Aim: 

The African lungfish Protopterus dolloi is an obligatory air-breather, which aestivates during the dry season. Aestivation associates with morpho-functional modifications in many tissues and organs, including heart and kidney. Due to its pleiotropic modulatory effects, nitric oxide (NO), generated by nitric oxide synthases (NOSs), may coordinate organ rearrangement and adaptive adjustments during environmental stress.

Methods: 

Cardiac and renal NOSs expression and localization were analysed by immunofluorescence, western blotting and NADPH-diaphorase, in both freshwater (FW) and aestivating [6 days (6DA) and 40 days (40DA)] P. dolloi. The ventricular rearrangement during aestivation was examined by morphometric analysis on trasmission electron microscopy images.

Results: 

In heart and kidney endothelial NOS (eNOS) is the major NOS isoform eNOS locates in the epicardium, the trabecular endothelial endocardium, and myocardiocytes of both FW and aestivating fish eNOS expression increases in 6DA, but decreases in 40DA fish. Renal eNOS is present in vascular endothelial cells and in podocytes of renal corpuscles. In tubular epithelial cells it is restricted to the apical pole. During aestivation, eNOS expression increases and this is accompanied by an enhancement of total NOSs activity measured by NADPH-diaphorase. In the heart, aestivation is related with: decreased number of mitochondria and an increase in their size; increased mean cellular area, cytoplasmic compartment and sarcomere length and reduction of the interstitial spaces.

Conclusions: 

Results suggest that NO contributes, in an autocrine-paracrine fashion, to cardiac and renal morpho-functional readjustments during aestivation. Our findings are of evolutionary interest, documenting for the first time the presence of a NOS system in an ancestral fish, also indicating the deep phylogenetic roots of NO bio-synthesis.