Corticosteroid control of Na+/K+-ATPase in the intestine of the sea lamprey (Petromyzon marinus)

•Lamprey steroids 11-deoxycortisol (S) and deoxycorticosterone (DOC) were examined.•Corticosteroid receptors in the intestine had higher binding affinity for S than DOC.•Na+/K+-ATPase (NKA) is a target of corticosteroid control in the lamprey intestine.•Treatment with S, but not DOC, increased intestinal NKA expression and activity.•Treatment with S improves the capacity for osmoregulation in seawater.•Control of intestinal osmoregulation by corticosteroids is a basal vertebrate trait. Anadromous sea lamprey (Petromyzon marinus) larvae undergo a months-long true metamorphosis during which they develop seawater (SW) tolerance prior to downstream migration and SW entry. We have previously shown that intestinal Na+/K+-ATPase (NKA) activity increases during metamorphosis and is critical to the osmoregulatory function of the intestine in SW. The present study investigated the role of 11-deoxycortisol (S) in controlling NKA in the anterior (AI) and posterior (PI) intestine during sea lamprey metamorphosis. In a tissue profile, nka mRNA and protein were most abundant in the gill, kidney, and AI. During metamorphosis, AI nka mRNA increased 10-fold, whereas PI nka mRNA did not change. Specific corticosteroid receptors were found in the AI, which had a higher binding affinity for S compared to 11-deoxycorticosterone (DOC). In vivo administration of S in mid-metamorphic lamprey upregulated NKA activity 3-fold in the AI and PI, whereas administration of DOC did not affect intestinal NKA activity. During a 24 h SW challenge test, dehydration of white muscle moisture was rescued by prior treatment with S, which was associated with increased intestinal nka mRNA and NKA activity. These results indicate that intestinal osmoregulation in sea lamprey is a target for control by S during metamorphosis and the development of SW tolerance.