Nicole Morel

In vitro intestinal transport and antihypertensive activity of ACE inhibitory pea and whey digests

Angiotensin I converting enzyme (ACE) inhibitory peptides cause an antihypertensive effect if they reach the systemic circulation. This was investigated for the high ACE inhibitory activity present in peas and whey in vitro gastrointestinal digests. The samples retained high ACE inhibitory activity when incubated in Caco-2 homogenates or rat intestinal acetone powder, both sources of small intestine peptidases. Only little ACE inhibitory activity was transported through Caco-2 cell monolayers in 1 h. As the Caco-2 model is tighter than intestinal mammalian tissue, sufficient absorption of these peptides might occur in vivo. After intravenous administration of 50 mg protein kg−1 BW in spontaneously hypertensive rats (SHR), pea digest exerted a transient, but strong antihypertensive effect of 44.4 mmHg. Whey digest exerted no effect at this dose. These results suggest that pea digest could be a promising source of ACE inhibitory peptides for use in the prevention and treatment of hypertension.

Regulation of Calcium Channels in Vascular Smooth Muscle

Most contractile responses of vascular smooth muscle are dependent on Ca entry, as indicated by the absence or the reduction of the responses when tissues are bathed in solution devoid of Ca. At rest, Ca influx across the plasma membrane is about 20 nmol Ca/g tissue per minute. Opening of Ca channels in the plasma membrane causes a rapid increase of Ca influx resulting from the large electrochemical gradient existing between the extra- and intracellular compartments (1). Different molecular structures appear to ensure Ca movement across the plasma membrane. In addition to their typical electrical properties, the L subtype of voltage-operated Ca channels (VOCs) can be distinguished from other types of Ca channels by their sensitivity to Ca agonists and antagonist dihydropyridines. We have investigated whether, besides the control exerted by membrane potential, VOC activity could be regulated by agonists and intracellular messengers in vascular smooth muscle cells.

Pharmacology of Calcium Antagonists in Arterial Smooth Muscle

Interaction of calcium antagonists with calcium channels has been studied in vascular smooth muscle from normotensive and hypertensive (SHR) rats by measuring calcium fluxes, contraction and specific binding of dihydropyridines. Inhibition of KC1-evoked contraction by several dihydropyridines showed a pronounced time dependency, in which the inhibition increased slowly after depolarization to attain a steady-state value. The time course of the development of inhibition by (+)PN 200–110 paralleled the time course of binding to isolated membranes. The effect of the membrane potential on dihydropyridine binding was investigated in intact mesenteric arteries. Only one class of specific binding site was observed. Depolarization increased (+)[3H]PN 200–110 binding by inducing a decrease in KD without changing Bmax. KD or Ki values determined in depolarized arteries were similar to corresponding values measured from membrane preparations, and to IC50 values for steady-state inhibition of contractions. Thus, depolarization induces a conformation of calcium channels with enhanced affinity for dihydropyridines. Binding of these drugs to the high-affinity conformer induced by depolarization is responsible for inhibition of calcium influx and contraction. In SHR arteries the state of the calcium channels makes them more easily activated by agonist dihydropyridines, but the properties of the binding site in depolarized arteries appear unchanged.