Antihypertensive effect of diltiazem in young or adult rats of genetically hypertensive strains

Altered neural and vascular mechanisms in hypertension

Essential hypertension is a multifactorial disorder which belongs to the main risk factors responsible for renal and cardiovascular complications. This review is focused on the experimental research of neural and vascular mechanisms involved in the high blood pressure control. The attention is paid to the abnormalities in the regulation of sympathetic nervous system activity and adrenoceptor alterations as well as the changes of membrane and intracellular processes in the vascular smooth muscle cells of spontaneously hypertensive rats. These abnormalities lead to increased vascular tone arising from altered regulation of calcium influx through L-VDCC channels, which has a crucial role for excitation-contraction coupling, as well as for so-called "calcium sensitization" mediated by the RhoA/Rho-kinase pathway. Regulation of both pathways is dependent on the complex interplay of various vasodilator and vasoconstrictor stimuli. Two major antagonistic players in the regulation of blood pressure, i.e. sympathetic nervous system (by stimulation of adrenoceptors coupled to stimulatory and inhibitory G proteins) and nitric oxide (by cGMP signaling pathway), elicit their actions via the control of calcium influx through L-VDCC. However, L-type calcium current can also be regulated by the changes in membrane potential elicited by the activation of potassium channels, the impaired function of which was detected in hypertensive animals. The dominant role of enhanced calcium influx in the pathogenesis of high blood pressure of genetically hypertensive animals is confirmed not only by therapeutic efficacy of calcium antagonists but especially by the absence of hypertension in animals in which L-type calcium current was diminished by pertussis toxin-induced inactivation of inhibitory G proteins. Although there is considerable information on the complex neural and vascular alterations in rats with established hypertension, the detailed description of their appearance during the induction of hypertension is still missing.

Calcium channel blockers as antihypertensive agents

Because of their unique action on the cardiovascular system, the calcium channel blockers have generated a great deal of excitement among pharmacologists, physiologists, and clinicians. One obvious potential application for these drugs is in antihypertensive therapy and, although experience with these agents for this indication is limited in the United States, it is considerable in Europe and Japan. These agents' ultimate role in antihypertensive therapy, however, has not been established. Since the available calcium channel blockers are structurally diverse, it is uncertain whether they will have comparable effects in hypertension. The rationale for the use of calcium channel blockers in treating hypertension and the relevant pharmacologic actions of these agents is discussed, along with a summary of some of the clinical trials, observations from our own experience with these drugs, and speculation about their future role in antihypertensive therapy.