Relative luteinizing hormone-stimulable adenylyl cyclase of the preovulatory follicle: a predictor of ovulation in the domestic hen

The regulation of the ovulatory cycle of the hen (Gallus domesticus) is an enigma. The hen's ovulatory cycle is approximately 26 h in length. She lays an egg each day at a progressively later time. The hen then skips a day, resets her "clock", and a new sequence is started. We investigated if the ovary regulates the ovulatory cycle. Our biologic endpoint was the measurement of basal and luteinizing hormone (LH)-stimulable adenylyl cyclase (AC) activity in granulosa layers of the largest (F1) and second largest (F2) follicles. F1 and F2 follicles were obtained at lights off on nights before the first (C1; n = 7), second (C2; n = 7), or terminal ovulation (CT; n = 5) or the night before the day when no ovulation was expected (Cskip; n = 6). F1 and F2 follicles removed on C1, C2, CT, and Cskip had been these specific follicles for 32 h, 12 h, 10 h, and 8 h, respectively. Mean basal activity (pmol/min/mg protein) for the follicles was: C1 = 27.2, C2 = 44.1, CT = 60.5, and Cskip = 68.7. No significant differences were found in LH-stimulable AC activities of these F1 follicles. Relative LH (expressed as fold increase over basal) stimulation was significantly correlated (P less than 0.001) with maturity of the F1 follicle (C1 greater than C2 greater than CT greater than Cskip). No differences in AC activity were found for the F2 follicles whether they were C1, C2, CT or Cskip. For the Cskip, relative LH AC activity for the F1 follicle (2.8) was similar to that for the F2 follicle (2.7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Presence and hormonal control of plasminogen activator in granulosa cells of the domestic hen

Plasminogen activator (PA) has been implicated in the control of ovarian cell differentiation and in the process of follicular rupture at the time of ovulation in rats. This study was conducted to evaluate whether PA activity is present in granulosa cells of the largest preovulatory (F1) follicle in the ovary of the domestic hen, and if so, to examine its hormonal regulation. An in vitro assay system, which measures the plasmin-mediated lysis of a chromogenic substrate, S-2251, was validated for use with granulosa cells of the hen to assess levels of both cell-associated and secreted PA. Chicken luteinizing hormone (cLH) suppressed PA activity in a dose-dependent fashion, with the highest dose (100 ng/ml incubation medium) resulting in levels that were 21.8% (cell-associated) and 50.9% (secreted) those of basal values (overall mean of 5 separate assays). Similarly, the ovarian steroid, testosterone, at the lowest dose administered (2 ng/ml medium), was found to inhibit both cell-associated and secreted PA activity (29.0% and 73.0% versus basal, respectively; N = 5 assays), whereas progesterone at the highest dose (50 ng/ml media) significantly depressed only cell-associated PA activity (71.9%), but not secreted PA, compared to basal levels (N = 5). By contrast, prostaglandin (PG) E1 or PGE2 at 10(-6) M, stimulated both cell-associated (a 20.9% and a 32.1% increase, respectively, compared to basal levels) and secreted (a 17.1% and a 28.3% increase, respectively, compared to basal) PA activity (N = 5); however, PGE2 at 10(-6) M, when combined with cLH at 100 ng/ml, was only partially effective in reversing the inhibitory action of cLH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of granulosa and theca layers in the control of progesterone secretion in the domestic hen

