The effects of
cardiac glycosides on systolic arterial pressure (SAP) and heart rate (HR) were studied in spontaneously hypertensive (SH) and normotensive (NT) Wistar rats.
Ouabain (2 mg/kg), given by i.p. injection to unanesthetized rats, produced a significant decrease in SAP in both SH and NT rats with little concomitant HR change. Baroreceptor
denervation abolished the response. To analyze the effects more completely, experiments were done on acutely anesthetized rats.
Ouabain was administered i.p. 30 min after induction of
anesthesia with
alpha-chloralose (60 mg/kg i.p.).
alpha-Chloralose alone produced a significant SAP decrease in both SH and NT rats and
bradycardia in SH but no significant HR change in NT rats.
Ouabain i.p. further reduced SAP in SH but had no effect on NT rats. When given by i.a. bolus injection (250 microgram in 0.1 mg of
heparin-saline) to anesthetized (
pentobarbital, 40 mg/kg i.p.) rats with intact left carotid sinus nerves,
ouabain produced a transient but significant reduction in SAP of SH but NT rats or SH rats with sinoaortic
denervation.
Digitoxin, given by stomach tube (4--5 mg/kg) for 1 week, decreased SAP in SH but not NT rats.
Digitoxin produced significant SAP increases in SH rats with sinoaortic
denervation. Arterial baroreceptor discharge is increased by
cardiac glycosides. The present results suggest that the reflex hypotensive effects of digitalis drugs are due, at least in part, to sensitization of baroreceptors and that SH rats may be more sensitive to these drugs possibly because of altered intrinsic baroreceptor properties.