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 These drugs block the action of ACh on the muscarinic type of cholinergic effector organs, but do not affect the nicotinic action of ACh on the postganglionic neurons or on skeletal muscle (e.g. atropine, glycopyrrolate).

Table 7.4 Cardiovascular effects of adrenergic agonists.

Agent	HR	CO	SVR	VR	MAP	Arrhythmias	RBF	AR	CNS stimulation
Phenylephrine	−	−	+++	++	+++	0	−	0	0
Norepinephrine	−	−	+++	++	+++	+	−	0	0
Epinephrine	++	++	+	+	+	+++	−	−	+
Ephedrine	++	++	++	++	++	++	±	−	+
Dopamine	+	++	−	+++	−	+	+++	0	0
Dobutamine	+	+++	0	±	+	±	++	0	0
Isoproterenol	+++	+++	−	−	±	+++	−	−	+

HR = heart rate, CO = cardiac output, SVR = systemic vascular resistance, VR = venous return, MAP = mean arterial pressure, RBF = renal blood flow, AR = airway resistance. + = increase, − = decrease, 0 = no change.

Note: Dopamine decreases SVR and MAP in the horse at clinical doses.

Table 7.5 Comparative effects of anticholinergic drugs.

Anticholinergic	Salivary and respiratory secretions	HR	Relax smooth muscle	Mydriasis	↓ Gastric H+ secretions	GIT tone	Alter fetal HR
Atropine	−	+++	++	+	+	−	+
Glycopyrrolate	−	+++	+++	0	+	−	0
Scopolamine	−	+	+	+++	+	−	+

HR = heart rate, GIT = gastrointestinal tract.

+ = increase, − = decrease, 0 = no change.