Elevation of plasma glucose levels by mammalian ACTH in the spiny dogfish shark (Squalus acanthias)

Abstract

The effect of a single intra-aortic administration of mammalian ACTH on plasma glucose levels was studied in the spiny dogfish shark (Squalus acanthias). Blood was collected from an indwelling cannula placed in the dorsal aorta via the anterior mesenteric artery and plasma glucose was estimated by the glucose oxidase method. Plasma glucose levels of starved, untreated dogfish were 50.3 ± 4.9 mg % at the completion of the operation and ranged from 15.6 to 105.3 mg %. Plasma glucose levels were 39.7 ± 1.9 mg % on the third postoperative day and remained relatively stable from the third through the fifth day when this aspect of the study was terminated; the range in plasma glucose values between individual dogfish during this period was from 25.0 to 59.9 mg %. Experimental treatment began on postoperative day 3 to 5. The initial plasma glucose level on the morning of treatment was used as time-zero.

Control plasma glucose levels declined approximately 7% within 45 min after the infusion of the hormone-free carrier solution. The levels returned to the time-zero levels at the 12- and 24-hour samples and to approximately 6% greater than the time-zero levels at 48 hr after the infusion. Plasma glucose levels showed a similar initial decline in the dogfish that received 40 units ACTH/kg body weight; however, the levels subsequently increased to approximately 19% greater than the time-zero levels at the 3-, 6-, and 12-hr samples. Plasma glucose levels then declined, but remained approximately 12% greater than the time-zero levels 48 hr after the infusion; the increases still evident at 48 hr were not significantly greater than the increases observed for the controls. The infusion of 20 units ACTH/kg body weight resulted in inconsistent and variable increases in plasma glucose levels. The data provide presumptive evidence for pituitary ACTH regulation of corticoid secretion in the dogfish and indicate that the pituitary-adrenocortical axis functions in relatively long-term physiological adjustments in carbohydrate metabolism.