Effects of Neonatal Gonadectomy on Skeletal Growth and Development in the Rat

Abstract

Skeletal growth and maturation were studied in neonatally gonadectomized male and female Long-Evans rats and their sham-operated, pair-fed controls. Total body lengths, weights and roentgenograms were obtained on the following days: 1, 7, 14, 21, 30, 60, 90, 120, 150 and 180. There were no significant differences in lengths and weights of sham-operated males, castrated males and ovariectomized females. In contrast, sham-operated females (controls) were significantly shorter and lighter than the other 3 groups after day 30. Skeletal maturation at all ages was the same for the 4 groups. These data show that sex differences of length and weight in the rat are primarily due to ovarian inhibition rather than to testicular enhancement. In addition, the data show that a deficiency of gonadal hormones does not appear to alter skeletal maturation in the rat. (Endocrinology 75: 805, 1964) T INFLUENCE of gonadectomy on growth in the rat has been studied extensively (1, 2). However, so far as we know, there has been only one other investigation (3) which touched briefly upon growth in neonatally gonadectomized rats. Although Jost (4) has postulated that hormones are not necessary for fetal growth, the possibility that gonadal hormones may have significant influences upon growth during infancy and childhood has prompted the present study. Materials and Methods Eleven male and 11 female Long-Evans rats were gonadectomized (gdx. groups) within 24 hr of birth, using ice as the anesthetic agent. A comparable number of male and female litter mates were sham-operated at the same time (sham-op, groups). Following the operative procedure, the litters were reduced to 8 rats and the animals were allowed to remain with their mothers until they were weaned at 20 days of age. After weanReceived April 16, 1964. This study was supported in part by Grants A-4356 and A-4770, National Institute of Arthritis and Metabolic Diseases, USPHS, and by the Simeon Burt Wolbach Research Funds, The Children's Hospital Medical Center, Boston, Massachusetts. 1 This investigation was carried out during the tenure of a fellowship from The Medical Foundation, Inc., of Boston, Massachusetts. Present address: Dept. of Pediatrics, Yale Univ. Sch. of Med., New Haven, Conn. ing, sham-operated controls were pair-fed to the gonadectomized animals, which were fed Purina Laboratory Chow ad lib. All animals were given tap water ad lib. and were maintained at a room temperature of 75 ± 2 F. Unanesthetized animals were measured from nose to tip of tail with head held stable and weighed on an automatic Mettler balance on the following days: 1, 7, 14, 21, 30, 60, 90,120,150 and 180. At the same times, total body roentgenograms were obtained using a nonscreen medical film with a 1 § second exposure at 32 kv and 10 mamp. The roentgenograms were then coded to avoid subjectivity and were evaluated using a modification of the method of Acheson et al. (Table 1) (5). On day 180, following roentgenograms and measurements, the animals were killed by exsanguination, autopsied, and their tissues were prepared for histological examination. The right tibia and humerus were removed, stripped clean of muscle, and total length was measured to the nearest mm. Results Growth (Fig. 1, 2) Males. Neonatal gonadectomy had no significant effect on either length or weight throughout the experiment. Females. The gdx. females were significantly longer than the sham-op, controls after 60 days of age. However, the increments of increase in length of the 2 groups did not differ significantly from period to period (the differences being established between 30 and 60 days). Subsequent to day 30, the gdx.