Potentiating effects of bradykinin-related substances on bradykinin-induced contraction of guinea pig ileum and hypotension in rats

Endogenous methionine enkephalin may play an anticonvulsant role in the seizure-susceptible El mouse

After the intracisternal injection of three protease inhibitors which prevent the degradation of methionine enkephalin (amastatin, Des-Pro2-bradykinin, and phosphoramidon) and a mixture of these protease inhibitors, we investigated the effect on convulsive seizures in the seizure-susceptible El mouse. We also measured the cerebral methionine enkephalin content by high-performance liquid chromatography coupled with radioimmunoassay. Protease inhibitors significantly decreased both the incidence of seizures and the seizure score in El mice in a dose-dependent manner. This anticonvulsant effect was reversed by naloxone (2 mg/kg, sc). The cerebral methionine enkephalin content increased significantly after the administration of protease inhibitors in comparison with saline injection. These findings suggest that it was not protease inhibitors but instead increase of endogenous methionine enkephalin that reduced the incidence of seizures and the seizure score in El mice. Together with our previous data, the present findings support our hypothesis that a deficit in anticonvulsant endogenous methionine enkephalin is involved in the pathogenesis of seizures in the El mouse.

Vasopressor and depressor effects of native angiotensins and inhibition of these effects in the Japanese quail

The amino acid sequence of angiotensin I (ANG I) from the Japanese quail, Coturnix coturnix japonica, obtained from incubation of homologous plasma and kidney extract was determined as H-Asp-Arg-Val-Tyr-Val-His-Pro-Phe-Ser-Leu-OH. A bolus, intravenous injection of native ANG I or of ANG II induced an immediate vasodepressor response and a subsequent vasopressor response in quail which has been lightly anesthetized with urethane (0.75 g/kg). The values for ED50 for the vasopressor and depressor effects of ANG II were 85 and 113 pmol/100 g body weight, respectively. The extent of the hypotension was dependent on the arterial pressure prior to injection. The effects of ANG I and II on heart rate were variable. Human [Asp1, Ile5, His9] ANG I and II were almost as potent as their quail counterparts with respect to the cardiovascular effects, but eel [Asn1, Val5, Gly9]ANG I and II were less than half as potent. Human ANG III had little effect on arterial pressure in the quail. A bolus injection (100 micrograms/100 g) or infusion (1 micrograms/100 g/min) of [Sar1, Ile8] ANG II almost abolished the cardiovascular effects of ANG I and II, but [Sar1, Ala8] ANG II and [Sar1, Thr8] ANG II, which are effective inhibitors in mammals, had no inhibitory effects. The vasopressor and depressor effects of ANG I were abolished, while those of ANG II were slightly enhanced, after injection (100 micrograms/100 g) or infusion (1 micrograms/100 g/min) of SQ14225, whereas des-Pro2 bradykinin and bradykinin potentiator B, which are effective inhibitors of ANG I converting enzyme in mammals, failed to inhibit the effect of ANG I. These results indicate that vascular ANG II receptors and ANG I converting enzyme in the quail may be different from those in mammals.