Moreover, in patients with osteoporosis, oral intake of HC in addition to injection of calcitonin had a stronger inhibitory effect on bone resorption than the injection of calcitonin alone [12]. These results suggest that dietary collagen peptides would effectively prevent age-related bone loss. However, it has not been demonstrated whether the intake of HC also has positive effect on bone mass or strength in growing bone. Some studies have investigated the effects of the intake level of protein on bone mass. Protein deficiency could decrease the secretion of insulin-like growth factor 1 (IGF-1) [13], which may prevent normal growth of bone mass. Recently, we also demonstrated that

a low protein intake suppressed the acquisition of bone mass and the increase of bone strength during growth learn more period [14]. Conversely, Adriamycin cell line a high protein intake results in higher urinary calcium (Ca) excretion, which may lead to accelerated bone resorption [15]. Similarly, AZD3965 we demonstrated that a high protein intake suppressed the increase of bone strength during growth period in which treadmill running was performed [14]. However, these studies used only casein protein as a protein source of the diet; it is not known

whether HC intake included in a high protein diet has positive effect on bone mass or strength when combined with running exercise during growth phase. Accordingly, the aim of this study is to investigate 1) the effect of HC intake alone and HC intake combined with treadmill running exercise on bone mass and strength in growing rats, 2) whether the intake of a high protein diet containing HC has a positive effect on bone mass and strength of growing rats trained with running exercise.

Methods Experimental animals and protocol Fifty-nine male Wistar rats, 5 weeks of age were obtained from CLEA Japan, Inc (Tokyo, Japan). Rats were randomized into four groups, the 20% casein group (Casein20), the 40% casein group (Casein40), the 20% HC group (HC20), and the 40% HC group (HC40). Each group was further divided into exercise groups (Casein20 + Ex, Casein40 + Ex, HC20 + Ex, HC40 + Ex) and non-exercise groups (Casein20, Liothyronine Sodium Casein40, HC20, HC40) (n = 7 or 8 each). The experimental period was 11 weeks. The animals were individually housed at 23 ± 1°C and humidity of 50 ± 5% on an inverted 12/12 h light/dark cycle. All animals received food and water ad libitum. Body weight and food intake were measured at 48 h intervals throughout the experimental period. All experimental protocols in the present study were approved by the Committee on Animal Research at the University of Tsukuba. Experimental diets Each group received one of two levels of protein for its diet, 20% or 40% to total diet weight. Since the recommended dietary percentage of protein for growing animals is 17.