Background and Purpose: Agonists acting at GPCRs promote biased signalling via Gα or Gβγ subunits, GPCR kinases and β‐arrestins. Since the demonstration of biased agonism has implications for drug discovery, it is essential to consider confounding factors contributing to bias. We have examined bias at human α_1A‐adrenoceptors stably expressed at low levels in CHO‐K1 cells, identifying off‐target effects at endogenous receptors that contribute to ERK1/2 phosphorylation in response to the agonist oxymetazoline.Experimental Approach: Intracellular Ca²⁺ mobilization was monitored in a Flexstation® using Fluo 4‐AM. The accumulation of cAMP and ERK1/2 phosphorylation were measured using AlphaScreen® proximity assays, and mRNA expression was measured by RT‐qPCR. Ligand bias was determined using the operational model of agonism.Key Results: Noradrenaline, phenylephrine, methoxamine and A61603 increased Ca²⁺ mobilization, cAMP accumulation and ERK1/2 phosphorylation. However, oxymetazoline showed low efficacy for Ca⁺² mobilization, no effect on cAMP generation and high efficacy for ERK1/2 phosphorylation. The apparent functional selectivity of oxymetazoline towards ERK1/2 was related to off‐target effects at 5‐HT_1B receptors endogenously expressed in CHO‐K1 cells. Phenylephrine and methoxamine showed genuine bias towards ERK1/2 phosphorylation compared to Ca²⁺ and cAMP pathways, whereas A61603 displayed bias towards cAMP accumulation compared to ERK1/2 phosphorylation.Conclusion and Implications: We have shown that while adrenergic agonists display bias at human α_1A‐adrenoceptors, the marked bias of oxymetazoline for ERK1/2 phosphorylation originates from off‐target effects. Commonly used cell lines express a repertoire of endogenous GPCRs that may confound studies on biased agonism at recombinant receptors.

Diabetes augments the risk of hypertension. Although several factors have been implicated in the development of such hypertensive state, we designed this study to investigate blood pressure development, the activity of angiotensin-converting enzyme (ACE) in blood as well as sympathetic neurotransmission in the vas deferens of diabetic rats. We used streptozotocin (STZ)-induced diabetic rats (60 mg/kg) in order to evaluate the systolic blood pressure (SBP), ACE activity and peripheral sympathetic neurotransmission. We observed the following changes of parameters: increase of SBP, decrease of heart rate, augmentation of plasma ACE activity, enhancement of phasic and tonic vas deferens contractions elicited by electrical stimulation at 5 Hz, increase of maximal response to noradrenaline (NA) and decrease of adenosine triphosphate (ATP)-elicited contraction of vasa deferentia. The results reveal that in the development of hypertension in diabetic rats, augmentation of circulating ACE activity precedes the sympathetic dysfunction. Additionally, it seems that the purinergic and noradrenergic neurotransmission is compromised.

Schinus terebinthifoliusRaddi (Anacardiaceae), popularly known as red aroeira, is used in traditional medicine to treat inflammatory, gastric, and respiratory disorders. The aim of this study was to evaluate the antihistaminic activity ofS. terebinthifolius (St)bark extract by using in vivo and in vitro experimental models. The effects ofStwere investigated on contractions induced by histamine, carbachol, and potassium chloride in isolated guinea pig ileum.Stwas also studied in response to hind paw edema induced by histamine in rats. Experiments revealed that althoughSt(250, 500, and 1,000 µg/mL) reduced the histamine‐induced contractions by 9.1 ± 1.8, 50.2 ± 2.0, and 68.9 ± 2.0%, respectively, it did not inhibit contractions induced by carbachol or KCl. The association ofSt(250 and 500 µg/mL) with hydroxyzine, an H₁‐antihistamine (0.125 and 0.250 µM), increased the inhibitory effect to 67.0 ± 3.2 and 85.1 ± 2.1%, respectively. Moreover,St(100, 200, and 400 mg/kg) decreased paw edema from its peak by 33.9, 48.4, and 54.8%, respectively, whereas hydroxyzine (70 mg/kg) inhibited the peak edema by 56.5%. Altogether, the results suggest that the bark extract ofS. terebinthifoliushas an antihistaminic effect (H₁).