of H2O2 (< 100 microM) had no effect on carbachol contractions. However, 3-AT unmasked an inhibitory effect of low concentrations of H2O2 (3-100 microM) on carbachol-induced contractions. We conclude that inhibition of catalase causes both pre- and postjunctional responses of isolated mammalian irides to be more susceptible to oxidative stress induced by H2O2.

Human, bovine, and rabbit retinal glutamate-induced [3H]D-aspartate release: role in excitotoxicity.

The pharmacological basis of glutamate-induced [3H]D-aspartate release was investigated in isolated human, bovine and rabbit retinas. Isolated mammalian retinas were preloaded with [3H]D-aspartate and then prepared for studies of neurotransmitter release using the superfusion method. Release of [3H]D-aspartate was elicited by K+ (50 mM) or by L-glutamate. In bovine retinas, L-glutamate, but not D-glutamate induced an overflow of [3H]D-aspartate that was partially inhibited by low external calcium, omega-conotoxin (10 nM) or nitrendipine (1 microM). Metabotropic glutamate receptor (GLUR) agonists also evoked [3H]D-aspartate release in both bovine and human retinas whereas polyamines only enhanced the excitatory effects of L-glutamate on [3H]D-aspartate release. Antagonists of GLURs and the polyamine site inhibited L-glutamate evoked [3H]D-aspartate overflow with the following rank order of potency: MCPG >ifenprodil > AP-5 > arcaine> MK-801. In conclusion, L-glutamate-induces a stereoselective, calcium-dependent release of [3H]D-aspartate from isolated mammalian retinas that can be mimicked by GLUR agonists (and blocked by both receptor and polyamine site antagonists).

Studies on the anti-inflammatory and related pharmacological properties of the aqueous extract of Bridelia ferruginea stem bark.

The anti-inflammatory profile of the aqueous extract of Bridelia ferruginea stem bark was investigated using both in vivo and in vitro models. The extract exhibited strong topical anti-inflammatory effect shown as inhibition of croton oil-induced ear oedema in mice, and reduced hind-paw swelling and growth retardation in the adjuvant-induced arthritis model in rats, following oral administration at 10, 20, 40 or 80 mg/kg. The extract (10-80 mg/kg, p.o.) caused an inhibition of increase in vascular permeability in both cyclophosphamide-induced haemorrhagic cystitis and acetic acid-induced vascular permeability in rats and mice, respectively. B. ferruginea produced stabilization of erythrocytes exposed to heat and stress-induced lysis. Antipyretic and analgesic properties of the extract were also observed.

Studies on the anti-inflammatory, antipyretic and analgesic properties of Alstonia boonei stem bark.

The methanol extract of the stem bark of Alstonia boonei was investigated for anti-inflammatory property. The analgesic and antipyretic properties of the extract was also evaluated. The extract caused a significant (P<0.05) inhibition of the carrageenan-induced paw oedema, cotton pellet granuloma, and exhibited an anti-arthritic activity in rats. Vascular permeability induced by acetic acid in the peritoneum of mice was also inhibited. The extract also produced marked analgesic activity by reduction of writhings induced by acetic acid, as well as the early and late phases of paw licking in mice. A significant (P<0.05) reduction in hyperpyrexia in mice was also produced by the extract. This study has established anti-inflammatory, analgesic and antipyretic activities of the stem bark of A. boonei.

Effect of isoprostanes on sympathetic neurotransmission in the human isolated iris-ciliary body.

Isoprostanes (IsoP's) are prostaglandin-like compounds that are derived from free-radical catalyzed peroxidation of arachidonic acid independent of the cyclcooxygenase enzyme. In the present study, we investigated the effect of IsoP's on norepinephrine (NE) release from human isolated iris-ciliary bodies. Isolated human iris-ciliary bodies were prepared for studies of [3H]NE release using the superfusion method. Both 8-iso-prostaglandin F2alpha (F2-IsoP) and the thromboxane (Tx) receptor agonist, U46619 enhanced field-stimulated [3H]NE release from isolated, superfused human iris-ciliary bodies without affecting basal tritium efflux. On the other hand, an equimolar concentration (10 microM) of 8-iso-prostaglandin E2 (E2-IsoP) inhibited evoked [3H]NE overflow. The Tx-receptor antagonist, SQ 29548 blocked the enhancements of electrically-evoked [3H]NE release induced by F2-IsoP and U46619. However, the inhibitory responses elicited by E2-IsoP was not antagonized by SQ 29548. We conclude that IsoP's can produce both excitatory and inhibitory effects on sympathetic neurotransmission in human isolated iris-ciliary bodies. The stimulatory effects of IsoP's on NE release may be mediated by Tx-receptors.

