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Biomedical subjects

J Boissin

Publications and source records attributed to J Boissin.

At least 37 records · Page 2Linked to original sources
PubMed1987

Annual cycles in plasma testosterone and thyroxine in the male aspic viper Vipera aspis L., (Reptilia, Viperidae), in relation to the sexual cycle and hibernation.

Blood samples were taken monthly from males of Vipera aspis kept in outdoor terraria. Plasma testosterone was estimated by radioimmunoassay and plasma thyroxine by the technique of isotopic competition, between October 1979 and September 1985. Plasma testosterone showed an annual bimodal profile. The highest peak was observed from February 15 to the end of March. 2 to 5 weeks after the first emergence from hibernation. Values then decreased greatly, to reach a minimum level when the vernal spermiogenesis was at its maximum. The secondary peak of plasma testosterone was lower and less well marked. It occurred at the end of summer, during the strongest spermiogenesis, and preceded the autumnal facultative mating period. Plasma thyroxine was at a maximum concentration from February to March after which levels decreased markedly. The seasonal profile of plasma thyroxine was clearly marked during the period of hibernation. From September to October, 2 months before the beginning of hibernation, thyroxine levels began to decrease, and they reached a minimum in November-December. Endocrine reactivation of the thyroid appeared at the end of hibernation. However, in contrast to the plasma testosterone, endocrine activity of the thyroid began 2 to 3 weeks before the end of hibernation. Mechanisms of reactivation for testicular and thyroidal endocrine structures are discussed.

Animals↗
PubMed1987

Thyroid and gonadal regulation of hair growth during the seasonal molt in the male European badger, Meles meles L.

In the male badger we showed that hair growth and molt are related to plasma testosterone and thyroxine cycles. We established the action of testosterone by castration and subcutaneous testosterone implants, and the action of thyroxine by thyroidectomy and dietary supplementation with thyroxine. The following groups of animals were studied: controls, thyroidectomized, thyroidectomized and thyroxine-treated, castrated, castrated and thyroxine-treated, thyroidectomized and castrated and thyroxine-treated, castrated and testosterone-implanted, and intact testosterone-implanted. In control animals, molt and hair growth occurred during the summer, with a maximum growth in autumn. Molt ended at the beginning of winter when the plasma testosterone level had started to rise, and began again after this level had started to decline. Both the start of molt and the period of maximum hair growth coincided with high thyroxine levels of about 20 ng/ml. Castration advanced molt and hair follicle activity, whereas testosterone implants delayed both molt and hair growth. In thyroidectomized badgers, neither hair growth nor seasonal molt was observed. However, when thyroxine levels were restored to 20 ng/ml or more by dietary T4 supplementation, molting was resumed in animals that had undergone either thyroidectomy or thyroidectomy plus castration. In those that underwent castration only, the molt was advanced leading to early hair growth further stimulated by the suppression of testosterone. Testosterone had an inhibitory effect on the molt--since testosterone implants in intact control animals delayed it by 4 weeks--but did not inhibit it completely. On the other hand, a T4-enriched diet advanced the date of the molt. However, the molt could not be induced, nor could hair follicle growth be reactivated, at all times during the annual cycle. Thus, in castrated animals. T4 enrichment of the diet in early January, at the end of the molt, caused follicle reactivation only toward the end of May, despite the lack of testosterone. This 18-week latency period from January to May might therefore constitute a "refractory period" in this species. The above findings show that the regulation of the seasonal molt and hair growth in the European badger involves both the thyroid and genital axes. This regulation is discussed in terms of joint control by the hypothalamus and pituitary governed, in turn, by an external factor--the photoperiod--considered to be the main synchronizer.

Animals↗
PubMed1986

Circadian participation in the photoregulation of testis activity and prolactin secretion in the mink, a short-day breeder.

