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At least 739 records · Page 41Linked to original sources
PubMed1984

Hormonal correlates of polyandry in the spotted sandpiper, Actitis macularia.

Plasma samples from naturally breeding populations of spotted sandpipers, Actitis macularia, were analyzed by radioimmunoassay for circulating levels of immunoreactive luteinizing hormone (irLH), and four steroid hormones. Plasma levels of irLH, corticosterone (C), and estradiol-17 beta (E) did not differ between males and females. Males had curiously high levels of E (0.64 pg/ml in nonnesting males; 0.35 pg/ml in nesting males) which are similar to those of nonlaying females (0.23 pg/ml). Testosterone (T) and dihydrotestosterone (DHT) were higher in nonnesting males (0.95 ng/ml for T; 0.20 ng/ml for DHT) than in females (0.18 ng/ml for T; 0.12 ng/ml for DHT) or nesting males (0.17 ng/ml for T; 0.09 ng/ml for DHT). These data do not support earlier suggestions that in polyandrous mating systems, females have higher circulating levels of androgens than males.

Androgens↗
PubMed1984

The effects of modifying incubation on prolactin secretion in free-living pied flycatchers.

Plasma prolactin concentrations in female pied flycatchers are high during incubation, but fall from 156 +/- 27 to 67 +/- 6 ng/ml (P less than 0.01) between 2 and 4 days after the young hatch. The timing of the fall in prolactin could be determined by factors associated with the hatching of the eggs and growth of the offspring; alternatively, prolactin may remain high for a fixed period (16 days) after the onset of incubation. To distinguish between these possibilities, eggs were exchanged between nest boxes to ensure incubation periods of either 10, 14, or 19 days by different females. The results showed that the period of high prolactin secretion was shortened by 2-4 days where the eggs hatched early, but, conversely, was not lengthened in those females with extended incubation periods, the levels actually falling in these birds before the eggs hatched. There was, however, a secondary rise in prolactin 3 days after hatching, when the level of 114 +/- 11 ng/ml 22 days after the onset of incubation was much higher than that (30 +/- 4 ng/ml) at a comparable stage in the control females. Thus, high prolactin secretion cannot be maintained for longer than 16-17 days in incubating birds, but newly hatched, naked young can stimulate prolactin release in female flycatchers over a flexible period.

Animals↗
PubMed1986

Corticosterone secretion through long incubation shifts in Diomedea albatrosses.

Blood samples were collected from free-living incubating Diomedea albatross during single incubation shifts, both daily (wandering albatross D. exulans and every 2 days (grey-headed albatross D. chrysostoma and black-browed albatross D. melanophris), and the concentration of corticosterone was determined. Within 48 hr a significant increase in the corticosterone concentration was observed in each species. The magnitude of the increase was greater in the grey-headed and black-browed albatrosses than in the wandering albatross. Corticosterone concentrations rose steadily through the incubation shift in grey-headed and black-browed albatrosses, but fluctuated erratically in wandering albatrosses. All three species of albatross fast during incubation and the increase in adrenocortical activity is probably related to the voluntary deprivation of food and water.

Animals↗
PubMed1986

Variations in plasma corticosterone, estrone, estradiol-17 beta, and progesterone concentrations with forced renesting, molt, and body weight of captive female American kestrels.

Corticosterone, progesterone, estradiol-17 beta, and estrone were quantified in plasma collected weekly (April-September) from renesting and nonlaying female American kestrels (Falco sparverius) paired with males in captivity. Hormone levels and body weights for laying females were maximal during courtship and egg-laying periods, while those for non-layers showed no such distinct peaks. This demonstrated that these profiles were not controlled solely by photoperiod. Plasma corticosterone levels were elevated in all females during August and September when kestrels are preparing for migration. For laying females, body weight was positively correlated with plasma estrogen levels. A low spring body weight gain, and not stress, may have prevented the females from breeding in captivity. The photoperiodic control of molt did not appear to be mediated directly by the hormones studied, since there were no changes in hormone levels associated with the onset of molt.

Animals↗
PubMed1986

Evidence that vasoactive intestinal polypeptide is a physiological prolactin-releasing factor in the bantam hen.

Vasoactive intestinal polypeptide (VIP)-like material was localised immunohistochemically in the hypothalamus of the bantam hen. Abundant immunoreactive VIP terminals were seen in the external layer of the median eminence and most immunoreactive VIP cell bodies were located in the basal hypothalamus. A few immunoreactive VIP cell bodies and many fibres were found in the preoptic hypothalamus. Intravenous injections of synthetic porcine VIP over a dose range of 12.5 to 100 micrograms kg-1 body wt resulted in dose-related increase in concentration of plasma prolactin in incubating bantams deprived of their nests for 24 hr. These doses of VIP did not stimulate the release of growth hormone. Studies in vitro showed that synthetic VIP directly stimulated prolactin release from the anterior pituitary gland. The glands from incubating bantams were more responsive to the prolactin-releasing effects of VIP than were the glands from laying birds. Studies in vitro showed that the amount of prolactin released in response to an iv injection of 50 micrograms kg-1 VIP was greater in incubating birds deprived of their nests for 24 hr than in laying hens. Prolactin release was not stimulated in ovariectomized hens after an injection of 50 micrograms kg-1 VIP unless the birds were first treated with oestrogen or oestrogen and progesterone. It was concluded that a VIP-like material in the bantam hypothalamus may be a physiological prolactin-releasing factor acting at least in part at the level of the anterior pituitary gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Hormonal changes associated with natural and manipulated incubation in the sex-role reversed Wilson's phalarope.

