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Biophysics of Pericardium, Great Vessels and Chambers of Frog Heart and their Haemodynamic Inter -relationships

Intravenous infusions on intact dog hearts both in closed- and open-chest experiments indicate that a rise in the intra-atrial pressure is accompanied by either a positive, a negative or a no chronotropic effect, irrespective of the integrity of vagi. Positive chronotropic effects of similar intensity were also obtained even after bilateral vagotomy, topical application of cocaine or parenteral administration of atropine, tetraethylammonium or hexamethonium compounds. Moreover, the rise in the intra-atrial pressure or the degree of visible distention of the right atrium was not necessarily associated with a parallel rise in the heart rate. Thus, the infusion acceleration response obtained with some infusions only, fails to fulfill the requirements of a reflex action. There is, therefore, no justification for labeling it as a "reflex" effect, as advocated by Bainbridge. The chronotropic effects of the infusions seem to be due to stretch-induced alterations in impulse generation as a result of changes in the intra-atrial pressure and possibly depend upon the initial conditions at the pacemaker.

It was observed that the heart rate was minimum at zero transmural pressure. The mean heart rate at zero transmural pressure was 23+/-5/min. This mean heart rate increased from 23+/-5/min to a peak value of 40+/-6/min (74% acceleration) when the transmural pressure was raised from 0 to +4 mm Hg and to a similar peak value of 36+/-8/min (56% acceleration) when the transmural pressure was lowered from 0 to -4 mm Hg. The peak values attained at +/-4 mm Hg were highly significant (p less than 0.001). It is concluded that the heart rate at zero transmural pressure represents the basic intrinsic pacemaker frequency independent of neural, humoral, thermal and haemodynamically induced mechanical influences.

The effect of increasing the intraluminal pressure in the right heart on the activity of isolated perfused dog hearts and the effect of increasing the intraluminal pressure on the activity of isolated right atria of dogs, rabbits, guinea pigs and albino rats have been studied. It has been observed that there is a direct relationship between the magnitude of intraluminal right atrial pressure and the inotropic and chronotropic responses of the whole heart and right atrium up to certain critical pressures (5–15 mm Hg). Some modifications in this behavior of the hearts due to repeated changes in the intraluminal pressure have also been described. It has been suggested that stretch of the cardiac tissue due to increased intraluminal pressure may cause alterations in membrane metabolism at the pacemaker.

On a demontre que la distension pericardiale produit des changements chronotropiques dans le cœur de grenouille isole en perfusion. Sur 26 cœurs, l'acceleration cardiaque (18 a 148%) se produit dans 12 avec un volume de fluide pericardique atteignant 4 ml. Dans les 14 cœurs restant nous avons observe une bradycardie, des irregularities de conduction, un blocage cardiaque et une arythmie. On en conclut que ces effects chronotropiques et les variations du parametre d'impulsion sont dues aux changements dans l'activite du «pacemaker».

Concentration-response curves were obtained for the action of acetylcholine (ACh) on frog hearts perfused under controlled dynamic conditions. The cardiac output, frequency of contractions, and arterial pressure developed by the heart were continuously recorded electronically. The minimum concentration of ACh that affected pace-maker frequency and ventricular tone was about the same, and was unaffected by the presence of anticholinesterases. The action of ACh on pace-maker frequency was potentiated by anticholinesterases, the degree of potentiation increasing with concentration of ACh. There was a limit to the degree of inhibition of ventricular tone attainable with ACh, this limit varying from 40 to 100 per cent in different hearts. Inhibition of ventricular tone by ACh was often unaltered, or even reduced, by anticholinesterases. The sensitivity of the conducting system to ACh varied greatly from heart to heart, and was independent of the sensitivity of either pace-maker or ventricular muscle. The concentration of ACh required to arrest the heart was always less in the presence of anticholinesterases. The results are explained in terms of differences in the amount and type of cholinesterase present in the component tissues of the heart, and by competition between the direct atropine-like action of some anticholinesterases on muscle and their action in inhibiting cholinesterase.

The influence of stretch due to increased intraluminal pressure on the formation and conduction of electrical impulse was studied electrocardiographically in 12 isolated sinoauricular chambers of frog hearts perfused with frogs' Ringer. The impulse frequency was found to be directly proportional to the degree of intraluminal perfusion pressure up to a certain critical head of pressure (2–6 cm Ringer), beyond which the impulse frequency declined. At higher pressures the electrogram showed a diminished amplitude of the action potential and broadening and notching of sinus waves and auricular complexes. The duration and conduction velocity of electrical impulse was increased.

MENSTRUATION is initiated and maintained by a complex coordinated activity of the endocrines. Its various phases are known to be associated with many hematologic changes, both biochemical and cytologic (1). The total leukocyte count of peripheral blood increases during the menstrual flow (2). Opinion varies regarding the behavior of the level of circulating eosinophils, and both eosinophilia and eosinopenia have been reported during the menstrual period. The relationship of the adrenal cortex to some reproductive functions is well known (3). Recently, widespread changes in serum electrolyte levels have been reported during the menstrual cycle, presumably due to alterations in adrenocortical activity (4). The menstrual cycle includes two significant events—ovulation and vascular crisis—which may work as endogenous stressing agents. The present work was undertaken in order to obtain comprehensive data regarding the level of circulating eosinophils during the various phases of the menstrual cycle and to find...

L'etirement mecanique est une force motrice fondamentale pour l'autoregulation intrinseque du rhythme du cœur en modifiant l'activite du «pacemaker» de la meme maniere que la distension du myocarde influe sur le reponse inotropique. L'etirement est un mecanisme biologique de base pour la rythmicite cardiaque et la contractilite et il met en interdependance positive le retour veineux et le debit sanguin. La sensibilite a l'etirement est une propriete des reponses chronotropiques. Elle fait du cœur une pompe autoregulatrice unique en son genre.

A study of the relationship between the actions of acetylcholine and nicotine on frog hearts indicates that both the excitatory and inhibitory effects of acetylcholine are antagonised by nicotine. Hearts stopped by acetylcholine and also spontaneously stopped hearts were restarted by nicotine. It has been suggested that exogenously administered acetylcholine and nicotine act through same receptors in a competitive manner.