The ovulatory cycle of the domestic hen is approximately 26 h in length. The hen ovulates an egg each day at a progressively later time until she finally skips a day, resets her "clock" and a new sequence is started. The ovarian component of this unique timing mechanism is the focus of this report. In Experiment 1, we asked whether there was a difference in luteinizing hormone (LH)-stimulated progesterone (P4) secretion by the granulosa layer removed from the largest follicle (F1) that had been the F1 follicle for 8, 12, or 32 h. In Experiment 2, our objective was to determine whether the theca layer of an F1 follicle influenced P4 secretion by the granulosa layer of that follicle and whether such an interaction depended on the maturity of the F1 follicle (had been a F1 follicle for 8 h or 32 h). Results from Experiment 1 revealed that there was no significant difference in LH-stimulated P4 secretion by the granulosa layer in a perifusion system regardless of the length of time the follicle had been the largest follicle. In contrast, in Experiment 2, when granulosa and theca layers from the same follicle were co-incubated in a perifusion system, P4 secretion from the more mature F1 follicle (32 h) increased in response to LH, whereas P4 secretion from the less mature F1 follicle (8 h) was not elevated by LH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lacker's model: control of follicular growth and ovulation in domestic species

Lacker (1981) and Lacker & Akin (1988) developed a mathematical model of follicular maturation and ovulation; this model of only four parameters accounts for a large number of results obtained over the past decade or more on the control of follicular growth and ovulation in mammals. It establishes a single law of maturation for each follicle which describes the interactions between growing follicles. The function put forward is sufficient to explain the constancy of the number of ovulations or large follicles in a female as well as the variability of this number among strains or species and for either induced or spontaneous ovulators. According to the model, the number of ovulations or large follicles lies between two limits that are themselves simple functions of two parameters of the model. Moreover, Lacker's model exhibits interesting characteristics in agreement with results obtained by physiologists: in particular, it predicts that the number of ovulating or large follicles is independent of:

1. the total number of maturing follicles,
2. the process of recruitment of newly maturing follicles towards the terminal maturation (Poisson or other),
3. the form of the LH or FSH secretion curves as functions of the systemic level of oestradiol. The model further predicts that
4. selection and dominance of follicles result from the feedback between the ovary and the hypophysis through the interactions between follicles; these interactions are expressed by the maturation function of the model.
5. recovery from atresia is possible for a follicle: from decreasing, the rate of secretion of oestradiol may increase.
6. the revised model suggests a renewal of follicles during the sexual cycle, as “waves of follicular growth”.

Lacker's model is a model of strict dominance; it maintains a hierarchy of the follicles as soon as they start their final maturation to the ovulations as that is observed in bird or reptile ovary. Such a strict hierarchy is possible but it is probably not a general situation in all mammals. We therefore modified the maturing function of the follicle in order to make it compatible with the observations of physiologists: follicles always interact as in the initial model but they individually become old, the hierarchy of follicles can be modified with time and the largest follicles do not indefinitely grow as in the initial model.     

Distribution of follicular growth, atresia and ovulation in the ovary of the domestic hen (Gallus domesticus) at different ages

Ovaries of laying hens of 14, 18, 30, 45 and 86 weeks of age were divided transversely into two or more distinct regions. Differences in follicular populations between these regions were observed. The central segments of the ovary in birds of 14 weeks of age produced most of the visible (greater than 0.5 mg) developing follicles (P less than 0.01). This was a transient effect during ovarian maturation. In birds of 18 weeks of age, but not yet in lay, more follicles of greater than 8 mm in diameter were observed in the anterior part of the ovary than the posterior part (P less than 0.05). Follicles of this size are almost certain to ovulate. The posterior segment of the ovary of birds of 30, 45 and 86 weeks of age contained more follicles beginning the rapid growth phase, as measured by follicles of 1.4-1.8 mm in diameter, than did the anterior segment (P less than 0.01). Higher levels of atresia in the posterior segment (P less than 0.001) resulted in fewer follicles of greater than 8 mm (P less than 0.001) and fewer post-ovulatory follicles than in the anterior segment. We conclude that most of the eggs produced during the hen's laying year must be from ovulations from the anterior part of the ovary.     

The hyperstriatum and nesting behaviour in the domestic hen

Bilateral ablation of the ventral hyperstriatum resulted in hens ceasing to use trap-nests which they had formerly used. The appetitive component of their pre-laying behaviour was normal in form but was not directed towards the trap-nests, as it was in control birds. In the absence of trap-nests in a pen control birds laid in corners and were conservative in choice of site but both these characteristics were abolished by these ablations. Other bilateral ablations involving the Wulst had less drastic effects on pre-laying behaviour while bilateral ablations in the posterior telencephalon had no effect on this behaviour pattern.     

