In two groups of anesthetized (sodium pentobarbital), mature Sprague-Dawley rats, 1) aged 2 years and weighing 300-400 grams, 2) aged 6 months weighing 200-300 grams, baroreflex-induced circulatory responses to pressor (graded doses phenylephrine) and depressor (graded doses nitroglycerine) agents were compared to those occurring during progressive hemorrhage in the same animals. Graded withdrawals of blood from the femoral artery elicited progressive hypotension accompanied by bradycardia rather than expected tachycardia. Graded doses of phenylephrine (2.5 ug to 40 ug bolus, via femoral vein) regularly induced elevations in arterial blood pressure with associated reflex bradycardia. Similarly graded doses of nitroglycerine induced a marked decline in arterial blood pressure, without expected tachycardia. As hypotension became more severe (during hemorrhage), atrioventricular conduction slowed and A-V block developed, resulting in statistically greater slowing in ventricular than in atrial excitation and contractile cycles. Heart failure during hemorrhage in the rat is characterized sequentially by severe bradycardia, depressed atrial contractile force, impaired conduction and A-V block, terminating in ventricular, atrial, and finally, in pacemaker failure. Baroreceptor reflexes were blunted or even absent in both young and old animals during induced hypotension.

Animals↗

PubMedDate not supplied

Selective vagal innervation of the heart.

Parasympathetic ganglia are imbedded (1) in the epicardial fat pad located on the posterior surface of the dog's heart and (2) immediately overlying the point of penetration by the coronary sinus into the interatrial septum. The fat pad is situated between the inferior vena cava and the inferior left atrium. It contains multiple encapsulated ganglia, each consisting of two to 80 separate cells, richly intermingled with neural elements. Destruction of these ganglia by surgical excision and/or phenol painting interrupts both right and left vagal inhibition of atrio-ventricular (A-V) conduction, without obviously altering vagal modulation of sinoatrial function. Excision or phenol destruction of the fat pad overlying the right pulmonary vein inlets to the left atrium interrupts both right and left vagal inhibition of sinoatrial function, again without interfering with vagal control of atrioventricular nodal function. Well organized, encapsulated autonomic ganglia are also found throughout this fat pad. These experiments thus identify and localize separate concentrations of ganglion cells which differentially modulate automaticity and A-V conduction in the canine heart.

Animals↗

PubMedDate not supplied

Regional cardiac distribution of the sympathetic nerves.

Explore the source record for details and available documents.

Animals↗