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[Lactation and sensitivity to corticotropicaxis to stress]
1. The plasma corticosterone levels were measured in nursing female rats which had been removed from their pups for 12 hrs, at 9 a. m. every day till weaning (day 22). The mean value found in this condition (14.6 +/- 2.7 mug/100 ml) does not differ significantly from that found for the cyclic female (13.7 +/- 4.2 mug/100 ml). 2. Suckling for a period of either 3 or 30 min increases the content of plasma corticosterone to the same value ; this value is maximal (+ 22.8 mug/100 ml) 30 min after suckling has started. 3. When mothers have been anaesthetized by a pentobarbital injection 40 min before suckling, plasma corticosterone increase, measured in the same conditions, is lower (+ 12.3 mug/100 ml). 4. The response to psychic (+ 25.5 mug/100 ml) or systemic (+ 46.6 mug/100 ml) stresses in mothers which have been removed from pups for 12 hr is impaired with respect to cyclic females (+ 62.7 mug/100 ml and + 83.8 mug/100 ml respectively). 5. Psychic stress applied immediately after suckling does not increase the plasma corticosterone level ; systemic stress does so slightly (+ 25 mug/100 ml). 6. In lactating rats the response to stress of the hypothalamo-pituitary-adrenal axis seems to be the same as that of intact or castrated males or ovariectomized females ; but differs from the response of cyclic females or of pregnant females when their basal corticosterone level is low.
1. The plasma corticosterone levels were measured in nursing female rats which had been removed from their pups for 12 hrs, at 9 a. m. every day till weaning (day 22). The mean value found in this condition (14.6 +/- 2.7 mug/100 ml) does not differ significantly from that found for the cyclic female (13.7 +/- 4.2 mug/100 ml). 2. Suckling for a period of either 3 or 30 min increases the content of plasma corticosterone to the same value ; this value is maximal (+ 22.8 mug/100 ml) 30 min after suckling has started. 3. When mothers have been anaesthetized by a pentobarbital injection 40 min before suckling, plasma corticosterone increase, measured in the same conditions, is lower (+ 12.3 mug/100 ml). 4. The response to psychic (+ 25.5 mug/100 ml) or systemic (+ 46.6 mug/100 ml) stresses in mothers which have been removed from pups for 12 hr is impaired with respect to cyclic females (+ 62.7 mug/100 ml and + 83.8 mug/100 ml respectively). 5. Psychic stress applied immediately after suckling does not increase the plasma corticosterone level ; systemic stress does so slightly (+ 25 mug/100 ml). 6. In lactating rats the response to stress of the hypothalamo-pituitary-adrenal axis seems to be the same as that of intact or castrated males or ovariectomized females ; but differs from the response of cyclic females or of pregnant females when their basal corticosterone level is low.