Cold shock-induced norepinephrine triggers apoptosis of haemocytes via caspase-3 in the white shrimp, Litopenaeus vannamei

The total haemocyte count (THC), haemolymph norepinephrine (NE) level, caspase-3 mRNA expression and activity levels, and apoptotic haemocyte rate were measured when shrimp Litopenaeus vannamei (20–25 g) were transferred from 28 to 22 °C after 0, 2, and 7 days, and the caspase-3 mRNA expression and activity levels and the apoptotic cell rate of haemocytes, in vitro, were determined after incubation with 2 × 10−8 M NE for 0, 30, 60, and 120 min at 27 ± 1.0 °C. For shrimp transferred from 28 ± 1.0 to 22 ± 0.5 °C after 2 and 7 days, the THC decreased by 17.9% and 18.0%, but the NE concentration, caspase-3 transcription and activity levels, and apoptotic cell rate increased by 62.5% and 37.3%, 5100.0% and 446.6%, 148.6% and 152.0%, and 88.7% and 200.1%, respectively, compared to those of shrimp held at 28 ± 0.5 °C which served as the control. Similar tendencies were observed for the apoptotic cell rate, and caspase-3 transcription and activity levels of haemocytes exposed to 2 × 10−8 M NE in vitro. These results suggest that NE plays an important role in the apoptosis of haemocytes in L. vannamei under hypothermal stress, which causes depressive effects on immunological responses.