Hepatic Circulation Time in Unanesthetized Dogs

Abstract

No report on the rate of blood flow through the liver in unanesthetized dogs has been found in the literature. Since we have had available a number of animals angiostomized according to the technique of London, 1 with cannulae on the hepatic and portal veins, we have determined circulation time by the cyanide method.

Our experience with the angiostomy technique has been discussed elsewhere. 2 We have had little difficulty in preparing the animals so that satisfactory injections could be made into the portal and hepatic veins. The time required for KCN injected into either vein to reach the carotid sinus was determined by recording respiration with a pneumograph strapped to the chest, the arrival of the cyanide at the carotid sinus being indicated by the first increase in respiratory excursion. The dogs, previously accustomed to lying quietly during the withdrawal of blood, were held gently on a table with the pneumograph in place until respiratory rate and amplitude were constant. The long needle, attached to a syringe containing the cyanide, was passed down the London cannulae into the vein and the respiration again watched for a short period. Making sure the animal was quiet, the KCN was injected and the time marked on the drum. The increase in respiration was usually abrupt after injection into the hepatic vein and gradual after portal injection. But in no case was it difficult to determine the onset of respiratory stimulation. Typical results are illustrated by Fig. 1.

The difference between the time required for respiratory stimulation after intra-portal injection and that required after intra-hepatic injection was taken as the hepatic circulation time. The results are summarized in Table I. It was necessary to inject from 3 to 6 mg. of KCN into the portal vein to obtain a response, as compared with one mg. in the hepatic. This may in part be due to distribution of the cyanide over a larger volume of blood by passage through the vascular bed of the liver, and in part to diffusion of the cyanide from the liver capillaries. It is also suggestive of a detoxifying action on the part of the liver. It is significant that 6 mg. of KCN were usually required when injected intra-portally in normal dogs, while respiration was as a rule stimulated by 3 mg. of KCN injected into the portal in depancreatized dogs. It is not improbable that there was some interference with liver function in the hypophysec-tomized and depancreatized animals, even though the latter were maintained on insulin and raw pancreas.

Since all values for hepatic circulation time in the operated animals are well within the limits of variation found in the normals it appears that adrenal denervation, pancreatectomy, or hypophysectomy did not appreciably change the rate of blood flow through the liver in these dogs. A conclusive statement concerning the effect of these surgical procedures should await determinations on a larger series of animals. But it may be pointed out that the average for the normal group is 13 seconds, that for the whole series 12 seconds.

The variations in rate of blood flow in the normal animals are comparable to the variations that we have observed 2 in fasting glucose output from the liver in such dogs, although no relationship between blood flow and glucose output can be assumed until parallel determinations are made.