ACTION OF HISTAMINE ON THE JUGULAR VENOUS PRESSURE AND CEREBRAL CIRCULATION OF THE DOG. EFFECTS OF ANTIHISTAMINIC DRUGS (PYRILAMINE AND CHLORPHENIRAMINE) AND A HISTAMINE LIBERATING AGENT (48/80 B.W.)

¹ Therapeutic Chemistry Laboratory, Istituto Superiore di Sanita, Rome, Italy

The venous pressure in the central portion of the peripherally ligated external jugular vein and its ramifications (external and internal maxillary and superior cerebral veins) has been measured in the dog.

The effects of histamine, antihistaminics, a histamine liberating agent (48/80), epinephrine, nitroglycerine and dibenamine on the cerebral venous, general arterial and cerebralspinal fluid pressures have been recorded by this technique. Histamine in small doses of 0.1 microgm./kgm. to 1.0 microgm./kgm. produced a transient venous hypertension sometimes accompanied by arterial hypotension.

With large doses of histamine 5 microgm./kgm. and above there was seen an arterial and venous hypotension which followed by an altered sensitivity to vasoactive drugs given after the pressure had returned to normal.

The antihistaminics, pyrilamine and chlorpheniramine completely antagonized the effect of small doses of histamine but not that of large doses.

Dibenamine antagonized the action of small doses of histamine and this is attributed to its strong antihistaminic action rather than to its adrenergic blocking action.

48/80, a histamine liberating agent, produced a delayed venous hypertension which is attributed to released histamine. With small doses of 48/80 the action of the released histamine can be antagonized by the antihistaminics and dibenamine.

The implications of these findings to the problems of headache and cerebral vascular control is discussed.