Effect of insulin on blood sugar level and glycogen content in organs of some cyclostomes and fish

Abstract

Mammalian insulin was injected intraperitoneally (30–80 IU/kg) into cyclostomes ( Lampetra fiuviatilis, Lampetra planeri), cartilaginous fish ( Dasyatis pastinaca), and marine and freshwater bony fish ( Scorpaena porcus, Spicara smaris, Trachuras mediterraneus ponticus, Gobiidae sp., and Cyprinus carpio). In all the animals studied the hormone caused a decrease of the sugar content in the blood, but the duration of hypoglycemia varied in different species. In experiments performed with the same insulin dosage and at identical temperatures hypoglycemia, in lampreys lasted 11 days, in skates 7 days, in low-active scorpion fish 4 days, and in highly active sea bass 1 day. The experiments with lampreys kept at a water temperature of 3–5°C coinciding with the water temperature in the river during the winter season, revealed even more prolonged hypoglycemia—11 days after the injection the sugar concentration in the blood remained low. The introduction of insulin neither increases the glycogen concentration in muscles of larval lampreys nor affects the glycogen content in adult lamprey muscles. It induces a notable rise of glycogen in muscles of skate and a transient increase, 6–7 hours after the injection, in scorpion fish. At the height of hypoglycemic convulsion the glycogen content of scorpion fish and sea bass muscles decreases. The glycogen content in the cardiac muscle of lamprey, skate, scorpion fish, and carp during advanced hypoglycemia is found to be reduced. Similar changes induced by insulin are observed in the brain of lamprey and scorpion fish. The effect of insulin on the glycogen content of the liver is rather uncertain. An increase of glycogen in that organ was observed in ammocoete larvae, lamprey, skate, and scorpion fish in a few experiments only. A notable decrease of the glycogen concentration occurs in the scorpion fish liver 48–72 hours after insulin injection during hypoglycemic seizures.