Effects of pinacidil on serotonin-induced contractions and cyclic nucleotide levels in isolated rat aortae: comparison with nitroglycerin, minoxidil, and hydralazine

Pinacidil is a novel, clinically effective vasodilator used for the treatment of hypertension whose mechanism of action has not been precisely defined. In vitro, pinacidil (ED50 = 0.3 microM) was approximately 30-fold less potent than nitroglycerin and 700-fold more potent than minoxidil or hydralazine in relaxing rat aortic strip preparations. Aortic relaxations produced by nitroglycerin and acetylcholine were dramatically antagonized by methylene blue (10(-5) M), an inhibitor of soluble guanylate cyclase. In contrast, relaxation to hydralazine or minoxidil was unaffected and relaxation to pinacidil was only modestly inhibited (approximately threefold) by methylene blue (10(-5) M). Furthermore, aortic relaxation to pinacidil was similar in preparations with and without an intact endothelium. Relaxation induced by pinacidil (10(-7)-10(-4) M) was not associated with any elevation in either cyclic AMP (cAMP) or cyclic GMP (cGMP) levels in vitro, although nitroglycerin (10(-6) M) but not minoxidil (10(-3) M) or hydralazine (10(-3) M) significantly elevated cGMP levels. Thus, pinacidil was a potent relaxant agonist in vitro, in contrast to minoxidil and hydralazine, which were considerably weaker in this regard. Vascular relaxation produced by pinacidil was independent of an intact endothelium and was not associated with elevations in either cAMP or cGMP. These data are consistent with the proposal that the antihypertensive activity of pinacidil is due to nonspecific arterial vasodilation.

Felodipine as a replacement for minoxidil in the treatment of severe hypertension

The new calcium antagonist felodipine has been compared with minoxidil in the management of severe hypertension in a group of 17 men. Satisfactory control of blood pressure was achieved in all patients with a combination of beta blocker, loop diuretic and minoxidil after inadequate control on a standard regimen of beta blocker, thiazide and vasodilator. The optimal dose of felodipine was titrated after a placebo phase. In a double blind crossover trial blood pressure on felodipine (150/88 +/- 19/8 mmHg, SD) was the same as on minoxidil (148/87 +/- 23/11 mmHg, NS) and the postural difference was similar (NS) on both drug regimens. Body weight was lower on the felodipine regimen (P less than 0.01), as was supine heart rate (P less than 0.05). There was a small rise in plasma liver enzymes on felodipine therapy (P less than 0.01). Felodipine was well tolerated and may be useful in the management of severe hypertension.

The response of plasma catecholamines to the vasodepression caused by beta-adrenoceptor antagonists in the spontaneously hypertensive rat

The 15-20% decrease in mean arterial pressure (MAP) seen in conscious spontaneously hypertensive rats (SHR) after the administration of a single dose of the beta-adrenoceptor antagonists atenolol, betaxolol, oxprenolol, pindolol, propranolol or sotalol was not accompanied by an increase in plasma norepinephrine (NE) concentration. In marked contrast, plasma NE concentration increased by 50-75% when MAP was lowered at the same rate, and to the same extent with the vasodilator minoxidil. Atenolol, betaxolol and propranolol significantly suppressed plasma renin activity (PRA), whereas oxprenolol, pindolol and sotalol did not alter PRA significantly. Based on these observations, I conclude that beta-adrenoceptor antagonists impair the normal baroreflexly-mediated increase in plasma NE concentration which occurs in response to a decrease in MAP and this sympatho-inhibitory effect does not require the suppression of renin release.

Renal and cardiovascular effects of acute and chronic administration of felodipine to SHR

