Background and purpose: Increasing evidence suggests that the sympathetic nervous system profoundly interacts with skeletal muscle, influencing both muscle fiber function and composition. β2-Adrenoceptors (β2-ARs), the predominant adrenergic receptor subtype in muscle fibers, have been shown to enhance protein synthesis, reduce protein degradation, facilitate muscle contraction and relaxation, and improve neuromuscular junction (NMJ) transmission upon activation. In this study, we investigated the effects of Formoterol, a highly selective β2-AR agonist, on the presynaptic terminal of motor neurons. Experimental Approach: We used electromyography, FM1-43 fluorescent dye assays, and transmission electron microscopy to evaluate the neuromuscular junction following β2-receptor activation. Key Results: We demonstrated that β2-AR activation by Formoterol enhances muscle contractility and both spontaneous and evoked exocytosis of acetylcholine (ACh)-containing synaptic vesicles at the mouse diaphragm NMJ. Formoterol-induced morphological changes in diaphragmatic NMJs were consistent with increased exo-endocytic activity. Notably, Formoterol-evoked exocytosis displayed sexual dimorphism, with females showing a significantly milder response compared to males. In females, Formoterol-induced synaptic vesicles exocytosis was mediated solely by P/Q-type voltage-activated Ca2+ channels, whereas in males, it involved both P/Q-type channels, TRPV1 calcium channels, and an additional, yet unidentified, component. Orchiectomized males exhibited responses to Formoterol similar to the females., whereas ovariectomy did not modify female drug responses, indicating that male sex-hormonal environment orchestrates the sex-differences herein described. Conclusion and implications: These findings not only highlight the importance of sex-specific mechanisms but also reveal a novel effect of β2-AR activation directly on presynaptic terminals, enhancing exocytosis at the NMJ and thereby increasing neuromuscular transmission.

Background and purpose: Bradykinin [BK-(1-9)] is an endogenous nonapeptide involved in multiple physiological and pathological processes. A long-held belief is that peptide fragments of BK-(1-9) are biologically inactive. Here, we have tested the biological activities of BK-(1-9) and two major peptide fragments in human and animal systems. Experimental Approach: Levels of BK peptides in male Wistar rat plasma were quantified by mass spectrometric methods. Nitric oxide was quantified in human, mouse and rat cells, and loaded with DAF-FM. We used aortic rings from adult male Wistar rats to test vascular reactivity. Changes in blood pressure and heart rate were measured in conscious adult male Wistar rats. Key results: Plasma levels of BK-(1-7) and BK-(1-5) in rats were increased following infusion of BK-(1-9). All tested peptides induced NO production in all cell types tested. However, unlike BK-(1-9), NO production elicited by BK-(1-7) or BK-(1-5) was not inhibited by B1 or B2 receptor antagonists. BK-(1-7) or BK-(1-5) also induced concentration-dependent vasorelaxation of aortic rings, without involving B1 or B2 receptors. In vivo, either intravenous or intra-arterial administration of BK-(1-7) or BK-(1-5) induced similar hypotension response. Conclusions and implications: BK-(1-7) and BK-(1-5) are endogenous peptides present in plasma. They are formed, at least partially, through the BK-(1-9) proteolysis. BK-related peptide fragments show biological activity, not mediated by B1 or B2 receptors. These BK-fragments could constitute new, active components of the kallikrein-kinin system.