Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fifty-one patients with urgent hypertension were treated in the emergency department with either oral nifedipine or oral clonidine in a randomized double-blind prospective study. Nifedipine was administered as a single dose of 20 mg. Clonidine was administered as an initial dose of 0.1 mg with hourly doses of 0.1 mg. Nifedipine was successful in reducing diastolic blood pressure in 83% of the patients within 45 minutes and in 96% of the patients within two hours, with a mean reduction in systolic blood pressure of 47 mm Hg and diastolic blood pressure of 29 mm Hg. Thirty percent of those who initially responded to nifedipine experienced a subsequent increase in diastolic blood pressure to pretreatment levels within three hours. Clonidine was successful in reducing diastolic blood pressure in 79% of the patients within four hours, with a mean reduction in systolic blood pressure of 51 mm Hg and diastolic blood pressure of 30 mm Hg. Our results indicate that both nifedipine and clonidine are safe and effective in the treatment of urgent hypertension. Nifedipine had a much more rapid onset of action with a greater initial success rate, and it was free from the sedative side effects of clonidine. We believe that either nifedipine or clonidine may be used as first-line therapy in the treatment of urgent hypertension.
 ...
PMID:Oral nifedipine vs oral clonidine in the treatment of urgent hypertension. 231 Feb 88

An endogenous substance in brain, clonidine-displacing substance, binds to the same receptor populations as clonidine and is biologically active. Since receptor binding sites can be modeled by using specific antiligand antibodies, we tested the hypothesis that polyclonal antibodies raised in rat and rabbit against the clonidine analog p-aminoclonidine coupled to hemocyanin would recognize compounds structurally related to clonidine, including clonidine-displacing substance. Binding to anti-p-aminoclonidine antibodies was examined by using a competitive radioimmunoassay with tritiated p-aminoclonidine as the radioligand. Central vasodepressor agents that, like clonidine, are known to bind with high affinity to both imidazole sites and alpha 2-adrenergic receptors in brain inhibited radioligand binding to anti-p-aminoclonidine antibodies. All of these agents contain imidazol(in)e and phenyl ring moieties as part of their chemical structures (e.g., oxymetazoline); a number of other compounds without one or both of these rings failed to cross-react with the antisera. Clonidine-displacing substance, partially purified from bovine brain, also inhibited specific radioligand binding to anti-p-aminoclonidine antibodies. The inhibition was dose dependent and high affinity (IC50, 4 Units). The endogenous substance had no effect on the apparent affinity of the antibodies for the radioligand, but blocked a specific number of binding sites. Immunoprecipitation experiments showed that authentic clonidine-displacing substance, that which displaces tritiated p-aminoclonidine binding to membrane receptors, is recognized by anti-p-aminoclonidine antibodies. We conclude that a unique subset of structural determinants required for ligand interaction with both imidazole and alpha 2-adrenergic receptors is critical for binding to anti-p-aminoclonidine antibodies, and that since clonidine-displacing substance is recognized by highly clonidine-specific antisera, it may also contain these determinants within its structure, namely the imidazol(in)e and phenyl ring systems.
Hypertension 1989 Apr
PMID:Clonidine-specific antisera recognize an endogenous clonidine-displacing substance in brain. 292 35

The role of central nervous system alpha-adrenergic and beta-adrenergic receptors in the increased renal sympathetic nerve activity and antinatriuresis resulting from environmental stress (air stress) in conscious spontaneously hypertensive rats (SHR) was examined. Intracerebroventricular administration of the alpha 2-adrenergic receptor agonist clonidine (1, 5, and 15 micrograms) prevented the effects of air stress on renal sympathetic nerve activity and urinary sodium excretion. Clonidine, 5 and 15 micrograms, lowered baseline mean arterial pressure and renal sympathetic nerve activity and increased baseline urine flow rate and urinary sodium excretion; clonidine, 1 micrograms, had no effect on these baseline levels. Intravenous administration of 5 micrograms, but not 1 microgram of clonidine, abolished the renal responses to air stress. Intracerebroventricular administration of alpha 2-adrenergic receptor antagonists (yohimbine, rauwolscine) reversed the effects of clonidine, alpha 2-adrenergic receptor blockade alone, alpha 1-adrenergic receptor blockade (20 micrograms prazosin), or combined alpha 1-adrenergic and alpha 2-adrenergic receptor blockade (30 micrograms phenoxybenzamine) had no effect on the renal sympathetic nerve activity or antinatriuretic responses to air stress. Intracerebroventricular, but not intravenous, administration of the beta 2-adrenergic receptor antagonist ICI 118551 (30 micrograms) prevented the increased renal sympathetic nerve activity and antinatriuretic responses to air stress. In contrast, intracerebroventricular administration of the beta 1-adrenergic receptor antagonist atenolol (30 micrograms) had no effect on the renal responses to air stress. These results indicate that the increased renal sympathetic nerve activity and antinatriuresis resulting from environmental stress in conscious SHR can be prevented by pharmacological stimulation of central alpha 2-adrenergic receptors or by blockade of central beta 2-adrenergic receptors.
Hypertension 1986 Feb
PMID:Central adrenergic receptor control of renal function in conscious hypertensive rats. 300 80