Renal function and salt and water turnover were studied in SHR during acute and chronic administration of felodipine, which is an efficient antihypertensive vasodilating Ca2+ antagonist. In conscious SHR acute administration of felodipine in hypotensive doses increased renal sympathetic nerve activity but caused renal vasodilation, increases in GFR and a 2-3 fold increase in urinary flow rate and sodium excretion. The fraction of filtered sodium excreted (FENa) was approximately doubled. The diuretic and natriuretic effects of felodipine are therefore suggested to be due to a direct inhibitory action on the renal tubular cells, resulting in reduced sodium reabsorption. Nifedipine also induced diuresis and natriuresis in this system, while minoxidil reduced water and sodium excretion. Throughout 6 months of felodipine treatment, the mean arterial pressure (MAP), remained 25-20 per cent reduced. Felodipine in combination with metoprolol reduced MAP 25-30 per cent and also caused regression of left ventricular hypertrophy, while felodipine alone prevented its further progression. Also during chronic administration, felodipine induced diuresis but had no effect on plasma volume and on sodium or potassium excretion in SHR. It is concluded that in SHR felodipine induces diuresis; on acute treatment this is secondary to reduced tubular sodium reabsorption, although during chronic treatment the sodium loss is compensated for while the diuresis remains. Thus, the cardiovascular and renal effects of Ca2+ antagonists like felodipine differ substantially from those of other potent antihypertensive vasodilators e.g. minoxidil.

Effects of long-term verapamil treatment on blood pressure, cardiac hypertrophy and collagen metabolism in spontaneously hypertensive rats

The effects of long-term treatment with verapamil on blood pressure, cardiac hypertrophy and collagen content, collagen concentration and prolyl hydroxylase activity were studied in spontaneously hypertensive rats (SHR). Verapamil administration (0.75 mg . ml-1 in drinking water) was commenced: to pregnant SHR 3 to 5 days before delivery and continued to the mothers and offspring during the nursing period; or to SHR at 10 weeks of age. Both groups were maintained on verapamil treatment up to the age of 45 weeks. Verapamil treatment significantly decreased blood pressure, heart rate and the ratio of ventricular weight to body weight in treated SHR. Verapamil did not significantly change the cardiac collagen concentration and prolyl hydroxylase activity. Since, however, the cardiac muscle mass was diminished by verapamil administration, treatment actually slightly reduced the collagen content of the heart. In the aorta collagen concentration was increased by verapamil treatment. Contrary to these results, minoxidil treatment was observed to increase the cardiac collagen concentration, content and prolyl hydroxylase activity in SHR. These results suggest that the factors governing myocardial connective tissue proliferation and regression may be independent of those governing muscle fibre hypertrophy and that particular drug actions on myocardial collagen metabolism must be taken into account.

In vitro suppression of human lymphocyte activity by minoxidil

The in vitro effect of minoxidil on normal human lymphocyte activity was studied. At a concentration of 0.1 mg/ml, minoxidil significantly inhibited phytohemagglutinin-dependent lymphocyte DNA synthesis (p less than 0.05), and at 0.01 mg/ml, 0.05 mg/ml, and 0.1 mg/ml, it suppressed mitogen-dependent production of leukocyte migration inhibition factor (p less than 0.04, p less than 0.01, and p less than 0.01, respectively), without compromising cell viability. Minoxidil thus appears to exert a suppressive effect on normal human T-lymphocytes in vitro. The physiologic relevance of these findings remains uncertain.

Effects of minoxidil on blood pressure and cardiac hypertrophy in two-kidney, one-clip hypertensive rats

Rats made severely hypertensive by renal arterial clipping were treated for 24 days with the arterial vasodilator minoxidil (40, 80, and 120 mg/L drinking water). In all three treated groups of animals, blood pressure initially decreased markedly and to a similar extent. Subsequently partial tolerance developed to the antihypertensive effects of minoxidil. All three doses induced hypertrophy of the right ventricle to a similar degree. In contrast, the hypertension-induced hypertrophy of the left ventricle was further increased in a dose-dependent fashion by minoxidil.

Whole body and regional hemodynamic effects of minoxidil in the conscious dog

Microsphere estimates of whole body hemodynamics and tissue blood flow were made in conscious and pentobarbital-anesthetized dogs treated orally with the peripheral vasodilator minoxidil. Under both circumstances, 1.0-30 mg/kg minoxidil significantly reduced mean arterial pressure 21-41% and total peripheral resistance 52-75% 4 h after administration. Dose-dependent increases in heart rate and cardiac output were evident under conscious conditions, with both parameters approximately doubling at 1.0 mg/kg. The near maximal vasodilation achieved with this dose of minoxidil was due to diminished vascular resistance in all major tissue beds. The enhanced cardiac output was associated with significant 50-87% increases in blood flow to the skin, skeletal muscle, bone, stomach, large intestine, and pancreas. Far more dramatic six- to 10-fold increases in regional myocardial blood flow were seen at this dose, which appeared to be only partially dependent on increased cardiac work. Comparable blood flow patterns were seen with acute minoxidil at doses greater than 1.0 mg/kg, and with chronic minoxidil at 1.0 and 30 mg/kg/day. These experiments establish minoxidil's relative vasodilation in the major tissue beds of the dog which contributes to its hypotensive activity.

