Peter J. Sharp

The relationship between heat production and concentrations of plasma thyroid hormones in the domestic hen

Abstract A low-amplitude daily rhythm of heat production was seen in sexually immature hens exposed to 14 hr light/day at 30° with the lowest values occurring during the dark period. Thyroidectomy depressed heat production during the light and dark periods. Fasting depressed the level of the rhythm of heat production in intact hens and depressed it further in the thyroidectomized hens. The amplitude of the daily rhythm of heat production in laying hens exposed to 14 hr light/day and held at 20° was greater than that in the same birds held at 32°. The increase in temperature caused a reduction in heat production during the light period but not during the dark period. Fasting lowered heat production during the light and dark periods when the hens were held at 20° and during the dark period when they were held at 32°. The increase in temperature caused a reduction in the concentration of plasma triiodothyronine (T 3 ) but did not alter the concentration of plasma thyroxine (T 4 ). In fed hens held at 20 and 32°, the concentration of plasma T 3 increased during the light period and fell during the dark period: the converse changes were observed in the concentrations of plasma T 4 . In fasted hens held at 20 and 32°, the concentration of plasma T 3 was uniformly depressed during the light and dark periods: the concentration of plasma T 4 was increased during the light and dark periods but tended to fall after the birds had been fasting for 48 hr. It was concluded that in the hen (1) heat production is related to the concentration of plasma T 3 and not to that of plasma T 4 , and (2) daily rhythms in concentrations of plasma thyroid hormones are controlled by the feeding pattern.

Seasonal changes in the concentrations of plasma luteinizing hormone and testosterone in willow ptarmigan (Lagopus lagopus lagopus) with observations on the effects of permanent short days

Concentrations of plasma testosterone (T) and luteinizing hormone (LH) were measured by radioimmunoassay in captive male willow ptarmigan (Lagopus lagopus lagopus) in Tromso (69°40′ N) during an annual cycle and while maintained for up to 22 months on permanent short days (6L, 18D). In birds exposed to natural changes in day lengths, the concentrations of T and LH were at their lowest between July and October and increased slightly during December and January. The concentration of plasma LH began to increase steeply in late March when the day length was between 14 and 16 hr and was associated with a temporary depression in the concentration of plasma T. Plasma T began to increase steeply in late March when the day length was between 14 and 16 hr and was associated with a temporary depression in the concentration of plasma T. Plasma T began to increase steeply in late April, about 1 month later than the increase in plasma LH, and the concentrations of both hormones reached seasonal maximum values in May. In late May and early June the concentrations of plasma T and LH fell, with the concentration of T falling before that of LH. The rate of fall in T and LH during June was not modified by the presence of a mate. In birds maintained on a permanent short day length for up to 22 months, the concentrations of plasma T and LH did not show seasonal or cyclical variations; they were similar to the values observed in December and January in birds exposed to seasonal changes in day length.

The interaction between day length and the gonads in the regulation of levels of plasma thyroxine and triiodothyronine in the Japanese quail.

Abstract Changes in the concentrations of plasma thyroxine (T 4 ) and triiodothyronine (T 3 ) were measured in intact and gonadectomized quail of both sexes after transfer from short (6L:18D) to long (18L:6D) days and upon return to short days. The concentration of free thyroxine (FT 4 ) was also measured in intact birds after transfer from short to long days. In both intact and gonadectomized birds, the concentration of plasma T 4 increased after transfer to long days while no consistent change was seen in the concentration of plasma T 3 . However, after 15–24 days of photostimulation, the concentrations of plasma T 4 and T 3 began to fall in the intact birds but remained unchanged in the gonadectomized birds. The transitory increase in plasma T 4 observed in intact birds after photostimulation was associated with an increase in concentrations of plasma FT 4 . The decrease in plasma T 4 and T 3 in photostimulated intact birds began when gonadal growth was nearly complete. The concentration of plasma T 3 in sexually mature male and female quail was lower than in sexually immature birds. In gonadectomized birds of both sexes, the concentration of plasma T 4 fell while that of plasma T 3 remained unchanged after transfer from long to short days. In sexually mature males and females, the transfer back to short days did not change the concentration of plasma T 4 but caused an increase in that of plasma T 3 . These observations are consistent with the view that in the quail long day lengths may directly stimulate the hypothalamo-pituitary-thyroid axis and the production of T 4 and that the production of T 3 is not directly dependent on day length. It is suggested that in sexually mature birds the concentrations of plasma T 4 and T 3 are depressed because of a reduction in the concentration of plasma thyroid-hormone-binding proteins. The production of these proteins is suggested to be inhibited by gonadal steroids.

Concentrations of plasma prolactin and luteinizing hormone following nest deprivation and renesting in ring doves (Streptopelia risoria).

