The Role of Arginine Vasotocin in the Control of Posterior Lymph Heart Function in the Toad Bufo marinus (L.)

Chronically cannulated, fully hydrated Bufo marinus were given a sham saline injection followed by three bolus infusions of arginine vasotocin (A VT). Posterior lymph heart pressure and rate and lymph flow were measured, Arginine vasotocin injection was found to reduce lymph heart rate by as much as 25%, from a control of 55.75 ± 1.56 beats min⁻¹ to 41.75 ± 4.13 beats min⁻¹ with 30-s-2-min decreases after injection. Lymph flow increased in response to the first and third A VT injections. Posterior lymph heart pressure was not affected by A VT injection. In vivo, this regulation of lymph heart contraction may be a water- and/or energy-conserving mechanism. The observed increase in lymph flow is likely the result of an A VT-stimulated increase in cutaneous permeability that would cause large quantities of water to be cutaneously absorbed even in fully hydrated animals.

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