Thyroxin induced moult in domestic hen

Two identical experiments were carried out in domestic hens treated with a lower (0.2 mg/animal) or a higher (0.4 mg/animal) dose of thyroxin (T4), for 21 consecutive days. The low dose diminished egg production, but did not result in moulting while the higher dose stopped egg laying on the 16th day and caused the loss of contour feathers from the 14th day on. The new plumage was completely developed in this group on about the 42th day. The plasma progesterone concentration showed an increase in both thyroxin treated groups, but is was only continuous and significant in the fowls treated with 0.4 mg T4. In this group the peak value of progesterone was synchronous with the most intensive feather loss. In the other group the tendency for increased levels of progesterone was of shorter duration and not significant. Plasma oestrone levels were depressed by the treatment in both groups and increased significantly only in the moulted fowls after administration of T4 was stopped. This increase may be associated with feather growth and regeneration of the oviduct. Plasma 17-beta oestradiol and testosterone concentrations did not change in the T4 treated groups. Plasma corticosterone concentration increased continuously only in the moulting animals. The results suggest that on one hand thyroxin has a role in the endocrine regulation of moulting and, on the other, that a thyroxin-progesterone synergism is of significance in the process.     

Effects of intermittent lighting on sleep and activity in the domestic hen

This experiment deals with the effects of two different light-dark regimes on general activity, behavioural patterns and sleep in domestic hens (Gallus domesticus). The light-dark schemes were composed of a traditional 14 h light-10h dark period and the Biomittent Lighting Program (BMLP), which consists of only 15 min light during every hour of the traditional 14 h photoperiod. Although it was found that hens are more active during the day than during the night, they were much less active under the BMLP-regime compared to the traditional regime. More specifically, there is considerable lowering of their activities during the dark portions of the day; behavioural observations revealed that they spend these periods not with resting behaviour, but with passive wakefulness. They more or less concentrate their daily activities during the 15-min light periods. Under the night period of the BMLP-regime, hens appeared to be more restless. Sleep recordings showed that sleep tended to decrease in favour of more drowsiness.

It was concluded that circadian rhythmicity of the hens is maintained under both lighting schemes, although the BMLP-regime imposes more passive wakefulness during the day and slightly more activity during the night.     

Catecholamine content of the preovulatory follicles of the domestic hen

The role of catecholamines in ovarian function of the domestic hen has not been examined extensively. The aim of this study was first to determine the location of catecholamines in the preovulatory follicle of the domestic hen. Second, norepinephrine (NE), epinephrine (EPI) and dopamine (DA) were measured in the isolated theca layer of the five largest preovulatory follicles at specific times during the ovulatory cycle and changes in catecholamine content were correlated with ovarian events. The five largest preovulatory follicles were removed from chickens at 24, 18, 12, 6 and 2 h before ovulation of the largest (F1) follicle. Theca and granulosa layers were isolated, frozen, weighed and prepared for measurements of catecholamines by the double isotope radio-enzymatic assay. Catecholamines were localized primarily in the theca layer with only small amounts present in the granulosa layer. Norepinephrine was present in the theca layer in concentrations 6- and 30-fold those of EPI and DA, respectively. The content of NE and EPI in the theca layer of the F1 follicle was significantly (p less than 0.01) higher at 6 h before ovulation than at other times for the F1 follicle. In contrast, NE and EPI content of the theca layer of second (F2) and third (F3) largest follicles did not change during the ovulatory cycle. The content of DA was elevated (p less than 0.05) at 12 h before ovulation in F1 and F2 follicles. There was a significant reduction in NE in the theca layer of the fifth largest (F5) follicle between 24 and 18 h before ovulation of the F1 follicle.(ABSTRACT TRUNCATED AT 250 WORDS)