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Biomedical subjects

C Aron

Publications and source records attributed to C Aron.

At least 91 records · Page 5Linked to original sources
PubMed1980

A hormonal and temporal analysis of the mechanisms involved in the control of ovulation induced by hemiovariectomy in the rat.

The present study was undertaken to investigate the mechanisms of the stress-related ovulatory effects of hemicastration in the rat. Previous work (Roos et al., 1976) had shown that ovulation induced by unilateral ovariectomy (ULO) was suppressed in adrenalectomized females when ULO was performed on dioestrus III at 10--11 h in 5-day cyclic rats. Using the same experimental schema an increase in blood progesterone within 1 to 4 hours after ULO has been found to be present in adrenal intact females and suppressed in adrenalectomized rats. PB treatment (30 mg/kg, i.p.) concomitant with ULO at 10--11 h on dioestrus III significantly decreased the number of ovulating females without preventing blood progesterone concentration to increase at 12--13 h. A partial blockade of ovulation resulted from PB injection at 13 or 18 h. The ovulatory effects of ULO observed in females injected with PB at 23 h on dioestrus III or at 5 h on prooestrus were identical to those observed in hemiovariectomized non PB treated females. Only a small proportion of hemiovariectomized females displayed an LH release at 15--16 h and 17.30 h--18.30 h on dioestrus III. In contrast a significant FSH release was observed in this interval of time following ULO. Microscopic examination of the ovaries on prooestrus at either 11 h or 16 h revealed the presence of corpora lutea with morphological features corresponding to very different stages of development. We can conclude that progesterone of adrenal origin constituted the trigger of ovulation and caused LH-release during a time period extending from 13 h to 23 h on dioestrus III following ULO in the rat.

Adrenalectomy↗
PubMed1979

[Mechanisms of ovulation in mammalian females].

The aim of this review was to briefly recapitulate the most important mechanisms involved in ovulation in the Mammals. The rabbit served as a model for the study of reflex ovulation. The triggering of ovulation by coitus was shown to be dependent on the activation of the hypothalamo-pituitary axis by sensory signals of multiple origin. The fundamental aspects of the hormonal and nervous machinery that governs spontaneous ovulation have been envisaged. The timing of LH ovulatory release and the mechanisms of action of this hormone at the ovarian level have been defined. Evidence was given that steroid hormones from ovarian and/or adrenal origin could evoke or modulate ovulatory processes. The structures responsible for both the tonic and clonic secretion of LH in subprimate and in primate mammals have been localized in the hypothalamus. The nervous endocrine mechanisms involving interactions between LHRH, neurotransmitters, prostaglandins and steroid hormones have been elucidated. Short loop feed back effects of pituitary hormones were shown to control LHRH secretion. Several examples were given attesting that the limbic system, the thalamus and the neocortex on one hand, and the environmental factors, on the other hand, were capable of modulating the activity of the hypothalamic structures implicated in the control of either ovulation or estrous rhythm regulation. An unitarian conception of the ovulatory mechanisms, based on the fact that coital-induced ovulation and estrogen-induced ovulation could occur in spontaneous and reflex ovulators respectively, has been proposed.

Adrenal Cortex↗
PubMed1978

Action of testosterone propionate on the gonadotrophic function of the pituitary gland in the cyclic female rat.

Four-day cyclic female rats were injected with 5 mg testosterone propionate (TP) at dioestrus II at 10.00. A blockade of ovulation was observed on the morning of oestrus in most of these animals. No LH surge occurred in the afternoon of pro-oestrus. By contrast the size of follicles exceeding 400 micrometer in diameter did not differ in the afternoon of pro-oestrus in TP-treated and control females. Moreover both the number of follicles and the blood FSH concentration appeared to be higher at 14.00 on pro-oestrus in TP-treated than in control females. The effects of TP in vivo are thus in agreement with the observations which showed that TP caused a blockade of LH release and the maintenance of FSH release in vitro.

Animals↗
PubMed1978

The adrenal cortex and the luteotrophic action of estrogens during the estrous cycle in the rat.

The aim of this study was to evaluate the effects of estradiol benzoate (EB) on ovarian progesterone secretion in the presence or in the absence of the adrenals. 4-day cyclic female rats were injected with 10 microgram EB on the morning of diestrus I. An increase in the rate of ovarian progesterone secretion in diestrus II at either 10--11 a.m. or at 2 : 30--3 : 30 p.m. was only observed in one of two experimental series. A very significant increase in the peripheral blood progesterone concentration was noted in adrenalectomized EB-treated females as compared to EB-injected intact females, thus suggesting that the adrenals might inhibit the luteotrophic action exerted by EB on the ovary. Experiments in dexamethasone (DEX)-EB-treated females confirmed this view. Peripheral blood progesterone concentration was significantly greater in DEX-EB-treated females than in EB-treated females. The possible mechanisms were discussed in the light of experiments involving the administration of metyrapone (MET) prior to EB injection. While blood progesterone concentration increased following MET-treatment only, no cumulative effects resulted from combined MET and EB-treatment. Progesterone of adrenal origin was then supposed to be implicated in the inhibitory action of the adrenal cortex on the luteotrophic action of EB in cyclic female rats.

Adrenalectomy↗
PubMed1977

New data concerning the control by the adrenals of sexual receptivity in the rat.

