The stimulatory effect of alloxan diabetes on citrulline formation in rabbit liver mitochondria

The effect of alloxan diabetes on citrulline formation from NH₄Cl and bicarbonate was studied in rabbit liver mitochondria incubated with glutamate or succinate as respiratory substrate, as well as with exogenous ATP in the presence of uncoupler and oligomycin. In contrast to ornithine transcarbamoylase, the activity of carbamoyl-phosphate synthetase (ammonia) was higher in mitochondria from diabetic animals than in those from normal ones. In diabetic rabbits the rates of citrulline synthesis were stimulated under all conditions studied. In contrast, levels of N-acetyglutamate, an activator of carbamoyl-phosphate synthetase (ammonia), were significantly increased only in the presence of glutamate, while the highest rates of citrulline formation occurred in uncoupled mitochondria incubated with exogenous ATP as energy source. Treatment of animals with alloxan resulted in an increase of both the intramitochondiral ATP level and the rate of adenine nucleotide translocation across the mitochondrial membrane. The results indicate that the stimulation of citrulline formation in liver mitochondria of diabetic rabbits is mainly due to an increase in carbamoyl-phosphate synthetase (ammonia) activity and an elevation of content of intramitochondrial ATP, a substrate of this enzyme.     

Comparative study of the structural characteristics of aldolase in rabbit muscles in normal states and in alloxan diabetes

It is shown that the activity of aldolase synthesized in rabbit muscles under diabetes is higher than that at normal state. This fact is probably a result of some structural alterations in NAD-binding site with Trp-291 and -311 in it which overlaps a considerable part of C-terminal region of the protein. The hydrophobic part of the enzyme containing Trp-147 under diabetes seems to remain unaltered. This consideration is based on the longwave shift in aldolase fluorescence lambda max (from 320 to 324 nm) under this pathology, suggesting a transition of Trp-291 and -311 into more polar environment and is confirmed by the disappearance of the difference in lambda max in the NADH presence. The NADH-originated shift in lambda max position for the both proteins ended at the same wave-length at 314 nm. The position of lambda max at 324 nm resulting from possible structural modification of NAD-binding site under diabetes correlates with an increase in the Stern-Volmer quenching constant value (from 4359 to 7500 M-1 for aldolase under normal and diabetic states, respectively). These quenching data evidence in favour of the suggestion on the existence of two classes of tryptophanyls in the aldolase molecule.     

The lack of effectiveness of (−)-epicatechin against alloxan induced diabetes in Wistar rats

(?)-Epicatechin, a naturally occurring flavonoid, has been reported to protect pancreatic beta cells from alloxan-induced diabetes (1) and to stimulate beta cell regeneration when given after alloxan administration (2,3). However, in the present study, we have not been able to confirm these findings. Administration of (?)-epicatechin (100 mg/kg/day for 15 days) beginning three days after alloxan administration (140 mg/kg) had no significant effect on blood glucose levels when compared to alloxan control animals. Another study which failed to demonstrate an antidiabetic effect of (?)-epicatechin (4) has been criticized for not using fresh solutions of (?)-epicatechin because of its instability in aqueous solution (5). We have found, however, that (?)-epicatechin is stable for at least five days based on thin-layer chromatographic analysis and optical rotation measurements.     

Pharmacokinetics of oltipraz in rat models of diabetes mellitus induced by alloxan or streptozotocin

Pharmacokinetic parameters of oltipraz were compared after intravenous (10 mg/kg) and oral (30 mg/kg) administration in rat model of diabetes mellitus induced by alloxan (rat model of DMIA) or streptozotocin (rat model of DMIS) and their respective control male Sprague-Dawley rats. In rat models of DMIA and DMIS, the expressions and mRNA levels of CYP1A2, 2B1/2, and 3A1(23) increased, and oltipraz was metabolized mainly via CYP1A1/2, 2B1/2, 2C11, 2D1, and 3A1/2 in male Sprague-Dawley rats. Hence, it would be expected that the AUC and CL values of oltipraz would be significantly smaller and faster, respectively, in rat models of diabetes. This was proven by the following results. After intravenous administration, the AUC values were significantly smaller in rat models of DMIA (40.1% decrease) and DMIS (26.0% decrease) than those in respective control rats, and this could be due to significantly faster CL values in rat models of DMIA (40.1% increase) and DMIS (26.0% increase). The faster CL could be due to increase in hepatic blood flow rate and significantly faster CL(int) in rat models of diabetes, since oltipraz is an intermediate hepatic extraction ratio drug in male Sprague-Dawley rats. After oral administration, the AUC values of oltipraz were also significantly smaller in rat models of DMIA (54.0% decrease) and DMIS (63.2% decrease). This could be due to increase in hepatic blood flow rate, significantly faster CL(int), and changes in the intestinal first-pass effect in rat models of diabetes. However, this was not due to decrease in absorption in rat models of diabetes.     

Variations in rabbit oviduct microvascular architecture after ovulation induced by hCG

Rabbits were induced to ovulate by injection with hCG and vascular corrosion casts of the oviducts were examined by scanning electron microscopy after 24 and 48 h, when the ova would be expected to be at the ampullary-isthmic junction, and traversing the isthmus respectively. At 24 h there was dilatation of the isthmic subserosal venous plexus. It is suggested that venous distension in the isthmic subserosal venous plexus, due to raised venous pressure or to reduced venous wall tone, may occlude the isthmic lumen to ova, and thus explain the known pre-isthmic delay in ovum transport. By 48 h after hCG, distension was no longer evident, consistent with the possibility of ovum transport.