It has been demonstrated that an endogenous mechanism is involved in photoperiodic time measurement in the mink, a short-day-breeding mannal. A study of testicular activity (testicular volume, plasma testosterone concentration) and plasma prolactin level was carried out in sexually resting minks (the experiment began in November). Groups of minks were kept in the natural photoperiod or subjected to different resonance light-dark (LD) cycles (LD 4:8, LD 4:20, LD 4:32, LD 4:44); an additional group of animals was reared in an ahemeral photoperiod (LD 4:16). A rapid increase of testicular activity was observed in control animals or those kept in LD 4:20 (T 24) and LD 4:44 (T 48). In the other groups of animals, those kept in LD 4:8 (T 12), LD 4:32 (T 36), and LD 4:16 (T 20), testicular function remained at rest. Prolactin secretion was, in contrast, stimulated in the groups kept in LD 4:8 (T 12). LD 4:32 (T 36), and LD 4:16 (T 20), and remained low in the groups kept in LD 4:20 (T 24) and LD 4:44 (T 48). These results show that the effects of the different photoperiodic regimens do not depend on the duration of the photophase, but rather on the period of the LD cycles. The LD cycles that allow an increase of testicular function are those that are inhibitory to reproduction in birds and long-day-breeding mammals. To explain these results, it is suggested that in the mink exposure to light during the circadian photosensitive phase induces inhibition of testicular activity and stimulation of prolactin secretion. To explain the opposite effects of a single photoperiod on testicular function and secretion of prolactin, the hypothesis has been advanced that, in the mink, long days might simultaneously inhibit hypothalamic luteinizing-hormone-releasing hormone (LH-RH) activity and prolactin-inhibiting factor (PIF) activity.

Animals↗
PubMed1986

[Effect of thyroidectomy on variations during the spring and summer of the testicular activity and blood prolactin in the mink].

The possible role of thyroid hormones in the setting of sexual quiescence was investigated in the mink, since levels of thyroid hormones were earlier shown to rise while testicular activity decreased. When performed at the beginning of the sexual period, thyroidectomy transiently stimulated testosterone production, and significantly prolonged the duration of maximal testicular development. These results indicate that mink conforms to a pattern of inhibitory thyroid-testis interactions similar to that previously described in several species of birds and mammals. Thyroidectomy was unable, however, to prevent ultimately the installation of sexual quiescence which also appears independent of the photoperiod. On the other hand, thyroidectomy did not modify, from February to October, the general pattern of prolactin secretion, even though the vernal stimulation of prolactin secretion, induced by increasing daylength, was significantly enhanced in the absence of thyroid hormones.

Animals↗
PubMed1985

Incidence of a circadian cycle of photosensitivity in the regulation of the annual testis cycle in the mink: a short-day mammal.

Like the birds or long-day mammals studied up until now the photoregulation of the annual testicular cycle in the mink, a short-day mammal, depends on phase relationships existing between the daily cycle of alternating period of light-dark and the circadian cycle of photosensitivity. Our results show, however, that the characteristics of photoresponse in the mink are exactly the opposite of those of long-day animal species. For long-day species light has a stimulating effect on the central machinery of gonadotropic control (LH-RH) whereas in the mink, the secretion of gonadotropins is induced by short days. Interpreted according to this hypothesis, the sexual cycle of the mink under natural photoperiodic conditions is also explained by seasonal gonadotropic stimulation beginning after the autumn equinox when in our latitudes daily light duration is less than 12 hr. However, the end of the reproduction period which, in nature, seems to be the result of the inhibition of the gonadotropic function by long days could, in fact, be the result of a more complex mechanism. Different inhibiting mechanisms already shown in long-day animals could also be involved during this phase of the sexual cycle in the mink.

Animals↗
PubMed1985

[Testicular activity of the ferret kept for over 4 years under permanent light and constant temperature].

Five male ferrets, aged 2 months, were kept in constant light (4-5 lx) and temperature (15 +/- 1 degree C) from July 1979 to September 1983. Under these experimental conditions, the testicular size displayed spontaneous variations. Four cycles, characterized by a marked testicular enlargement followed by an equivalent decrease, were observed in three ferrets. The two others exhibited only three spontaneous cycles. The mean interval between two successive maximums equalled 340 +/- 28 days.