Vasodilators and ventricular septal defect: comparison of prazosin, minoxidil, and hydralazine in a chronic lamb model

The volume overloading of the left ventricle which results from left to right (L-R) shunting through a ventricular septal defect (VSD) may be reduced by pharmacologic agents which lower systemic vascular resistance (Rs) in excess of pulmonary arteriolar vascular resistance (Rpa). To study agents capable of decreasing the L-R shunt through systemic vasodilatation, we created a chronic lamb model with VSD and administered three vasodilators, prazosin (0.05 mg/kg), hydralazine (0.75 mg/kg), and minoxidil (0.25 mg/kg). Prazosin increased the Rpa while lowering Rs, resulting in an increase in Rpa/Rs by 43% (p less than or equal to 0.005). Prazosin decreased the pulmonary flow (Qp) slightly, decreased L-R shunt by 16%, reduced the pulmonary to systemic flow ratio (Qp/Qs) by 22% (p less than or equal to 0.005), and lowered the left atrial mean pressure (LA) by 16% (p less than or equal to 0.005) with no effect on heart rate. Hydralazine lowered the Rpa and Rs equally and thus did not change the Rpa/Rs or the volume of L-R shunt (7.6 versus 8.1 liters/min/m2). No change in LA was seen with hydralazine but heart rate increased from 162 to 200/min (p less than or equal to 0.01). Minoxidil did not change the L-R shunt (6.9 versus 6.8 liters/min/m2) and, in general, produced effects intermediate between prazosin and hydralazine. The data support a selective systemic vasodilation with prazosin, a property not shared by either minoxidil or hydralazine, which results in a reduction of shunting and left ventricular volume overloading in lambs with VSD.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct effects of minoxidil on epidermal cells in culture

Minoxidil, a potent antihypertensive agent, induces generalized hypertrichosis when administered systemically, or localized hair regrowth when applied topically to sites of severe alopecia areata. The pharmacologic mechanisms by which minoxidil stimulates hair growth are unknown. This study was designed to examine whether minoxidil has direct effects on neonatal murine epidermal cells in culture. In the presence of minoxidil, cultures showed a marked dose-dependent second peak of DNA synthesis 8-10 days after culture initiation. In addition, two morphologically distinct cell types appeared. Indirect immunofluorescence staining with keratin-specific antibody revealed cytoplasmic keratin fibers, suggesting the epidermal origin of these cells. Our experiments demonstrate that minoxidil can affect epidermal cells in culture by altering their growth pattern and phenotypic appearance.

Inhibitory effect of captopril on renal responses to frusemide in sodium-restricted rats

Indomethacin (10 mg kg-1 orally) caused a moderate inhibition of the renal responses to frusemide (30 mg kg-1 orally) only in Na+-deficient rats, suggesting that renal prostaglandins (PG) are necessary for optimal effects of frusemide during Na+ restriction. Captopril (1, 3 and 10 mg kg-1 orally) also inhibited frusemide-induced diuresis and natriuresis in Na+-deficient rats; the large effect of captopril at 10 mg kg-1 was accompanied by arterial hypotension. In normal rats, captopril did not disturb blood pressure or affect the renal effects of frusemide. By comparison, minoxidil (10 and 20 mg kg-1 orally) caused hypotension and reduced the natriuretic effects of frusemide in both normal and low-Na+ states. Since circulating angiotensin II (AII) is a stimulus for PG synthesis during Na+ restriction, it is suggested that captopril may impair the renal responses to frusemide through hormonal and haemodynamic changes resulting from inhibition of A II formation.

Pyrimidine and triazine 3-oxide sulfates: a new family of vasodilators

Di- and triaminopyrimidine 3-oxides (e.g., 2,4-diamino-6-piperidinylpyrimidine 3-oxide and 2,4-diamino-6-(diallylamino)triazine 3-oxide) react with sources of sulfur trioxide, such as sulfur trioxide trimethylamine or chlorosulfuryl chloride, to yield the corresponding heterocyclic O-sulfates. These sulfates are inner salts with unusual physical properties. The structure of the O-sulfate of 2,4-diamino-6-piperidinylpyrimidine 3-oxide was confirmed by X-ray. These O-sulfates are hypotensives. They apparently act by direct vasodilation.

