The effects of handling, ether vapor anesthesia and blood sampling on serum LH and prolactin were determined in intact, castrate and dexamethasone-treated male rats. Cage removal and transport to an adjacent room increased LH and prolactin levels by 10 and 15 min after the initial animal disturbance. Intact male rats subjected to repeated ether anesthesia and blood sampling showed a more rapid increase in serum LH and prolactin than the preceding rats, since serum LH and prolactin was increased by 4, 8 and 15 min after initial cage disturbance. In a group of rats subjected to serial blood sampling over a longer time interval, both prolactin and LH levels remained higher than 90 min after initial animal handling. At 90 minutes after a single blood sampling, blood prolactin concentration remained higher than in controls. Serum LH levels returned to control levels 90 min after the stress of a single blood sampling. Although serum prolactin was increased in the castrate group subjected to serial anesthesia and blood sampling, LH concentrations were reduced under the same conditions. Injection of 5 and 50 mug of dexamethasone/100 g body wt for 8 days markedly reduced adrenocortical responsiveness to the stress of serial anesthesia and blood sampling at 1, 4, 8 and 15 min after initial rat disturbance. The 50 mug dexamethasone treatment reduced the stress-stimulated increase in serum prolactin at all blood sampling intervals. The dexamethasone-treated groups also showed smaller increases in serum LH at 8 and 15 min after first animal handling than the control rats. These results indicate that serum LH and prolactin concentrations are consistently increased by acute stress in intact male rats, the duration of the stress stimulation of LH and prolactin is at least 90 min under the conditions of this study, serum LH levels of castrate male rats are decreased by acute stress and dexamethasone administration lowers stress stimulation of LH and prolactin release.

Changes in serum LH and prolactin concentrations in response to bilateral gonadectomy and gonadal steroid replacement were measured in mature young (4-6 months) and old (23-30 months) female and male Long-Evans rats. On day 13 after gonadectomy, female rats were injected with oestradiol benzoate (OB) and male rats with testosterone propionate (TP) for a period of 12 days. They were then permitted a recovery period of 6 weeks. Serum prolactin and LH concentrations were measured by radioimmunassay in single blood samples taken at various intervals before and after gonadectomy and during and after steroid treatment. Serum LH levels were about the same in intact young old female rats, but after ovariectomy LH rose several fold higher in young than in old remale rats. In male rats, after orchidetomy the increase in serum LH was greater in young than in old rats. Oestradiol benzoate and TP injections into female and male young and old rats produced variable effects on LH release. Serum prolactin concentrations were approximately six times higher in old intact than in young intact female rats, and after ovariectomy showed a much greater percentage reduction in old than in young female rats. Administration OB produced a greater absolute increase in serum prolactin in old than in young female rats. Serum prolactin values were about the same in old and young male rats, and the effects of castration and TP administration on serum prolactin were not markedly different in the two age groups. These results indicate that old female and male rats are less capable of releasing LH than young rats of both sexes, but old females release more prolactin than young females.

Although stress or injections of ACTH or adrenal glucocorticoids have been associated with impaired reproductive performance in many species, the mechanisms by which these treatments affect reproduction remains obscure. Previous studies have indicated that stress may influence several stages of the normal reproductive process. Rowell (1970) reported increased follicular phase length and longer menstrual cycles following stress in baboons, and Hagino, Watanabe & Goldzieher (1969) found that stress, ACTH or glucocorticoids could block PMSG-induced ovulation in rats. Adrenocortical activation in the

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