Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats

The continuous recording of renal blood flow in instrumented rats allows us to temporarily determine the sequence of events which lead up to the disease process that we're studying. In our case, it's hypertension and we're trying to determine whether a reduction of renal blood flow, which occurs in hypertension, precedes or is a consequence of the high blood pressure. The system that we'll be demonstrating today and the preparation of the animal is really designed to enable a continuous 24-hour determination of renal blood flow for many weeks at a time to study chronic events and to study the rat in their home environment, cages.

As with all surgical techniques, practice, patience and attention to detail, we will required to master these procedures until the implement can be carried out on time. To begin shave the entire abdomen in a region on the nap around the seventh cervical vertebrae of an anesthetized rat with an electric clipper. After shaving, wipe the area three times alternating with 10%povidone iodine, and 70%ethanol.

Place the rat in the prone position. Make a one centimeter cut with the scalpel on the nap and the left flank. Then perform a blunt dissection with hemostatic forceps in clear subcutaneous space from the flank incision to the back of the neck.

Attach the skin button to the flow probe and pass the flow probe through this subcutaneous tunnel from the neck to the flank incision with hemostatic forceps. Then place the rat in the supine position and make a four to five centimeter midline abdominal incision. Dissect the area around the left renal artery with curved microdissecting forceps exposing the space sufficient to place the flow probe.

Then bluntly, pierce the left quadratus lumbar muscle with the hemostatic forceps and pull the head of the flow probe through the renal artery under the fatty tissue into the abdominal cavity. Place the polyester fiber mesh on the abdominal wall. Hook the tip of the flow probe to the left renal artery and connect it to the flow meter.

Add some gel around the probe tip and value of the flow rate will appear on the flow meter. Glue the polyester fiber mesh attached to the probe to the abdominal wall using tissue adhesive and hold until dry and bonded. Once the probe is in place, disconnect the flow probe from the flow meter and cover the abdomen with saline soaked gauze.

To suture the probe, turn the rat to the prone position. Attach the skin button to the flow probe and make a circular loop of the flow probe subcutaneously at the flank. Suture the incision at the neck and the button to the skin.

Then suture the flank with four ott surgical sutures. Connect the flow probe to the flow meter again, and turn the rat back to the dorsal position to check renal blood flow. Make final flow probe adjustments to optimize its position on the renal artery.

Finally, suture the muscle with three ott silk in the skin with four ott surgical suture. When the rat is fully recovered from anesthesia return the rat to a movement response caging system connect the flow probe to the blood flow meter and allow a recovery period of about a week to stabilize the probe and flow measurement. The mean arterial pressure and blood flow were continuously measured in dull salt sensitive rats while switching from a low to high salt diet.

This representative data from a male rat was recorded over a period of four weeks and is shown with a minute average. A clear diurnal difference was observed in mean arterial pressure and blood flow. While blood pressure increases with a high salt diet blood flow tends to decrease rather than increase suggesting increased renal vascular resistance.

The great advantage of this technique is that it can study renal blood flow over long periods of time, and most importantly in unanesthetized conditions. This is of great importance when studying response to various stimuli where you can use the same animal under controlled unanesthetized conditions and follow that same animal over short periods or very long periods to see what the response is to some particular stimulus or pathological disease is.