Pharmacologic characteristics and actomyosin content of aorta from neonatal rats

Publisher Website
Google Scholar
Abstract
Previously published observations suggested that the increasing force-generating ability of aorta from maturing rats may be due to an increasing actomyosin content. The purpose of these experiments was to determine if this relationship was maintained in neonatal rat aortas, and to characterize their contractile responsiveness to pharmacologic agents. Thoracic aortas from rats 3-25 days old were examined for their responsiveness to potassium chloride (K+), norepinephrine (NE) and isoproterenol (Iso) and these results were correlated with the total protein and actomyosin contents. There was a positive correlation between animal age and the maximum contractile response to K+ and NE. Of the aortas from animals less than 6 days old, only 5 of 11 responded to NE and 2 of 7 responded to Iso, whereas all responded to K+. For those preparations from animals older than 6 days there was no change with age in the ED50 value for Iso or for NE except from 15-23 days when there was a significant decrease. The K+ ED50 value decreased significantly after 6 days of age, reaching a stable value by 15 days. The amount of total protein per tissue wet weight increased with animal age. However, the amount of actomyosin per total protein did not change with animal age. Only from 14-21 days old was there a significant increase in the amount of actomyosin per tissue wet weight. The ability of the aorta to contract evidently develops before its responsiveness to adrenergic receptor stimulants. In addition, the positive correlation between maximum contractile response and animal age previously observed in older animals is also seen in aortas from neonatal animals. This increase in maximum contractile response with age is not due to an increase in the amount of actomyosin.