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

Introduction

Citrullus colocynthis extracts were reported to have beneficial effects on glucose homeostasis and body weight maintenance, in either alloxan- or streptozotocin (STZ)-induced diabetic rats (1,2). The present study aimed to examine the possible protective action of Citrullus colocynthis extracts against the diabetogenic actions of STZ, since information currently available on the subject is insufficient. (1). To this end, the in vitro effect of an H₂O-methanol Citrullus colocynthis seeds extract on the deleterious effect of STZ in glucose-stimulated insulin secretion from isolated rat pancreatic islets was initially examined. Additionally, the protective action of an aqueous extract from Citrullus colocynthis seeds against the STZ-induced impairment of glucose homeostasis was investigated in vivo in rats.

Materials and methods

The aqueous extract of Citrullus colocynthis seeds was prepared as described in a previous study (3). For the hydromethanolic extract, 50 g of seeds were ground and defatted in hexane. This material was then heated and stirred 3 times for 3 h in a water:methanol mixture (30:70). Following filtration and centrifugation, the solution was evaporated until dry, and a hygroscopic red-orange residue (4.5% dry matter) was obtained.

STZ was purchased from Sigma Chemical Co. (St. Louis, MO, USA).

The in vitro experiments were carried out in islet groups (n=8/group), obtained from fed female Wistar rats. Islets were prepared by the collagenase procedure (4) and incubated for two successive periods of 60 min each at 37°C in 1.0 ml of a salt-balanced medium (5) containing 1.0 mg/ml bovine serum albumin, 16.7 mM D-glucose and, as required, STZ (1.9mM) and/or the H₂O-methanol extract (500 μg/ml). The insulin content of the incubation media was measured using radio immunoassay (6).

The in vivo experiments were carried out using female Wistar rats injected intraperitoneally with saline (5 ml/kg body wt.) or with crude aqueous extract (90 mg/kg body wt.), either daily for 21 successive days, or only once 24 h prior to the intraperitoneal injection of STZ (0.25 mmol/kg body wt.). The glycemia was measured in blood samples collected from the tail tip, using a glucometer (Accu-Chek).

The results are presented as the mean values (± SEM) with the number of individual determinations (n) or...