Effect of glucose loading on the blood glucose level and histology of the principal islets in Channa punctatus.

Glucose was administered to a fresh water teleost, Channa punctatus. Three groups of 40 fish each were injected intramuscularly with 2, 1 and 2 g/kg body weight glucose. Blood glucose level of the experimental fish was assayed according to Nelson (1944) at predetermined intervals, ranging from 0 to 120 hr post-injection. The principal islets were removed at autopsy and fixed for histological examination. A group of 20 fish injected with plain distilled water served as controls. A dose dependent hyperglycemic response was obtained after the glucose loading in Channa punctatus. The peak values were recorded within one hr of the injection. The beta cells in the principal islets were degranulated as a consequence of the glucose injection. The degenerative changes in the beta cells, which included loss of specific granules, pycnosis of nuclei and vacuolization, occurred in synchrony with the fluctuations in the glycemic level. The histological changes in the beta cells were interpreted to be resulting from an increased demand for insulin to metabolize the excess glucose, thereby indicating the role of these cells in the blood glucose homeostasis in this fish.