Protective action of Citrullus colocynthis seed extracts against the deleterious effect of streptozotocin on both in vitro glucose-stimulated insulin release from rat pancreatic islets and in vivo glucose homeostasis

Abstract

Citrullus colocynthis extracts improve glucose homeostasis in alloxan- or streptozotocin (STZ)-induced diabetic rats. Little is known, however, regarding the protective effect of these extracts against the β-cytotoxic action of STZ. In the present study, an H₂O-methanol extract was found to suppress the inhibition of glucose-stimulated insulin secretion by STZ in rat-isolated pancreatic islets. Similarly, when an aqueous extract from Citrullus colocynthis seeds was injected daily for 21 days prior to STZ administration, the perturbation of glucose homeostasis otherwise generated by the β-cytotoxic agent was minimized in rats.

Keywords: Citrullus colocynthis extracts; glucose-stimulated insulin release; glycemia; rat isolated pancreatic islets; streptozotocin.

Figure 1.

Left panel: insulin output over two successive 60-min incubations conducted in the sole presence of D-glucose (16.7 mM; closed circles and solid line) or in the presence of the hexose and the H₂O-methanol extract (500 μg/ml; open triangle and dash-dotted line), streptozotocin (STZ) (1.9 mM; open circles and dotted line), or both the H₂O-methanol extract and STZ (crosses and dashed line). The mean values (± SEM) for insulin output are expressed as a percentage of the average insulin output recorded within the same experiment(s) during the first incubation in the sole presence of D-glucose and refer to 17–20 (open and closed circles, crosses) or 39 (open triangle) individual determinations. Right panel: effect of the H₂O-methanol extract upon insulin output from islets incubated in the absence (no STZ) or the presence of STZ during the first incubation (STZ-1) or both the first and second incubation (STZ-2). The mean values (± SEM) are expressed relative to the average insulin output recorded during the same experiment(s) and incubation period in islets exposed to D-glucose in the absence of the H₂O-methanol extract and refer to 37–39 (no STZ) or 18–19 (STZ-1 and STZ-2) individual determinations.

Figure 2.

Correlation between Day 7/Day 2 ratio in glycemia and the Day 2/Day 0 ratio in glycemia subsequent to streptozotocin (STZ) administration either to the control (open circles and solid line) or the experimental rats, injected either once 24 h prior to STZ administration (cross) or daily for 30 days prior to such an injection (closed circles and dashed line). Mean values (± SEM) refer to the number of animals indicated at the top of the figure. The oblique solid and dashed lines are the regression lines.