ABSTRACT

The hypothesis was advanced that the long-day castration response in quail should become less pronounced in birds made refractory by exposure to long photoperiods. This was tested by pretreating two groups of castrated quail with testosterone for 9 weeks to suppress LH secretion whilst exposing them either to short days or to long days. The castration response was then measured on long days by withdrawing the testosterone and following the subsequent rate of increase in LH secretion. In both groups LH concentrations increased steadily for 7 weeks after removing the testosterone but the rate of increase in the group previously exposed to long days was only 50% of that in the group previously held on short days (P<0·025). The long-day castration response in quail not pretreated with testosterone was not altered by retaining the birds for 9 weeks on short days before transfer to long days.

J. Endocr. (1988) 116, 363–366

SUMMARY

Follicle-stimulating hormone (FSH) was measured in Japanese quail using a heterologous radioimmunoassay, the specificity of which was confirmed by its cross-reactions with purified chicken FSH and luteinizing hormone (LH).

Plasma concentrations of FSH, LH and testosterone were determined in quail during the testicular growth and sexual maturation which follows their transfer from short to long daylengths. All three hormones could be detected in short-day birds but their concentrations were greatly increased following photostimulation. Plasma FSH increased 12-fold during the first 9 long days, remained at this level for a week, and then declined steadily so that by the time the birds were sexually mature the level of FSH had decreased to one-third of the maximum level. LH reached a high level (five times the short day level) after 4 long days. Thereafter two patterns of LH secretion could be distinguished. In one experiment the high level of LH was maintained unchanged throughout sexual maturation while in another experiment LH secretion decreased significantly between days 11 and 28 of photostimulation.

A strong correlation existed between testicular growth and the plasma FSH concentration. It was maximal during the phase of rapid testicular growth and decreased as spermiogenesis began.

The pituitary FSH content increased during photostimulation. Castration caused a 20-fold rise in plasma FSH compared with that in intact quail. The change in LH concentration after castration was about eightfold.

The changes in hormone secretion were strikingly similar to those found during sexual development and puberty in the rat.

SUMMARY

Blood samples were taken every 3 h, over a 27 h period, from (1) a group of 12 intact male quail on short days (lights on 09.00–17.00 h) and during the 2nd, 15th and 36th day of photostimulation (lights on 09.00–05.00 h); (2) 12 castrated male quail on the 2nd, 20th and 43rd long day, and (3) 12 intact male quail on the 12th long day. Plasma LH was measured in all samples and FSH in the 43rd long day castrate and 12th long day intact male samples. Although there was considerable variation in the levels of LH and FSH, both between birds and between samples taken from the same bird, statistical analyses failed to reveal any diurnal (or circadian) rhythm at any time. There was a marked correlation between the LH and FSH levels in all samples.

Possible episodic LH secretion was investigated by taking blood samples every 15 min for between 3 and 6 h from six intact male quail and six laying females on long days. Samples were obtained from each bird at three time-periods which were arranged so as to overlap and cover the first 12 h of the daily photoperiod. Statistical analysis suggested that episodes of secretion occurred 6–10 times/day in males, and 4–8 times/day in females. The pulses appeared to occur at random.

ABSTRACT

Castrated Japanese quail responded to a single long day with a five- to eightfold increase in plasma LH levels. A rise in LH secretion appeared 19–24 h after dawn and LH levels were still increased 3 days later, despite the fact that the birds had been returned to a short daylength. Pituitary LH content decreased, reflecting these changes in secretion, although significant falls in content were only found 36–96 h after dawn, when LH secretion was maximal. Hypothalamic gonadotrophin-releasing hormone content was not altered. One interpretation of this is that increased synthesis of the peptide compensates fully for the increased secretion.

