Attenuated cardiovascular effects of prostaglandin I2 and prostaglandin F2α in cold acclimated American bullfrogs, Rana catesbeiana

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Abstract
American bullfrogs, Rana catesbeiana respond to prostaglandins with changes in heart rate and blood pressure. These studies compare responses of warm (22°C) and cold acclimated (5°C) bullfrogs to prostaglandins. Gas chromatographic analysis determined equivalent fatty acid profiles in total lipids of heart and artery tissue from warm and cold acclimated animals. Arachidonic acid was the fatty acid precursor found in greatest abundance in both groups. For cardiovascular experiments, bullfrogs were cannulated by using a T‐cannula implanted in the right sciatic artery. In warm acclimated bullfrogs, preinfusion systemic arterial pressure (SAP) was 14.7 ± 0.5 mm Hg, and heart rate was 33.0 ± 1.7 beats/min. Cold acclimated bullfrogs had SAP values of 8.0 ± 0.8 mm Hg, and heart rate was 6.9 ± 0.3 beats/min. Arachidonic and eicosapentaenoic 3‐acid infusions (2,000 μg/kg body weight [bw]) were hypertensive in cold acclimated and hypotensive in warm acclimated animals. These effects were blocked by indomethacin (4 mg/kg bw). In both warm and cold acclimated bullfrogs, prostaglandin F2α (3–100 μg/kg bw) was hypertensive, while prostaglandin I2 (0.03‐3 μg/kg bw) was hypotensive, with both prostaglandins stimulating a greater absolute response in warm acclimated animals. In addition, both prostaglandins increased heart rate in warm but not in cold acclimated bullfrogs. The results suggest diminished cardiovascular sensitivity to prostaglandins at low environmental temperatures.

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