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  • Title: Evidence that the putative 5-HT1A receptor agonists, 8-OH-DPAT and ipsapirone, have a central hypotensive action that differs from that of clonidine in anaesthetised cats.
    Author: Ramage AG, Fozard JR.
    Journal: Eur J Pharmacol; 1987 Jun 19; 138(2):179-91. PubMed ID: 2957220.
    Abstract:
    Thoracic preganglionic sympathetic nerve activity, blood pressure, heart rate and femoral arterial conductance were recorded in anaesthetised, paralysed cats. Cumulative dose-response curves were constructed for 8-OH-DPAT, ipsapirone and clonidine. All three drugs caused dose-related falls in blood pressure which were associated with minimal changes in femoral arterial conductance. However, 8-OH-DPAT and ipsapirone differed from clonidine in that their hypotensive action was associated with moderate sympathoinhibition and a profound bradycardia, whereas clonidine caused profound sympathoinhibition and, as it did not increase central vagal tone, only a moderate bradycardia. 8-OH-DPAT also caused sympathoinhibition in bi-vagotomised cats and decreased carotid sinus nerve activity along with blood pressure. As 8-OH-DPAT and ipsapirone bind selectively to central 5-HT1A receptors it is concluded that central stimulation of these receptors causes sympathoinhibition and an increase in vagal tone, whereas stimulation of central alpha 2-adrenoceptors causes only sympathoinhibition. In addition, the present data suggest a peripheral vasodilator mechanism may also contribute to the hypotensive effects of 8-OH-DPAT and ipsapirone in the cat. The nature and relative importance of this remains to be established.
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