Veterinary Neuropharmacology

PHARMACOLOGICAL ACTIONS

• H₂ antagonists block histamine induced gastric secretion, cardiac stimulation (in guinea pigs), uterine relaxation in rat) and bronchial relaxation (H₂ blockers potentiate histamine induced bronchospasm)
• Attenuate fall in BP due to histamine,specially at the late phase response with high doses
• Selective in action
• Have no effect on H₁ mediated responses or on other transmitter/autacoid.
• Significant in vivo action of H₂ blockers is marked inhibition of gastric secretion.
• Basal, psychic,neurogenic and gastric phases of secretion are suppressed dose dependantly.
• Secretory responses to Ach, gastrin, insulin, alcohol,food are attenuated.
• Reflects the permissive role of histamine in amplifying responses to other secretions.
• Reduces acid output,volume of pepsin content and intrinsic fator secretion.
• Normal vitamin B₁₂ absorption is not interfered
• Have antiulcerogenic effect (60-70% inhibition of 24hour acid output).
• Gastric ulceration due to NSAIDs, cholinergic and histaminergic agents is prevented
• They do not possess any direct effect on gastric or oesophageal motility or sphincter tone.