The actions of dopamine on the blood pressure and heart rate of conscious hypertensive rats: evidence for reduced dopaminergic activity in rats of the Japanese strains

Apis mellifera venom and melittin block neither NF-kappa B-p50-DNA interactions nor the activation of NF-kappa B, instead they activate the transcription of proinflammatory genes and the release of reactive oxygen intermediates

Many alternative treatment approaches, originating from Asia, are becoming increasingly popular in the Western hemisphere. Recently, an article published in a renowned journal reported that venom of apis mellifera (bee venom (BV)) and melittin mediate immune-modulating effects by blocking the activation of the transcription factor NF-kappaB. Such a modus operandi would corroborate the many claims of beneficial effects of BV treatment and give immediate credit to this form of therapy. Fibroblast-like synoviocytes from rheumatoid arthritis patients and dermal fibroblast cells and white blood cells from healthy volunteers were used to study the effects of BV and melittin on the activation of NF-kappaB and a series of genes that are markers of inflammation. EMSAs demonstrate that neither BV nor melittin blocked IL-1beta-induced NF-kappaB activation; neither did they affect phosphorylation or degradation of IkappaB. Contrary to published data, even high concentrations of BV and melittin were without any effect on NF-kappaB-p50-DNA interactions. More importantly, in fibroblast-like synoviocytes, but also in dermal fibroblasts as well as in mononuclear cells exposed to BV or melittin, mRNA levels of several proinflammatory genes are significantly increased, and Western blot data show elevated cyclooxygenase-2 protein levels. Furthermore, exposure to BV higher than 10 mug/ml resulted in disintegration of all cell types tested. In addition, large quantities of oxygen radicals are produced in a dose-dependent manner in leukocytes exposed to BV. Taken together, data presented in this work do not corroborate an earlier report regarding the effectiveness of BV as an inhibitor of the transcription factor NF-kappaB.

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

Up-regulation of dopamine receptors in the brain of the spontaneously hypertensive rat: an autoradiographic analysis

Recent evidence points to a dysfunction of brain dopaminergic mechanisms in the spontaneously hypertensive rat. Using in vitro receptor autoradiography, we assessed the density of D1 and D2 dopamine receptors in the brain of spontaneously hypertensive rats and their normotensive controls the Wistar-Kyoto rat. Brain sections from five- and 15-week-old rats were incubated with 1 nM [3H]SCH 23390 (D1 receptor antagonist) or 15 nM [3H]sulpiride (D2 receptor antagonist), and exposed along with radioactive standards to 3H-Hyperfilm. The binding density of selected brain regions (anteromedial prefrontal cortex, cingulate cortex, lateral septal nucleus, nucleus accumbens, caudate-putamen, globus pallidus, amygdaloid complex) were quantified using computer-assisted densitometry. These experiments showed a significant increase in the binding density of [3H]SCH 23390 in the nucleus accumbens and caudate-putamen of five- and 15-week-old spontaneously hypertensive rats. The binding density of [3H]SCH 23390 was increased in the lateral septal nucleus of five-week-old and globus pallidus of 15-week-old spontaneously hypertensive rats. The binding density of [3H]sulpiride was also greater in the nucleus accumbens of five-week-old spontaneously hypertensive rats. The present investigation demonstrates an up-regulation of D1 dopamine receptors in spontaneously hypertensive rats with established hypertension. More importantly, up-regulation of D1 and D2 dopamine receptors in the striatum of young prehypertensive spontaneously hypertensive rats suggests that dopamine may be involved in the pathogenesis of hypertension in this strain of genetically hypertensive rats.

Effect of experimentally-induced hypertension on angiotensin converting enzyme activity in the aortic endothelium and smooth muscle cum adventitia of the Sprague Dawley rat

The effect of experimentally-induced hypertension on the angiotensin converting enzyme (ACE) activity in the endothelium and smooth muscle cum adventitia of the Sprague Dawley rats was investigated. The ACE activity in both tissues of the 1-clip 2-kidney renovascular hypertensive rats and the deoxycorticosterone acetate/salt hypertensive rats were significantly higher than those of the normotensive control. These findings (i) support the suggestion that the 1-clip 2-kidney renovascular hypertensive rat represents a model of renin- and angiotensin-dependent hypertension and that the increased vascular ACE activity could play a role in the maintenance of hypertension (ii) provide new information regarding the association of increased vascular ACE activity and hypertension in the mineralocorticoid/salt treated hypertensive rats which may account for the finding by others that captopril is effective in preventing the development of hypertension in this low renin model of hypertension. On the other hand, the data also bring forth the possibility that the observed increase in vascular ACE activity could be the result of hypertension.