Animals↗
PubMed1984

Seasonal reproductive endocrine profiles in two wild mammals: the red fox (Vulpes vulpes L.) and the European badger (Meles meles L.) considered as short-day mammals.

The annual cycle of the testicular function (testis and epididymis weights and plasma testosterone levels) were considered in relation to seasonal variations in plasma LH and prolactin concentrations in two wild European mammals: the badger and the fox. Phase relationships were established between the annual prolactin cycles and daylight duration. The influence of castration on the seasonal variations in plasma LH levels was also studied. The resumption of activity in the testicular function occurs during autumn for both species. The reproduction period begins in winter but it is over by the beginning of spring for the fox whereas for the badger it lasts until early summer. In the same way, the annual cycle of the gonadotrophic function which, in the fox, presents only one maximum at the end of autumn, is bimodal in the badger with one maximum in January and a second in June. On the other hand, both species have a similar annual prolactin cycle, which shows an increase from the winter solstice onwards, in synchronization with the increase in daily light duration. The highest prolactin levels are measured in spring followed by a decrease during summer. This result calls into question the role played by prolactin in the regulation of the testicular function in as far as the two species have an annual reproductive cycle of the 'short-day' type (onset of activity occurring before the winter solstice) but show seasonal prolactin variations similar to those described for 'long-day' species.

Animals↗
PubMed1983

[Variations in the plasma concentration of prolactin, LH and FSH and in testicular activity during the first year of life in the roe deer (Capreolus capreolus L.)].

Plasma prolactin, LH, FSH, testosterone patterns, and spermatogenic activity were determined during the first year of life in roe deer. A high gonadotrophic activity was observed a few months after birth, in autumn, along with an increase of testis volume and spermatogenic activity. Some spermatozoa could be seen in seminiferous tubules in December. A second increase of pituitary gonadotrophic activity appears in early spring when testicular volumes comparable to the adult are achieved. The first period of gonadotrophic activity coincides with the autumnal decrease in photoperiod, whereas the second coincides with the progressive increase in day length. It is suggested that the precocious LH and FSH release induces the first pubertal testicular activity.

Animals↗
PubMed1983

[Role of blood thyroxine levels in the regulation of the annual cycle of body weight in the adult male badger (Meles meles L.)].

Male Badgers were shown to display an annual body weight (BW) cycle characterized by an autumnal phase of fattening, coinciding with depressed plasma levels of thyroxine, and a phase of emaciation starting in late winter and leading to a minimal BW in summer, when plasma thyroxine concentrations were peaking. Surgical thyroidectomy in the fall did not suppress the BW cycle, but the onsets of fattening and of emaciation were advanced, respectively by 1 and 2 months. On the other hand thyroxine supplementation in late winter through spring, enhanced the seasonal BW loss. The possible interaction of thyroid hormones with other lipolytic factors in the control of the BW cycle is discussed.

Animals↗
PubMed1983

[Circadian photosensitivity and photoperiodic control of the annual cycle of blood prolactin in the mink].

An annual cycle in plasma prolactin was evidenced in male Minks with a minimum in fall and a maximum in June. In two series of night interruption experiments, it was found that the photoperiodic control of the prolactin cycle involved a circadian rhythm in sensitivity to light whose photosensitive phase culminated 16 hrs. after dawn. The same photosensitivity rhythm also induced the annual testis cycle, although, in the latter case "long days" had an inhibitory effect instead of the stimulatory control for prolactin.

Animals↗
PubMed1982

Circadian photosensitive phase and photoperiodic control of testis activity in the mink (Mustela vison Peale and Beauvois), a short-day mammal.

