Ischemia-reperfusion induced elevation of diastolic tension in the isolated guinea pig heart and the effects of calcium antagonists.

Characteristics of the temporal elevation of diastolic tension, produced by ischemia-reperfusion in isolated and paced Langendorff's hearts of guinea pigs, were studied. The elevation of diastolic tension corresponded with an elevation of left ventricular end diastolic pressure after a short ischemic period in the isovolumic heart. These phenomena were thought to be a result of incomplete relaxation. The degree of the elevation of diastolic tension depended upon the duration of ischemic period (3-10 min). This elevation was reproducible in one preparation; nearly the same changes were obtained in a second trial after 35 min of reperfusion when the ischemic period was within 5 min. An increment in the pacing rate to 150% of the first trial value doubled the elevation of diastolic tension by the second 5 min ischemia. Inhibition of glycolytic flux by iode acetic acid augmented the elevation after 3 min of ischemia. In addition, 5 min of ischemia with iode acetic acid caused contracture and recovery was slight. On the other hand, either lowering the Ca2+ concentration in the perfusing solution to a half the normal value, or treatment with Ca2+ antagonists (such as diltiazem), reduced the elevation of diastolic tension significantly. Diltiazem also suppressed the increment in elevation produced by a high pacing rate. It can be concluded that the temporal elevation of diastolic tension during reperfusion reflects the ischemic failure of the heart. This change is presumably due to intracellular Ca2+ overload or accumulation. In addition, since ischemic changes were reproducible in this preparation, it is a useful model for estimating the effects of drugs on the ischemic heart.

Inhibition of platelet aggregation by diltiazem. Comparison with verapamil and nifedipine and inhibitory potencies of diltiazem metabolites.

The inhibitory effects of three calcium blockers, diltiazem (d-form), verapamil, and nifedipine, on ADP- and collagen-induced platelet aggregation of human and rabbit platelets were compared. The potency of diltiazem was greater than those of verapamil and nifedipine in human platelet-rich plasma. A similar order of the inhibitory potencies was observed in rabbit platelet-rich plasma, but this order was reversed when washed platelets were aggregated in buffered saline. Antiaggregatory potencies of metabolites on diltiazem and their optical isomers were examined in human platelet-rich plasma. All the metabolites except deacetyl-N-demethyl diltiazem showed greater activity than diltiazem in ADP- or collagen-induced platelet aggregation. The potencies of the l-isomers of the deacetyl-N-demethyl metabolites were greater than those of the d-isomers. On the other hand, the inhibitory effect of the d-isomer of deacetyl-O-demethyl diltiazem was greater than that of the l-form at lower concentrations, whereas the relationship was opposite at higher concentrations. There was no marked difference in antiaggregatory potency between the d- and l-forms of diltiazem and N-demethyl diltiazem.

Development of diltiazem, a calcium antagonist: coronary vasodilating and antihypertensive actions.

We found that the coronary vasodilating action resides in novel 1,5-benzothiazepine derivatives. The calcium antagonistic property of diltiazem has been demonstrated in vascular and visceral smooth muscles as well as in cardiac ventricular muscle. Although the vasodilating action of diltiazem was the most potent in coronary and vertebral artery, it also dilates other peripheral arteries including renal artery. Antihypertensive action of diltiazem has been shown in several experimental models, such as SHR, renal hypertensive and DOCA/saline rats. Diuretic effect of diltiazem was observed in SHR. Following chronic administration of diltiazem to SHR, the increment of blood pressure was significantly lowered without changing body fluid. In addition, hypotensive action of diltiazem by i.c.v. was observed only at a very high dose. We assume that the vasodilating action of diltiazem is primarily involved in the mechanism responsible for its antihypertensive action.

[Effects of diltiazem on catecholamine release from cat adrenal glands (author's transl)].

Effects of diltiazem on catecholamine (CA) release evoked by several secretagogues were investigated in cat adrenal glands perfused in situ with Locke solution. All compounds were introduced into the perfusion medium. It was found that the release of CA stimulated by either acetylcholine (ACh) (10(-4) M) or high K+ (56 mM) was reduced by approximately 50 and 90% in the presence of 10(-5) and 10(-4) M diltiazem respectively, while diltiazem at 10(-6) M exhibited little or no influence on the Ca release. In addition, diltiazem at a concentration of 10(-6) M or higher produced a dose-related decrease in the CA release evoked by introduction of CaCl2 (2.2 mM) into Ca2+-free perfusion medium. On the other hand, removal of Na+ from the perfusion medium (osmolarity was adjusted with osmotically equal amount of sucrose) caused an increase in release of CA from the glands. Diltiazem (10(-5) M or higher) also reduced this CA release, but its activity was weaker than those found in experiments with ACh, high K+, and Ca2+. In all cases, the effects were reversible on washout. On the contrary, diltiazem, even at a higher concentration of 10(-4) M, exhibited no inhibitory effect on the release of CA induced by acetaldehyde (3 X 10(-3) M). It was suggested that diltiazem, through its Ca2+-antagonistic action, may reduce the evoked CA release which depends on extracellular Ca2+.

