Novel C-2 substituted carbapenem derivatives. Part IV. Synthesis and biological activity of five membered heteroaromatic derivatives.

The synthesis, antibacterial activity, and stability to human dehydropeptidase-1 (DHP-1) of a novel series of (5R,6S)-6-[(1R)-1-hydroxyethyl]-2-heterocyclylcarbapen-2-em-3-carb oxylates are described. Of the compounds investigated 1,5-disubstituted pyrazol-3-yl and 3-substituted isoxazol-5-yl derivatives have the best combination of antibacterial activity and stability to DHP-1. They are particularly active against community-acquired respiratory tract pathogens and have stabilities to DHP-1 superior to that of meropenem.

Adenine nucleotides and ventricular fibrillation.

The isolated perfused rat heart was used to study the influence of adenine nucleotides and their metabolites on vulnerability to ventricular fibrillation. In this model the incidence of ventricular arrhythmias after coronary artery ligation is determined by the extracellular K+ concentration; with perfusate K+ of 2.0 and 3.0 mmol/l hearts develop a high incidence of ventricular arrhythmias and fibrillation while arrhythmias are not encountered with perfusate K+ of 9.0 mmol/l. Assay of adenine nucleotides in uninvolved and ischaemic myocardium of these hearts showed a direct relationship between incidence of ventricular fibrillation and tissue levels of cyclic AMP but not tissue levels of lactate, high energy phosphates, adenosine, inosine and hypoxanthine/xanthine. Administration of dibutyryl cyclic AMP to isolated rat hearts reduced the ventricular fibrillation threshold; this action of cyclic AMP was effectively antagonized by adenosine and its N-ethylcarboxamido analogue but not by 2-chloroadenosine, phenylisopropyladenosine, cyclohexyladenosine and the adenosine deaminase inhibitor, EHNA. 2-Chloroadenosine, like adenosine, inhibited the increase in heart rate caused by DBcAMP. All the adenosine analogues had antiarrhythmic activity against spontaneously occurring ventricular arrhythmias during coronary artery occlusion. Adenosine analogues also antagonized the effect of dibutyryl cyclic AMP whereby it prolongs the QT interval. Adenosine, by as yet incompletely defined mechanisms, may act as an antagonist to the cyclic AMP mediated increase in vulnerability which contributes to the genesis of ventricular fibrillation in the early phase of myocardial ischaemia.

Permissive action of potassium on arrhythmogenesis in the rat heart.

The isolated perfused rat heart was used to assess the influence of extracellular potassium ([K+]0) on vulnerability of the heart to ventricular fibrillation (VF). The VF threshold is reduced when [K+]0 is lowered from 5.9 to 2.0 and 3.0 mmol/l. The vulnerable period is not only widened but VF can be obtained by stimuli on the R wave. The opposite effects are encountered when [K+]0 is increased to 9.0 mmol/l. These alterations in vulnerability to VF are accompanied by an increased incidence of tachyarrhythmias and spontaneous VF during coronary artery ligation and following reperfusion on reduction of [K+]0, with elimination of these arrhythmias on increasing [K+]0 to 9.0 mmol/l. The cellular biochemical responses that accompanied the altered electrical behaviour on alterations of [K+]0 involved the tissue levels of cyclic AMP in both non-ischaemic and ischaemic myocardium and tissue levels of Ca2+ whereas tissue levels of high energy phosphates, adenosine, inosine, hypoxanthine, lactate, Na+, K+ and Mg2+ did not discriminate between hearts vulnerable and hearts resistant to VF. In this model the extracellular K+ level is a determinant of vulnerability to ventricular fibrillation while ischaemic tissue levels of Ca2+ provide the best correlation with alterations in vulnerability.

Improved performance of the isolated rat liver when perfused with purified bovine serum albumin.

Three groups of isolated rat livers were perfused at 35 C with Krebs-Ringer bicarbonate buffer containing commercial bovine serum albumin (BSA) which had been purified by gel filtration on a column of Sephacryl S-200 and used within 12 hr of purification, or BSA which had been purified by gel filtration and stored at -70 C until used. The ability of livers to produce bile, retain potassium, and to maintain a constant level of glucose in the perfusate was greatly improved in the presence of purified albumin which had not been frozen. Such livers also showed the highest rates of urea synthesis, but the rate of release of aspartate aminotransferase (GOT) from cells and the bile salt content of the bile produced were similar to those found with unpurified BSA. Livers perfused with purified albumin which had been stored in the frozen state were slightly inferior to those perfused with nonfrozen albumin in their ability to produce bile and urea, to retain potassium and GOT within cells, and to maintain a constant concentration of glucose in perfusates. The concentration of bile salts in the bile produced by this group was also lower than that found with the other two groups. Overall, isolated rat livers benefited from perfusion with purified albumin, although freeze storage of this material rendered it slightly inferior to the nonfrozen material in its ability to support the liver.

The effect of insulin and hydrocortisone on the isolated rat liver.

Isolated rat livers were perfused at 35 degrees C with bovine serum albumin (40 g/l) in Krebs Ringer bicarbonate buffer, or with the same solution containing insulin (0.22 x 10(-6) mol/l), hydrocortisone (0.068 x 10(-3) mol/l), or both hormones together. Observations on the synthesis of bile and on perfusate levels of potassium, aspartate aminotransferase, urea and glucose showed that the presence of insulin and/or hydrocortisone had no beneficial effect on the perfused rat liver in vitro. There is little justification of the isolated liver.

The effect of colloid concentration on the functional characteristics of isolated perfused rat liver.

The volume of bile produced by isolated perfused rat liver was dependent on the concentration of bovine serum albumin (BSA) in the perfusate, the lowest volumes being obtained with Krebs Ringer bicarbonate (KRB alone and with 70 g/l. BSA in KRB. Increasing amounts were produced as the concentration of BSA was reduced from 70 g/l. to 8.5 g/l. The concentration of bile salts in the bile decreased rapidly during the first hour, but much more slowly thereafter. The highest concentration observed during the first hour was with KRB alone and the lowest with 20 g/l. BSA; subsequently, the highest concentrations were obtained with 70 g/l. BSA and the lowest with 20 g/l. BSA. Urea synthesis was lowest with KRB alone, but increased as the concentration of BSA increased; however, values obtained with 8.5, 20, and 40 g/l. were fairly close together. With KRB alone there was a rapid release of potassium during the first hour, but thereafter the rate of release was similar to that found when BSA was present. The lowest concentrations of potassium were obtained with 20 and 40 g/l. BSA. With KRB alone, GOT was released from the start of perfusion of 300 units per minute. With BSA present, GOT release was delayed 4 hours, and thereafter the rate was dependent on the concentration of BSA, being lowest with 20 and 40 g/l. (200 units per min), higher with 8.5 g/l. (350 units per min) and highest with 70 g/l. (400 units per min).