Photoperiodic control of growth hormone secretion and body weight in rams.

This study was undertaken to assess the influence of photoperiod on growth hormone (GH) secretion in rams and its possible influence on body weight. Twenty young adult rams were divided into two groups. One was subjected to an annual (AR) and the other to a semestral (SR) light regime during the same 18-month period. In both groups, daylength (DL) varied gradually between 8 to 17 hr. Plasma prolactin (PRL) and GH profiles consisting of 6 hr samples were determined and animals were weighed throughout the course of the experiment. Maximal PRL secretion was observed with largest DL. In contrast, GH secretion increased during increasing DL but it began to decrease before maximal DL was reached in both light regimes. Mean GH secretion was maximal when the DL was about 11 hr in SR and between 8 to 12 hr in AR. Similarly, body weight increased when DL increased and plateaued during decreasing DL in both AR and SR animal groups. Significant (P less than 0.05) differences were observed throughout the course of the experiment according to the effects of decreasing or increasing DL in each group. Analysis of variance showed that the effect of DL on plasma PRL and GH levels and weight velocity (WV) was significant (P less than 0.05) in both light regimes. This suggests that in SR, plasma PRL and GH levels and WV vary according to a six month period.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiodic control of LH release in the ram. I. Influence of increasing and decreasing light photoperiods.

The influence of variations in the duration of light photoperiod on LH release has been studied in intact and castrated rams submitted to a 6 months "annual" light rhythm. Blood was collected once a month and the plasma LH levels were determined by radioimmunoassay. In intact rams, the LH level is decreased when the light photoperiod is increased, but as soon as this photoperiod begins to decrease, a sharp increase (about 80%) in the LH level is observed. Thereafter a slow decline in plasma LH occurs until the photoperiod reaches a minimum. In the castrated animals, the plasma LH level is three to four times higher than in the intact animals but the pattern of the variations with regard to the light photoperiod duration, is essentially the same. Thus an increase of 59 and 43% in plasma LH occurs in the two breeds used when the light photoperiod begins to decrease. These results indicate that hypothalamo-hypophyseal activity is modulated by gradual changes in the duration of light photoperiods either in the presence or absence of androgens.

Photoperiodic control of LH release in the ram. II. Light-androgens interaction.

The intensity of negative feedback of androgens on hypothalamo-hypophyseal activity was compared in two groups of castrated rams under 8.00 or 16.00 h of daily illumination respectively following a conditioning period. In experiment I, two groups of 15 rams under each light photoperiod were slaughtered at different times after a 200 mg testosterone propionate (TP) intramuscular injection. Animals receiving the vehicle only acted as controls. The hypophyseal LH concentration, which increases when there is temporary inhibition of the release into the blood, was taken as a criterion of the inhibition due to TP. In both groups of rams the LH concentration increased in the pituitary following TP treatment. A return to the pre-injection level was observed 48 h later only in animals under a 8.00 h light photoperiod, indicating a shorter negative effect of the injection than in the case of rams under 16.00 h light photoperiod. In experiment II, the inhibitory effect of TP was assessed at two doses, i. e. 300 and 600 mg, by the decrease in the plasma LH level following an intramuscularly injection. In both cases the decrease in LH release was more pronounced in rams under 16.00 h of daily illumination than in those under 8.00 h (mean decrease in LH release: 21.2 and 33.2% respectively in 300 and 600 mg treated rams under 16.00 h daylight as against 9.2 and 14.8% in rams under 8.00 h). Thus it appears that to the intrinsic action of the photoperiod is superposed on a modulatory effect of steroid action on the hypothalamo-hypophyseal activity. The hypothesis is therefore presented that, in rams a decreasing light photoperiod acts in two ways: 1) by stimulating the activity of the hypothalamo-hypophyseal system, 2) by decreasing the intensity of the negative feedback effect of steroids.

Endocrine control of spermatogenesis in the ram.

