Comparisons of apomorphine-induced erection and spontaneous erection in rats by telemetric assessment of intracavernosal pressure

Abstract

Although there are several methods for assessing erectile function in rats, the standard methods for telemetric monitoring have not been established. Theoretically assessment of spontaneous erection (SE) seems to be a physiologic method but it needs long measuring time and additional efforts. Apomorphine-induced erection (AIE) is one available and simple method; however, the correlation with SE has not been assessed. We compared erection profiles of AIE and SE in normal and two disease rat models using telemetric assessment of intracavernosal pressure (ICP). Seven-week-old male Sprague-Dawley rats were assigned to normal control, diabetes mellitus (DM) and hypercholesterolemia (HC) group. After 19 weeks a telemetric pressure sensor (C40; Data Sciences) was surgically implanted in the corpus cavernosum. One week later, ICP was recorded in freely moving rats after intraperitoneal apomorphine (100 μg/kg) injection (AIE) or during SE. Sexual events were visually identified and recorded. Only the pressure increases that occurred during sexual behavior were analyzed. We compared the erectile profiles such as duration, maximal ICP and the area under the curve (AUC, area under time × ICP curves). Two-way anova revealed no significant effect of the measuring methods on the mean AUC (F1,43 = 2.756, p-value = 0.104), but a significant effect of different disease models on mean AUC (two-way anova: F2,43 = 12.929, p-value < 0.001) was observed. The mean AUC of normal control rats was significantly higher than that of DM and HC rats (Bonferroni post hoc test: p < 0.001 and p = 0.001, respectively). ICP measurements using a telemetric device showed no significant difference in AUC between AIE and SE. AIE is easy and requires less time than SE measurements. Therefore, AIE could be a useful method to evaluate ICP in rats.