Isolated precontracted arteries of various vascular beds relax in response to acetylcholine only if the endothelium is present. One explanation for this is that this drug stimulates the endothelial cells to release a vasodilator substance that in turn relaxes the underlying smooth muscle. To determine whether this mechanism is concerned also in the acetylcholine contraction of isolated porcine coronary arteries transverse strips of the extramural part of the left circumflex artery were used for recording isometric tension in the muscle bath. Dose-response curves for acetylcholine showed no significant difference before and after removal of endothelium. As a functional check on the removal of endothelium, the responsiveness of each preparation to a known endothelium dependent dilator (substance P) was tested before and after removal. These findings suggest that endothelial cells are not concerned in the acetylcholine induced contraction of porcine coronary arteries. Acetylcholine appears to act directly on smooth muscle of the porcine artery.

In bioassay and organ bath experiments, the responses of different canine venous preparations to arterial and their own EDRF were studied. Vena jugularis, vena femoralis and vena mesenterica relaxed on both EDRFs released by acetylcholine. Vena saphena, venae cordis and vena portae did not show endothelium-dependent dilation, either under bioassay or in organ bath experiments. All the veins tested relaxed completely after sodium nitroprusside administration. The identity of EDRF and nitric oxide is not confirmed by this study.

Dynamic characteristics of heart rate in response to sinusoidal variations of work load were analysed in 8 male and 3 female untrained students exercising in a sitting position on a bicycle ergometer. The mean work load was 90 watt in men and 60 watt in women, the amplitudes being 50 and 30 watt respectively. Nine different frequencies were used, the periods varying from 0.5 to 15.0 min. By means of harmonic analysis, the fundamental components in the response of the heart rate have been shown to prevail over the 2nd and 3rd harmonics, indicating a mainly linear behaviour of the control system in the work-load range studied. A comparison of the frequency response of untrained males and females observed in this study and of trained sportsmen, investigated by wigertz (1970), reveals differences between the groups. The individual and ensemble mean frequency responses have been described by several transfer functions, the best fit having been obtained with functions containing two time constants including one with a highly damped oscillating element. The dominating dynamic parameter is a time constant of about 20 to 30 sec. This time constant tends to be shorter and its portion of the frequency response diminishes in order from the untrained females and males to the trained sportsmen. The individual time constant decreases as the PWC170 increases, and is therefore a suitable criterion for estimating the physical performance of individuals under dynamic conditions.

No abstract

The experiments were performed on open-chest mongrel dogs, the hearts being paced at a constant rate. Both vagi were cut in the neck and the peripheral ends were stimulated with frequencies of 1, 5, 10, 15, 20, 25, 30, 35, 40 and 50 cycles per sec (30 sec, 8 V, 2 msec). Adrenergic beta-receptors were blocked with propranolol and adrenergic alpha-receptors with dihydroergotamine. Coronary flow was measured with electromagnetic flowmeters on the descending branch of the left coronary artery. A significant increase in coronary flow was observed with rising frequency of stimulation. This increase was 15 percent with 30 Hz and decreased with higher frequencies. The total coronary resistance reached its lowest level at the frequency of 30 cycles per sec. The results clearly indicate the parasympathetic control of myocardial blood flow.