Dogs have blood vessels manipulated, and then undergo extensive conscious circulatory system testing

Anderson W, Shweta A, Evans R, Edgley A and Gao Y 2007. 'Total peripheral resistance responsiveness during the development of secondary renal hypertension in dogs', Journal Of Hypertension, 25, 3:649-662.

Institution: Department of Physiology, School of Biomedical Sciences, Monash University

Aim

The study aimed to determine whether blood pressure and blood flow resistance is affected differently in dogs that suffer from induced hypertension in the face of vasoconstricting agents.

Definitions:
Hypertension – condition of high blood pressure caused by hormones produced by the kidneys when the arteries supplying blood to this area are narrowed.
Vasoconstriction – constriction of blood vessels which results in increased blood pressure

The Experiment

In the study there were a total of 17 dogs that were subjected to experimental procedures. The dogs were one year old and the experiment lasted 10 weeks after which the dogs were killed. Initially the dogs underwent a surgical procedure to place six catheters as well as an inflatable balloon cuff around a renal artery. A thermistor (electrical resister) was also inserted into the aorta and the right kidney was removed. All wires and catheters were made accessible from the exterior of the dogs back, which was protected by a canvas jacket.

The balloon cuff was inflated in the dogs so that the renal artery was constricted by 87%. Dogs were separated into treated and untreated groups. The treated group received the drug enalapril (a drug used to treat high blood pressure).

Daily experimental procedure for the one-year-old dogs included 4-5 hours of laying still in a laboratory setting. Over this time numerous compounds were administered which altered their blood pressure values. Measurements concerning blood pressure, heart rate, venous pressure, cardiac output and renal blood flow were taken surrounding the infusion of the compounds into the dog’s blood. 4 dogs required anaesthesia during this experimental period as there were not trained for receiving extended cardiac measurements, the rest of the dogs were subjected to the manipulations of their circulatory systems whilst fully conscious.

The dogs were permitted one hour of exercise daily, and there was no mention as to the living arrangements provided throughout the experiment. Measurements were continued for 10 weeks, after which all dogs were killed and kidney samples were taken.

Results

The study found there to be no amplification of response to vasoconstricting agents during the development of hypertension. As expected there was an increase in blood pressure due to hypertension, however when exposed to vascular-constricting agents the blood pressure response was relative to its base value and did not increase in an amplified manner. Amplification affects were also not seen when comparing drug treated and non-drug treated dogs.

Appropriate Human Model?

The study itself admits the flaws in the using an animal model for studying human hypertension. The study goes into great length of previous findings reported in rabbits that have contradicting results to the current study. They explain how the differences in results surrounding hypertension are found due to the difference in species and circulatory mechanisms at controlling blood pressure. The article concludes its findings with the following statement:

"We also, however, caution that the choice of models will influence the findings in this area. It is not surprising therefore that much confusion surrounds the more complex genetic forms of hypertension in animals, and the human situation where interactions between genes, environment and disease processes are entwined."

With this acknowledged, why would the study be approved when it will result in no further clarification of the issue in humans? Also the approval to kill the dogs after the conclusion of the experiment can also be called into question.

Funding

This experiment was funded by the National Health and Medical Research Council (NHMRC) and the Alfred Hospital Medical Research Committee.

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