J. Endocr. (1987) 113, 419–422

ABSTRACT

Welsh Mountain ewes (n = 6) were rendered hypothyroid by daily treatment with methylthiouracil (35 mg/kg), beginning in early August and ending in late February. Plasma thyroxine levels were reduced by mid-September to about 33% of those in untreated ewes (n = 6). The two groups of ewes were held under natural daylengths until 5 October, then on 12 h light:12 h darkness (12L:12D) until 28 February when the photoperiod was reduced to 8L:16D. The onset of reproductive cyclicity in October was similar in both groups of ewes but the end of the reproductive period occurred later (P < 0·05) in the hypothyroid ewes (29 January±7 days (s.e.m.)) than in the untreated controls (6 January±7 days). As a result, the duration of the seasonal reproductive period was significantly (P < 0·05) longer in the hypothyroid (122±9 days) than in the untreated ewes (91±10 days). The number of oestrous cycles (duration 15·4 and 15·7 days in the hypothyroid and untreated ewes respectively) was 7·0±0·6 in the hypothyroid ewes and 5·0±0·5 (P < 0·05) in the normal ewes. Reducing the photoperiod overcame the reproductive refractoriness and anoestrus in both groups, the hypothyroid ewes beginning to cycle on 13 April (±0·5 days) after an anoestrous period of 72·8±7·1 days. The untreated ewes began to cycle 2 weeks later on 26 April (±1·7 days) after an anoestrous period of 112·0±8·5 days (P < 0·001).

Hypothyroidism appears, therefore, to affect the development of the refractoriness which ends the reproductive season in the sheep as well as its intensity. Such effects are similar to those found after full thyroidectomy but less pronounced since thyroidectomy is able to suspend anoestrus completely.

Journal of Endocrinology (1990) 127, 103–109

ABSTRACT

The breeding season in quail ends when they become relatively refractory to long photoperiods. The processes underlying the development of this refractoriness are dependent upon the thyroid gland.

Thyroidectomized male Japanese quail transferred from short (8 h light: 16 h darkness; 8L: 16D) to long (20L: 4D) daily photoperiods mature their gonads and develop the androgen-dependent cloacal gland at rates only marginally slower than controls. However, when the birds are retransferred to short days thyroidectomized individuals do not show the rapid testicular regression and moult which occurs in controls under such conditions. The testes remain large for a long period, eventually decreasing in size slowly and irregularly. Once such thyroidectomized birds are transferred back to short days the administration of thyroxine has little effect upon the slow rate of gonadal regression but if the hormone is administered during the preceding period of long days normal regression does occur under short days, even though treatment has ceased. This suggests that a process dependent upon thyroid hormones takes place under long daylengths that ensures the termination of reproduction when they are exposed either to short daylengths or to decreasing daylengths after the summer solstice. This view was substantiated by further experiments in which thyroidectomy was performed after the birds had been exposed to long daylengths. When transferred to 8L: 16D normal testicular regression and moult occurred rapidly. Presumably the thyroiddependent process had proceeded to an adequate extent in these quail before the thyroid glands were destroyed. Further support came from treating intact quail chronically with thyroxine. Its administration to quail on 20L: 4D had no observable effect; the testes grew rapidly to maximal size and remained large. However, if the birds were given thyroxine under 12L: 12D the gonads first developed to maximal size and then, after about 12 weeks of treatment, regressed spontaneously whether or not thyroxine was still being administered. It seems that thyroxine had made the quail so relatively refractory that 12L: 12D was no longer sufficiently stimulatory to overcome the developing inhibition on the photoperiodic system. The results in quail are very reminiscent of the finding that the absolute photorefractoriness and spontaneous testicular regression which develops in starlings under long daylengths is thyroid dependent. Quail do not become absolutely refractory on long daylengths and regress their gonads spontaneously but they do develop a 'relative' refractoriness so that only a small decrease in photoperiod is necessary to switch off the reproductive system. We suggest that quail-type refractoriness is homologous with that in starlings and that both involve progressive changes induced by exposure to long daylengths which profoundly alter the photoperiodic response: these changes will not occur without a functional thyroid gland.

J. Endocr. (1985) 107, 211–221

ABSTRACT

Melatonin was measured by radioimmunoassay in homogenates of pineal glands from quail (Coturnix coturnix japonica) kept under different photoperiods and in darkness. Under 8-, 12- and 16-h daylengths melatonin levels were increased during the dark period, the duration of the increase depending on the duration of the dark period. As the daylength was increased the peak occurred closer to lights-off, reflecting the more rapid melatonin rise under the longer photoperiods. The pineal melatonin rhythm continued in darkness with an amplitude relative to that seen under a light/dark cycle of slightly less than one-half after 2 days in darkness and one-third after 6 days in darkness. The corresponding average periods of the rhythm were 25·5 h and 25·7 h. These results show that there is a circadian rhythm of melatonin in the pineal gland of the quail which is entrained by light/dark cycles and which continues in darkness.

