Effects of intracerebroventricular injection of histamine and H1, H2 receptor antagonists on electrocardiographic parameters in broiler chickens

The aim of this study was to assess the effects of exogenous histamine and H1 and H2 central receptors
on electrocardiographic (ECG) parameters, heart rate and mean electrical axis in broiler chickens. For this
purpose, Ross broiler chickens (750-800 g weight) received intracerebroventricularly (ICV) histamine.
Moreover, to determine the receptors involved in histamine-induced alterations in ECG changes, H1 and H2
blockers were administered to histamine-treated chickens. All ECGs were standardized at 1 mV = 20 mm,
with paper speed of 50 mm/sec. Leads І, ІІ, ІІІ, aVR, aVL and aVF were recorded. Injection of histamine
(200 and 300 μg) decreased the duration of T wave and QRS complex and elevated the heart rate as
compared to the control group (P<0.05). Chlorpheniramine (100 μg), an H1 receptor antagonist, increased the duration rate of T wave and QRS complex and reduced the heart rate (P<0.05). Cimetidine, an H2 receptor antagonist (100 μg) had no effect on ECG parameters. Pretreatment with chlorpheniramine (100 μg)
significantly attenuated histamine effects (200 μg) on the duration of T wave, QRS complex and heart rate
(P<0.05). Mean electrical axis, calculated from leads ІІ and ІІІ, did not differ between groups and it was
between -93° and -99° in all chickens. In conclusion, exogenous histamine intracerebroventricularly results in
sinusoidal tachycardia in broiler chickens and central H1 receptors mediate the stimulatory effects of
histamine on heart rate, but H2 receptors had no role in this manner.