Systemic and lymphatic heart performance during forced submersion, in the toad Bufo arenarum (Annura, Bufonidae)

CERVINO, C.O.; CASTILLO, L.; RODRÍGUEZ, E.M.

Revista Española de Herpetología

Asociación Herpetológica Española

Año: 2007 vol. 21 p. 95 - 106

0213-6686

The activity of systemic (SH) and lymphatic hearts (LH) was characterized in the anuran Bufo arenarum during an entire, forced submersion. Prior to submersion, a SH frequency of 28.9 beats / min was recorded, while both posterior LH showed a similar but asynchronic rate of 50.5 beats / min. At the beginning of forced submersion, a reflex apnea (characterized by cessation of buccal pumping) was evident immediately after the nares were covered by water. At the same time, a slow decrease of SH rate was observed, stabilizing at 10 beats / min after 15 min. LH activity completely stopped after 10 min of submersion. Emersion comprised an initial brief phase with no buccal pumping, followed by activation of the buccal pump together with a sudden increase of SH rate and reactivation of LH. Bilaterally vagotomized animals consistently showed a higher SH rate than intact controls and also showed bradycardia during the entire submersion period, following a pattern parallel to that of control toads. Several mechanisms, possibly both nervous and non-nervous (such as blood chemical stimuli), could be triggering and maintaining the systemic bradycardia, as well as the inactivity of LH during submersion. The results reported in this work do not enable to draw definite conclusions about the mechanisms responsible for SH bradycardia and cessation of LH activity during submersion. In view of the correlation of buccal pump activity with the establishment of deep changes in the physiology of both kinds of hearts, said activity becomes a necessary factor for the occurrence of heart rate modifications.