Olcegepant blocks neurogenic and non-neurogenic CGRPergic vasodepressor responses and facilitates noradrenergic vasopressor responses in pithed rats.

BACKGROUND AND PURPOSE: Olcegepant (BIBN4096BS) is a selective non-peptide CGRP receptor antagonist with acute antimigraine properties. Since systemic vascular tone is modulated by perivascular (primary sensory CGRPergic and sympathetic) nerves, this randomized study investigated in pithed rats the effect of acute i.v. treatment with olcegepant on the neurogenic and non-neurogenic: (i) CGRPergic vasodepressor responses; and (ii) noradrenergic vasopressor responses. The pithed rat is an experimental model predictive of systemic (cardio) vascular side effects. EXPERIMENTAL APPROACH: Seventy-five male Wistar rats (divided into 15 groups, n = 5 each) were pithed, artificially ventilated and prepared for: (i) spinal stimulation (T9 -T12 ; 0.56-5.6 Hz) of the sensory CGRPergic vasodepressor outflow or i.v. bolus injections (0.1-1 µg·kg-1 ) of α-CGRP, substance P or acetylcholine, which induced frequency-dependent or dose-dependent vasodepressor responses; or (ii) spinal stimulation (T7 -T9 ; 0.03-3 Hz) of the sympathetic vasopressor outflow or i.v. bolus injections (0.03-3 µg·kg-1 ) of noradrenaline, which produced frequency-dependent or dose-dependent vasopressor responses. KEY RESULTS: Olcegepant (1000 and 3000 µg·kg-1 , i.v.) dose-dependently blocked the vasodepressor responses to sensory nerve stimulation or i.v. α-CGRP, without affecting those to substance P or acetylcholine. Whereas it potentiated the vasopressor responses to sympathetic nerve stimulation or i.v. noradrenaline. CONCLUSIONS AND IMPLICATIONS: Olcegepant (i.v.) selectively blocked the neurogenic and non-neurogenic CGRPergic vasodepressor responses. This blockade by olcegepant potentiated the neurogenic and non-neurogenic noradrenergic vasopressor responses in pithed rats, an effect that might result in an increased vascular resistance and, consequently, in a prohypertensive action.

The role of dopamine D2, but not D3 or D4, receptor subtypes, in quinpirole-induced inhibition of the cardioaccelerator sympathetic outflow in pithed rats.

BACKGROUND AND PURPOSE: Quinpirole (a dopamine D2-like receptor agonist) inhibits the cardioaccelerator sympathetic outflow in pithed rats by sympathoinhibitory D2-like receptors. The present study was designed to identify pharmacologically the specific D2-like receptor subtypes (i.e. D2 , D3 and D4) involved in this sympathoinhibition by quinpirole. EXPERIMENTAL APPROACH: One hundred fourteen male Wistar rats were pithed, artificially ventilated with room air and prepared for either preganglionic spinal (C7-T1) stimulation of the cardioaccelerator sympathetic outflow (n = 102) or i.v. bolus injections of exogenous noradrenaline (n = 12). This approach resulted in frequency-dependent and dose-dependent tachycardic responses, respectively, as previously reported by our group. KEY RESULTS: I.v. continuous infusions of quinpirole (0.1-10 µg kg(-1) min(-1)), but not of saline (0.02 mL min(-1)), dose-dependently inhibited the sympathetically induced tachycardic responses. Moreover, the cardiac sympathoinhibition induced by 3 µg kg(-1) min(-1) quinpirole (which failed to affect the tachycardic responses to i.v. noradrenaline) was: (i) unchanged after i.v. injections of the antagonists SB-277011-A (D3 ; 100-300 µg kg(-1)) or L-745,870 (D4 ; 30-100 µg kg(-1)); and (ii) markedly blocked and abolished by, respectively, 100 and 300 µg kg(-1) of the D2 preferring receptor subtype antagonist L-741,626. These doses of antagonists, which did not affect per se the sympathetically induced tachycardic responses, were high enough to completely block their respective receptors. CONCLUSIONS AND IMPLICATIONS: The cardiac sympathoinhibition induced by 3 µg kg(-1) min(-1) quinpirole involves the dopamine D2 receptor subtype, with no evidence for the involvement of the D3 or D4 subtypes. This provides new evidence for understanding the modulation of the cardioaccelerator sympathetic outflow.