[Effects of diltiazem on cardiac function in the dog (author's transl)].

Effects of diltiazem (Dil) on cardiac function were studied in the anesthetized open chest and heart-lung preparation of dogs. In the anesthetized dog, Dil (0.03-0.3 mg/kg, i.v.) increased max dp/dt and raised left ventricular end-diastolic pressure (LVEDP). Dil also produced an increase in cardiac output and coronary blood flow, but produced a decrease in blood pressure and heart rate (HR). In the cardiac denervated dog (bilateral stellectomy and vagotomy), the increase in max dp/dt caused by Dil, although not so remarkable was apparent. Therefore, the effects of Dil on cardiac function were examined in the heart-lung preparations of the dog, in which arterial pressure (AP) and venous pressure (VP) were kept constant (spontaneously beating) or AP, VP and HR were kept constant (atrial pacing). In these preparations Dil (about 1 mg/l) decreased max dp/dt and raised LVEDP. The cardiac function curve (relationship between stroke work and LVEDP) was shifted rightward by Dil. On the other hand, max dp/dt was increased when VP was increased under constant AP and HR. This increase in max dp/dt was also found under the influence of Dil. These results suggest that the augmentation of max dp/dt induced by Dil in the open chest dog is due both to a neural reflex in response to the systemic hypotension and to the Starling mechanism produced by increase in venous return, though Dil itself has a negative inotropic property.

Effect of diltiazem on insulin secretion. II. Experiments on perfused rat pancreas, anesthetized dogs and conscious rats.

Effect of diltiazem on insulin secretion was investigated in the perfused rat pancreas. Experiments were also carried out in anesthetized dogs and conscious rats with and without glucose loading. In the perfused rat pancreas, diltiazem reduced both glucose- and tolbutamide-induced insulin secretion and these effects of diltiazem were reversed with removal of the compound. Inhibition of the glucose-induced insulin secretion caused by diltiazem was counteracted by increasing the concentration of calcium ion. In experiments on intact animals, diltiazem at vasoactive doses produced no significant influence on the basal level of plasma insulin or glucose-induced insulin secretion. These data taken together with findings in previously reported work suggest that diltiazem reduces insulin secretion from pancreatic B-cells in vitro possibly by the calcium-antagonistic property, while the compound exhibits practically no inhibitory action on the insulin secretion in vivo.

[Bronchodilating action of (--)-1-(3, 4, 5-trimethoxybenzyl)-7-hydroxy-1, 2, 3, 4-tetrahydroisoquinoloine HCl (l-MTI) (author's transl)].

Bronchodilating action of l-MTI was investigated by intravenous administration to anesthetized animals and the results were compared to those seen with isoproterenol. Bronchoconstriction was induced by histamine or serotonin. Under pentobarbital anesthesia, the bronchodilating activity of l-MTI was approx. 1/20 that of isoproterenol in cats and dogs, but less than 1/100 that of isoproterenol in monkeys and guinea pigs. The results indicate that the bronchodilating activity of l-MTI is variable and species dependent. It was demonstrated, however, that in guinea pigs, l-MTI did not produce any bronchodilating activity, when the animals were anesthetized with urethane. The absence of the bronchodilating response in animals under this anesthesia was also seen in vagotomized, adrenalectomized and reserpinized, norepinephrine-infused guinea pigs. On the contrary, l-MTI exhibited the bronchodilating action in reserpinized, pithed or hexamethonium-treated guinea pigs anesthetized with urethane. On th other hand, isoproterenol produced a bronchodilating action in all preparations mentioned above. It was also evident that l-MTI suppressed the bronchodilating action of isoproterenol in pentobarbital anesthetized guinea pigs. In addition, l-MTI increased the heart rate of guinea pigs with a low beating rate, but decreased it when the control rate was high. These results suggest that at least in guinea pigs, l-MTI acts as a partial agonist and that the effect of l-MTI on the bronchial system depends on the sympathetic tone and/or sympathetic bronchodilator reflex, as proposed by McCULLOCH ET AL. (9).

[Vasodilator action of (+/-)-1-(3, 4, 5-trimethoxybenzyl)-6-hydroxy-1, 2, 3, 4-tetrahydroisoquinoline hydrochloride (CV-705) in anesthetized dogs (author's transl)].

