Severe insulin-induced hypoglycemia in the spiny dogfish shark (Squalus acanthias).

The effect of a single intraaortic infusion of mammalian insulin on plasma glucose was studied in the spiny dogfish shark (Squalus acanthias). Insulin was administered, and blood samples were collected, from an indwelling cannula placed in the dorsal aorta via the anterior mesenteric artery. Plasma glucose was estimated by the glucose oxidase method.Control plasma glucose levels were 37.4 ± 2.5 mg% at time-zero, increased gradually to 45.9 ± 4.4 mg% by 4 days after the infusion of the hormone-free carrier solution, and to 58.1 ± 5.5 mg% by Day 6 when sampling was terminated. The time-zero plasma glucose levels of the dogfish that received 0.5 IU/kg body wt insulin were 46.5 ± 3.2 mg%, declined to 10.2 ± 1.3 mg% by 24 hr after the infusion, and then returned to approximately the time-zero levels by Day 4. The initial plasma glycose levels of the animals that received 50 IU/kg body wt insulin were 38.6 ± 2.6 mg%. The levels fell to 2.1 ± 0.6 mg% by Day 3 and then increased slowly to approximately the time-zero levels between Days 13 and 14 after the treatment. The lowest plasma glucose levels in individual dogfish occurred either on Day 2 or 3 and averaged 1.4 ± 0.3 mg%. No convulsions or other symptoms were observed in the insulin-treated animals. The results indicate that both the magnitude and the duration of the hypoglycemia were dependent on the dose of insulin infused. In addition, the observations that the dogfish were able to tolerate the virutal absence of circulating glucose for extended periods suggest that glucose is not an essential source of energy in this species.