Effect of inhibition of cyclooxygenase on pre- and postjunctional actions of peroxides in the iris-ciliary body.

In the present study, we investigated the effect of inhibition of cyclooxygenase (COX) with flurbiprofen (FBF) on peroxide-induced enhancement of field-stimulated [3H]norepinephrine ([3H]NE) release from bovine isolated irides. Furthermore, the effect of FBF was examined on peroxide-induced attenuation of contractions evoked by carbachol on this tissue. Irides were prepared for studies of neurotransmitter release and for measurement of contractile tension in vitro. Pretreatment of tissues with FBF (10 microM) caused significant (P < 0.001) rightward shifts of concentration-response curves to H2O2 and also decreased cumene hydroperoxide (cuOOH)-induced enhancement of evoked [3H]NE release. FBF (10 microM) partially prevented the attenuation of carbachol-induced contractions induced by H2O2 (300 microM) and cuOOH (300 microM). We conclude that inhibition of the biosynthesis of prostanoids reduced both the prejunctional stimulatory effects of H2O2 and cuOOH on sympathetic neurotransmission and inhibitory effects of peroxides on carbachol-induced contractions the in the bovine isolated iris.

Effects of the aqueous extract of Bridelia ferruginea stem bark on carrageenan-induced oedema and granuloma tissue formation in rats and mice.

The anti-inflammatory activity of the aqueous extract of the stem bark of Bridelia ferruginea was evaluated using carrageenan-induced paw oedema in rats and mice, and the cotton pellet granuloma method. The extract at doses ranging from 10 to 80 mg/kg p.o. significantly inhibited the carrageenan-induced rat paw oedema, with an ID50 value of 36 mg/kg. However, a low activity was produced in the mouse paw oedema. The extract also suppressed the granulomatous tissue formation of chronic inflammation. B. ferruginea therefore proved to be effective in both the acute and chronic phases of the inflammatory process.

Central nervous system depressant effect of Hoslundia opposita vahl.

The chloroform extract of the dried root of Hoslundia opposita has been evaluated for effects on the central nervous system (CNS). The extract significantly potentiated the phenobarbitone sleeping time in mice and produced a 60% protection against leptazol-induced convulsion. Neuropharmacological screening revealed CNS depression.

Biological effects of Myristica fragrans (nutmeg) extract.

The chloroform extract of nutmeg has been evaluated for antiinflammatory, analgesic and antithrombotic activities in rodents. The extract inhibited the carrageenan-induced rat paw oedema, produced a reduction in writhings induced by acetic acid in mice and offered protection against thrombosis induced by ADP/adrenaline mixture in mice.

Evaluation of the anti-diabetic property of Morinda lucida leaves in streptozotocin-diabetic rats.

The hypoglycaemic and anti-hyperglycaemic activities of a methanol extract of Morinda lucida Benth. (Rubiaceae) leaves were studied in normal and streptozotocin-diabetic rats. In normal rats, the extract demonstrated a significant (P < 0.05) and dose-dependent hypoglycaemic activity within 4 h after oral administration. The plasma glucose level of 400 mg kg(-1) of the extract at 4 h was 42.5 +/- 0.4 mg/100 mL (control 67.4 +/- 1.2 mg/100 mL). After 12 h, the plasma glucose level of rats administered 50, 100, 200 or 400 mg kg(-1) extract fell to 51.9 +/- 1.2, 47.3 +/- 0.8, 43.1 +/- 0.4 and 40.0 +/- 0.5 mg/100 mL, respectively. In hyperglycaemic rats, the extract produced a significant (P < 0.05) anti-diabetic effect from day 3 after oral administration, with 400 mg kg(-1) extract-treated animals having a plasma glucose level of 248.7 +/- 5.3 mg/100 mL compared with glibenclamide (10 mg kg(-1))-treated animals with a plasma glucose level of 251.5 +/- 5.8 mg/100 mL. These results suggest that the leaves of Morinda lucida have a strong glucose lowering property when administered to streptozotocin-treated rats.