Although beta(2)-adrenoceptors represent 15-25% of beta-adrenoceptors in the guinea pig heart, their functionality is controversial. We assessed the inotropic effects of beta(2)-adrenoceptor partial agonists in right papillary muscles. Salbutamol induced a small but significant concentration-dependent negative inotropic effect (NIE, -5% at 60 nM) followed by a moderate positive inotropic effect...

Peter H. Tonner, MD* BACKGROUND: The IV anesthetic, etomidate, has structural and clinical similarities to specific 2-adrenoceptor agonists such as dexmedetomidine. We investigated whether the sedative effects of etomidate may be mediated by 2-adrenoceptors. METHODS: The anesthetic potency of etomidate (1–20 M) was determined in Xenopus laevis tadpoles in the absence and presence of the specifi...

Alpha-2 adrenoceptors are important in baroreflex regulation. We tested the impact of alpha-2 adrenoceptors on heart rate variability (HRV) and spontaneous baroreflex sensitivity (BRS) in conscious mice with telemetry (TA11PA-C20). Baseline beat-to-beat measurements (2 hours between 8:00 am to 12:00 pm) were compared with measurements after intraperitoneal alpha-2 adrenoceptor blockade (yohimbi...

Phenylpropanolamine (dl-norephedrine) was one of the most widely used therapeutic agents to act on the sympathetic nervous system. Because of concerns regarding incidents of stroke, its use as a nasal decongestant was discontinued. Although considered an alpha1-adrenergic agonist, the vascular adrenergic pharmacology of phenylpropanolamine was not fully characterized. Unlike most other circulat...

PURPOSE Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measur...

Experiments were carried out on the isolated rabbit papillary muscle driven at 0.5 Hz in order to further elucidate the mechanism of the positive inotropic effect evoked by dopamine. The dose-response curve for dopamine was not affected by the antagonists pimozide (10(-6) M), yohimbine (10(-5) M) pindolol (3 x 10(-8) M) and phentolamine (10(-6) M) when these agents were given separately. Only t...

The regulation of triglyceride mobilization by catecholamines was investigated in the teleost fish Oreochromis mossambicus (tilapia) in vivo and in vitro. In vitro experiments were carried out with adipocytes that were isolated for the first time from fish adipose tissue. For the in vivo experiments, cannulated tilapia were exposed to stepwise decreasing oxygen levels (20, 10, and 5% air satura...

We studied isolated canine arteries and veins to compare the pharmacological properties of their postjunctional alpha-adrenoceptors. Rings of femoral and splenic arteries and of femoral and saphenous veins were mounted for isometric tension recording in organ chambers filled with KrebsRinger bicarbonate solution. The four blood vessels contracted when exposed to methoxamine, norepinephrine, phe...

2-adrenoceptors are essential presynaptic regulators of norepinephrine release from sympathetic nerves. Previous studies in mice with targeted deletions in the 3 2-adrenoceptor genes have indicated that these receptors are essential for embryonic development. In the present study, we searched for the 2-adrenoceptor subtype(s) involved in placental development and its molecular mechanism using m...

1 Atipamezole (4-(2-ethyl-2,3-dihydro-1H-inden-2-yl)-1H-imidazole) was first introduced as a potent and specific alpha2-adrenoceptor antagonist, but in some tissues [3H]atipamezole identifies an additional population of binding sites, distinct from both classical alpha2-adrenoceptors and I1- and I2-imidazoline receptors identified with [3H]para-aminoclonidine or [3H]idazoxan. 2 In the present s...