Central monoamine oxidase and phenolsulfotransferase activities in spontaneously hypertensive rats

The activities of monoamine oxidase and phenolsulfotransferase in the hypothalamus and anterior pituitary gland of spontaneously hypertensive rats and the normotensive control (Wistar Kyoto rat) rats were investigated. The monoamine oxidase activity (determined using dopamine as substrate) in both these tissues was not significantly different between the normo- and hypertensive animals. Hypothalamic phenolsulfotransferase does not sulfate-conjugate dopamine at pH of 6.5 and pituitary phenolsulfotransferase does not sulfate-conjugate dopamine or 3,4-dihydroxyphenylacetic acid at the same pH. Hypothalamic phenolsulfotransferase activity determined using 3,4-dihydroxyphenylacetic acid as substrate was significantly higher in the spontaneously hypertensive than the Wistar Kyoto rats, while pituitary enzyme (determined using phenol as substrate) was the same in both strains of animals. We proposed that in the spontaneously hypertensive rats the higher level of hypothalamic phenolsulfotransferase could (by removing 3,4-dihydroxyphenylacetic acid as sulfated acid) increase the deamination of dopamine by monoamine oxidase. This could in turn result in the presence of high amount of sulfated 3,4-dihydroxyphenylacetic acid in the anterior pituitary gland reported in our earlier study, and be partly responsible for the reduced central dopaminergic activity found in the hypertensive rats.

Levels of dopamine and 3,4-dihydroxyphenylacetic acid in the adenohypophysis of normo- and hypertensive rats

The levels of dopamine and its metabolites in the adenohypophysis of the normo- and hypertensive rats were determined. Dopamine was present as the free and sulfate-conjugated form in the adenohypophysis of the spontaneously hypertensive rat (SHR), Wistar Kyoto (WKY) and Sprague-Dawley (SD) rats. The levels of both the free and conjugated dopamine in the adenohypophysis of the SHR were 5.49 +/- 2.91 (mean +/- SEM) and 4.27 +/- 3.31 pmoles/mg protein respectively. These values were not significantly different from those of the WKY and SD. 3,4-Dihydroxyphenylacetic acid (dopac), present as the free and sulfate-conjugated form, was found to be the only metabolite of dopamine in the adenohypophysis of the three animals. The levels of both free and conjugated dopac in the adenohypophysis of the SHR were 7.0 +/- 2.5 and 75.5 +/- 33.5 pmoles/mg protein respectively and these values were significantly different from those of the WKY (1.12 +/- 0.47 and 4.17 +/- 0.48 pmoles/mg protein) and SD (1.87 +/- 0.62 and 3.5 +/- 1.11 pmoles/mg). The results indicate that (a) there is no deficiency of free dopamine in the adenohypophysis of the SHR and hypertension in these animals is unlikely to be related to the catecholamine level in the endocrine gland, (b) the dopamine turnover in either the tuberoinfundibular tract or the adenohypophysis of the SHR is greatly enhanced.

Effects of dopamine on blood pressure and heart rate after microinjection into the hypothalamus of spontaneously hypertensive and normotensive Wistar-Kyoto rats

In anaesthetized spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats, 0.0125-0.4 mg/kg dopamine (DA) given intracerebroventricularly (icv) produced dose-related decreases in mean arterial blood pressure (MAP) and heart rate (HR), whereas intravenous DA produced dose-related increases in MAP and HR. SHR was significantly more responsive to icv DA compared with the normotensive controls. DA (0.02 mg/kg) significantly reduced MAP in a biphasic manner, when microinjected into the arcuate nucleus or third ventricle of SHR, with no significant changes in HR. No such effect occurred in WKY rats. Metoclopramide given concurrently with DA into the third ventricle attenuated the hypotensive response to DA. Saline injection had no significant effect on MAP and HR. The hypotensive responses to DA were not confounded by the spread of injected DA into the adjacent hypothalamic areas. These results support the hypothesis that there exists an abnormal sensitivity in SHR to centrally administered DA and that the arcuate appears to be the brain site involved in this abnormality.