Vagal afferents inhibit the antidiuresis and antinatriuresis secondary to bilateral carotid occlusion in the chloralose-anesthetized dog.

It has been reported that bilateral carotid occlusion (BCO) does not alter renal excretory function in conscious dogs on a high-salt diet with intact vagi provided renal perfusion pressure (RPP) is held constant. In contrast, low carotid sinus pressures in chloralose-anesthetized dogs with severed vagi elicit significant reductions in renal excretory function which were mediated by renal sympathetic nerves. The purpose of the present study was to investigate the influence of BCO on renal function in chloralose-anesthetized, volume expanded dogs with and without intact cervical vagi and with RPP held constant. A total of 10 dogs, volume expanded with hypotonic saline, were prepared to measure systemic arterial pressure (SAP), carotid sinus pressure (CSP), RPP, and urine flow. With the cervical vagi intact, BCO elicited an increase in SAP from 132 +/- 4 mm Hg to 172 +/- 5 mm Hg (p less than 0.01). This was associated with significant and paradoxical increases in urine flow (+35%), sodium excretion (+63%), osmolar clearance (+32%), and free water clearance (+33%). These changes were also accompanied by small but significant increases in ERBF (+11%) and GFR (+12%). Bilateral cervical vagotomy alone (Vx) increased SAP (129 +/- 6 mm Hg to 146 +/- 5 mm Hg, p less than 0.05). Urine flow and free water clearance were decreased but sodium excretion and osmolar clearance were increased. No change in ERBF or GFR was measured. BCO after Vx elicited a greater increase in SAP as compared to BCO alone (194.5 +/- 6.2 mm Hg) which was accompanied by significant decreases in urine flow (-60%), sodium excretion (-55%), osmolar clearance (-43%), ERBF (-13%), and GFR (-19%). Therefore, the results of this study demonstrate that the contrasting influences of BCO on renal function reported previously in conscious and anesthetized animal models may be due to the presence or absence of the inhibitory influences of afferent fibers contained in the cervical vagi, probably cardiac in origin.

Effect of indomethacin on modest pressure natriuresis in chloralose-anesthetized, non-laparotomized dogs.

To determine if indomethacin (indo) would attenuate the effects of changed renal perfusion pressure on sodium excretion as reported by others, we performed clearance studies in chloralose-anesthetized dogs without the major stress of laparotomy. Mean renal arterial pressure was varied by a balloon-tipped catheter indwelling the aorta suprarenally. With pressure decreases to mean values above 85 mm Hg during isotonic saline infusion, sodium output decreased only by 10.7 +/- 2.4% per 10 mm Hg pressure decrease without indo pre-treatment but decreased by 22.0 +/- 3.8% per 10 mm Hg pressure decrease with indo pre-treatment. The greater, rather than lesser, pressure effect on excretory function after indo in these experiments with chloralose anesthesia suggest that renal prostaglandin (PG) activity does not mediate normally pressure natriuresis. Instead, the data suggest that, in the absence of major stress, the renal pressure effects on excretory function may become more sensitive after indo. In addition, we postulate that the normal acute pressure natriuresis may be modest and may average no more than 20% change for each 10 mm Hg change in mean pressure above 90 mm Hg when stress is minimal and when vasoactive preglomerular autoregulation is nearly perfect. This is a phenomenon which keeps intrarenal tissue pressure and urine output relatively constant with arterial pressure elevations.

Reusable tubular membrane oxygenator for isolated organ hemoperfusion.

A reusable tubular membrane oxygenator is described for hypotraumatic hemoperfusion of isolated organs in physiological studies. The constructed oxygenator was of approximately 0.24-m2 effective surface area and contained 450 silicone rubber capillaries of 0.51-mm nominal ID, 34.9 cm long, fixed by conical-shaped, plastic blood headers at manifolds made from Dow-Corning MDX-4-4210 silicone elastomer. During ex vivo hemoperfusions in dogs at inlet hemoglobin saturations near 67%, oxygen transfer rates of the oxygenator increased serially, from 16.6 +/- 1.7 ml/min per m2 (mean +/- SD) at blood flows of 100 ml/min to 34.1 +/- 3.8 ml/min per m2 at flows of 500 ml/min. The oxygenator was thromboresistant and of much loss priming blood volume and wall compliance than the nonresuable Travenol membrane oxygenator of 0.26-m2 effective surface area. The tubular oxygenator was easily cleaned and reassembled, with reproducible oxygen transfer rates. It should prove useful for hemoperfusion studies in organs of moderate size, such as the isolated canine kidney, stomach, and pancreas.