Abstract
Seminal plasma (SP) plays an important role in the motility, viability and maintenance of the fertilizing capacity of mammalian spermatozoa. This study is the first on brown bear (Ursus arctos) SP components, and has two main objectives: 1) to define the SP composition in bear ejaculate and 2) to identify variations in SP composition in relation to high and low levels of testosterone in serum during the breeding season. Forty-eight sperm samples from 30 sexually mature male brown bears (Ursus arctos) were obtained by electroejaculation, and their serum testosterone levels were assessed to sort the animals into 2 groups (high and low testosterone levels, threshold 5 ng/dl). The biochemical and protein compositions of the SP samples were assessed, and sperm motility was analyzed. We found that lactate dehydrogenase was significantly higher in the low-serum-testosterone samples, while concentrations of lipase and Mg+ values were significantly higher in the high-serum-testosterone samples. In contrast, sperm motility did not significantly differ (P>0.05) between the testosterone level groups (total motility: 74.42.8% in the high-level group vs. 77.1±4.7% in the low-level group). A reference digital model was constructed since there is no information for this wild species. To do this, all gel images were added in a binary multidimensional image and thirty-three spots were identified as the most-repeated spots. An analysis of these proteins was done by qualitative equivalency (isoelectric point and molecular weight) with published data for a bull. SP protein composition was compared between bears with high and low serum testosterone, and three proteins (binder of sperm and two enzymes not identified in the reference bull) showed significant (P<0.05) quantitative differences. We conclude that male bears with high or low serum testosterone levels differs only in some properties of their SP, differences in enzyme LDIP2, energy source LACT2, one protein (similar to BSP1) and Mg ion were identified between these two groups. These data may inform the application of SP to improve bear semen extenders.
Highlights
According to mitochondrial DNA studies [1], the Cantabrian brown bear (Ursus arctos cantabricus) is the only existing pure brown bear population on the Iberian Peninsula
We found that LDIP2 showed significantly higher values in the low-testosterone samples, while LACT2 and Mg showed significantly higher values in the high-testosterone samples
The composition of seminal plasma and its relationship with the serum testosterone levels in brown bear during the breeding season have been assessed in this work
Summary
According to mitochondrial DNA studies [1], the Cantabrian brown bear (Ursus arctos cantabricus) is the only existing pure brown bear population on the Iberian Peninsula. Artificial insemination is one of the most valuable tools in ex situ reproduction programs for endangered animals, so sperm cryopreservation is very important to the creation of a genetic resource bank for the brown bear [2,3,4]. Genetic variability could be restored to the endangered wild population by storing sperm samples in genetic banks. SP is a complex fluid that contains different components, such as proteins, enzymes, macro- and microelements, lipids and nutrients, and it plays an important role in spermatozoa motility, viability and the maintenance of fertilizing capacity [5,6]. Some authors have observed that the proteins contained in SP influence the female genital tract and ovum fertilization [5,7,8]. Analysis of various enzyme activities and its influence on sperm function has been reported, among others alkaline phosphatase and lactate dehydrogenase [10], lipase [11] and glutamic oxaloacetic transaminase [12]
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