Biomedical subjects

O A Brown

Publications and source records attributed to O A Brown.

20 records · Page 2Linked to original sources

PubMedDate not supplied

Hormonal modulation of antioxidant enzyme activities in young and old rats.

The correlation between serum levels of pituitary and thyroid hormones and the activity of two antioxidant enzymes (AOE), catalase (CAT) and superoxide dismutase (SOD), in different immune and nonimmune organs of young and old rats was investigated. Serum levels of growth hormone (GH), prolactin (Prl), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroxine (T4), and triiodothyronine (T3) as well as the activity of AOE in liver (CAT and SOD), spleen (CAT and SOD), thymus (SOD) and mammary tissue (SOD) were determined in 7- and 29-month-old Sprague-Dawley female rats. A marked hyperprolactinemia and lower levels of TSH, LH, FSH and GH were observed in the old rats when compared to the young ones (p < 0.05). Old animals showed a higher SOD activity in liver and thymus but a lower activity in spleen than their young counterparts (p < 0.05). In addition, CAT activity in spleen was lower in old than in young rats (p < 0.05). The Spearman's test revealed a positive correlation between: 1) serum levels of TSH and the activity of SOD in liver and 2) serum levels of Prl and GH and the activity of SOD in mammary tissue of young and old animals (p < 0.05). Likewise, CAT in liver showed a highly significant correlation with serum TSH (but not T4 and T3) levels in young (p < 0.01) but not in old rats. Our results confirm that aging is associated with alterations in the endocrine balance and the activity of AOE in lymphoid as well as in nonimmune organs. In addition, our findings suggest that Prl and GH may be physiological modulators of mammary SOD activity, and that TSH can possibly influence the activity of both CAT and SOD in liver via a thyroid-independent pathway. Furthermore, our data show that, when significant, the correlation between hormone levels and AOE activity deteriorates with age.

Aging↗

PubMedDate not supplied

The thymus-pituitary axis and its changes during aging.

The pituitary-thymic axis constitutes a bidirectional circuit where the ascending feedback loop is effected by thymic factors of epithelial origin. The aim of the present article is to review the evidence demonstrating that aging brings about a progressive disruption in the integration of this network. In doing so, we briefly review the experimental evidence supporting the view that immune and neuroendocrine aging are interdependent processes. The advantages and limits of the nude mouse as a model of thymus-dependent accelerated aging is also discussed. Next, we review a number of studies which show that the endocrine thymus produces several bioactive molecules, generally called thymic hormones, which in addition to possessing immunoregulatory properties are also active on nervous and endocrine circuits. In particular, the reported activities of thymosin fraction 5 (TF5), thymosin alpha-1 and thymosin beta-4 on beta-endorphin, ACTH, glucocorticoids, LHRH and LH secretion in different animal and cell models are reviewed. The known hypophysiotropic actions of other thymic hormones like thymulin, homeostatic thymus hormone (HTH) and thymus factor are summarized. Aging has a significant impact on pituitary responsiveness to thymic hormones. Thus, it has been reported that TF5 and HTH have thyrotropin-inhibiting activity in young but not in old rats. Furthermore, intravenous administration of HTH was also able to reduce plasma GH and increase corticosterone levels in both young and old rats, although these responses were much weaker in the old animals. Further evidence on this topic is discussed. It is proposed that in addition to its central role in the regulation of the immune function, the thymus gland may extend its influence to nonimmunologic components of the body, including the neuroendocrine system. The early onset of thymus involution might therefore act as a triggering event which would initiate the gradual decline in homeostatic potential that characterizes the aging process.

Aging↗