Clonidine produced an increase of cGMP content and a decrease of the endogenous type II inhibitor of protein kinase in rat hypothalamic slices. When administered to rats, the effect of clonidine on type II inhibitor activity in the hypothalamus and brain-stem depended on the dose. Low doses (10-50 micrograms X kg-1 i.p.) produced an increase, probably by stimulating presynaptic alpha 2-adrenoceptors, whereas large doses (200-1000 micrograms X kg-1 i.p.) produced a decrease of type II inhibitor activity by stimulating postsynaptic receptors. The development of vasopressin hypertension was associated with a gradual reduction of the response of the type II inhibitor to low and high doses of clonidine. In vasopressin-hypertensive rats neither small nor large doses of clonidine were able to induce changes in type II inhibitor activity suggesting subsensitivity of pre- and postsynaptic alpha 2-adrenoceptors. However, clonidine appeared to be equally effective in blocking electrically stimulated [3H]noradrenaline release from hypothalamic slices of vasopressin-hypertensive and control, normotensive rats. Reduced reactivity of postsynaptic alpha 2-adrenoceptors seems to be of great importance since treatment of vasopressin-hypertensive rats with 6-hydroxydopamine resulted in a decrease of blood pressure and reappearance of the sensitivity of postsynaptic alpha 2-adrenoceptors to clonidine.
 ...
PMID:Changed sensitivity of alpha 2-adrenoceptors mediating a decrease in protein kinase inhibitor activity in the brain of vasopressin-hypertensive rats. 300 71

Clonidine was administered intravenously in an attempt to limit sympatico-adrenal activity and thereby reduce the incidence of arterial hypertension associated with coronary artery by-pass graft surgery (CABG). Forty patients scheduled for CABG were assigned to two groups. Twenty patients received clonidine 4 micrograms kg-1 before surgery, 2 micrograms kg-1 after cardiopulmonary by-pass and 1 microgram kg-1 when the skin was sutured. The other 20 patients served as controls. All patients were anesthetized with fentanyl, droperidol, nitrous oxide and alcuronium. During surgery 5 min after sternotomy, mean arterial pressure was 13 mmHg lower (P less than 0.01) in the clonidine group, while after operation the difference between the groups was negligible. Both during and after surgery the plasma catecholamine concentrations were significantly lower in the clonidine group (P less than 0.01). The greatest difference between the groups was seen 90 min after operation, when plasma noradrenaline and plasma adrenaline concentrations in the clonidine group were less than 1/3 of those in the control group (P less than 0.01). As judged by catecholamine concentrations clonidine was effective in attenuating sympatico-adrenal hyperactivity during and after surgery. Postoperative arterial hypertension was not reduced, however, and it is concluded that other factors besides sympatico-adrenal hyperactivity must be important.
 ...
PMID:Clonidine and the sympatico-adrenal response to coronary artery by-pass surgery. 301 39

Studies from this laboratory have shown that the first filial offspring of female spontaneously-hypertensive rats and male Wistar-Kyoto (WKY) normotensive rats develop stress-induced hypertension. The present study sought to examine the effects of intracerebroventricular administration of clonidine (8 micrograms) on cardiovascular and sympathoadrenal responses to aversive classical conditioning in these borderline hypertensive rats (BHR) and in normotensive WKY control rats. Clonidine caused significant reductions in resting arterial pressure, vascular resistance, heart rate and concentrations of epinephrine (E) in plasma for both hypertensive and normotensive rats. Central administration of normal saline to control rats of each strain did not alter basal cardiovascular or sympathoadrenal function. The presentation of a conditioned stimulus (CS) elicited a significant increase in arterial pressure and total peripheral resistance in hypertensive rats treated with saline and clonidine and in normotensive rats treated with saline. In contrast, normotensive rats treated with clonidine showed no increases in arterial pressure or vascular resistance following the onset of the conditioned stimulus. The aversive conditioning session instigated significant increases in the concentrations of norepinephrine (NE) and E in plasma in saline-treated rats. Hypertensive and normotensive rats treated with clonidine-showed a blunted increase in plasma concentrations of NE and E during this period; however, concentrations of E in hypertensive rats increased significantly from the baseline period after injection. These data suggest that an abnormality in central alpha 2-adrenoceptor-mediated inhibition of sympathoadrenal discharge and sympathetic vasomotor tone may predispose the hypertensive rat to develop stress-induced hypertension.
 ...
PMID:The effects of intracerebroventricular injection of clonidine on conditioned pressor and adrenergic responses in rats. 302 85

