Receptor subtypes involved in the action of calcium entry blockers

Local analgesic efficacy of tramadol following intraplantar injection

Several studies have suggested that systemic tramadol, an opioid, can represent a valuable treatment in severe pain conditions because of their effects on central pain pathways. However, there are not enough studies supporting that tramadol is efficacious when administered locally. Therefore, we studied the potential local analgesic effects of tramadol in peripheral nociception. In addition, we tested the antinociceptive effects of tramadol-CaCl(2) or naloxone combinations after subcutaneous intraplantar injection in a validated rat model of acute thermal nociception. Local analgesic effects of tramadol were compared with those of lidocaine. The effects of tramadol on thermal paw withdrawal latencies were monitored using the plantar test. The antinociceptive potency of tramadol is higher and long-lasting than that of lidocaine. Naloxone was unable to inhibit the increased antinociceptive response produced by tramadol. Ca(2+) modified the effect of tramadol. When Ca(2+) dose was increased in the solution, thermal antinociceptive potency of tramadol, but not lidocaine was prolonged. Thermal nociceptive responses were not affected in the non-injected paws, indicating a lack of systemic effects with doses of tramadol and lidocaine that elicited local analgesia. These results suggest that intraplantar tramadol administration can produce local analgesic effect with a different action mechanism than that of lidocaine. In addition, extracellular Ca(2+) may play an important role in the local analgesic action of tramadol.

Beneficial interactions between pharmacological, pathophysiological and hypertension research

The treatment of essential hypertension continues to be carried out by drugs, combined with the adaptation of life style. The development of various types of antihypertensive drugs has not only greatly improved the management of hypertension, but also offered significant methodological sophistication of the pharmacological and pathophysiological sciences. Antihypertensive drugs and related experimental agents have been widely used in pharmaco-logical and pathophysiological research. The beneficial effects of such agents will be illustrated by means of several examples, emphasizing the sympathetic nervous system, the renin-angiotensin-aldosterone system, and calcium homeostasis as major targets. As pharmacological tools, which are also antihypertensives, we discuss various types of centrally acting antihypertensives, ganglionic and peripheral neuronal blocking agents, alpha- and beta-adrenoceptor antagonists, angiotensin converting enzyme (ACE)-inhibitors, renin-inhibitors, angiotensin II-receptor antagonists (AT1-blockers) and calcium antagonists. Finally, a few remarks will be made concerning the beneficial therapeutic effects of classic and newer antihypertensive drugs, such as beta-blockers, diuretics, calcium antagonists, ACE-inhibitors and AT1-blockers.

Calcium antagonists and vasodilatation

Calcium antagonists comprise a diverse group of chemically unrelated agents that interact with voltage-operated calcium channels (L-type) and thereby inhibit smooth muscle contractility. They are used to treat several major cardiovascular disorders, including hypertension and angina pectoris; they are also studied in congestive heart failure and in atherosclerosis. The current view is that their therapeutic action is related to vasodilatation. This view is an oversimplification, as will be shown in this review. It will also be illustrated that all calcium antagonists are not identical pharmacological agents.

Characterization of alpha 2-adrenoceptors in the rat: proximal tubule, renal membrane and whole kidney studies

In the present study, alpha 2-adrenoceptors have been characterized in rat renal proximal tubules which were isolated by a Percoll gradient technique. Competitive binding curves with [3H]rauwolscine (0.5 nM) and alpha 2-adrenoceptor agonists and antagonists were consistent with an alpha 2B-adrenoceptor subtype. However, the rank order of potency (Ki) for clonidine and UK 14,304 was reversed from that reported for other tissues (clonidine, 48 nM greater than UK 14,304, 330 nM). This rank order was confirmed in a crude renal membrane preparation consisting of whole kidney as well as separated medullary and cortical segments. An intrarenal infusion of clonidine at 11 nmol/kg per min resulted in a greater diuresis and natriuresis than an equimolar dose of UK 14,304 suggesting that clonidine also had a greater affinity in the collecting tubules. Further displacement studies in proximal tubules with [3H]rauwolscine and calcium channel blockers demonstrated that verapamil was the most potent (Ki, 2.3 microM), followed by diltiazem (48% displacement at 100 microM) and then nifedipine (no displacement at 100 microM). These studies indicated that alpha 2-adrenoceptor in the rat proximal tubule may be of the alpha 2B-adrenoceptor subtype. Further studies will be required to determine whether the reverse rank order of potency of clonidine and UK 14,304 is consistent with an alpha 2-adrenoceptor subtype which is different from that found in other tissue.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.