I.S. de la Lande

Pharmacological and enzymic constituents of the venom of an Australian ‘bulldog’ and Myrmecia pyriformis

Abstract In addition to histamine, a non-histamine smooth muscle stimulant and histamine-releasing activity, the presence in the venom of Myrmecia pyriformis of hyalur onidase and red cell lysing activity has been confirmed. The venom does not possess bradykinin-releasing activity. It is highly toxic to mice. Dialysis, sensitivity to heat and to proteolytic enzymes, butanol-acetic paper chromatography and paper electrophoresis have been employed to assist in the identification and separation of the above activities. The results indicate that portion of the histamine-releasing activity and all the hyaluronidase activity are distinct from the smooth muscle stimulant and red cell lysing components.

Effect of acetylcholine on the response of the isolated rabbit ear artery to stimulation of the perivascular sympathetic nerves

Abstract In the isolated rabbit ear artery, low concentrations of exogenous acetylcholine inhibited the response of the artery to periarterial electrical stimulation, while much greater concentrations of acetylcholine were required to inhibit the response to exogenous noradrenaline. This action of acetylcholine on periarterial stimulation was suppressed by atropine and potentiated by cholinesterase inhibitors. Neither atropine nor cholinesterase inhibitors, in concentrations which modified the effects of exogenous acetylcholine, altered the response of the artery to periarterial stimulation. The study failed to confirm that either a cholinergic element or endogenous acetylcholine has an effect in the arterial sympathetic nerve response.

Effect of progesterone on the metabolism of noradrenaline in rabbit uterine endometrium and myometrium

Summary1.The metabolism of (−)-3H-noradrenaline was examined in the endometrium and the myometrium from rabbits which had received 17β-oestradiol, either alone (oestrogen-dominated) or with progesterone (progesterone-dominated).2.The progesterone treatment resulted in a 2.5-fold increase in 3H-NMN formation in the endometrium, with no change in 3H-DOPEG, 3H-DOMA or 3H-OMDA formation. In the myometrium, progesterone caused a 5-fold increase in 3H-NMN formation and a 2.5-fold increase in 3H-OMDA formation, but did not affect 3H-DOPEG or 3H-DOMA formation.3.In the progesterone-dominated endometrium, both 3H-NMN and 3H-OMDA formation were strongly inhibited by cocaine 30 μmol/l. When O-methylation was inhibited by a COMT inhibitor, cocaine prevented the resultant increases in deamination of noradrenaline to 3H-DOPEG and in the accumulation of 3H-noradrenaline by the tissue. The 3H-noradrenaline which accumulated in endometria, in which both MAO and COMT were inhibited, was firmly bound; desipramine 3 μmol/l and (+)-amphetamine 10 μmol/l were equieffective with cocaine 30 μmol/l in inhibiting the accumulation.4.Cocaine 30 μmol/l was without effect on 3H-NMN and 3H-OMDA formation in the progesterone-dominated myometrium, nor did it prevent the increase in 3H-DOPEG formation produced by COMT inhibition.5.Fluorescent histochemical analysis of the endometrium indicated that the epithelial cells of the endometrial glands were the site of cocaine-sensitive noradrenaline accumulation.6.It is concluded that progesterone stimulates O-methylation in the endometrium and myometrium in different ways. In the endometrium, it increases the activity of an unusual cocaine-sensitive extraneuronal uptake system associated with endometrial glands, presumably by causing the glands to proliferate. In the myometrium, it increases the activity of a cocaine-insensitive extraneuronal O-methylating system.

Cocaine-sensitive O-methylation of noradrenaline in dental pulp of the rabbit: Comparison with the rabbit ear artery

SummaryIncisor pulp from the rabbit metabolises exogenous noradrenaline in concentrations between 0.12 and 1.2 μmol/l mainly to NMN.Effects of chronic sympathetic denervation indicated that in incisor pulp the NMN is extraneuronal in origin, and that DOPEG and DOMA formation, as well as a major part of the noradrenaline which accumulates in the tissue, are associated with the sympathetic nerves.NMN formation was unaffected by hydrocortisone 210 μmol/l, but was strongly inhibited by cocaine 30 μmol/l. These effects contrasted with those in the rabbit ear artery, where NMN formation was increased by cocaine 30 μmol/l and decreased by hydrocortisone 210 μmol/l.In COMT-inhibited denervated pulp, cocaine inhibited the accumulation of noradrenaline.Monoamine fluorescence histochemistry of pulp exposed to noradrenaline 50 μmol/l indicated that cocaine-sensitive uptake occurred in fibroblasts.It is concluded that O-methylation of noradrenaline in dental pulp involves prior uptake of the amine by a process resembling uptake, but which is distinguished from uptake1 by its extraneuronal location.

