Sodium sensitivity and sympathetic nervous system in hypertension induced by long-term nitric oxide blockade in rats

Effects of metoclopramide and metoclopramide/dopamine on blood pressure and insulin release in normotensive, hypertensive, and type 2 diabetic subjects

The objective is to determine cardiovascular and insulin release effects under metoclopramide (MTC) and dopamine (DA) infusion by using an acute comparative design with the intravenous infusion of both drugs. We evaluated 15 normal (normotensive and normoglycemic) subjects, 13 hypertensive, and 15 type 2 diabetic subjects. Subjects were submitted to an experimental design in which we first gave them a 0.9% saline solution for 30 minutes, and then administered MTC at 7.5 microg kg min through an intravenous infusion during a period of 30 minutes. Although subjects were receiving MTC, we added an intravenous infusion of DA at 1-3 microg kg min during 30 minutes. Blood pressure, heart rate, serum lipid profile, and insulin levels were measured. Sympathetic reactivity by the cold pressor test was also measured. In normotensive subjects, there was a systolic blood pressure and heart rate increase during MTC plus DA infusion. In subjects with diabetes mellitus there was a heart rate increase without changes in blood pressure during the MTC plus DA infusion period. In hypertensive subjects, MTC induced a significant decrease of systolic and diastolic blood pressure. During MTC plus DA period there was an increase of heart rate but no significant changes in blood pressure. During cold pressor test in both diabetic and hypertensive subjects, there were significant increases of both blood pressure and heart rate. Insulin serum levels increased in normotensive and hypertensive subjects but were attenuated in subjects with diabetes mellitus. We conclude that there is a pharmacologic interaction between MTC and DA, that the pressor effects of DA are due to activation to beta and alpha adrenergic receptors, and that the cardiovascular effects of DA in type 2 diabetic subjects are attenuated by a probable defect in sympathetic system and to endothelial dysfunction.

NITRIC OXIDE and SYMPATHETIC NERVE ACTIVITY IN THE CONTROL OF BLOOD PRESSURE

1. Endothelial dysfunction marked by impairment in the release of nitric oxide (NO) is seen very early in the development of hypertension and is considered important in mediating the impaired vascular tone evident in essential hypertensive patients. 2. Recently, a hypothesis has emerged that NO acting as a neurotransmitter in the brain can modulate levels of sympathetic nerve activity and thereby blood pressure. The NO inhibition model of hypertension has been used to explore the possibility that a decrease in levels of NO can cause an increase in levels of sympathetic nerve activity that can mediate the hypertension. 3. In the present review, we examine the literature regarding the role of NO in setting the mean level of sympathetic nerve activity and blood pressure. Although the acute effects of NO inhibition are well understood, the chronic interaction between the sympathetic nervous system and NO has only been investigated using indirect measures of sympathetic nerve activity, such as ganglionic blockade. This has led to inconsistent results regarding the role of NO in modulating sympathetic nerve activity chronically. 4. Some of the conflicting results may be explained by differences in the 'background' levels of angiotensin (Ang) II. Evidence suggests that NO may interact with AngII and baroreceptor afferent inputs in the central nervous system to set the mean level of sympathetic nerve activity. 5. We suggest chronic NO inhibition can increase sympathetic nerve activity if baroreceptor input is intact and AngII levels are elevated. Although studies exploring the actions of NO or AngII in isolation are useful for gathering initial information, future studies should focus on their interactions and their role in setting the long-term levels of sympathetic activity and blood pressure.

Role of actions of calcium antagonists on efferent arterioles--with special references to glomerular hypertension

Although calcium antagonists are used as a first-line antihypertensive agent, controversy attends the renal microvascular effects of calcium antagonists. Since calcium antagonists elicit predominant vasodilation of the afferent arteriole, they might ostensibly aggravate glomerular hypertension. Recently, novel types of calcium antagonists have been developed, some of which are reported to dilate efferent as well as afferent arterioles. The present review attempted to characterize the renal microvascular action of calcium antagonists, and evaluated the consequences of renal injury following the treatment with these antagonists. In contrast to predominant afferent arteriolar action of conventional calcium antagonists (e.g. nifedipine, nicardipine, amlodipine and diltiazem), novel antagonists (e.g. manidipine, nilvadipine, benidipine and efonidipine) potently dilated both afferent and efferent arterioles. The vasodilator action on efferent arterioles appears to be mediated in part by the blockade of T-type calcium channels, particularly through the inhibition of the intracellular calcium release mechanism. The comparison of the anti-proteinuric action of calcium antagonists in subtotally nephrectomized rats showed that efonidipine and enalapril, both possessing vasodilator action on efferent arterioles, exerted more prominent action than other calcium antagonists. Finally, in patients with chronic renal disease, a 48-week treatment with efonidipine reduced proteinuria, and this effect was seen even when the mean arterial blood pressure failed to reach below 100 mm Hg. In conclusion, although calcium antagonists potently inhibit afferent arteriolar constriction, efferent arteriolar responses to these agents vary, depending on the types of calcium antagonists used. These divergent actions of these agents on the efferent arteriole may alter differently the glomerular hemodynamics, and could affect the final outcome of underlying renal diseases.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Gustatory Evaluation of Still and Carbonated Waters: A Preference Rating Study

We studied the sensory preference for six still waters and four carbonated waters, nonflavored, by 11 tasting experts (4 women and 7 men). Five tasters rated the still waters, four tasters rated the carbonated water, and seven tasters rated twice on each of the still waters when evaluated with a dry red wine. All ratings were performed through answering a set of questions regarding the specific taste and/or smell of the waters. All tasters and the statistician were blinded to the water brands during rating and analysis. Multidimensional preference analysis and correspondence analysis were used to portray the underlying sensory preference. Still waters with higher mineral content tended to be less favorable for drinking purposes. On the other hand, carbonated waters with more minerals (but not over a certain limit) were favorable, and still waters with higher mineral content were preferable as mouth cleaners for red wine. The methodology can be carried to the food and beverage industries, to the functional foods industry, and to medical research where the preference of patients toward certain medications is of interest.