A possible influence of the central alpha 2-adrenergic system on beta-endorphin was examined in rat anterior pituitary, neurointermediate lobe, and plasma. The concentration of beta-endorphin in anterior pituitary, neurointermediate lobe, and plasma was determined by radioimmunoassay 15 minutes after subcutaneous injection of clonidine in 14-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Clonidine reduced the concentration of the plasma beta-endorphinlike immunoreactivity in SHR and to a lesser extent in WKY. No significant changes in the concentration of beta-endorphinlike immunoreactivity were observed in anterior pituitary. Clonidine increased the concentration of neurointermediate lobe beta-endorphinlike immunoreactivity in SHR in a dose-related manner but did not affect the concentration in WKY. Administration of yohimbine (1 mg/kg) completely blocked the clonidine-induced increase of neurointermediate lobe beta-endorphinlike immunoreactivity in SHR, while prazosin (1 mg/kg) had no effect. These data suggest that the central alpha 2-adrenergic activation increases the neurointermediate lobe concentration of beta-endorphinlike immunoreactivity in SHR by suppressing beta-endorphin release from the neurointermediate lobe into the circulation.
Hypertension 1987 Jun
PMID:Central alpha 2-adrenergic stimulation increases neurointermediate lobe immunoreactive beta-endorphin in spontaneously hypertensive rats. 303 77

The placental transfer of clonidine was investigated in five pregnancies. Clonidine readily crosses the placenta. The drug elimination in neonates was slow, but the only clinical abnormality was that of a raised arterial blood pressure. Hypertension for at least 24 h was observed in four cases. It is suggested that this may be related to a withdrawal syndrome due to the sudden cessation of the placentally transferred drug.
 ...
PMID:Clonidine: placental transfer and neonatal adaption. 320 82

Recent studies have demonstrated that the neurons of the lower brainstem that are responsible for maintaining normal levels of arterial pressure reside in a specific area of the rostral ventrolateral medulla. In rat, the critical zone corresponds to a small region containing a subpopulation of the adrenergic C1 group, defined immunocytochemically by the presence of the epinephrine-synthesizing enzyme phenylethanolamine N-methyltransferase. Neurons of this region (the C1 area), possibly including the adrenergic neurons, directly innervate preganglionic neurons in the spinal cord, and are tonically active and sympathoexcitatory. The excitatory transmitter released into the spinal cord is unknown. The discharge of C1 area neurons is locked to the cardiac cycle and, in turn, leads to firing of sympathetic preganglionic neurons. The C1 area neurons are inhibited by baroceptor input and mediate the vascular component of baroceptor reflexes. They also mediate somato-sympathetic pressor responses from skin and muscle and participate in reflex responses to hypoxia. The neurons are directly innervated by local neurons containing gamma-aminobutyric acid, acetylcholine, enkephalin, and substance P, all of which modulate arterial pressure. The C1 area is the site of the hypotensive actions of clonidine. Clonidine appears to act on imidazole receptors in the C1 area to lower arterial pressure. The natural ligand for these receptors may be a newly defined substance in brain, clonidine-displacing substance. Neurons of the C1 area appear to be the critical neuronal group governing the normal resting and reflex control of arterial pressure. They may play a critical role in the maintenance of elevated arterial pressure in hypertension and as a site of action of antihypertensive drugs.
Hypertension 1988 Feb
PMID:The C1 area of the brainstem in tonic and reflex control of blood pressure. State of the art lecture. 327 78

In order to estimate the neuroendocrine function of the central nervous system eventually leading to growth hormone (GH) secretion in essential hypertension, 17 patients with mild arterial hypertension (7 obese and 10 with normal body weight) were examined. The control group consisted of 16 normotensive volunteers (7 obese and 9 with normal body weight). The GH secretion was determined by radioimmunoassay during nocturnal sleep. In all the subjects, the serum GH was also measured after placebo and after the centrally acting alpha 2-adrenergic agonist-clonidine administered i.v. in a dose of 0.15 mg. The fasting serum insulin concentration was also measured in all the subjects. Clonidine decreased the mean arterial pressure in all the subjects investigated. However, in response to clonidine an increase in GH secretion in all hypertensive and normotensive cases with normal body weight was demonstrated, whereas in all obese hypertensive and normotensive patients no significant GH rise was found. It indicates that inhibition of GH secretion in patients with essential hypertension is related to coexistent obesity rather than with that of arterial hypertension. A strong (r = 0.76) and significant (p less than 0.0005) correlation demonstrated between the maximal GH concentration during the nocturnal sleep and after clonidine suggests that the mechanism of GH inhibition in response to both these stimuli is similar and it probably is related to the inhibition of neurohormonal secretion of the growth hormone releasing factor (GRF). However, the negative correlation between the fasting insulin concentration and GH response to clonidine shown in obese subjects only, points to a more complex mechanism of GH inhibition in obesity.
 ...
PMID:Growth hormone (GH) secretion during nocturnal sleep and after clonidine in patients with essential hypertension. 328 64


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>