The action of vitamin B1 (thiamine) on the cardiovascular system of the cat.

Vitamin B1 administered in a high dose (160 mg/kg) parenterally is known to cause neuromuscular and ganglionic blockade. The effects on the cardiovascular system however have not been sufficiently investigated. In artificially ventilated cats under light ethrane-anesthesia, following parameters were measured continuously before and after B1 administration : Left ventricular pressure, left ventricular end-diastolic pressure, LV dP/dt max, electrocardiogram, heart rate, central venous pressure, and peripheral blood pressure (systolic, diastolic, mean). The data indicate a three-phase reaction after B1 injection : Phase 1--shortly after injection there is a drop of all parameters lasting for 30 sec. The LVEDP showed no change while CVP increased. The drop could not be eliminated by the pretreatment with antihistaminiergic or anticholinergic drug. Sequential stimulation with norepinephrine was able to re-establish base-line values. In Phase 2 (two minutes after injection) all parameters return to their control values ; except CVP which stays elevated. Phase 3 (around the 7th minute after injection) shows a gradual decrease of all parameters; CVP returns to control values. It is suggested that phase 1 represents an immediate alpha-blockade, phase 2 reveals a compensatory reflex mechanism, and phase 3 shows full ganglionic blockade.