Glucagon, plasma

Systemic effects of nickel exposure include hyperglycemia, increased levels of plasma glucagon, damage to the pancreatic islet cells, decreased body weight, reduced food and water intake, and hypothermia (NAS 1975 USEPA 1980 USPHS 1993). Acute administration of nickel salts caused prompt hyperglucagonemia and subsequent hyperinsulinemia in rats, rabbits, and guinea pigs (WHO... 

Horak E, Sunderman FW Jr. 1975a. Effects of Ni(II) upon plasma glucagon and glucose in rats. Toxicol Appl Pharmacol 33 388-391. 

Horak, E. and F.W. Sunderman, Jr. Effects on Ni(ll) upon Plasma Glucagon and Glucose in Rats, Toxicol Appl Pharmacol, 33, 388 (1975). 

In summary, the data demonstrate that plasma glucose levels are maintained during an activity that greatly increases the use and oxidation of glucose stores within the body. The data also reveal that exercise is associated with an increase in the glucagon/insulin ratio and, a more subtle point, that plasma glucagon levels may fluctuate in a manner independent of insulin levels. 

FIGURE 4,9 I ia ma glucose and hormone le> els before, during, and after Insulin infusion. Normal human subjects were infused with insulin for the I-hour period Indicated by the black bar. Glucose, in.sulin, and glucagon levels were measured at the indicated times. While plasma insulin increased to six times its basal level, plasma glucose fell precipitously and plasma glucagon rose. (Redrawn with permission from Boili et at., 1984.J... 

We have been discussing the sequence of events occurring with an increase in plasma glucagon. What happens with a decline in plasma glucagon A drop in glucagon results in a decrease in intracellular cAMP, the removal of the covalently bound phosphate groups on phosphorylase, and a drop in the rate of glycogen... 

The enzymes marked with the section symbol ( ) are regulated by covalent phosphorylation. In short, changes in the plasma glucagon/insulin ratio produce changes in the phosphate group content of these enzymes. Addition or removal of the phosphate group regulates the enzyme s activity, in accordance with the body s metabolic needs. 

Lipoprotein lipase may be activated by changes in plasma glucagon and insulin. This activation appears to occur by an increase in migration of the enzyme to the capillary wall. For example, a decrease in the glucagon/insulin ratio, as with feeding, may provoke an increase in the proportion of enzyme located on the luminal wall and a decrease in the proportion that is intracellular. Feeding appears to provoke activation of the enzyme in adipose tissue, but not of the enzyme located in muscle or other hssues. 

The hormonal picture, as far as glucagon and insulin are concerned, is similar during exercise and fasting. The concentration of plasma glucagon increases during both states, and this elevation stimulates the synthesis of cAMP in cells and the phosphorylation of various enzymes involved in energy metabolism. The arrays of enzymes that become phosphorylated are largely identical for both conditions, and the resultant patterns of activation or inactivation of enzymes are similar or identical. 

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