Prior studies showed that repeated airpuff startle-reaction stimuli applied to normotensive inbred Wistar-Kyoto rats bred in La Jolla or Sprague- Dawley rats elicit pressor responses on all trials except trial-dependent bradycardia or tachycardia. However, hypertensive inbred spontaneously hypertensive rats bred in La Jolla exhibited no bradycardia. Peripheral methylatropine blocked bradycardia and unmasked tachycardia, which implies concurrent autonomic discharges on early trials. As shown here, vendor inbred Wistar-Kyoto rats from Charles River Laboratories (WKY(CR)) fail to show bradycardia. Because stress-induced parasympathetic responses are important to understanding arrhythmogenesis, we tested whether (WKY(CR)) and inbred spontaneously hypertensive rats from Charles River Laboratories (SHR(CR)) exhibit any parasympathetic activation by blunting sympathetic chronotropic responses with cardioselective β-adrenoceptor antagonists. WKY(CR) or SHR(CR) were pretreated with either nonselective propranolol, β1-selective metoprolol, β1-selective celiprolol (with β2-receptor agonist activity) or ICI 118,551, a selective β2-receptor antagonist. Neither propranolol nor metoprolol affected resting HR in WKY(CR), but both decreased HR in SHR(CR), whereas celiprolol raised resting HR only in WKY(CR). Although control WKY(CR) nor SHR(CR) exhibited bradycardia, bradycardia was unmasked in both by all β1-selective agents but not by ICI 118, 551. However, ICI 118,551 reduced tachycardia responses over all trials in WKY(CR), which suggests β2-adrenoceptor involvement in the stress-induced tachycardia. Significant cardiac contributions to the pressor responses in both WKY(CR) and SHR(CR) were found. We conclude that the mild airpuff startle-reaction stress stimulus elicits simultaneous parasympathetic and sympathetic discharge on early trials in both normotensive and hypertensive rats, that both β1- and β2-adrenoceptors are involved in HR responses and that the airpuff induces simultaneous sympathetic and parasympathetic responses, the latter having a potential cardioprotective role.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 1995|