THE EFFECT OF CASTRATION ON THE WEIGHT AND COMPOSITION OF THE MUSCLES OF THE GUINEA PIG123

Abstract

Male guinea pigs of the inbred Hartley strain were castrated at 3-4 months of age. A group of normal animals was killed at the time of castration and paired groups of normal and castrated guinea pigs at intervals of 6, 12 and 27 weeks after castration. In addition a group of guinea pigs was castrated 21 weeks later than the 1st group and killed at the same time as the 27-weeks groups. The internal organs and 49 individual muscles were studied. Castration had a variable effect on the muscles (1) immediate cessation of growth with minor regression in some instances. When castration was performed in the adult animals, marked regression in the mass of these muscles occurred. (2) Growth continued but at a slower rate for variable periods and no significant effect. The muscles of the head and neck region and the retractor penis were affected to the greatest degrees. Other muscles also showed marked changes, e.g., psoas major, pectorals and certain muscles of the extremities. The heart decreased and the adrenals increased slightly after castration. The thymus increased only in the oldest castrates. The accessory sex organs immediately regressed after castration. The other organs showed no changes. Growth rate of the castrated animals was only slightly retarded. The N (protein) and water concentrations were not altered even in those muscles which showed great changes in mass. The various parts of the skeleton also were not changed possibly due to the fact that castration was performed after puberty.