A mechanism of action of phenylephrine on heart.

Phenylephrine exerted a positive chronotropic and inotropic effect on isolated, spontaneously beating, atria of reserpinised rabbits. Addition of phenoxybenzamine and phentolamine resulted in a depression of control contractile amplitude. Practolol, however, was devoid of this effect. The positive inotropic response to phenylephrine was significantly antagonised by all the three blockers used, while positive chronotropic response was annulled by phentolamine and practolol, but not with phenoxybenzamine. It is, therefore, suggested that phenylephrine exerts its cardiostimulant effects through mediation of both alpha and beta-1 adrenoceptors. A probable mechanism of action could be, that phenylephrine acts on some specific chemical group, shared by alpha and beta1 receptors. This specific group is probably blocked by both alpha and betaceptor antagonists separately, so phenylephrine becomes ineffective in presence of these antagonists.

Single plane cineangiographic study of normal left ventricular volumes in human subjects.

Single plane cine angiographic estimation of left ventricular volumes in 10 Indian subjects with no evidence of left ventricular disease was carried out. The figures obtained were end diastolic volume 72.43+/-10.27 ml/M2, endsystolic volume 26.82+/-7.46 ml/M2, stroke volume 45.61+/-12.23ml/M2, ejection faction 62.30+/-10.90%. These values compare well with those already reported in literature from Western countries. No study in Indian subjects was available for comparison so far.