Ring doves with increased plasma prolactin and low plasma LH (Group A) or with low plasma prolactin and low plasma LH (Group B) which had been incubating sterile eggs for 12 or 18 days, respectively, had their nests and eggs removed for 3 days. Upon nest return, observations were made on the birds readiness to renest and on changes in plasma prolactin and LH. Birds from Group A demonstrated a far greater tendency to resume incubation than birds from Group B. Nest deprivation resulted in a sharp fall in the concentration of plasma prolactin in birds which were deprived of their nests after 12 days of incubation (Group A). Following resumption of incubation no subsequent increase in the prolactin levels was observed in Group A or B. The concentration of plasma LH rose sharply after nest deprivation in both sexes of both groups and declined after return of the nests. Birds in Groups A and B which returned to their nests laid a new clutch of eggs while continuing to incubate. The total length of uninterrupted sitting following nest return was 20.9 +/- 0.48 days (n = 8). These results suggest that (1) once the mechanism responsible for the increase in plasma prolactin during incubation is disrupted, it cannot be reactivated unless the whole reproductive cycle is repeated. (2) The inhibition of LH secretion during incubation involves neural mechanisms which do not necessarily involve the anti-gonadotrophic action of prolactin.

Endocrine changes in photostimulated willow ptarmigan (Lagopus lagopus lagopus) and Svalbard ptarmigan (Lagopus mutus hyperboreus)

Changes in plasma luteinizing hormone (LH), testosterone, thyroxine (T4), and triiodothyronine (T3) and the height of supraorbital combs were compared in captive willow ptarmigan (Lagopus lagopus lagopus) and Svalbard ptarmigan (Lagopus mutus hyperboreus) exposed to an artificial annual cycle of daylength simulating that at 70 degrees N. Plasma LH and testosterone and comb height increased more slowly in Svalbard than in willow ptarmigan as daylength increased. In both species, plasma LH and testosterone fell abruptly, and the supraorbital combs regressed in June, marking the development of long-day refractoriness. Comparison with free-living Svalbard ptarmigan (K.-A. Stokkan, P. J. Sharp, and S. Unander (1986) Gen. Comp. Endocrinol. 61, 446-451) at 80 degrees N, showed a similar slow increase in reproductive function before the onset of the breeding season. However, maximum plasma LH levels and comb size were higher in free-living than in captive Svalbard ptarmigan. Furthermore, long-day refractoriness developed earlier in captive than in free-living Svalbard ptarmigan. In both species of ptarmigan, the development of long-day refractoriness was associated with increased plasma prolactin. This increase was larger and occurred earlier in the Svalbard than in the willow ptarmigan. Seasonal changes in thyroid hormones were not as marked as for the other hormones measured. In both species, plasma T4 tended to increase and plasma T3 to decrease as daylength increased. A small increase in plasma T3 was seen after the development of long-day refractoriness in both species. It is concluded that captivity depresses the photoperiodic response of Svalbard ptarmigan more than that of willow ptarmigan.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental and hormonal factors in seasonal breeding in free-living male Indian rose-ringed parakeets (Psittacula krameri).

Seasonal changes in testicular activity, plasma luteinizing hormone (LH), estradiol (E2), testosterone (T), and 5 alpha-dihydrotestosterone (5 alpha-DHT) were related to pair bond formation, nest building, nest defense, and parental behavior in free-living Indian rose-ringed parakeets (Psittacula krameri) in northwest India. Spermatozoa production occurred between January and March when daylengths were short (10-12 hr) and ambient temperature was seasonally low (8-20 degrees C). At other times of the year the testes were regressed. Plasma LH levels increased during the prebreeding period (September-December) when the birds were forming pairs and selecting or defending nest sites. Plasma LH levels increased further between January and March and decreased to seasonal low values during the post breeding period between April and June when the birds were caring for young. Concentrations of plasma androgens and estrogens were similar during the prebreeding and postbreeding phases of the breeding cycle. During the breeding period, the ratios between plasma 5 alpha-DHT and testosterone and between plasma estradiol and testosterone increased. It is proposed that the absence of marked seasonal changes in plasma steroid levels is related to nest defense behavior which occurs during the prebreeding, breeding, and postbreeding phases of the breeding cycle. Winter breeding makes it possible for the parakeets to avoid competition with other birds for nesting sites, to avoid fledging young during the monsoon period, and to take advantage of the winter pea crop which provides the female with extra nutrients for egg production.

A comparison of the responses of captive willow ptarmigan (Lagopus lagopus lagopus), red grouse (Lagopus lagopus scoticus), and hybrids to increasing daylengths with observations on the modifying effects of nutrition and crowding in red grouse