In the ram, the size of the testes is related to the concentrations of FSH, LH and testosterone in the blood. A significant linear relationship is observed between testicular size and the level of FSH until a maximum after which no further increase in testis size is observed. Testicular size is also linearly related to the mean level (25 consecutive hours of sampling) of LH and testosterone in the blood, with apparently no upper limit, and to the frequency of peaks of these hormones in the sampling period. Spermatogenesis in the ram is sensitive to variations in the levels of circulating hormones; there is a positive correlation between the number of renewing spermatogonia or the efficiency of spermatogonial multiplication and the mean LH value in the peripheral blood of the adult. Some of these relationships operate over long periods and involve the Sertoli cells. The level of circulating LH in the non-pubertal lamb is directly correlated with number of Sertoli cells per testis, and the latter is correlated with the number of renewing spermatogonia per testis in the adult ram. Treatment of hypophysectomized rams with PMSG, hCG or testosterone shows that spermatogonial divisions are sensitive to the hormonal milieu with specific stages being controlled by the LH-like activity of hCG (A1 spermatogonia), and the FSH-like activity of PMSG (transition from intermediate spermatogonia to leptotene spermatocytes). Testosterone has only a small effect at the beginning of the spermatogenic cycle (production of leptotene spermatocytes) and quantitatively maintains meiosis and spermiogenesis, but the differentiation of spermatids is dependent on information stored at the beginning of meiosis and requires the support of both testosterone and other factors.

[Evidence of a circadian sequence of photogonadsensitivity in the ferret]. / Mise en évidence d'une séquence circadienne de photogonadosensibilité chez le furet.

Using "skeleton" photoperiods with a primary photofraction of 3 hrs. 30 min. and secondary photofraction of 30 min. located at various intervals after the onset of darkness, the occurrence of a photoinducible phase in the androgenic function has been evidenced in the Ferret. This photo-inducible phase seems to be located around 12 hrs. after the onset of the primary photofraction, since the ferrets who received the 30 min. photofraction 8 hrs. after the onset of darkness responded with a maximal increase in plasma testosterone.

[Demonstration of the influence of the photoperiod on the plasma concentration of the growth hormone in the ram]. / Mise en évidence de l'influence de la photopériode sur la concentration plasmatique de l'hormone de croissance chez le Bélier.

The influence of photoperiod on GH release has been studied in Rams subjected to two different light regimes. The first group was submitted to natural daylight variations. The second group received daily the following split photoperiod: 7 L, 9 D, 1 L, 7 D, known to stimulate the release of prolactin. The experiment lasted 5 months, from January to June. In the first group, plasma GH concentrations decreased significantly from January to February (10.1 +/- 0.4 vs 8.7 +/- 0.3 ng X hr./ml; P less than 0.02), then increased from April to June (9.3 +/- 0.4 vs 10.5 +/- 0.7 ng X hr./ml; P less than 0.02). In the second group, GH concentrations were higher than in the first group in April (11.9 +/- 0.9 vs 9.3 +/- 0.4 ng X h/ml; P less than 0.05). However, it decreased between April and June (11.9 +/- 0.9 vs 9.7 +/- 0.4 ng X hr./ml; P less than 0.02) and then did not differ from that of the first group. These results show that plasma GH concentrations are affected by photoperiodic changes and suggest the existence of seasonal variations in GH plasma levels in the Ram.

[Relationship between estrogens during gestation, birth weight, and later growth in Charolaise calves]. / Relations entre les aestrogènes au cours de la gestation, le poids à la naissance et la croissance ultérieure des veaux de race charolaise

In Charolais breed linear relationships were found between the oestrogen level in plasma of cows at 220 days of pregnancy and the birth weight (r = .84) and the daily gain of weight from 1-180 days (r=.87).

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.

Seasonality of reproduction in sheep and its control by photoperiod.

