T. Y. Lot

Effects of extracts of seed and leaf of Piper guineense on skeletal muscle activity in rat and frog

The pharmacological effects of leaf and seed extracts of Piper guineense were investigated on phrenic nerve hemidiaphragm activity following electrical stimulation in vitro. Copyright

Effects of Daniellia oliveri stem bark and leaf extracts on rat skeletal muscle

The stem bark and leaves of Daniellia oliveri were screened phytochemically and the effects of their respective methanol extracts on the skeletal muscle of rats were investigated using the isolated phrenic nerve hemidiaphragm muscle preparation. Both were found to contain tannins, cardiac and saponin glycosides. In addition, the bark, but not leaves, contained cyanogenetic glycosides. The methanol extracts were found to possess neuromuscular blocking properties. The leaf extract appeared to act primarily by inhibiting the influx of extracellular Ca2+ principally by inhibiting K+ channels. The inhibitory action of the bark extract appeared to be mediated by interference with transmitter release and an action on multiple sites. Copyright

Effects of Dopamine on the Gastrointestinal Tract of Chicks

Abstract— The effects of dopamine on the gastrointestinal tract of chicks have been investigated. Dopamine caused concentration‐related contractions of the upper oesophagus, crop or lower oesophagus but relaxed the duodenum, ileum, large intestine or caecum in a concentration‐related fashion. By means of specific antagonists, the presence of muscarinic, histamine (H1), α‐adrenergic, 5‐HT‐ergic and dopaminergic receptors were established in the lower oesophagus and their stimulation caused contraction while β‐adrenergic‐receptor stimulation caused relaxation. Contraction of the lower oesophagus induced by dopamine was abolished by lysergic acid diethylamide and was antagonized by moderate concentrations of haloperidol or pimozide. Tachyphylaxis developed to repeated administration of a large concentration of dopamine. These findings suggest that contraction of the lower oesophagus of chicks by dopamine is largely mediated by 5‐hydroxytryptamine release and that stimulation of dopaminergic receptors contributes to a lesser extent.

Changes in smooth muscle sensitivity to agonist drugs during development

The receptors in the expansor secundariorum muscle of chicks were characterized pharmacologically and the changes in their response to nerve stimulation and agonist drugs determined during development. The muscle responded to noradrenergic nerve stimulation, noradrenaline and 5-hydroxytryptamine without any change in sensitivity during development. Expansor muscles from 15-day-old chicks were more sensitive to isoprenaline than muscles from older animals. The muscle from 15-day-old chicks responded to acetylcholine and histamine; the sensitivity to both drugs decreased progressively with increasing age of the chicks and disappeared by day 40 posthatching. The normal developmental decrease in response to acetylcholine and histamine were prevented by surgical denervation of the muscle; an intervention that also induced supersensitivity to noradrenaline greater than isoprenaline greater than 5-hydroxytryptamine. The muscle responded to potassium chloride without any change in sensitivity during development or following surgical denervation. These findings indicate that sympathetic nerves influence the responsiveness of the expansor secundariorum muscle to drugs, especially the development decrease in response to acetylcholine and histamine.

Effects of stem bark and leaf extracts of Bridelia ferruginea on rat bladder smooth muscle.

The effects of ethanol extracts of Bridelia ferruginea leaves and stem bark on purinergic neurotransmission in the rat bladder were investigated. The stem bark extract potentiated the contraction of the bladder evoked by exogenous adenosine 5-triphosphate (ATP) but depressed KCl-induced contractions in a dose-related pattern; these two opposite actions might account for the lack of effect on field stimulation of the bladder purinergic nerves. The leaf extract depressed purinergic nerve-mediated contraction of the rat bladder in a dose-related fashion. This action could be attributed to blockade of purinergic neurotransmission since the leaf extract did not affect KCl-induced contractions.

Effects of Daniellia oliveri bark on isolated rat bladder.

