Adrenergic control of immune and metabolic responses in bivalve hemocytes: evidence from Mytilus galloprovincialis.

Catecholamines (CAs) play a central role in the neuroendocrine regulation of immune functions in bivalve mollusks under acute stress. However, the precise effects of different CAs-adrenaline, noradrenaline, and dopamine-on hemocyte immune parameters and cellular metabolism remain incompletely characterized, particularly in the Mediterranean mussel Mytilus galloprovincialis. In the present study, we investigated the in vitro effects of these catecholamines on phagocytosis, adhesion, aggregation, reactive oxygen species (ROS) production, and mitochondrial membrane potential (MMP) of mussel hemocytes. Hemocytes were incubated with adrenaline (1 and 10 μM), noradrenaline (1 and 10 μM), dopamine (1 and 3 μM), and the adenylyl cyclase activator forskolin (10 μM). Adrenaline (10 μM; 30 min) and noradrenaline (10 μM; 60 min) significantly enhanced phagocytosis by increasing phagocytic index (PI) and/or phagocytic activity (PA) of hemocytes. In contrast, dopamine (1 and 3 μM) reduced PA and suppressed hemocyte aggregation. Both adrenaline (1 μM) and noradrenaline (10 μM) stimulated hemocyte adhesion. Adrenaline and dopamine did not alter ROS levels, but noradrenaline reduced ROS production in a concentration- and time-dependent manner. Forskolin-induced cAMP activation reduced ROS production and aggregation of hemocytes but did not affect phagocytosis. Adrenaline (10 μM) significantly increased MMP, indicating enhanced aerobic metabolism, whereas noradrenaline induced a decrease of the parameter. Collectively, these results demonstrate functional diversification of CA effects on mussel hemocytes: adrenaline and noradrenaline are predominantly immunostimulatory, while dopamine exerts suppressive effects. The differential regulation of ROS production and MMP suggests that CAs are involved in modulation of metabolic rearrangements and oxidative protection of hemocytes. This study provides new evidence for the involvement of adrenergic signaling in the neuroendocrine-immune crosstalk and metabolic adaptation of bivalves under acute stress, contributing to a broader understanding of the evolution of immunomodulatory mechanisms in invertebrates.