The photoperiodic responses of two races of Lagopus lagopus from different latitudes and of hybrids between them were compared under the same lighting conditions. The captive birds were descended from northern Norwegian willow ptarmigan (Lagopus lagopus lagopus) and Scottish red grouse (Lagopus lagopus scoticus). Under natural conditions, the red grouse begin to lay eggs 3 weeks earlier than the willow ptarmigan. Photosensitive birds were transferred from an 8-hr daylength to a lighting regime in which the daylength was increased by 1 hr per week for 11 weeks. At the start of the study, the red grouse had greater LH levels and comb sizes than the wilow ptarmigan or the hybrids. The critical daylength needed to stimulate LH secretion was less than 12 hr in both races but it was not clear whether it was greater in the willow ptarmigan than in the red grouse. However, the races differed quantitatively: the willow ptarmigan had lower LH levels at 12, 13, and 14-hr photoperiods than did the red grouse or the hybrids. In all the males, comb heights increased significantly (P < 0.05) after the photoperiod was increased to 12 hr and reached their maximum in the red grouse, hybrids, and willow ptarmigan at photoperiods of 13, 14, and 16 hr, respectively. The female red grouse, hybrids, and willow ptarmigan laid their first eggs after the photoperiod was increased to 15, 17, and 19 hr, respectively. At the end of the study the red grouse but not the hybrids or willow ptarmigan were becoming photorefractory. A low-protein diet did not alter the timing of the onset of seasonal breeding in captive female red grouse although it did cause a reduction in the rate of lay and egg weight. The onset of seasonal breeding was delayed, however, when the birds were crowded. It was concluded that in L. lagopus, the photoperiodic response seems to be determined by inherited factors. Further, the absence of a clear difference between the critical daylengths in red grouse and willow ptarmigan raises the possibility that differences in the timing of the onset of seasonal breeding in these races may be caused by modifications in the neural or endocrine pathways “downstream” from the biological clock.

Environmental, dietary, and hormonal factors in the regulation of seasonal breeding in free-living female Indian rose-ringed parakeets (Psittacula Krameri)

The roles of environmental, dietary, and hormonal factors in the timing of seasonal breeding were assessed in free-living female Indian rose-ringed parakeets, Psittacula krameri, in northwest India (22 degrees 2N, 73 degrees E). The ovaries and oviducts began to enlarge in January, were fully developed in February, and began to regress in March. During this time there was no significant change in the concentration of plasma luteinizing hormone (LH) or estradiol. The concentration of plasma LH decreased (P less than 0.01) at the end of the breeding season. Pair bond formation occurred between September and December and was associated with an increase in levels of plasma LH but no change in plasma estradiol. Concentrations of plasma testosterone (T) and 5 alpha-dihydrotestosterone (5 alpha-DHT) did not vary significantly during the year and were similar to those in males except for higher values of 5 alpha-DHT and lower values of T during the pre- and postbreeding periods, respectively. The similar levels of plasma androgens in both sexes may be related to the equal roles that both sexes play in the defence of their nest holes. An analysis of crop sac contents showed that the birds fed chiefly on pigeon peas (Cajanus cajan) during the breeding season and on cereal grains at other times of the year. It is suggested that pigeon peas provide the extra nutrients, including calcium, required for egg production. Since pigeon peas ripen between November and March, the production of the crop may play a role in the timing of seasonal breeding. A further factor appears to be competition for nest sites. By breeding in winter, the parakeet avoids competing with other species which nest in holes.

The response of the pituitary gland to luteinizing hormone-releasing hormone in broody bantams

The concentration of plasma LH increased significantly (P < 0.001) after an iv injection of 20 μg LHRH/kg body wt in out-of-lay, laying, incubating, and brooding bantams. The increase in out-of-lay (2.6 ± 0.4 [SEM] ng/ml, n = 12) and laying (1.8 ± 0.3 ng/ml, n = 6) birds was significantly less (P < 0.05) than in incubating (5.0 ± 0.8 ng/ml, n = 10) or brooding (4.6 ± 0.7 ng/ml, n = 5) birds. It was concluded that LH secretion in incubating bantams may be suppressed because of a reduction in the secretion of gonadotrophin-releasing factor.

Development of photorefractoriness in willow ptarmigan (Lagopus lagopus lagopus) and red grouse (Lagopus lagopus scoticus) exposed to different photoperiods

Abstract The relationship between daylength and the development of photorefractoriness was investigated in willow ptarmigan ( Lagopus lagopus lagopus ) and red grouse ( Lagopus lagopus scoticus ) using comb height, plasma LH levels, and, in willow ptarmigan only, plasma testosterone (T) as indicators of reproductive function. Photosensitive birds were transferred from a 6-hr daylength (6L:18D) to 14-hr (14L:10D), 18-hr (18L:6D), or continuous (LL) daylengths. In both races, LH levels increased more after exposure to 18L:6D and LL than after exposure to 14L:10D. Willow ptarmigan held on LL and 18L:6D, and red grouse held on LL, 18L:6D, and 14L:10D, became photorefractory after 8–12 weeks of photostimulation. Unlike red grouse, willow ptarmigan maintained on 14L:10D did not become photorefractory during the 20-week study. In willow ptarmigan which had been exposed to 14L:10D for 15 weeks, plasma LH and T were further increased after transfer to LL and then fell after 6–7 weeks as the birds became photorefractory. It seems that, although the process leading to the development of photorefractoriness started after exposure to 14L:10D, this photoperiod was too short to complete the process. The observation that red grouse become photorefractory while held on 14L:10D whereas willow ptarmigan did not, is consistent with the observation that in the wild, the daylengths experienced by breeding red grouse are shorter than those seen by breeding willow ptarmigan.