Temporal effects of infused corticosterone and aldosterone on plasma glucose levels in the American bullfrog (Rana catesbeiana)

Elevation of plasma glucose, alanine, and urea levels by mammalian ACTH in the American bullfrog (Rana catesbeiana)

The effects of a single infusion of mammalian ACTH on plasma glucose, alanine, urea, and lactate were determined in the American bullfrog (Rana catesbeiana). The ACTH (10 U/250 g body wt) was administered, and serial blood samples were collected via a nonocclusive cannula chronically placed in the right truncus arteriosus. Plasma metabolite levels were estimated by standard enzymatic techniques. The plasma metabolites declined following the surgery to levels that were relatively stable by postoperative Day 2. The levels did not vary significantly for the remainder of the 3- or 4-day pretreatment period and in the control bullfrogs during the 48-hr experiments. Plasma glucose levels were essentially unchanged from the time-zero levels at 6 hr following ACTH infusion. Plasma glucose levels subsequently increased to levels that were approximately 24% greater than the control levels by 24 hr and then declined to near control levels by 48 hr. Plasma alanine increased to levels that were approximately 60% greater than the control levels by 12 hr after ACTH treatment and returned to essentially the time-zero levels by 24 hr. Plasma urea rose to levels that were approximately 110% greater than the control levels by 45 min after ACTH infusion, but urea returned to essentially the time-zero levels by 1.5 through 3 hr. Plasma urea increased again to levels that were approximately 90% greater than the control levels by 6 hr and returned to essentially the initial levels by 24 hr. Plasma lactate levels were not significantly influenced by ACTH treatment. The results suggest that a function of the bullfrog hypothalamic-pituitary-adrenocortical axis is to regulate gluconeogenesis from alanine, and probably other glucogenic amino acids.

Plasma levels of glucose, alanine, lactate, and beta-hydroxybutyrate in the unfed spiny dogfish shark (Squalus acanthias) after surgery and following mammalian insulin infusion

Serial blood samples were collected from the unfed spiny dogfish shark (Squalus acanthias) by use of a cannula chronically implanted in the dorsal aorta. Plasma glucose, alanine, lactate, and beta-hydroxybutyrate levels were estimated by standard enzymatic procedures. The metabolite levels were estimated immediately after the surgery, for an additional 3 to 5 postoperative days before experimental use, and for 7 to 9 days after a single infusion of mammalian insulin (50, 100, and 250 IU/kg body wt) or the control solution. Plasma glucose, alanine, and lactate levels declined for 1 or 2 days after the surgery, but beta-hydroxybutyrate levels were essentially unchanged. Plasma glucose levels remained relatively stable for the remainder of the pretreatment period, and in the control animals during the subsequent treatment period. In contrast, plasma alanine and beta-hydroxybutyrate levels increased during both the pretreatment period and the treatment period in the control animals. Plasma lactate levels increased in the control animals after Day 3 of the treatment period. Insulin infusions resulted in severe, prolonged depressions of plasma glucose and alanine levels. Plasma lactate levels also fell after insulin infusion, but the depressed levels were interrupted by precipitous, large increases, followed by sharp declines, that were evident for one to three sampling periods and whose onset varied between Days 3 and 5 in individual animals. The levels increased again in some animals between Days 6 and 9. Plasma beta-hydroxybutyrate levels were comparatively resistant to insulin. After an early decline, plasma beta-hydroxybutyrate rose to levels that were near the control levels by Days 2 through 4, but fell to near the initial levels by Day 5 and thereafter. The results suggest that the spiny dogfish, a species that consumes reliable and abundant amounts of protein and lipid, but little carbohydrate, and that may feed as seldom as every 2 weeks, uses ketone bodies (beta-hydroxybutyrate and presumably acetoacetate) as primary fuels. Glucose is apparently synthesized by gluconeogenesis, alanine and lactate are probable substrates, and ketone bodies are the likely sources of energy. The evidence supports the hypothesis that glucose is synthesized to maintain muscle glycogen reserves that are used for anaerobic glycolysis when the animal is engaged in predation, escape, or other circumstances that dictate vigorous swimming. If other tissues and organs require glucose as a fuel source, the amounts must be exceptionally small.

The effect of dexamethasone on plasma glucose and liver glycogen levels in premetamorphic Rana catesbeiana tadpoles and frogs

Premetamorphic Rana catesbeiana tadpoles and adult frogs demonstrate significant elevations in plasma glucose levels following dexamethasone (dex) injections. This response is greatest in the tadpole 24 hr after dex administration and is still detectable at 48 hr. Liver glycogen levels increase in the frog, but not in the tadpole, following daily injections of dex for five consecutive days. The response of the tadpole to dex occurs at a time when hepatic cytosolic glucocorticoid receptors have been observed, but when endogenous corticosterone is absent.