J. Endocr. (1985) 107, 317–324

SUMMARY

Rates of testicular growth and plasma levels of FSH, LH and testosterone were determined in Japanese quail exposed to various fixed photoperiods (number of hours of light: number of hours of darkness): 12L: 12D, 13L: 11D, 14L: 10D, 16L: 8D and 20L: 4D and to natural daylengths. All five artificial photoperiods stimulated spermatogenesis, with the testes reaching maturity after 30–40 days. Maximum rates of testicular growth occurred with 14L: 10D, 16L: 8D or 20L: 4D but the rate was reduced by 50% in birds exposed to 12L: 12D. This reduction was due to decreased growth in the seminiferous tubule epithelium (and hence in tubule diameter); the duration of spermatogenesis hardly being affected. Near maximum growth rates occurred with 13L: 11D.

The hormone profiles offer an explanation for the differential rates of testicular growth. In the three longest photoperiods, FSH rose from 20 ng/ml to peak levels of 300–400 ng/ml after 10 days. As the testes matured, so the level of FSH decreased to 50–100 ng/ml. This pattern was not seen under 12L: 12D; the level of FSH rose slowly to about 100 ng/ml and showed no peak of secretion. With 13L: 11D a small peak was found, which decreased at maturity. In quail with testes > 1500 mg, the level of FSH was invariably about 100 ng/ml. Patterns of LH secretion were rather similar with all treatments, but testosterone was affected by photoperiod; lower levels were found under 12L: 12D than 20L: 4D. The rate of photoperiodically induced testicular growth was proportional to the levels of FSH, and possibly also testosterone, in the circulation.

Outdoors, testicular growth began when daylengths reached about 12 h. Maturity occurred within the next 40 days. The levels of FSH rose steadily but did not show a peak of secretion. In general, the highest levels of hormone were found in July just before gonadal regression which occurred when the daylengths were still quite long.

SUMMARY

Experiments were undertaken to localize those hypothalamic areas in the male quail (Coturnix coturnix japonica) where electrical stimulation would increase LH secretion. The posterior basal hypothalamus was stimulated with rectangular pulses (height 500 μA) through a bipolar electrode for 6 min, blood samples being taken for LH assay 20 min before, and 2, 10, 20 and 30 min after stimulation. The highest plasma concentration was observed in the 2 min sample. Over the next 30 min the LH level decreased to the resting concentration. The relative increase in LH level was greatest in sexually immature quail and least in photostimulated castrated birds, although the highest absolute levels were seen in the castrated quail. There were no statistical differences between the magnitude of the LH increases in sexually immature, mature and castrated quail.

Various hypothalamic regions were then stimulated with a smaller current (200 μA) applied for only 2 min. A highly significant rise in LH followed stimulation of either the tuberal hypothalamus (postero-dorsal part of the infundibular nuclear complex, PD-INC), or the preoptic region (POR) while stimulation 0·5–1·5 mm away from these regions did not change LH secretion. Stimulation of the anterior basal hypothalamus, or of the suprachiasmatic area, caused a significant rise in LH concentration although this was less than that seen after stimulation of the POR. Stimulation in the POR or the PD-INC was ineffective if the tuberal hypothalamus had been deafferentated surgically some days previously. The data complement the studies in which destruction of the PD-INC or the POR by electrolytic lesions has been shown to block photoperiodically induced testicular growth and LH secretion.

SUMMARY

The effect of exogenous oestrogen and follicle-stimulating hormone (FSH) on the concentration of serum lipids and protein has been investigated in the South African clawed toad, Xenopus laevis Daudin. Oestradiol-17β was implanted i.p. in mature females; the rate of absorption was 13·6 μg./day. Within 10 days the plasma concentration of all lipid components increased significantly (unesterified and esterified fatty acids, cholesterol, phospholipids). The lipid concentration tended to level out after treatment for 20 days. In contrast, oestradiol caused a steady and continued rise in the plasma protein level for up to 70 days after implantation. Electrophoresis showed that the increased protein concentration was due to the emergence of a new plasma protein or proteins with a high phosphorus, calcium and lipid content. Injections of oestradiol benzoate showed the responses to be dose-dependent; the lowest effective dose was 1·0 μg./100 g. body weight/day. Implants of oestradiol in males and hypophysectomized females resulted in a similar elevation of protein and lipid components. Mammalian FSH depressed the plasma lipid content in both untreated and oestradiol-implanted females but had no effect on the newly emergent proteins and their associated components. The results are discussed in relation to the effects of oestradiol on plasma constituents in other oviparous vertebrate groups.