Silks are protein polymers that differ in their components and structures according to the insects producing the silk.
1)Silks from silkworm (Bombyx mori) and spiders (Nephila clavipes and Araneus diadematus) are composed of 2 major peptides, sericin and fibroin, 2) which are well known to have pharmacological activities including anti-diabetic effect. [3][4][5][6][7][8][9] Hydrolysis of silk proteins from silkworms leads to different peptide sizes, which eventually creates peptides that are 18-19 amino acids in length, while enzymatic degradation results in specific sizes or compositions of peptides 10,11) exerting diverse bioactivities 4,12,13) such as anti-diabetic, [5][6][7][8][9] hypocholesterolemic, 10,14,15) anti-oxidant, 16,17) immunoregulatory, 18) anti-tumor, 17,19) anti-viral, 20) anti-bacterial 21) effects. Silk amino acids (SAA) were also shown to decrease blood triglycerides and to preserve hepatic function. 10,14) In our previous studies, we found that repeatedly treating resting rats with a SAA preparation lowered blood levels of tissue injury parameters from the muscles and the liver.22) Also, it increased glucose and albumin levels, and potentiated hematopioesis including lymphocyte counts. Furthermore, a high dose (800 mg/kg) of SAA exerted stamina-enhancing activity in forced swimming mice by preventing tissue injuries and increasing anti-fatigue parameters.23) Such effects led us to investigate the effects of a SAA preparation on the physical stamina (energy-boosting) and male reproductive function in a forced swimming model. Forced swimming tests have been used to evaluate the behavioral performances of rodents to predict the efficacy of anti-depressant treatments, [24][25][26] since the animals exhibit immobility behavior considered a depression-like response, as a reflection of helplessness when subjected to an incapable situation.27) Similarly, weight-loaded swimming tests have also been used as a reference for measuring the fatigue level objectively and quantitatively. [28][29][30] Recently, forced swimming tests were adopted not only to assess adjustment of rodents, but also to evaluate male reproductive function under repeated stress situations. [30][31][32][33] The aim of the present study was to determine the effects of SAA, an amino acid preparation from silk (cocoon), on physical stamina and male reproductive function. Especially, we analyzed not only the maximum swimming time and blood and tissue parameters of muscular and hepatic injuries, but also hormone concentration and sperm counts following weight-loaded forced swimming.
MATERIALS AND METHODSMaterials A preparation of SAA from acid (HCl) hydrolysate of silk proteins was obtained from Worldway Co., Ltd. (Jeoneui, Korea). The SAA preparation was mainly composed of Ala (34.36%)ϾGly (27.23%)ϾSer (9.58%)Ͼ Val (3.49%)ϾThr (2.00%), and minor amino acids.
23)Animals Eight-week-old male ICR mice (29-31 g, nϭ10 per group) were procured from the Daehan Laboratory Animal Center (Eumseong, Korea). The animals were maintained at a const...
