6-NITRODOPAMINE IS THE MAJOR ENDOGENOUS MODULATOR OF HUMAN EPIDIDYMAL VAS DEFERENS CONTRACTILITY

RESUMO

INTRODUÇÃO: 6-nitrodopamine is a novel catecholamine that is released from vascular tissues such as human umbilical cord vessels (Britto-Júnior et al., 2020) and Chelonoidis carbonaria aortic rings (Campos et al., 2020), and from rat isolated vas deferens (Britto-Jr et al., 2021). The receptor responsible for the contractions induced by 6-ND in the vas deferens is selectively blocked by tricyclic antidepressants such as amitriptyline, desipramine and clomipramine (Britto-Jr et al., 2021; Ximenes et al., 2021) and by the a1-adrenergic receptor antagonists such as doxazosin, tamsulosin and silodosin (Britto-Jr et al., 2022). The clinical use of tricyclic antidepressants has been associated with delayed ejaculation (Rothmore, 2020) and the tricyclic antidepressant clomipramine is useful in the treatment of premature ejaculation in man (Waldinger et al., 2004; Waldinger, 2018). Although tricyclic antidepressants act in the central nervous system, the findings in the rat and vas deferens open the exciting possibility that they could be acting as 6-ND receptor antagonists in the human vas deferens.

OBJETIVOS: The objectives of this study are: a) to evaluate the effects of tricyclic antidepressants in the HEVD contractility induced by 6ND. b) to evaluate the effects of tricyclic antidepressants in the HEVD contractility induced by electric-field simulation (EFS). c) to verify the major catecholamine released from HEVD.

MÉTODOS: Participants were invited to participate in the study were patients who underwent vasectomy surgery from Hospital e Maternidade Salvalus. The Informed Consent Form was obtained from those who agreed to participate. The human epididymal vas deferens (HEVD) were obtained from 94 patients aged 28-53 years. The investigation followed the principles outlined in the Declaration of Helsinki and the protocol was approved by the Ethics Committee of the Institute of Biomedical Sciences of the University of São Paulo – ICB/USP (protocol number 4.468.508). The HEVD arrival at the laboratory were dissected free of connective tissue and bisected longitudinally into 15-mm-length strips suspended two strips in a 5 mL organ bath containing Krebs-Henseleit’s solution (KHS) and ascorbic acid (3 mM) continuously gassed with a mixture (95% O2 / 5% CO2) at 37 ºC for 30 min, in the absence and the presence of L-NAME (100 mM). Two aliquots of 2 mL of the supernatant were transferred to black Eppendorf tubes and stored at -20 °C until analysis by LC-MS-MS (Campos et al., 2020). For pharmacological assays, the HEVD strips were suspended vertically between metal hooks in 10-mL organ baths containing KHS, continuously gassed with a mixture of 95%O2: 5%CO2 at 37°C. Tissues were allowed to equilibrate under a resting tension of 10 mN, and the isometric tension was registered using a PowerLab system (ADInstruments, Sydney, Australia). Following a 45-min stabilization period, the strips were initially contracted with a single concentration of KCl (80 mM) to verify the tissue viability. Cumulative concentration-response curves to 6-ND were performed in HEVD strips in the absence and presence of amitriptyline (30-300 nM, 30 min), desipramine (30-300 nM, 30 min) and carbamazepine (30-300 nM, 30 min). In separate HEVD preparations, cumulative concentration-response curves to dopamine, noradrenaline and adrenaline were performed in the absence and presence of amitriptyline (100 nM, 30 min), desipramine (100 nM, 30 min) and carbamazepine (100 nM, 30 min).

RESULTADOS: 6-ND was the major catecholamine released from HEVD (1.52±0.86), and the release was reduced in the presence of L-NAME (0.61±0.23), indicating that the synthesis/release of 6-ND is coupled to nitric oxide synthesis, as observed in rat vas deferens (Britto-Júnior et al., 2021) and human umbilical cord vessels (Britto-Júnior et al., 2020). Amitriptyline (100 nM), desipramine (100 nM) and carbamazepine (100 nM) caused significant inhibition of HEVD contractions induced by EFS. At this concentration (100 nM), these drugs selectively provoked a rightward shift of the 6-ND induced HEVD contractions, but they did not affect the HEVD contractions induced by dopamine, noradrenaline or adrenaline.

CONCLUSÃO: Our results clearly demonstrate that 6-ND is a major endogenous modulator of HEVD contractility. Furthermore, the observation that tricyclic antidepressants do antagonize both EFS-induced and 6-ND induced contractions of HEVD, indicates that 6-ND may play a pivotal role in the human ejaculatory process.

PALAVRA-CHAVE: 6-nitrodopamine