Interaction between calcium and slow channel blocking drugs on atrial rate

Enantioselective synthesis and pharmacological evaluation of a new type of verapamil analog with hypotensive and calcium antagonist activities

PURPOSE

The syntheses and evaluation for cardiovascular activity in the rat of both enantiomers of a verapamil analog in which the cyano group has been replaced by hydroxyl.

METHODS

(+)- and (-)-alpha-[3-[[2-(3,4-Dimethoxyphenyl)ethyl]methylamino]propyl]- 3,4-dimethoxy-alpha-(1-methyl ethyl)benzyl alcohol were prepared from chiral sulfoxides produced by microbial biotransformations using Mortierella isabellina ATCC 42613 or Helminthsporium species NRRL 4671, and were examined for hypotensive and calcium antagonist activity using anaesthetized normotensive rats and isolated rat aorta and atria.

RESULTS

The analogs showed a pharmacological profile similar to that exhibited by verapamil, possessing a remarkable hypotensive activity, accompanied by a significant bradycardia, in anaesthetized normotensive rats. In vitro, these analogs displayed clear inhibitory effects: in isolated rat aorta they inhibited, in a concentration-dependent fashion, the contractions and 45Ca2+ uptake induced by norepinephrine and high KCl, and in isolated rat atria the analogs considerably decreased the rate of contraction (negative chronotropic effects). No significant differences between the quantitative cardiovascular effects produced by the two enantiomers of the verapamil analogs were observed.

CONCLUSIONS

The results suggest that, like that of verapamil, the cardiovascular activity exhibited by the new compounds seems to be due, at least in part, to a blockage of transmembrane calcium channels present in vascular smooth muscle cells.

Potentiation by calcium channel blockade of hypoxic myocardial depression in the neonate

The objectives of this study were to examine the independent and combined effects of beta blockade (practolol) and calcium channel blockade (verapamil) on cardiac responses to hypoxia in the neonate. Lambs were anaesthetized with pentobarbital (20 mg/kg) and were prepared for measurements of left ventricular (LV) performance under controlled hemodynamic conditions. Force generation was assessed from curves relating LV systolic pressure (SP) to end-diastolic pressure (LVEDP) over a broad range of afterloading. Velocity was determined from simultaneous measurements of LV dP/dtmax. Values obtained at LVEDP 10 cm H2O were used to compare interventions. Practolol (P) caused no significant reduction in SP10, but dP/dt10 fell from 51 to 37 (X 10(2] mm Hg/sec (p less than 0.05). Verapamil (V), 2 micrograms/min/kg, reduced measures of contractility (p less than 0.01). Doubling the dose of V further reduced SP10 to 79% of control. Hypoxemia (PaO2, 32 torr) increased SP10 from 172 to 192 mm Hg, and dP/dt10 from 51 to 85 (X 10(2] mm Hg/s (p less than 0.001). After P, the same degree of hypoxia elicited no changes in LV function. During infusion of V (4 micrograms/min/kg), hypoxia reduced SP10 from 138 to 122 mm Hg (p less than 0.01) and dP/dt10 from 29 to 24 (X 10(2] mm Hg/sec (p less than 0.05). It is concluded that in the absence of adrenergic support, hypoxia significantly depresses both force and velocity parameters of contractility in hearts with calcium channel blockade.

Calcium antagonists--drug interactions

Evaluations of drug interactions should be done with caution. One needs to be aware of the reported interactions and apply the information on an individual basis. This review may therefore serve as a guide to the more common drug interactions and when drug therapy should be monitored closely in clinical practice. Major drug interactions with calcium antagonists are summarized in Table 2.