Short-Term in Situ Effects of Prolactin and Insulin on Ion Transport in Liver and Intestine of Freshwater Climbing Perch (Anabas testudineus Bloch)

The short-term in situ effects of prolactin and insulin on the transport of monovalent and divalent cations were examined in climbing perch Anabas testudineus to infer upon how these hormones regulate ion transport in the metabolic and osmoregualtory tissues of freshwater fish. Varied doses (10^-9, 10^-8 and 10^-7 M) of ovine prolactin (oPRL) and insulin were infused in these fish for 20 min and the specific activities of ion-specific ATPases were analyzed. The Na⁺, K⁺-ATPase activity in the intestine and liver showed significant increase after oPRL infusion. Infusion of oPRL significantly decreased the cytosolic H⁺-ATPase activity in the intestine and liver, but increased the cytosolic Ca²⁺-ATPase activity in these tissues. Infusion of oPRL decreased the mitochondrial Mg²⁺-ATPase and H⁺-ATPase activities in the liver but the activities of these transporters increased in the intestine. Similar to oPRL, insulin infusion produced dose-dependent effects on the transporter activities in the liver and intestinal tissues. The mitochondrial Mg²⁺-ATPase activity in the liver significantly decreased at 10^-9 and 10^-7 M insulin infusion whereas its activity increased significantly in intestine at 10^-8 M insulin. Likewise, insulin infusion produced significant increases in the activities of all tested transporters except the cytosolic H⁺-ATPase activity in the intestine. A direct action of insulin on ion transport was found in both liver and intestinal tissues, as evident in the activity patterns of ion-specific ATPases. Taken together the results point to vital roles of PRL and insulin in ion transport in both liver and intestinal tissues of climbing perch.