Catecholamine effects on blood pressure and heart rate in warm- and cold-acclimated American bullfrogs (Rana catesbeiana).

The effects of epinephrine (E), norepinephrine (NE), phenylephrine (PHE), and isoproterenol (ISO) were studied in vivo on the blood pressure and heart rate of the conscious American bullfrog, Rana catesbeiana. Bullfrogs were chronically cannulated with a T cannula in the right sciatic artery. In warm-acclimated (22 degrees, W-A) bullfrogs, baseline mean systemic arterial blood pressure (SAP) prior to catecholamine infusion was 16.8 +/- 1.1 mm Hg and mean preinfusion heart rate (HR) was 36.4 +/- 2.1 beats per min. In contrast, cold-acclimated bullfrogs (5 degrees, C-A) had baseline SAP values of 7.4 +/- 0.7 mm Hg and HR values of 6.9 +/- 0.3 beats per min. W-A bullfrogs infused with ISO (0.03 to 30 micrograms/kg body wt) demonstrated a dose-related increase in HR, while the HR of C-A bullfrogs did not respond to any tested dose of ISO. ISO administered to W-A bullfrogs exposed to 5 degrees for 60 min produced no significant HR increase. When the animals were returned to 22 degrees, the HR response to ISO was restored. ISO did not affect SAP in either group. E, NE, and PHE increased SAP in both W-A and C-A bullfrogs, with E the most effective. All three catecholamines affected the SAP of C-A animals less than the W-A group. In W-A bullfrogs, E, NE, and PHE decreased HR, while no effect on HR was observed in the C-A group.(ABSTRACT TRUNCATED AT 250 WORDS)