Seasonality of the reproductive cycle in sheep is a general phenomenon for mid-latitude breeds. The proximal part (breeding season) and also partially distal part (end of gestation and beginning of lactation) of this cycle is controlled by photoperiod, whatever the form of light regimens. Data are presented which indicate that male and female do not necessarily have the same photoperiodic sensitivity. Gonadal stimulation in the ram starts 1.5-2 months earlier than in the ewe under annual variations. Photoperiod controls the reproductive cycle by the intermediary of the hypothalamo-pituitary axis. There are both a steroid-independent and a steroid-dependent effect of light, depending on both decreasing and increasing daylength in mid-latitudes. Data are also presented which support Bunning's hypothesis on photoperiodic time measurement in mammals. Sheep measure photoperiodic time by using a circadian rhythm of photosensitivity. Daylength is not measured by the total duration of exposure to light but by the illumination of two special set points during the day, one of them entraining the circadian rhythm of photosensitivity and the other inducing or not inducing a physiological response if it is coincident, or not coincident, with photoinducible phase of that rhythm. A photoinducible phase has been found for prolactin secretion, and perhaps also for LH secretion. Melatonin secretion is used by sheep for measuring daylength. However, that secretion disappears during two set points during the day, thus raising the possibility of using alternatively melatonin and light pulse for controlling the reproductive cycle in sheep.

[Effect of light on variations in blood testosterone in the ram: demonstration of a photosensitive phase in diurnal rhythm]. / Influence de la lumière sur les variations de la testostéronémie chez le Bélier : mise en évidence d'une phase photosensible au cours du rythme diurne

6 groups each of 5 adult rams were subjected in light controlled pens to a pretreatment of normal variations in daylength during May and June. Then one group followed the normal daylength and the other five different "skeleton photoperiods" of 8 hrs of light per day consisting of: 7 hrs continuous light (7 L) + 1 hr light (1 L) situated at different times of the dark period (D) according to groups. Blood samples were taken once each week and hourly during one 24 hr period in June, July and September. Peripheral plasma testosterone measured by radio-immunoassay was used as an index of testicular activity. There was increase in the level of testosterone resuting from a rise in the number of peak release during the 24 hrs. In the different light treatments tested, only the treatment (7L+9D+1L)+7D) stimulated testosterone secretion with the pattern of testosterone of this group being similar to that of the control group. This indicates that there exists a photosensitive phase at 16 to 17 hrs after the beginning of the principal light (the subjective dawn).

Seasonal variation in LH and testosterone release in rams of two breeds.

Blood was collected hourly for 24 h in December, February, April, June and September from Préalpes du sud and Ile-de-France rams. Coincidence of the LH and testosterone peaks was found for 96.4% of a total of 670 LH peaks and 647 testosterone peaks. The number of LH and testosterone peaks increased by 66% in Ile-de-France rams and 200% in Préalpes du Sud rams between December and June (P less than 0.001). Values in June and September were similar in Préalpes du Sud rams. There were no differences between breeds in December, but in June, Préalpes du Sud had significantly more peaks than did Ile-de-France rams (P less than 0.025). The numbers of LH and testosterone peaks increased significantly (P less than 0.05) in Préalpes du Sud rams between December and February or April. These results indicate that, although numbers of peaks of LH and testosterone increase when the animals pass from the non-breeding to the breeding season, the genotype influences the pattern of release through the year.

[Use of progestagens in subcutaneous implants for the control of sexual cycles in the cow]. / Utilisation de progestagènes en implants sous-cutanés pour la maîtrise des cycles sexuels chez les bovins

PIP: Estrus synchronization and related fertility were studied in cattle using subcutaneous implants containing norethandrolone, SC 21009, or fluorogestone acetate. Lengthening the duration of treatment decreases the rate of estrus inhibition. For long-term (16-18 days) treatments, the percentage of cows showing estrus with 4 days from implant removal increases with the initial content of the implant; 61.5% and 84.6% with 6 and 12 mg SC21009 respectively. The progestagen content of the implant has little effect on fertility, but longer duration of treatment lowers fertility: 49.4% and 27.3% for 10 and 16 days, respectively, for SC 21009 implants. Fluorogestone acetate had little effect. Estradiol valerate injection at the time of implant insertion increases fertility regardless of treatment duration. The use of high-potency progestagens permits the use of small implants. Cross-link percentage must be studied for each progestagen. Of the progestagens studied, only SC 21009 is sufficiently potent for implant use.^ieng

Diurnal variation in release of LH and testosterone in the ram.

