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Abstract
1. A modification of Vane's cascade is reported, allowing the superfusion bioassay of prostaglandin-like substances (PLS) in the outflow of isolated and perfused heart of the frog Rana esculenta L. 2. Using both this technique and radioimmunoassay determination, the cyclo-oxygenase pathway in perfused frog heart has been investigated. 3. Arachidonate (AA) (2–20 μg) injected into the perfusing fluid, was transformed by the heart into PLS, as shown by the response of the bioassay tissues (rat stomach strip, chick rectum, rat colon). A compound capable of relaxing rabbit mesenteric artery and a rabbit aorta contracting substance were also generated. The release was inhibited by indomethacin (1.0 × 10 −5 M) 4. Radioimmunoassay determination of PGE 2, TXB 2 and 6-keto-PGF 1α in frog heart effluent, before and after AA injection (20 μg), gave the following yields (ng/ml of effluent). Basal: PGE 2 = 0.45 ± 0.15; TXB 2 = 0.46 ± 0.13; 6-keto-PGF 1 α - 2.21 ± 0.3. Following AA: PGE 2 = 1.55 ±0.35; 6-keto-PGF 1 α = 3.4 ± 0.4; TXB 2 = 1.00 ± 0.06. 5. Our results suggest that prostacyclin is a major product of the cyclo-oxygenase pathway in frog perfused heart. The biological significance of this finding is discussed in relation to both the absence of a coronary circulation in amphibians and to the spongy nature of frog myocardium.
Highlights
In amphibians, the development of a massive cutaneous and buccopharyngeal respiration dramatically alters the features of cardiac nourishment
Our results suggest that prostacyclin is a major product of the cyclo-oxygenasepathway in frog perfused heart
This lack of coronary supply is compensated by the transformation of the architecture of the ventricular wall into a complex interlacing of muscular fibers, separated by lacunar spaces extended to the epicardium, which allow the direct oxygenation of cardiac cells
Summary
The development of a massive cutaneous and buccopharyngeal respiration dramatically alters the features of cardiac nourishment. The portion of blood which passes through skin and oral mucosa is there actively oxygenated and, entering in this form into the right auricle, mixes with the venous blood coming from the other regions of the body: the striking reduction of coronary vasculature, common to all amphibians (Grant and Regnier, 1926), is presumed to be a consequence of this change in respiratory patterns (Foxon, 1955). This lack of coronary supply is compensated by the transformation of the architecture of the ventricular wall into a complex interlacing of muscular fibers, separated by lacunar spaces extended to the epicardium, which allow the direct oxygenation of cardiac cells. (3) to compare these features with those of an Urodele heart, namely that of the newt, Triturus cristatus Laur
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