Effect of minoxidil on cultured keratinocytes

Minoxidil has been shown to stimulate hair growth and these studies were undertaken to determine whether the drug had a direct effect on keratinocytes. Cultures of human epidermal cells were treated with minoxidil and it was found that they survived longer than control cultures. In addition, minoxidil prolonged the time that cells could be passed after reaching confluence. The results suggest that minoxidil slows the senescence of keratinocytes, which is similar to what has been found with epidermal growth factor.

[Antihypertensive vasodilators]

Antihypertensive vasodilators share the capability of producing vasodilation of arterioles. In addition, two of them, i.e. nitroprussiate and prazosine, also produce vasodilation of veinulae. Both of these agents cause a simultaneous decrease in pre-load and post-load, and may be used in heart failure. The effectiveness of vasodilators is offset by regulatory cardiac and/or renal mechanisms, and the association with a sympatholytic agent and/or a diuretic is generally needed. Consequently, vasodilators are usually the third step in the course of managing a hypertensive patient. Association with a betablocking agent is especially necessary in patients with coronary insufficiency, in order to prevent an increase in myocardial oxygen requirements and worsening of angina pectoris. Vasodilators are active within a fairly wide dosage range, making individualized dosages requisite. In treating hypertension by the oral route, daily doses above 200 mg for dihydralazine, 60 mg for minoxidil and 10 mg for prazosine are only exceptionnaly useful. In emergency treatment of hypertension, diazoxide and nitroprussiate can be used only in patients under continuous cardiovascular monitoring. Nitroprussiate must, in addition, be given through a controlled infusion device, but ensures more flexible and safer control of blood pressure. Dihydralazine may produce headache. This side effect occurs very early and is hardly compatible with continuation of treatment. Long term side effects are very uncommon or strictly biological for dosages below 200 mg/day. With currently used dosages (20 to 60 mg per day) minoxidil consistently produces hypertrichosis, outruling its protacted use in women.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors involved in the antihypertensive action of calcium antagonists

The main mechanism underlying the antihypertensive action of calcium antagonists is believed to be the vasodilation of peripheral vessels. To compare the effects of calcium antagonists with those of other vasodilators, nifedipine or its antihypertensive analog nitrendipine were tested in different normotensive and hypertensive rat strains and situations. The acute blood-pressure-lowering effect of nifedipine in the Dahl salt-sensitive rat was characterized by a rapid onset of action, the minimal effective oral dosage (0.1 mg/kg) being effective for up to 6 hours. Nifedipine was approximately 3 times more potent than hydralazine and equipotent to, but of shorter duration of action than, minoxidil. Natriuretic activity in normotensive Wistar and hypertensive Dahl salt-sensitive rats was observed with nitrendipine after an acute saline load (30 ml/kg by mouth), whereas vasodilators such as minoxidil and hydralazine decreased renal function under these conditions. Treatment of spontaneously hypertensive rats (SHR) with nifedipine in food (315 parts per million) for 60 weeks prevented the development of hypertension and resulted in decreased plasma renin activity and plasma aldosterone concentration in comparison to untreated SHR controls. Moreover, absolute and relative heart weights were reduced in the treated rats. Results suggest that the antihypertensive action of calcium antagonists, at least those of the dihydropyridine type, is not only due to peripheral vasodilation, since in contrast to other vasodilators a hyperdynamic circulation is not induced, the renin-angiotensin-aldosterone system is not activated, and sodium/volume retention cannot be expected because of a primary natriuretic effect. Therefore, a reduced volume load in addition to the decrease in afterload contributes to the antihypertensive effect of calcium antagonists and their prevention of heart hypertrophy.

[Intracellular and extracellular proteins binding androgenic hormones. Biochemical properties and clinical significance]

This paper has been designed to review some current concepts about biochemistry, pathophysiology and clinics of androgen-binding proteins, both TeBG and cellular receptors. Some important experimental models to clarify the interactions between androgens and target cells are mentioned. Further, major clinical applications in which binding parameters were or will be of great importance are discussed in details.