The vasodilator action of CV-705 was investigated in a number of vascular regions of anesthetized mongrel dogs and this action was compared with that of papaverine. When CV-705 was administered intravenously the vertebral, common carotid and internal carotid blood flow was increased considerably and was long-lasting. These effects were most remarkable among the regions tested. Femoral, aortic and coronary blood flow were also increased. On the other hand, the blood flow through superior mesenteric artery and portal vein increased only slightly. Renal blood flow was decreased slightly after an intravenous administration, whereas an increase was observed after an intra-arterial administration. Such a regional distribution of blood flow after CV-705 was quite similar to that observed with papaverine. CV-705 was well absorbed through the digestive tract. CV-705 given intravenously showed a weak hypotensive and positive chronotropic action. The increase in common carotid blood flow induced by intra-arterial administration of CV-705 was not affected by pre-treatment with atropine or triprolidine, but was partially suppressed by pre-treatment with propranolol. These results suggest that CV-705 has a papaverine-like action as well as a weak beta-adrenoceptor stimulating action, consequently a vasodilator action occurs.

Effect of diltiazem on insulin secretion. I. Experiments in vitro.

Effect of diltiazem on glucose-induced insulin secretion was investigated in the rat islets of Langerhans isolated by a collagenase digestion technique. It was found that B-cells, main constituents of isolated islet preparations, had a well-preserved ultrastructural appearance immediately following isolation or after incubation with glucose or glucose and diltiazem. The islets released a large amount of insulin upon stimulation with glucose and CaCl2. Diltiazem (10(-6)-10(-4) M) produced a dose-related inhibition of glucose-induced insulin secretion and this effect was antagonized by the increase in extracellular concentration of CaCl2. The inhibitory effect of diltiazem on the insulin secretion was also counteracted by dibutyryl-3',5'-cyclic AMP or by theophylline. Among calcium-antagonists tested, nifedipine produced the most powerful inhibitory action on the insulin secretion, while the effect of verapamil was similar to or somewhat stronger than that of diltiazem. It was suggested that diltiazem may reduce the intracellular concentration of free calcium ion, thus causing an inhibitory effect on the glucose-induced insulin secretion by the isolated islets of Langerhans.

Effects of diltiazem and lanthanum ion on the potassium contracture of isolated guinea pig smooth muscle.

Effects of diltiazem on K-induced contracture of the smooth muscle were examined in the isolated taenia coli and stomach strip of the guinea pig. Results were compared with those of lanthanum ion (La(3+)). K-contracture was evoked by isotonic K-Krebs solution. La(3+) inhibited K-contracture of the taenia coli and effects on the phasic response were found to be more remarkable than on the tonic response. After the removal of La(3+), the phasic response almost regained its normal magnitude, whereas the tonic response was significantly augmented. In contrast to the effects of La(3+), diltiazem inhibited the tonic response more markedly than the phasic response in both taenia coli and stomach strip. Inhibition of the phasic response was elicited, in association with decrease in the frequency of spike discharge during rapid depolarization of the membrane. The effects of diltiazem were completely reversed after washing out the compound. It is assumed that although both La(3+) and diltiazem inhibit the transmembrane influx of Ca(2+), additional mechanisms may differ.

Effects of diltiazem on electrical and mechanical activities of isolated guinea pig taenia coli.

Effects of diltiazem on electrical and mechanical activities of isolated guinea pig taenia coli were studied by means of the double sucrose-gap method. In the spontaneously active preparations, diltiazem (2.2 X 10(-6) M) suppressed both electrical activity and isometric contraction, while electrical and mechanical activities evoked by the depolarizing current pulse were not affected at the concentration of 2.2 X 10(-6) M. In the presence of 2.2 X 10(-5) M diltiazem, the evoked contractile force and the number of repetitive firings during depolarization were reduced, whereas the single spike was almost unchanged or somewhat inhibited. At 2.2 X 10(-4) M diltiazem, both electrical and mechanical activities were almost abolished. The contractile force and single spike suppressed by diltiazem were partly reversed by the addition of 5 mM CaCl2. There was little significant change in membrane potential and membrane resistance. Similar but somewhat weaker effects were observed when NaCl was replaced with sucrose. In some preparations, 2.2 X 10(-4) M diltiazem reduced the contractile force without significant influence on the electrical activity in Na+-free Locke solution. CoCl2 (3 mM) inhibited the evoked activities in both normal and Na+-free solutions. Possible mechanisms for the relaxing effects of diltiazem on isolated guinea pig taenia coli were discussed.