The proportion of receptive females during the night from proestrus to estrus (mating frequency) was estimated in 4-day cyclic rats ovariectomized at different times of the day of proestrus. A sharp decrease in mating frequency occurred in females ovariectomized at 15:00-16:00 as compared with intact animals. A slighter, although significant decrease in mating frequency, was observed in females ovariectomized at 8:00-9:00 and 13:00-14:00. Sexual receptivity was only partially recovered following ovariectomy at 17:30-18:30. Chronic adrenalectomy completely prevented estrous receptivity in females ovariectomized at any time of proestrus as compared to adrenalectomized nonovariectomized females which displayed a normal estrous receptivity during the night from proestrus to estrus. A higher blood progesterone level was observed in receptive rats between 15:00 and 16:00 than in nonreceptive ones. The temporal relationships between the ovary and the adrenals in the control of estrous receptivity were discussed in the light of these observations.

Adrenal Glands↗
PubMed1977

The role of follicle-stimulating hormone (FSH), in combination with luteinizing hormone (LH), in oestrogen-induced ovulation during the oestrous cycle in the rat.

Studies were undertaken to determine the role played by FSH in oestrogen-induced ovulation in 4-day cyclic female rats. About one half of the experimental animals receiving 10 microng oestradiol benzoate (OeB) subcutaneously, on the morning of dioestrus I, displayed luteinization or/and ovulation, when sacrificed on the morning of expected pro-oestrus. Pento-barbitone administered on dioestrus II at 18.00 did not prevent this action of OeB. A simultaneous LH and FSH surge was observed in the serum of half of the OeB-treated females killed by decapitation of dioestrus II at 17.30. The LH surge was decreased in OeB-treated females bled by cardiac puncture under pentobarbitone anaesthesia at dioestrus II at 17.30. This bleeding procedure almost completely suppressed the luteinizing effects of OeB. It was concluded that i) OeB caused a synergistic release of LH and FSH ii) bleeding by cardiac puncture as such may constitute a source of inhibition of OeB-induced luteinization.

Animals↗
PubMed1977

[New data on luteotropic mechanism of action of estrogens during the rat estrus cycle].

An increase in peripheral blood progesterone concentration was observed in diestrus II, at 17:30 in 4-day cyclic female rats subcutaneously injected with 10 microgram estradiol benzoate (EB) at 10:00-11:00 on diestrus I. Pentobarbital injection (30 mg/kg) at 13:30 on diestrus II did not prevent this effect on EB. By contrast PB injected at 13:30 on diestrus II as above completely suppressed the luteinizing or ovulating effects of EB. The action of estrogen on blood progesterone level was therefore concluded to be unrelated to the mechanisms underlying estrogen-induced ovulation luteinization in the cyclic female rat.

Animals↗
PubMed1976

[New data on olfactory control of estral receptivity of female rats].

Olfactory bulb deprivation increased sexual receptivity in 4-day cyclic female rats on the late afternoon of prooestrus (6-7, p.m.). The proportion of receptive females was higher in bulbectomized (B) than in sham operated (SH) animals. On the contrary the same proportion of B and SH females mated in the evening of prooestrus (10. 30-11. 30 p.m.). An increased lordosis quotient was observed in the B females at either of these two stages of the cycle.

Animals↗
PubMed1976

Progesterone action on estrous rhythm in the rat following ventromedial nucleus lesions.

Small bilateral lesions of the hypothalamic ventromedial nucleus (SVMN) were produced in 4 day cyclic female Wistar rats by passing a 2 mA cathodic current through stereotaxically oriented platinum unipolar electrodes for 7 sec. The 24 h lengthening of cycle which occurred in 111 our ot 208 females was shown to depend upon lesion placement. Early s.c. injection of 0.75 or 1.5 mg progesterone caused 24 h cycle prolongation more frequently in SVMN-lesioned females with maintained 4 day cycles than in 4 day cyclic unoperated, sham VMN-lesioned, or dorsomedial nucleus (DMN) lesioned females. This effect proved to be related to lesion placement. It was therefore concluded that the VMN is involved in the mechanisms whereby progesterone controls estrous cycle duration in the rat.

Animals↗
PubMed1976

Hormonal mechanisms involved in the control of oestrous cycle duration by the odour of urine in the rat.

The mechanisms involved in the reduced cycle duration following exposure to the odour of urine were studied in natural and experimental 5-day cyclic female Wistar rats. A decrease in the rate of ovarian progesterone secretion from the morning of dioestrus I to that of dioestrus II was observed in females whose cycle duration was reduced from 5 to 4 days following exposure to the odour of rat urine. No decrease in ovarian progesterone secretion occurred in females maintaining a 5-day cyclicity despite exposure to this odour. An increase in follicular growth was noted in females with cycle duration reduced from 5 to 4 days, when compared with those maintaining a 5-day rhythm. As a result of exposure to the odour of urine no reduced cycle duration occurred in females with cycles lengthened from 4 to 5 days as a result of progesterone injection on dioestrus I of 4-day cycles. Hence the decrease in ovarian progesterone secretion, induced by exposure to the odour of urine, is considered to cause a speeding up in follicular growth, thereby reducing oestrous cycle duration in 5-day cyclic rats.

Animals↗
PubMed1976

[Demonstration of a critical period of ovarian activity in the control of early receptivity induced by estrogen in the female rat with 4-day cycles].

A significant decrease in early receptivity during the night from dioestrus II to prooestrus was observed in estrogen-treated 4-day cyclic rats following bilateral ovariectomy on dioestrus II at 4-5 p.m. Early receptivity appeared then to be dependent on the presence of ovary at this stage of the cycle. The mechanism whereby the adrenals may compensate for the ovaries when removed on dioestrus I, at 10-11 a. m. (Roos et al. 1973), was not observed in the present experimental conditions.

Adrenal Cortex↗