VPT 321: Veterinary Neuropharmacology (2+1) copy 1

DRUGS ACTING ON AUTONOMIC GANGLIA

• Drugs acting on autonomic ganglia act on both sympathetic and parasympathetic ganglia without specificity and either (stimulate or inhibit discharges from post ganglionic fibres). These are classified into
  • Autonomic ganglionic stimulating drugs
  • Autonomic ganglionic blocking drugs

Autonomic Ganglionic Stimulating Drugs

• These are further divided into
  • Natural alkaloids.
    • Eg. Nicotine, Lobeline
  • Synthetic drugs.
    • Eg.Tetramethyl ammonium (TMA),
    • Dimethyl Phenyl Piperazinium (DMPP)

Autonomic ganglionic blocking drugs

• These are subdivided into
  •  Persisting depolarizing ganglionic blocking drugs.
    • Eg. Nicotine (large doses)
  • Non-depolarizing ganglionic blocking drugs.
    • Eg. Hexamethonium, Pentalinium, Pentamethonium, Mecamylamine, pempidine, Trimethaphan
•  Since drugs acting on autonomic ganglia affect both sympathetic and parasympathetic postganglionic fibers, the overall effects of these agents on various functions are depended upon the predominance of sympathetic or parasympathetic tone in particular structure as detailed below

  Organ	Predominant tone	Effect of ganglionic stimulation	Effect of ganglionic blockade
  Cardiovascular system & blood vessels	Sympathetic	Vasoconstriction, hypertension , decreased peripheral blood flow	Vasodilation, hypotension , increased peripheral blood flow, decrease venous return,, pooling of blood
  Heart	Parasympathetic	Bradycardia	Tachycardia
  GI tract	Parasympathetic	Increased tone and motility, increased secretion , defecation	Increased tone and motility, constipation
  Eye	Parasympathetic Parasympathetic	Miosis -	Mydriasis Cycloplegia
  Iris Ciliary muscle
  Urinary bladder	Parasympathetic	Urination	Urine retention
  Salivary glands	Parasympathetic	Watery salivation	Dry mouth
  Sweat glands	Sympathetic (Adrenergic)	Increased sweating	Anhydrosis