The stem bark of Daniellia oliveri was screened phytochemically and a methanol extract prepared.Condensed tannins, saponins, cyanogenetic and cardiac glycosides were identified in the crude drug. The cardiac glycoside components in the methanol extract were precipitated with acetone to yield a reddish‐brown residue. The n‐butanol soluble fraction of an aqueous solution of this residue tested positive for cardiac glycosides and was shown by TLC to contain steroidal compounds. This fraction was subjected to pharmacological studies on isolated rat bladder smooth muscle. It had no effect on purinergic neurotransmission but was a noncompetitive antagonist for muscarinic receptors. Copyright

Effects of Khaya senegalensis Purinergic Transmission in the Rat Bladder

AbstractThe effects of a methanol extract of the stembark of Khaya senegalensis (Meliaceae) on smooth muscle of rat bladder have been investigated in vitro. The extract showed a dual agonist action. At concentrations lower than 1 × 10−5 g/ml, the extract produced a dose-dependent relaxation of the rat bladder while greater extract concentrations produced a dose-dependent contraction. The relaxation was mediated by stimulation of adrenergic receptors and also by depression of the bladder by a direct action. The contraction was eliminated by 1 × 10−5 g/ml quinacrine, indicating it was due to purinoc-eptor stimulation.

Dopamine depresses non‐adrenergic, non‐cholinergic neurotransmission in the rat bladder

Abstract— The effects of dopamine on non‐adrenergic, non‐cholinergic (NANC) neurotransmission have been investigated using rat bladder strips in‐vitro. Dopamine administered alone did not produce any effect on the bladder but it depressed responses to NANC nerve stimulation in a dose‐related fashion. All doses of dopamine employed depressed KCl‐evoked contractions of the bladder to similar extents. The depressant action of dopamine on NANC transmission was not mediated by blockade of purinergic receptors, but was partially reversed by haloperidol. It is suggested that depression of NANC neurotransmission induced by dopamine in the rat bladder is partly mediated by dopaminergic receptors.

Mechanisms of action of dopamine in the peripheral nervous system of chicks and rats.

Abstract— The effects and mechanisms of action of dopamine on the lower oesophagus and expansor secundariorum muscle (ESM) of chicks and on the bladder of rat have been examined. Dopamine contracted the lower oesophagus in a concentration‐related fashion but failed to contract the muscle from chicks pretreated with reserpine or p‐chlorophenylalanine. Contraction of the ESM by dopamine was antagonized by prazosin but not by propranolol. Supersensitivity of the ESM to dopamine observed 3 or 28 days after surgical denervation of the muscle was comparable. Dopamine did not exert any agonist effect on the rat bladder but depressed responses to stimulation of non‐adrenergic, non‐cholinergic (NANC) nerves in the bladder. These findings indicate that dopamine contracts the upper oesophagus of chicks by releasing 5‐hydroxytryptamine, activates α‐adrenergic receptors causing contraction of the ESM but depresses NANC neurotransmission in the bladder.

Smooth muscle sensitization and neuromuscular depression induced by chronic administration of antimalarial drugs

The functional effects on chick smooth and skeletal muscle of chronic administration of 60 mg kg-1 chloroquine or quinacrine given as daily intraperitoneal injections for 70 days have been investigated. Noradrenaline and potassium chloride (KCl) contracted the normal expansor secundariorum muscle, a smooth muscle from the wing of chicks wholly innervated by noradrenergic nerves. The muscle was unresponsive to acetylcholine and histamine. Chronic administration of chloroquine or quinacrine induced supersensitivity of expansor muscles to KCl and the muscles were contracted by acetylcholine and histamine. These actions were more pronounced in quinacrine-treated chicks and could be due to direct smooth muscle sensitization that may result in postjunctional changes. The oesophagus is a smooth muscle that is predominantly under parasympathetic control. The oesophagus from chronically-treated chicks was more sensitive to acetylcholine and KCl than the control muscles. This sensitization was more marked for chloroquine than quinacrine. Chronic administration of chloroquine and quinacrine depressed skeletal muscle contractions evoked by acetylcholine and potassium chloride. These findings indicate that chronic chloroquine and quinacrine administration sensitise smooth muscle to agonist drugs but depress neuromuscular transmission.