Vasotropic substances in blood in intestinal ischemia shock

Serial, simultaneous rat mesoappendix assays of portal, hepatic, and femoral vein plasma in dogs in SMA shock (temporary ligation of the superior mesenteric artery) indicated the elaboration of an epinephrine inhibiting (eI) substance which appeared first in the portal vein. In dogs protected by intraportal vein injection of Dibenzyline, after onset of intestinal ischemia, an eI response was observed only in the portal vein, from which it disappeared within 8 hr. In vitro incubation of eI plasma with antiferritin serum inactivated the vasoinhibitory effects of most samples. Assay of shock plasma on the isolated rat gastric muscle strip elicited contractile responses. Pre-exposure of the muscle strip to BOL-148, a serotonin antagonist, attenuated this response. These myogenic effects were not altered by antiferritin serum or atropine. A progressive fall in plasma-bound iron levels was found in SMA portal blood. These findings establish the intestinal origin of vasotropic material in SMA shock. This material exhibits the vasotoxic properties of ferritin and the myogenic properties of serotonin.

Cardiac Actions of Methoxamine

The cardiac action of large doses of methoxamine and its antagonistic action to epinephrine were studied, using a dog heart-lung preparation. In doses of 4 mg. and above, methoxamine showed a marked negative inotropic action, while it produced only a slight decrease in the heart rate. Pretreatment of animals with 0.1 mg./Kg. of reserpine did not modify the inotropic action, but the decrease in the heart rate disappeared. Simultaneous with these changes, a decrease in the coronary flow and a rise of the pulmonary arterial pressure were observed. Methoxamine in doses of 1 mg. and more abolished both the positive inotropic and the positive chronotropic actions of epinephrine. The negative inotropic action of methoxamine was ascribed to a nonspecific, as yet undetermined mechanism, and the antagonistic action was ascribed to the competitive antagonism at the receptor site (thus methoxamine may be looked upon as a blocking agent of adrenergic β receptor). The weak negative chronotropic action was taken to be an expression of the blockade of the humoral effects of the intrinsic sympathomimetic amines.