Factors Influencing Quantitative Assessment of Adrenaline Threshold of Small Vessels in the Rat Mesocecum

Publisher Website
Google Scholar
Abstract
Modifications of the Chambers-Zweifach method for estimating the epinephrine threshold of small vessels of the rat mesocecum, including the following, are described: (a) the storage of epinephrine dilutions in 1 ml tuberculin syringes; (b) the use of an Orthoilluminator (Silge and Kuhne, San Francisco.) as a permanently alligned light source; (c) the use of the ground-glass screen in the Orthophot (Silge and Kuhne) for all observations of blood flow; (d) delivery of warmed Ringer-gelatin and topical applications of dilute epinephrine through a plastic adapter attached to the objective of the microscope; (e) temperature control of the Ringer-gelatin solution by means of a thermistor-controlled thyratron providing proportional delivery of heat; and (f) rigid requirement of one of the following for recognition of constrictor response to topically applied epinephrine: arrest of flow, reversal of flow or marked slowing of flow giving the test vessel a "beaded" appear ance lasting 50-60 seconds. The mean of initial thresholds on 210 Wistar rats, including males and females, was 0.49 [plus or minus] 0.015 [mu]g/ml of epinephrine; no significant difference was shown by comparing the sexes separately. The amount of spontaneous drift of threshold over 20-60 minutes was not statistically significant Sprague-Dawley rats required more urethan; in spite of heavy doses of anesthetic, the epinephrine threshold tended to decline significantly over similar periods. Among various factors, other than rat strain, causing drift of threshold within the usual test period of 30-90 minutes were food restriction, respiratory embarrassment and intravenous injections of small volumes of water or saline solutions. Some increase of stability was achieved by prior adrenodemedullation, but the differences between initial thresholds and those measured 20-60 minutes after the disturbing influence remained statistically significant.