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Objective: To test the hypothesis that ma huang induces a pressor response in the pulmonary vascular bed of the cat and identify the alpha (1)-adrenoceptor subtype pathway(s) involved in the mediation or modulation of these effects. Design: Prospective vehicle controlled study. Setting: University research laboratory. Subjects: Intact chest preparation; adult mongrel cats. Interventions: In separate experiments, the effects of phentolamine, the alpha-adrenergic antagonist; prazosin, a selective alpha (1)-adrenoceptor antagonist; BMY 7378, a selective alpha (1) D-subtype adrenoceptor antagonist; 5-methyl-urapidil, the selective alpha (1)A-subtype adrenoceptor antagonist; and chloroethylclonidine, an alpha (1)B-subtype and (1) D-subtype adrenoceptor antagonist, were investigated on pulmonary arterial responses to ma huang and other agonist agents in the pulmonary vascular bed of the cat. Measurements and Main Results: Under constant flow conditions, lobar arterial perfusion pressure and systemic pressure were continuously monitored, electronically averaged, and permanently recorded. In the feline vascular bed of the isolated left lower lobe, ma huang induced a dose-dependent vasopressor response that was not significantly attenuated following administration of 5-methyl-urapidil. However, the responses to Ma huang were significantly reduced after administration of phentolamine, prazosin, BMY 7378, and chloroethylclonidine. Conclusions: The results of the present study suggest that ma huang has potent vasopressor activity in the pulmonary vascular bed of the cat and that this response may be mediated or modulated by both alpha (1)B-subtype and (1)D-subtype adrenoceptor sensitive pathways [ABSTRACT FROM AUTHOR]

Objective: To test the hypothesis that St. John's wort induces a depressor response in the feline pulmonary vascular bed and identify the pathways involved in the mediation or modulation of these effects. Design: Prospective vehicle controlled study. Setting: University research laboratory. Subjects: Intact chest preparation; adult mongrel cats. Interventions: In separate experiments, the effects of L-N5-(1-Iminoethyl) ornithine hydrochloride (L-NIO), a nitric oxide synthase inhibitor, glibenclamide, an ATP-sensitive K+ channel blocker, meclofenamate, a non-selective cyclo-oxygenase (COX) inhibitor, nicardipine, a calcium channel blocker, bicuculline, a GABAA receptor antagonist, and saclofen, a GABAB antagonist, were investigated on pulmonary arterial responses of St. John's wort (SJW), pinacidil, an ATP-sensitive K+ channel activator, bradykinin, an inducer of nitric oxide synthase, 3-aminopropyl (methyl) phosphinic acid, hydrochloride (SKF-97541), a GABAB receptor agonist and muscimol, a GABAA receptor agonist. Measurements and Main Results: Lobar arterial perfusion pressure and systemic pressure were continuously monitored, electronically averaged and permanently recorded. Under elevated tone conditions in the isolated left lower lobe vascular bed of the cat, SJW induced a dose-dependent vasodepressor response that was not significantly altered after administration of L-NIO, glibenclamide, meclofenamate or saclofen. Responses to SJW were significantly reduced after administration of either nicardipine or bicuculline. When the calcium channel blocker nicardipine was administered in addition to the GABA blocker bicuculline, there was near complete attenuation of the SJW-induced vasodepressor responses. Conclusions: The results of the present study suggest that SJW has potent vasodepressor activity in the pulmonary vascular bed of the cat and that this response is mediated or modulated by both a calcium ... [ABSTRACT FROM AUTHOR]