Effect of Chronic Denervation on the Activities of Monoamine Oxidase and Catechol-O-Methyl Transferase and on the Contents of Noradrenaline and Adenosine Triphosphate in the Rabbit Ear Artery

When assayed on homogenates of the rabbit ear artery up to 192 h after sympathetic denervation, the activity of monoamine oxidase (MAO) showed a small but significant decrease (maximum 9%). The activity of catechol-O-methyl transferase (COMT) appeared unchanged, although it is possible that the small and variable nature of this enzyme activity compared with that of MAO may have masked a comparable effect of denervation. The maximum decreases in noradrenaline (NA) and adenosine triphosphate (ATP) contents were greater than 90% at 48 h, and 32% at 96 h after denervation. These results confirm the presence of neuronal as well as extra-neuronal MAO, and also the presence of extraneuronal comt in this artery. The decline in ATP contents after denervation suggest that part of the ATP is neuronal. However, the estimated ratio of NA to neuronal ATP is far in excess of that reported for isolated noradrenaline storage vesicles, suggesting that the major portion of the neuronal ATP was not present in these vesicles.

Fractionation of bulldog ant venom

Abstract The venom of an Australian Bulldog Ant, Myrmecia pyriformis, has been fractionated by means of low voltage starch gel electrophoresis and gel filtration on Sephadex G50 and G75 columns. The aims of the study were (a) to establish whether the biological activities which had previously been described resided in separate venom components, and (b) to isolate, in a purified form, the component possessing non-histamine smooth muscle stimulant activity. Starch gel electrophoresis demonstrated the presence of seven protein components. Sephadex gel filtration resulted in the separation of a fraction which appeared homogeneous on starch gel electrophoresis. This fraction, which was enzyme-free, possessed smooth muscle stimulant, red cell lysing and histamine-releasing activities and resembled the major peptide from bee venom, melittin.

The role of monoamine oxidase in the response of the isolated central artery of the rabbit ear to tyramine

1 Monoamine oxidase activity was demonstrated histochemically throughout the media of the rabbit ear artery but not in the adventitia at its border with the media where the sympathetic nerve terminals are concentrated. Neither intensity nor distribution of enzyme activity was perceptibly altered up to 60 days after sympathetic denervation. 2 Iproniazid and nialamide increased the sensitivity of the artery to intraluminal tyramine much more than that to extraluminal tyramine, so that the difference between the potencies for the two routes of administration became less marked. 3 The results indicate that inactivation by monoamine oxidase in the media is a factor contributing to the relatively low potency of intraluminal tyramine on the artery.

Presynaptic control of noradrenaline release from sympathetic nerves in human dental pulp

This study was undertaken to determine whether release of noradrenaline from sympathetic nerves in human dental pulp in vitro was modulated by presynaptic adrenoceptors and by dopamine receptors. Pulp was incubated for 30 min with 3H-noradrenaline (0.6 mumol/l) and then perfused continuously with Krebs solution. Field stimulation of the sympathetic nerves at 5 Hz increased the overflow of 3H into the perfusate three-to fourfold. The stimulation-induced overflow of 3H was abolished by tetrodotoxin (0.1 mumol/l) and under Ca(2+)-free conditions, indicating that the increased 3H was derived from nerves. The stimulation-induced overflow was inhibited by noradrenaline (0.1 and 1.0 mumol/l), the alpha 2-adrenoceptor agonist UK14,304 (0.1 mumol/l), dopamine (1.0 mumol/l) and the dopamine receptor agonist, apomorphine (1.0 mumol/l). When the receptor agonists were noradrenaline or dopamine, desipramine (0.3 or 3.0 mumol/l) was present to prevent their uptake by the sympathetic nerves. Clonidine (1.0 mumol/l; tested at 2 Hz as well as 5 Hz) and the alpha 1-receptor agonist methoxamine (1.0 mumol/l) were without effect. The alpha 2-receptor antagonist/rauwolscine (0.1 mumol/l) prevented the inhibitory effects of noradrenaline and UK14,304, but had little effect on the inhibition produced by dopamine. Inhibition of the stimulation-induced overflow by apomorphine was prevented by the dopamine receptor antagonist haloperidol (0.1 mumol/l). The resting overflow of 3H was unaffected by any of the above agents except dopamine, which caused a small increase. It is concluded that the sympathetic nerves in human dental pulp possess inhibitory presynaptic alpha 2-adrenoceptors and dopamine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a 5‐HT1‐like receptor mediating the amplifying action of 5‐HT in the rabbit ear artery

