[Simultaneous study of ocular vascular reactions of the anterior and posterior segments following clonidine and propranolol in normotensive and hypertensive experimental animals].
The influence of clonidine and propranolol on the vessels of the anterior segment and of the fundus, as well as on mean arterial pressure and heart rate, was investigated in normal rabbits, minipigs, and minipigs with experimentally induced hypertension. The vessel reactions were monitored by photography or fluorescein angiography. Following injection of clonidine, constrictions of episcleral and conjunctival vessels occurred in all the animals, but the fundus vessels of the rabbits were not affected. Difficulties were encountered in assessing the condition of the iris vessels. In minipigs, after administering 6-20 micrograms/kg, an average delay of 2 seconds in the inflow into the retinal vessels was recorded, due possibly to a (transitory?) vessel constriction upstream. Mean arterial pressure increased initially in all animals, but to a different extent in the two species. There was less uniformity as regards heart rate. The vessel reactions of the two species to propranolol were different: in rabbits, a reaction was only observed after administering 2.46 mg/kg bodyweight in episcleral and conjunctival vessels, though not in fundus vessels. Minipigs were given doses of 0.16, 0.5, and 0.8 mg/kg; after 0.5 mg/kg a vessel constriction took place in the episclera and the conjunctiva, becoming manifest after 20 minutes and attaining a maximum after 60 minutes. However, there appeared to be no reaction in the fundus vessels. After an abrupt decrease in mean arterial pressure, both this and the heart rate showed an almost identically slow decrease until the 50th minute, followed by a slight increase up to the 60th minute. The comparison of the circulation parameters reveals some interesting parallels, though also some contrasts. The mechanisms of action and characteristics of these two substances are discussed.