Evidence of a circadian photosensitive phase in male mink, whose annual reproductive cycle is characterized by the recrudescence of testicular development in autumn, was based on the study of testicular response after interrupting the dark period by light breaks (0.5 h) offered at various times. In this mammal, the experimental short days 4L:20D and 8L:16D stimulated testicular growth. Short photoperiods, including a main light period of 3.5 h and an additional 0.5 h light break 7.5 h after the beginning of the main photoperiod, were as effective as 8L:16D in stimulating testicular development. On the other hand, when a 0.5 h light break occurred 11.5 or 15.5 h after the beginning of the main photoperiod, the same inhibiting effect on testicular activity was obtained as for long photoperiods. However, when 0.5 h light breaks were given 19.5 after the beginning of the main light period, some minks recognized, as "dawn", the onset of the shorter of the two light periods offered. Thus our results proved the existence of a special phase in the day cycle in which light inhibited testicular development in the mink which appears to be a short-day animal. One explanation of the difference between long-day and short-day animals would be the following: if for long-day animals exposure to light during the photosensitive phase led to gonadostimulation, in short-day mammals, like mink, it exerted an inhibiting influence on testicular growth.

Animals↗
PubMed1982

[Season variations in lipolysis activity of adipocytes from fox, badger and hedgehog].

1. We have studied the seasonal variations of the lipolytic response to a beta agonist, isoproterenol, and to theophylline of the isolated adipocyte from fox, badger and hedgehog, related to the circannual variations of testes and thyroid activities. 2. With the fox, we find a coincidence, in spring, between the maximum lipolytic sensitivity of the adipocyte, the thyroid function and the return to sexual rest. 3. With the badger, in winter, the maximum reaction of the adipocyte is contemporary with testes activity and with thyroid rest. 4. With the hedgehog, we observe two maximums in the sensitivity of the adipocyte to the lipolytic agents, one in spring, which coincides with the maximal testes and thyroid activities, the other in autumn, before the deep hibernation state. 5. In conclusion, there is, with these wild mammals, a seasonal variation in the lipolytic reaction of adipocyte which coincides with that of energy needs.

Adipose Tissue↗
PubMed1981

Short-term variations of plasma testosterone concentrations in the European badger (Meles meles).

Badgers were sampled once during the sexually inactive season (July-November) and during the breeding season (February-April) and testosterone and dihydrotestosterone (DHT) concentrations were measured by radioimmunoassay after separation by chromatography. Concentrations of both hormones were higher in the breeding than non-breeding season, but the mean ratio of testosterone to DHT was greater in the breeding (14) than in the non-breeding season (7). During the breeding season (March 1979) 18 adult male badgers were bled at 12-min intervals for 3 h over a period of 24 h. Testosterone concentrations were measured without chromatography. An episodic pattern of release was observed. All the animals exhibited peaks of large amplitude (1-30 ng/ml) which lasted for about 2 h. The great variability in mean testosterone values for each animal (1-13 ng/ml) could also have been due to differences in individual sexual status.

Animals↗
PubMed1981

Relationship between antler development and plasma androgen concentrations in adult roe deer (Capreolus capreolus).

Four male deer (4-5 years old), living in normal park conditions, were captured every 2 weeks in the year to study annual variations in androgen levels and the relationship between testicular activity and the antler cycle. Data were also obtained from 77 wild adult males (greater than 3 years old) caught in the forest. Plasma androgen concentrations rose briefly in April and markedly in August; the high values in August corresponded with the breeding period. From the time of casting to maximum growth was about 60 days; mineralization of the antlers then lasted for 45 days only. The mineralization phase of antler growth corresponded to the reactivation of testicular function in late January (0.43 +/- 0.16 to 1.99 +/- 0.42 ng androgen/ml, N = 4).

Androgens↗
PubMed1980

[Binding capacity of the testosterone-binding plasma protein in 2 wild mammals with cyclic testicular activity, the fox and badger].

The binding capacity of the plasma testosterone binding globulin (TeBG) as determined by the equilibrium dialysis method, in fox and badger, was shown to wary in relation to the seasonal endocrine activity of the testis. During the winter breeding period, the TeBG binding capacity was low in the fox and high in the badger, whereas an opposite situation prevailed during the sexual quiescence phase. Independent of those seasonal variations, the binding capacity of TeBG was always lower in fox than in badger.

Animals↗