Catecholaminergic and opioidergic mechanisms involved in the hypotensive response of pindolol

The present study evaluated the involvement of opioidergic and catecholaminergic mechanisms in the hypotensive action of pindolol. Pindolol (1 mg/kg i.a.) was administered to unanesthetized spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats instrumented for direct arterial pressure monitoring. Peripheral administration of pindolol produced a significant decrease in blood pressure in both SHR and WKY rats with SHR animals having a greater response. Heart rate was reduced in SHR; however, a tachycardia was observed in WKY rats. Pretreatment with naloxone (100 micrograms/kg i.a.) 10 min prior to pindolol administration prevented the hypotensive response. Similar pretreatment with yohimbine, an alpha 2-receptor antagonist, also prevented the pindolol-induced hypotensive response in both SHR and WKY rats. Neither naloxone nor yohimbine alone significantly affected blood pressure or heart rate. These results suggest that opioidergic and catecholaminergic mechanisms are involved in the hypotensive action of pindolol.