SIALIC ACID CONCENTRATIONS IN THE PITUITARY GLANDS OF NORMAL AND CASTRATED RATS.

The concentration of sialic acid in the anterior pituitary of the young male rat does not change significantly with age during the period from 26 to 130 days after birth. Unlike the situation in the female rat, in which ovariectomy leads to a marked increase in sialic acid, castration at 30 days of age does not affect pituitary sialic acid concentration. These facts are related in a positive manner to the known changes in pituitary levels of the follicle-stimulating hormone (FSH) following ovariectomy or castration. {Endocrinology 76 : 994,1965) S acid is an important constituent of purified ovine and human follicle-stimulating hormone (FSH) (1) and is essential to the biological activity of this hormone (2). Although some sialic acid has been detected in purified preparations of ovine luteinizing hormone (LH), the quantities are so small that it seems unlikely that sialic acid is an integral part of the LH molecule. In addition, it has been reported that incubation of purified ovine, porcine or bovine LH preparations with the enzyme neuraminidase (sialidase) does not result in any appreciable loss of biological activity (3). We reported recently on the concentration of sialic acid in the anterior pituitary glands of female rats and found that a marked increase occurred following bilateral ovariectomy (4). It was suggested that this rise in pituitary sialic acid was probably related to the marked increase in production and storage of gonadotrophic hormones (FSH and LH) which occurs after gonadectomy in the rat. It has since been firmly established that, whereas a marked increase in pituitary FSH occurs in the female rat after ovariectomy, no such elevation of pituitary FSH takes place in the male rat after castration (5-8). Therefore, it was of interest to determine whether castration in the young male rat would have any effect on the concentration of pituitary sialic acid. Materials and Methods Male rats of the Sprague-Dawley strain were obtained from Josamar Laboratory Animals, Received November 30,1964. Supported by USPHS Grant GM 4723. Houston, Texas. Groups of 5 or 6 normal, intact animals were killed at intervals beginning at age 26 days and extending to age 130 days. Other animals were bilaterally castrated at age 30 days. These castrated animals were also killed in groups of 5 or 6 at several time periods up to 100 days after operation. All animals were killed by decapitation and the pituitary gland was quickly exposed by removing the brain. After separating and discarding the posterior lobes, the anterior lobes were weighed on a torsion balance and homogenized in glass tissue grinders. The sialic acid contained in these homogenates was determined by the thiobarbituric acid method of Warren (9). A reference standard of synthetic N-acetyl neuraminic acid was used and, for the tissue determinations, optical density readings were made at 532 and 549 m/*. In order to correct for interference by 2-deoxyribose, the correction equation recommended by Warren (ref. 9, equation 2) was used. All values are based on the assumption that the sialic acid was present in the form of N-acetyl neuraminic acid.