Prevention of ventricular fibrillation requires central β-adrenoceptor blockade in rabbits

Figures & data

Figure 1.  Rabbits, chloralose anesthesia. Series 1. Pre-occlusion levels of heart rate, mean arterial pressure and s.d. of R-R intervals per respiratory cycle.

Table I.  Rabbits anesthetized with chloralose – Series 1.

		Controls	Metoprolol	Atenolol
Mean arterial	Before^1)	77±4	63±4	61±4
pressure mm Hg	Δ Occl	−1±3	1±2	0±1
Pulse pressure	Before	39±2.6	37±2.6	37±2.9
mm Hg	Δ Occl	−6±1.4^2)	−3±1.0^2)	−4±0.9^2)
Heart rate	Before^1)	267±8	233±6	228±6
beats/minute	Δ Occl	4±2	−3±2	0±1
ST20	Before	0.04±0.01	0.04±0.01	0.03±0.01
mV	Δ Occl^1)	0.51±0.07^2)	0.24±0.04^2)	0.22±0.03^2)
s.d. R-R intervals	Before^3)	1.4±0.07	1.8±0.14	1.3±0.03
per respiratory cycle, ms	Δ Occl	−0.2±0.05^2)	0.0±0.08	−0.2±0.05^2)

Values before and changes five minutes after coronary artery occlusion (Δ Occl).

1) Difference between controls and both β-blockers (p < 0.05).

2) Difference before – after occlusion (p < 0.05).

3) Difference between β-blockers (p < 0.05).

Table II.  Rabbits anesthetized with chloralose – Series 1.

	Controls	Metoprolol	Atenolol
Arterial concentrations of
Norepinephrine (nM/l)	3.9±0.6	4.8±0.7	4.4±0.6
Epinephrine (nM/l)	0.8±0.3	0.9±0.2	0.8±0.2
Sodium (mM/l)	141±1.1	142±0.8	143±0.6
Potassium (mM/l)	2.9±0.08	3.0±0.07	2.9±0.07
Baroreceptor sensitivity
ms/mm Hg, after
2 µg/kg phenylephrine	0.8±0.19	1.1±0.31^1)	0.6±0.08^1)
4 µg/kg phenylephrine	1.1±0.20	1.1±0.26^1)	0.5±0.07^1)
Lung inflation peak intra-tracheal pressure
mm Hg	11±1.5	12±0.8	12±1.4

Values recorded before coronary artery occlusion.

1) Difference between β-blockers (p < 0.05).

Figure 2.  Rabbits, chloralose anesthesia. Series 1. Rabbits (percent) surviving in the three treatment groups during the 30-minute period after coronary artery occlusion. The difference in survival between the metoprolol animals and the other two groups was statistically significant (p < 0.05).

Figure 3.  Rabbits, chloralose anesthesia. Series 1. Pre-occlusion values for heart rate and s.d. R-R per respiration in controls (Δ), metoprolol (○) and atenolol rabbits (□). Filled symbols: Animals, which fibrillated after the subsequent coronary artery occlusion. Open symbols: Animals without VF after the coronary artery occlusion.

Table III.  Rabbits anesthetized with chloralose – Series 2.

		Controls	Metoprolol	Atenolol
Mean arterial	Before	91±3	87±4	85±2
pressure mm Hg	Δ	−3±2	−2±2	−2±4
Heart rate	Before	283±11	280±7	275±8
beats/minute	Δ	+9±16	−51±5^1)2)	−50±8^1)2)
s.d. R-R intervals	Before	1.8±0.09	1.8±0.18	1.7±0.19
per respiratory cycle (ms)	Δ	−0.1±0.14	0.3±0.13^1)3)	−0.1±0.15^3)
Peak lung inflation	Before	9±0.6	9±0.7	8±0.7
intratracheal	Δ	0±0.4	0±0.6	1±0.6
pressure (mm Hg)

Values before and changes (Δ) two hours after the start of β-blocker administration.

1) Difference before – after two hours of β-blocker administration (p < 0.05).

2) Difference between controls and both β-blockers (p < 0.05).

3) Difference between β-blockers (p < 0.05).