Effects of repeated stress on pituitary cyclic AMP, and plasma prolactin, corticosterone and growth hormone in male rats

Evidence for a role of endogenous corticotropin-releasing factor in cold, ether, immobilization, and traumatic stress

The role of corticotropin-releasing factor (CRF) in four model stresses (cold, ether, immobilization, and trauma) was examined in the guinea pig by using passive immunoneutralization with anti-CRF antiserum. Plasma corticotropin levels were measured at various times after exposure to stress, and groups treated with CRF antiserum were compared with those treated with normal rabbit serum. Of the four stresses tested, ether had the most pronounced effect on corticotropin secretion. Treatment with anti-CRF inhibited most of the ether-induced corticotropin secretory response, the difference between the normal serum- and the anti-CRF antiserum-treated groups being significant at 5 and 10 min (P less than 0.01). Corticotropin responses to cold stress in the two groups differed at the 0.05 level of significance at 10 and 20 min. After administration of trauma (leg fracture), a statistically significant difference (P less than 0.01) between the two groups also was evident, albeit only at 20 min. During immobilization, corticotropin levels differed significantly from control only in the normal serum-treated group but not in the anti-CRF-treated group. These findings show that CRF antiserum was effective in reducing corticotropin levels, indicating that CRF has an important role in mediating corticotropin response to stress. The fact that neutralization was incomplete might be due to an inability of the antiserum to sufficiently neutralize the endogenous CRF or, more likely, reflects the contribution of additional mediators, notably catecholamines and vasopressin, of corticotropin release upon stress.

Habituation of the prolactin response in rats to psychological stress

It is well known that stress is a stimulant for prolactin release. However, relatively few studies have investigated the role of psychological factors in prolactin secretion, and investigators have typically used one-time exposure and a single collection period in their studies. In our studies, attempts were made to carefully characterize the prolactin response to different psychological stressors by serially sampling blood from an indwelling cannula and to determine if repeated exposure to the stressor leads to habituation of the prolactin response. Exposure of the male rats to different novel situations such as being placed in a new cage, being placed on a platform in water, or being handled resulted in increased prolactin levels. As the rats habituated behaviorally to repeated exposure to similar situations, the prolactin response also attenuated. These findings show that psychological factors do play a role in influencing prolactin secretion and are consistent with the idea that as the psychological stress imposed by a stimulus becomes habituated, the prolactin response to that stimulus also becomes habituated.

Biochemical indices of reactivity and habituation in rats with hippocampal lesions

The response of rats with hippocampal lesions to acute and repeated footshock stress was assessed by measurement of pituitary cyclic AMP, plasma corticosterone and plasma prolactin. Levels of pituitary cyclic AMP and plasma prolactin and corticosterone were similar in never-shocked sham controls, and never-shocked hippocampal and neocortical lesion groups. Acute first time shock markedly elevated all measured stress indices with no statistically significant differences observed among surgical groups. In rats subjected to repeated stress (one 15 min footshock session per day for 10 days) and sacrificed 24 hours after the last shock session, levels of pituitary cyclic AMP and plasma hormones were similar to levels in never-shocked shams with the exception of the hippocampal animals. The rats with hippocampal lesions had higher levels of pituitary cyclic AMP, plasma corticosterone and plasma prolactin compared to never-shocked animals. We suggest that these data reflect a hyperreactive response of the hippocampal animals to a situation previously associated with shock. Finally, rats in all surgical groups subjected to repeated stress and sacrificed immediately after the last shock session showed a diminished cyclic AMP response to the stressor as compared to first footshock session response, demonstrating a habituation to the stressor as measured by this index. No differences in habituation were observed among hippocampal, neocortical and sham groups. Plasma hormone responses did not habituate in any group. These data support the behavioral observations of hyperreactivity in hippocampal animals and indicate that hippocampal animals are able to habituate to repeated stressful stimuli.

Factors related to the initiation and recurrence of uveitis. XL Edward Jackson memorial lecture

Uveitis comprises a complex group of diseases in which morbidity may depend on the nature of the initial inflammation as well as on the genetic, hormonal, and emotional background of the patient. Uveitis is initiated in every instance by some form of tissue injury. This may occur as an attack on individual cells by organisms such as Toxoplasma gondii or Herpesvirus hominis. Autoimmune disease may be produced as a late result of microbe-induced injury. The development of specific forms of autoimmunity seems to be dependent upon genetic as well as hormonal factors, particularly estrogens. Tissue injury of immunologic origin takes several forms, such as cytotoxic damage from sensitized lymphocytes, immune complex-mediated injury, and injury from the oxidative products of inflammatory cells. In some cases, permanent alteration of uveal vascular permeability results. Recurrent uveitis may be attributed in some instances to the reappearance of infectious organisms in the target tissue. In other cases, recurrence of inflammation may be attributed to the localization of immune complexes in the uveal tract. Changes in immunoregulation can be attributed to pregnancy, aging, and emotional factors. Neurohumoral pathways related to stress-mediated changes in immunoregulation have recently been described in laboratory animals. These pathways may be linked with stress-related recurrences of uveitis in humans.