Response of the blood glucose and the pancreatic islets of the lizard, Uromastix hardwicki (Gray) to exogenous insulin.

Uromastix hardwicki was found more resistant to insulin as compared to other poikilotherms and this insulin resistance appears to be related to the preponderance of glucagon secreting alpha-cells in this species. The magnitude and the persistence of hypolgycemia caused by insulin are directly dependent upon the quantity of the dose. The higher doses (2000 and 3000 U/kg) resulted into shocks, but the lack of correlation between hypoglycemia and shocks has been attributed to the direct effect of insulin on the nervous system. Histologically, insulin induced degranulation of both the beta- and alpha-cells. The physiological action of insulin is apparently greater at higher ambient temperature. The ability of insulin to damage beta- and alpha-cells in Uromastix hardwicki further gathers evidence for the similarity of these cell types with those of mammals and other vertebrates in being the source of insulin and glucagon respectively, and in controlling the blood glucose homeostasis in this lizard.