Effects of postnatal microwave exposure on thyrotropin level in the adult male rat.

Postnatal exposure of male rats to microwaves modulated the evolution of the thyrotropin level. Indeed, this treatment increased plasma TSH without affecting significantly plasma thyroxine. Moreover, the histological study of the thyroid demonstrated a high activity of this gland in irradiated animals. The modification observed in the thyrotropin level was correlated to an increase in hypothalamic noradrenaline described previously in rats submitted to the same irradiation.

Influence of postnatal exposition to microwaves on brain and hypothalamo-pituitary monoamines in the adult male rat.

Brain, hypothalamic and pituitary monoamines were measured in 90-day-old male rats after postnatal exposition to electromagnetic microwaves. The treatment decreased brain serotonin, increased brain 5-hydroxyindoleacetic acid and hypothalamo-pituitary catecholamines. The modifications observed in the levels of the monoamines were correlated with the variation of the gonadotrophin secretion described in a previous work. The mechanism by which microwaves could modify brain and hypothalamo-pituitary monoamines is discussed.

[Corticohypophysiotropic and corticotropic activity in adrenalectomized male and female rats after psychic stress]. / Activités corticohypophysiotrope et corticotrope chez le rat après une agression pyschique: effects du sexe et de la surrénalectomie.

We show modifications in the hypothalamic CRF activity and plasma ACTH concentration in adult rats of both sexes, which were five day sham-operated or adrenalectomized and killed either under basal conditions or after a 3 min period or psychological stress. 1. Under basal conditions, the inhibition of the basal release of ACTH is suppressed in 5 day adrenalectomized rats and a sex difference appears: plasma ACTH concentration is twice as great in females than in males. 2. After a 3 min period of psychological stress, the usual increase in hypothalamic CRF activity observed in sham-operated rats, which seems to be sex-related, does not appear in adrenalectomized male or female rats. However, in adrenalectomized rats, the maximal increase in plasma ACTH concentration occurred more rapidly, with a rate 10 times as great in males and 4 times as great in females, than in sham-operated rats. Differences between the sexes in the maximal increase in plasma ACTH concentration remains 1,6 times as great in females than in males. 3. Our results confirm that corticosteroids exert: (1) a tonic feedback inhibition of the basal release of ACTH, (2) a fast feedback inhibition of the stress induced release of ACTH; the promote an increase in the hypothalamic CRF content. Relative intensity of these two inhibitory mechanisms seems to be sex-related.

[Activation of the pituitary-adrenal axis by nipple suction in the lactating rat]. / Activation de l'axe corticotrope par la succion mamelonnaire chez la ratte en lactation.

The response of the pituitary-adrenal axis to suckling in lactating Rats is dependent on two factors: 1. a psychic factor, which is identical by its effects to the psychological stress of the strange environment (transitory increase of plasma corticosterone and no significant modification of the content of ACTH in the two lobes of the pituitary); 2. a specific factor namely the stimulation of the nipples, which is distinguishable from the psychic factor by a longer release of corticosterone by the adrenals and a durable and significant decrease of the content of ACTH in the pars distalis.

[Evolution of plasma corticosterone concentration in basal conditions or after psychic aggression during growth in the Rat. Influence of neonatal gonadectomy (author's transl)]. / Evolution de la concentration de la corticostérone plasmatique dans les conditions basales ou après agression psychique au cours de la croissance chez le rat. Influence de la gonadectomie néonatale.

Evolution, during growth, of basal plasma concentration of corticosterone and the adrenocortical response to psychic aggression was studied in animals of both sexes, normal or gonadectomized on the day of birth. 1. In the control animals : (a) The fluctuations of the basal plasma concentration of corticosterone took a similar course in the male and female; no significant difference was observed between males and females except on the 55th day. (b) The intensity of the response to aggression took the same course in all the test animals between the 15th and 60th day with an increase between the 15th and 45th day and a decrease between the 45th and 60th day. 2. In the animals whose gonads were removed at birth, the basal plasma concentration of corticosterone and the response to psychic aggression developed in a similar manner in the two sexes, during the period studied. 3. These results suggest the existence of an autonomous maturation of the adrenocortical function which is independent of genetic sex and gonadal secretions. These latter, however, play a determinant role in the amplitude of the response which is increased by estrogens and decreased by androgens. The existence of a mechanism whose maturation is accomplished, in part, independently of the gonadal secretions and is responsible for the response to aggression is discussed.

[Effect of estrus cycle, ovariectomy and lactation on variations of basal corticosterone levels or agression stress levels in rats]. / Influence du cycle estrien, de l'ovariectomie et de la lactation sur les variations de la corticostéronémie basale ou après agression chez la ratte.

In the Rat, the estrous cycle induces a rhythm of plasmatic corticosterone level : the fluctuations of basal or stress corticosteronemy are significantly superior during the periods of high estradiol secretion, proestrus and estrus, that during metaestrus and diestrus. Ovariectomy, performed at 60 days of age, is without effect on resting corticosteronemy, but reduces significantly the response to stress. Weaning unaffects the basal level of plasmatic corticosterone which remains comparable to diestrus level ; however, stress response decreased during lactation returns to normal level at the end of the first ovarian cycle (diestrus).

[Induction in the newborn and maintenance in adulthood of a "male-type" growth or "female-type" growth depends on the nature of gonadic secretion (author's transl)]. / Induction chez le nouveau-né et entretien chez l'adulte d'un type de croissance mâle ou femelle, selon la nature des hormones sécrétées par les gonades chez le rat

The influence on the growth of the presence of testosterone or estradiol at some stage of development was investigated from birth to adult age (90 days). 1. The presence of the androgenic molecule in the newborn organism, regardless of genetic sex (intact males, males orchidectomized at 9 days and neonatally injected orchidectomized males; neonatally injected intact and ovariectomized females), starts up a growth acceleration six weeks later. 2. The presence of the estrogenic molecule during this same period (neonatally injected intact and ovariectomized females; neonatally injected orchidectomized males) decreases the growth rate when animals come into puberty. 3. The development of the adult is immediately accelerated by androgen (excitatory effect) or reduced by estrogen (inhibitory effect). On the contrary, the effects of sex hormones present in the early postnatal period appear much later (inductive effect). Therefore, the activity patterns of sex hormones change with age: in the adult, androgen increases anabolism and estrogen decreases food intake; in the newborn, an undifferenciated mechanism responsible for growth is organized into "a male type" by androgen or "female type" by estrogen. The nature of this mechanism is discussed.

[Lactation and sensitivity to corticotropicaxis to stress]. / Lactation et sensibilité de l'axe corticotrope aux agressions

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.

[The role of the gonads in the maturation of corticotropic function in rats]. / Rôle des gonades dans la maturation de la fonction corticotrope chez le rat

The rates of pituitary and adrenals growth, in male and female Rats, are reversed at puberty. It seems that the stress induced plasma corticosterone increase is inhibited by testis before puberty and stimulated by ovarian after puberty.