Influence of lactation on the prolactin secreting cells of the hypophysis of impala (Aepyceros melampus): An immunocytochemical and computer image analysis study

Abstract

Acute stress in the course of wildlife management has been intensively investigated. Chronic stress, on the contrary, has not been researched at all, probably due to the difficulty in measuring it as a result of the overriding effect of the physiological response to the restraining of wild animals. It was therefore decided to evaluate the use of immunocytochemistry, combined with computer image analysis to try and determine the magnitude of the structural changes of various hormone-secreting cells of the hypophysis. Since it was a pilot study to determine whether the combination of immunocytochemistry with computer image analysis could be of value to distinguish between two normally diverse groups, it was decided to compare the relative activity of prolactin secreting cells of lactating and nonlactating impala ewes. After transforming the prolactin immunoreactive area data by log10 to fall inside the parameters for kurtosis and skewness, a significant difference (P < 0,05, 5-% level, 2-tail) with the parametric t-test could be shown between the mean prolactin immunoreactive area of lactating (3,0751 µm2) and non-lactating (3,0467 µm2) ewes. However, the Pearson product moment (r= 0,03) showed that this difference may not be important for all practical reasons. This may be due to either sampling errors or limitations of computer image analysis, as it was often difficult to distinguish individual prolactin immunoreactive areas. Furthermore, a significant increase in the total prolactin immunoreactive areas of lactating ewes was also established. This technique, however, could distinguish between the hypophyses of lactating and non-lactating impala ewes, and with further refinement could be a useful tool in determining chronic stress in wildlife populations.