Paradoxical relationship between the superior cervical ganglia and the antihypertensive action of propranolol in the spontaneous hypertensive rat.

The effect of dl-propranolol (1.0 mg/kg/day i.p.) on heart rate and blood pressure in young and old normo- and hypertensive rats was studied before and after bilateral sympathectomy of the superior cervical ganglia. Denervation alone produced no significant changes in blood pressure or heart rate in the normo- or hypertensive rat of either age. Thirty-five consecutive days of propranolol treatment significantly lowered blood pressure in the older established spontaneous hypertensive rat and prevented the increases from occurring in the younger, developing hypertensive rat. Blood pressure was not modified in the normotensive Wistar-Kyoto rat by propranolol. Denervation of the superior cervical ganglia at the beginning of the propranolol treatment or midway through the protocol abolished the antihypertensive effects in the young and old spontaneous hypertensive rat. A close temporal association of denervation with the loss of the antihypertensive effect was demonstrated. Although propranolol administration continued after denervation, the antihypertensive effects of the drug did not reappear.