Aestivation in the South American lungfish, Lepidosiren paradoxa: Effects on cardiovascular function, blood gases, osmolality and leptin levels

The African (Protopterus sp.) and South American lungfish (Lepidosiren paradoxa) inhabit shallow waters, that seasonally dry out, which induces aestivation and cocoon formation in Protopterus. Differently, L. paradoxa has no cocoon, and it aestivates in a simple burrow. In water PaCO2 is 21.8 ± 0.4 mmHg (mean values ± S.E.M.; n = 5), whereas aestivation for 20 days increased PaCO2 to as much as 37.6 ± 2.1 mmHg, which remained the same after 40 days (35.8 ± 3.3 mmHg). Concomitantly, the plasma [HCO3−]-values for animals in water were 22.5 ± 0.5 mM, which after 20 days increased to 40.2 ± 2.3 mM and after 40 days to 35.8 ± 3.3 mM. Initially in water, PaO2 was 87.7 ± 2.0 mmHg, but 20 days in aestivation reduced the value to 80.5 ± 2.2 and later (40 days) to 77.1 ± 3.0 mmHg. Meanwhile, aestivation had no effect on pHa and hematocrit.The blood pressures were equal for animals in the water or in the burrow (Pmean ∼ 30 mmHg), and cardiac frequency (fH) fell from 31 beats min−1 to 22 beats min−1 during 40 days of aestivation. The osmolality (mOsm kg H2O−1) was elevated after 20 and 40 days of aestivation but declined upon return to water. The transition from activity to aestivation involves new set-points for the variables that determine the acid–base status and PaO2 of the animals, along with a reduction of cardiac frequency.