Role of alpha adrenoceptors and nitric oxide on cardiovascular responses in acute and chronic hypertension

Changes in protein and gene expression of angiotensin II receptors (AT1 and AT2) in aorta of diabetic and hypertensive rats

Diabetes and hypertension have been associated with cardiovascular diseases and stroke. Some reports have related the coexistence of hypertension and diabetes with increase in the risk of developing vascular complications. Recently some studies have shown results suggesting that in the early stages of diabetes and hypertension exist a reduced functional response to vasopressor agents like angiotensin II (Ang II), which plays an important role in blood pressure regulation mechanism through the activation of its AT1 and AT2 receptors. For that reason, the aim of this work was to study the gene and protein expression of AT1 and AT2 receptors in aorta of diabetic SHR and WKY rats. Diabetes was induced by the administration of streptozotocin (60 mg/kg i.p.). After 4 weeks of the onset of diabetes, the protein expression was obtained by western blot and the mRNA expression by RT-PCR. Our results showed that the hypertensive rats have a higher mRNA and protein expression of AT1 receptors than normotensive rats while the AT2 expression remained unchanged. On the other hand, the combination of diabetes and hypertension increased the mRNA and protein expression of AT1 and AT2 receptors significantly. In conclusion, our results suggest that diabetes with hypertension modifies the mRNA and protein expression of AT1 and AT2 receptors. However, the overexpression of AT2 could be associated with the reduction in the response to Ang II in the early stage of diabetes.

Effects of one resistance exercise session on vascular smooth muscle of hypertensive rats

BACKGROUND

Hypertension is a public health problem and increases the incidence of cardiovascular diseases.

OBJECTIVE

To evaluate the effects of a resistance exercise session on the contractile and relaxing mechanisms of vascular smooth muscle in mesenteric arteries of NG-nitro L-arginine methyl ester (L-NAME)-induced hypertensive rats.

METHODS

Wistar rats were divided into three groups: control (C), hypertensive (H), and exercised hypertensive (EH). Hypertension was induced by administration of 20 mg/kg of L-NAME for 7 days prior to experimental protocols. The resistance exercise protocol consisted of 10 sets of 10 repetitions and intensity of 40% of one repetition maximum. The reactivity of vascular smooth muscle was evaluated by concentration‑response curves to phenylephrine (PHEN), potassium chloride (KCl) and sodium nitroprusside (SNP).

RESULTS

Rats treated with L-NAME showed an increase (p < 0.001) in systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) compared to the initial period of induction. No difference in PHEN sensitivity was observed between groups H and EH. Acute resistance exercise reduced (p < 0.001) the contractile response induced by KCl at concentrations of 40 and 60 mM in group EH. Greater (p < 0.01) smooth muscle sensitivity to NPS was observed in group EH as compared to group H.

CONCLUSION

One resistance exercise session reduces the contractile response induced by KCl in addition to increasing the sensitivity of smooth muscle to NO in mesenteric arteries of hypertensive rats.

α₁-Adrenergic receptors contribute to the acute effects of 3,4-methylenedioxymethamphetamine in humans

Preclinical studies implicate a role for α₁-noradrenergic receptors in the effects of psychostimulants, including 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"). The present study evaluated the effects of the α₁-noradrenergic receptor antagonist doxazosin on the acute pharmacodynamic and pharmacokinetic response to MDMA in 16 healthy subjects. Doxazosin (8 mg/d) or placebo was administered for 3 days before MDMA (125 mg) or placebo using a randomized, double-blind, placebo-controlled, 4-session, crossover design. Doxazosin reduced MDMA-induced elevations in blood pressure, body temperature, and moderately attenuated positive mood but enhanced tachycardia associated with MDMA. The results indicate that α₁-adrenergic receptors contribute to the acute cardiostimulant and to a minor extent possibly also to the thermogenic and euphoric effects of MDMA in humans.

Pharmacological identification of α1- and α2-adrenoceptor subtypes involved in the vasopressor responses induced by ergotamine in pithed rats

Ergotamine has been used in clinical practice for the acute treatment of migraine for over 90 years. So far, it is known that ergotamine interacts with diverse receptors (including α1/2-adrenoceptors, 5-HT1, 5-HT2 and D2-like receptors) and that produces increases in mean blood pressure which are significantly blocked by yohimbine, a classical α2-adrenoceptor antagonist with a moderate affinity for α1-adrenoceptors. Since α1/2-adrenoceptors mediate vasopressor and vasoconstrictor responses in the cardiovascular system, this study was designed to identify the α-adrenoceptor subtypes (α1A, α1B, α1D, α2A, α2B and α2C) involved in ergotamine-induced vasopressor responses in pithed rats. In male Wistar pithed rats baseline heart rate and blood pressure were recorded. Then, the vasopressor responses to intravenous (i.v.) bolus injections of ergotamine were determined after administration of vehicle or several α1⧸2-adrenoceptor antagonists. I.v. administration of the antagonists prazosin (α1, 0.1-30 µg/kg), rauwolscine (α2, 0.3-300 µg/kg), prazosin (0.1 µg/kg) plus rauwolscine (0.3 µg/kg), 5-methylurapidil (α1A, 100 and 300 µg/kg), L-765,314 (α1B, 100 and 300 µg/kg), BMY 7378 (α1D, 100 and 300 µg/kg), BRL44408 (α2A, 300 and 1000 µg/kg) and JP-1302 (α2C, 300 µg/kg), significantly blocked the vasopressor responses to ergotamine, whereas imiloxan (α2B, 1000 and 3000 µg/kg), JP-1302 (100 µg/kg) or the corresponding vehicles (saline 0.9%, propylene glycol 20% or dimethyl sulfoxide 10%; 1ml/kg) failed to modify the responses to ergotamine. The above results suggest that the vasopressor responses to ergotamine in pithed rats are mainly mediated by α1A-, α1B-, α1D-, α2A- and α2C-adrenoceptors and may explain its adverse/therapeutic effects.