The central vasomotor effects of 5-hydroxytryptamie

In the dog, injection of 5-hydroxytryptamine into the cerebral ventricles caused hypotension, inhibition of the pressor response to occlusion of the carotid artery and inhibition of the pressor or depressor response evoked by electrical stimulation of the central end of the cut vagus. Hypotension and inhibition of the vagal vasomotor response also occurred in dogs in which the carotid sinuses had been denervated and the vagi cut. The site of action was central. Local cerebral vascular changes could not have been responsible for the action. The central vasomotor effects of 5-hydroxytryptamine are mediated through the sympathetic outflow. Implications of these findings are discussed in relation to the effects of intravenous 5-hydroxytryptamine and the mechanism of action of reserpine.

The central action of lignocaine and its effect on cardiac output

Fifty-nine tests were performed on twenty-four anaesthetized dogs in a study of the effects of lignocaine on circulatory and respiratory functions. In single-dog experiments, it was shown that lignocaine (1 to 2 mg./kg. body weight) increased ventilation somewhat, but had no effect on O(2) consumption. Cardiac output was increased due to a rise in both heart rate and stroke volume. There was an elevation of arterial blood pressure. The central blood volume was increased, but central venous pressure, total peripheral resistance and the ventilationperfusion ratio were decreased. The increase in cardiac output after lignocaine was abolished both in decerebrate and in vagotomized dogs. In cross-circulation experiments with dogs, it was demonstrated that the primary site of action of lignocaine on cardiac output was central. The effect of lignocaine on cardiac output could be blocked by intravenous procaine.

Increase of pentobarbitone metabolism induced in rats pretreated with some centrally acting compounds

Rats treated with phenobarbitone, phenaglycodol, glutethimide, nikethamide, meprobamate, chlorbutol and chlorpromazine showed an increased metabolism of pentobarbitone and, at the same time, a diminished sleeping-time after pentobarbitone. This effect developed 24 hr after treatment, the maximum increase in metabolism occurring after about 48 hr. The increased pentobarbitone metabolism was inhibited by ethionine injected shortly before treatment. Using a liver slice preparation, increased pentobarbitone metabolism was also observed in vitro. These results are in accord with the view that the capacity of compounds to increase pentobarbitone metabolism may be related to their ability to act directly on microsomal enzyme systems.

A note on the demyelination produced in hens by dialkylfluoridates

Hens were treated with organophosphorus compounds until signs of neurotoxicity developed. The sciatic nerves, spinal cord, and medulla were then examined histologically by the Marchi method, to determine the extent and distribution of demyelination. The lesions were proportional to the dose of compound injected, and the spinal cord was more sensitive than the sciatic nerves. It is suggested that the spinal cord, and not the sciatic nerves, is the main site of damage in clinical paralysis following dyflos poisoning.