VPT 321: Veterinary Neuropharmacology (2+1)

PHARMACOLOGICAL EFFECTS

Cardiovascular system

• There is little effect on blood pressure.
• In animals that are exposed to high doses of acetylcholine, atropine can increase the blood pressure that has been reduced.
• High doses cause dilatation of cutaneous beds producing “atropine flush.”
• An increase in the heart rate with the degree of tachycardia depending  on the vagal tone, which is high in horses and dogs, producing marked effects.

Gastrointestinal tract

• Atropine brings about a reduction in the salivary and intestinal mucosal secretions.
• Reduction of salivary secretions leads to dry mouth.
• Very high doses  decrease gastric secretions. 
• At therapeutic doses of atropine the tone and motility of gastrointestinal tract from stomach to colon is decreased and reduce the spasm of the gastrointestinal tract.

Bronchioles

• Atropine produces a reduction in the bronchial secretions and causes bronchodilatation. Atropine is thus used for the temporary relief in heaves.

Eyes

• Mydriasis and photophobia are noticed.
• By acting on the ciliary muscle it brings about paralysis of accommodation and cyclopegia.
• Since the drug induces an increase in the intraocular pressure, it is contraindicated in the presence of glaucoma.

Urinary tract

• Relaxes the urinary sphincter. Thereby useful  in renal colic.

Sweat glands

• Anhydrosis is noticed in animals that sweat. In large doses it may bring about hyperpyrexia as sweat secretion is reduced.
• In equine, sweating is controlled by adrenergic mechanisms and hence anhydrosis is not noticed.
• These drugs have least effect in species that do not use cholinergic sweating as an important component of thermoregulation.

On central nervous system

• In therapeutic doses there is minimal effect. In toxic doses mania and excitement are observed in domestic animals followed by depression and coma.
• In human beings hallucination and disorientation are noticed. Scopolamine has more effects on the central nervous system than atropine.