The time of appearance of plasma LH and testosterone peaks through the day determined in 75 Préalpes du Sud and 41 Ile-de-France rams in December and in 44 Préalpes du Sud and 11 Ile-de-France rams in June. The distribution of peaks throughout the day was non-random for the two hormones in the two breeds and for both times of the year (P less than 0.01 at least on each occasion; P less than 0.001 on pooled data from the two breeds). The most striking features were the occurrence of (1) a minimum of LH and testosterone peaks immediately after 'dawn' (lights on) in both months; (2) a maximum of peaks 3 h after 'dawn' in June and 4 h after 'dawn' in December. For several hours after the increase in frequency of peaks the probability of measuring peaks of LH values in December and June when adjusted for the time of 'dawn' suggest that dawn could act as a synchronizer of gonadotroph activity.

Photoperiodic and melatonin treatments for the control of seasonal reproduction in sheep and goats.

The control of seasonal reproductive activity in sheep and goats in open sheds, needs extra-light (E) during the photosensitive phase (equivalent to long days, LD), followed by treatment with melatonin (equivalent to short days, SD). In autumn-born Ile-de-France or Lacaune ram lambs, 2 months of E followed by decreasing daylength for 90 days, advanced onset of the first breeding season by allowing males to reach their maximum testis volume and sperm production earlier than for untreated ram lambs. Substitution of decreasing daylength with melatonin implants allowed a transient increase in testis volume. Adult Ile-de-France rams maintained under short light rhythms with 2 month-period, demonstrated, during at least 2 consecutive years, a testis volume equivalent to that observed during the normal breeding season. These light-treated rams produced, during non-breeding season, spermatozoa in the same quantity and quality as during the normal breeding season. In anovulatory out-of-season dairy goats, E treatment was demonstrated to be necessary before melatonin treatment and melatonin to be necessary after E treatment to stimulate oestrous and ovulatory activities. Stimulation of the anovulatory females by the introduction of treated males ("male effect"), appeared to be necessary to obtain maximum stimulation of the treated females. Two months of E, followed by melatonin treatment (daily injection or drenching or subcutaneous implants) allowed cycles with ovulation to be maintained for more than 2 months. Although effective for control of out-of-season reproductive activity, melatonin slightly decreased milk production when applied soon after kidding. So, total control of reproduction in sheep and goats by manipulation of photoperiod in open sheds and melatonin treatments appears feasible in both sexes.

Influence of 2 Br-alpha-ergocryptine (CB 154) on the secretion of prolactin, LH, FSH and testosterone and on testicular growth in rams subjected to different photoperiods.

The influence of 2-Br-alpha-ergocryptine (CB 154) on the secretion of gonadotrophins and on testicular function has been studied in rams subjected to either a normal photoperiod or an abnormal photoperiod causing hyperprolactinaemia. The CB 154 treatment significantly lowered the mean frequency of LH and testosterone pulses in hyperprolactinaemic animals as compared to solvent-treated ones. Also, only those groups subjected to an abnormal photoperiod (groups 2 and 3) exhibited a significant rise in the frequency of LH and testosterone peaks after CB 154 was withdrawn. During treatment, plasma FSH concentrations increased significantly only in group 1 which was subjected to normal photoperiodic variations. Testicular growth was delayed in CB 154-treated rams compared to solvent-treated ones only in group 3 (hyperprolactinaemic).