Bradykinin‐mediated estrogen‐dependent depressor response by direct activation of female‐specific distribution of myelinated Ah‐type baroreceptor neurons in rats

AIM: To understand the direct impact of bradykinin in autonomic control of circulation through baroreflex afferent pathway. METHODS: The mean arterial pressure (MAP) was monitored while bradykinin and its agonists were applied via nodose (NG) microinjection, the expression of bradykinin receptors (BRs) in the NG (1(st)‐order) and nucleus tractus solitarius (NTS, 2(nd)‐order) were tested in adult male, age‐matched female, and ovariectomized rats under physiological and hypertensive conditions. Additionally, bradykinin‐induced depolarization was also tested in identified baroreceptor and baroreceptive neurons using whole‐cell patch‐clamp technique. RESULTS: Under physiological condition, bradykinin‐induced dose‐ and estrogen‐dependent reductions of MAP with lower estimated EC(50) in females. B(2)R agonist mediated more dramatic MAP reduction with long‐lasting effect compared with B(1)R activation. These functional observations were consistent with the molecular and immunostaining evidences. However, under hypertensive condition, the MAP reduction was significantly less dramatic in N(’)‐Nitro‐L‐Arginine‐methyl ester (L‐NAME) induced secondary and spontaneous hypertension rats in males compared with female rats. Electrophysiological data showed that bradykinin‐elicited concentration‐dependent membrane depolarization with discharges during initial phase in identified myelinated Ah‐types baroreceptor neurons, not myelinated A‐types; while, higher concentration of bradykinin was required for depolarization of unmyelinated C‐types without initial discharges. CONCLUSION: These datasets have demonstrated for the first time that bradykinin mediates direct activation of baroreflex afferent function to trigger estrogen‐dependent depressor response, which is due mainly to the direct activation/neuroexcitation of female‐specific myelinated Ah‐type baroreceptor neurons leading to a sexual dimorphism in parasympathetic domination of blood pressure regulation via activation of B(2)R/B(1)R expression in baroreflex afferent pathway.