1 The nature of the 5‐hydroxytryptamine (5‐HT) receptors which amplify the vasoconstrictor effect of methoxamine was examined in the rabbit isolated perfused ear artery with intact endothelium. Indices of amplification were leftward shifts of methoxamine dose‐response (DR) curves produced by 5‐HT (0.3 μm) (Method I), and the appearance of vasoconstrictor responses to 5‐HT receptor agonists when methoxamine was present in a near‐threshold concentration (Method II). 2 The amplifying effect of 5‐HT (Method I) was unaffected by prazosin (0.08 μm), was partly depressed by 5‐HT2‐receptor antagonists in high concentrations (ketanserin 0.5 μm, LY53857, 1.0 μm), and was abolished by a non‐selective antagonist of 5‐HT1 and 5‐HT2 receptors (methiothepin, 0.01 μm). 3 Amplifying potencies of agonists assessed by both Methods I and II were in the order 5‐carboxamidotryptamine (5‐CT)>5‐HT>α‐methyl 5‐HT. The potency of sumatriptan (assessed by Method II only) was intermediate between those of 5‐HT and α‐methyl 5‐HT. 4 Ketanserin and LY53857 inhibited the amplifying action of 5‐CT to about the same extent as that of 5‐HT. 5 The amplifying potencies of the agonists are in marked contrast to the reported contractile potencies in the rabbit aorta where the receptor is 5‐HT2, but are almost identical with reported contractile potencies in the dog saphenous vein where the receptor is 5‐HT1‐like. 6 It is concluded that a 5‐HT1‐like receptor mediates the amplifying interaction between 5‐HT and methoxamine in the rabbit ear artery which can be weakly blocked by ketanserin and LY53857. 7 Since 5‐CT was equipotent when applied separately to the intimal and adventitial surfaces of the artery, it is suggested that the 5‐HT1‐like receptors are distributed uniformly across the artery wall.

Metabolism of [3H]-noradrenaline in human dental pulp in vitro

Slices of pulp from human maxillary and mandibular molar and promolar teeth were incubated with [3H]-noradrenaline (0.2 mumol/l) for 30 min after which the [3H]-noradrenaline and [3H]-metabolites in the tissue and medium were assayed by column chromatography. The deaminated metabolites 3,4-dihydroxy phenyl glycol (DOPEG) and 3,4-dihydroxy mandelic acid (DOMA) constituted 81% of the metabolites formed. Cocaine, an inhibitor of uptake1, decreased the formation of DOPEG and DOMA as well as the accumulation of [3H]-noradrenaline. In contrast to findings in rabbit pulp, when the disposition of exogenous noradrenaline in human pulp was examined by monoamine fluorescence histochemistry there was no evidence of extraneuronal accumulation of noradrenaline by connective tissue cells. In further experiments, pulp that had been incubated in [3H]-noradrenaline (0.6 mumol/l) for 30 min and superfused for 200 min contained [3H]-noradrenaline (183 pmol/g) and [3H]-DOMA (89 pmol/g). The 3H that overflowed into the perfusate between 85 and 90 min consisted mainly of metabolites. Stimulation of the sympathetic nerves through field electrodes increased the overflow of [3H]-noradrenaline into the perfusate threefold without affecting the overflow of metabolites. The increase was much greater (eightfold) in the presence of an alpha-adrenoceptor antagonist (rauwolscine; 0.1 mumol/l), plus inhibitors of uptake1 (desipramine; 0.3 mumol/l) and uptake 2 (corticosterone; 10 mumol/l). The results are interpreted as evidence that in human dental pulp the disposition of exogenous noradrenaline is determined largely by uptake by sympathetic nerves. After uptake, noradrenaline is deaminated by intraneuronal monoamine oxidase to DOPEG and DOMA.(ABSTRACT TRUNCATED AT 250 WORDS)