Wilson's phalarope (Phalaropus tricolor) is characterized by intense female intrasexual competition and exclusive male parental care. Females occasionally are polyandrous and no territories are defended. Prolactin (Prl) and testosterone (T) were analyzed from plasma samples obtained from individuals of different reproductive stages. Males tended to have higher plasma Prl levels than females throughout the breeding season. Prolactin levels of males declined posthatch, reaching baseline levels when chicks were approximately 9 days old--the time when chicks approach thermal independence and brooding is minimal. Testosterone levels dropped at the onset of incubation and remained low through the brooding period. Eggs were manipulated such that some males incubated clutches for shortened periods, others for extended periods. Regardless of the length of incubation, Prl levels were determined primarily by environmental events, i.e., incubation, hatching, and brooding.

Animals↗
PubMed1989

Increased levels of arginine vasotocin and neurophysin during nesting in sea turtles.

Arginine vasotocin (AVT) and neurophysin (NP) levels were measured by radioimmunoassay in two species of sea turtle, the olive ridley, Lepidochelys olivacea, and the loggerhead, Caretta caretta, during the brief period of nesting and oviposition. In both species, AVT was low in animals which were not reproductively active. AVT was also low at the time animals emerged from the surf to nest, but increased significantly during oviposition and then declined as the animals returned to the water. NP increased in concert with AVT, also reaching highest levels during oviposition. In both species, however, NP levels remained elevated over prenesting levels at the time of return to the water. These findings are consistent with the hypothesis that an AVT-neurophysin complex is released from the neurohypophysis during nesting, and that AVT is a physiological regulator of oviducal contractions in sea turtles.

Animals↗
PubMed1983

Serum prolactin levels and crop-sac development in ring doves during a breeding cycle.

Using a turkey prolactin radioimmunoassay, the serum prolactin levels of male and female ring doves (Streptopelia risoria) during the breeding cycle were measured and their circulating prolactin levels were compared to crop-sac weight on a within-bird basis. During the early phase of the incubation period, crop weight showed a delayed response to prolactin stimulation and there was no correlation; during the midincubation period when prolactin and crop-sac weight were increasing, there was a strong positive correlation; around hatching, when prolactin was at its peak, there was no correlation. There were again strong positive correlations at later samples, when squabs were developing and both prolactin and crop-sac weight were declining. Thus, it appears that the correlation between the circulating prolactin level and crop-sac development depends on the stage of the breeding cycle. While males and females showed similar pattern of circulating prolactin during the period of incubation and parental care, only females consistently showed a postovulatory rise of prolactin. These results were discussed in the context of the role of prolactin in the breeding cycle.

Animals↗
PubMed1987

Endocrine events associated with spawning behavior in the sea lamprey (Petromyzon marinus).

Levels of estradiol, progesterone, and testosterone were determined in plasma of sea lamprey (Petromyzon marinus) undergoing certain behaviors associated with spawning in natural and artificial stream environments. Significantly higher levels of estradiol, progesterone, and testosterone were found in males than in females. In the artificial spawning channel, levels of estradiol were significantly higher in females exhibiting resting and swimming behaviors than in fanning, nest building, and spawning behaviors. No significant correlation was found with either progesterone or testosterone levels and the various reproductive behaviors. The data presented are the first experimental evidence that suggest gonadal steroids may be correlated with certain reproductive behaviors in the sea lamprey.

Aggression↗
PubMed1989

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.

Animals↗
PubMed1991

Effects of presence of squabs upon plasma concentrations of prolactin and LH and length of time of incubation in ringdoves on "extended" incubatory patterns.

The effects of a brief exposure to newly hatched squabs upon the concentrations of plasma prolactin and LH secretion and length of incubation time in ring doves were investigated using a novel experimental procedure. After 5 days of incubation birds were deprived of their nests for 3 days. On return to their nests, the birds immediately resumed incubation and laid a second clutch of eggs after 5 days at which time the first clutch was removed. A consequence of this procedure was that at the time of hatching, concentrations of plasma prolactin had passed their peaks and were falling to baseline values, while concentrations of plasma LH were beginning to increase. This experimental manipulation made it possible to demonstrate that brief exposure to newly hatched squabs significantly affects the concentration of plasma prolactin, an effect which was more pronounced in females than in males. This increased secretion of prolactin was associated with a reduction of plasma LH which reached significance in females but not in males. Birds exposed to squabs spent a significantly longer period of time on their nests as compared to those birds not exposed to squabs. This observation is consistent with a role for prolactin in maintaining readiness to incubate.

Animals↗
PubMed1991

Testosterone and avian life histories: the effect of experimentally elevated testosterone on corticosterone and body mass in dark-eyed juncos.

To assess whether alterations in the normal pattern of testosterone (T) secretion might be beneficial or detrimental, we studied a breeding population of dark-eyed juncos in which we elevated T experimentally and measured its effect on potential correlates of fitness. We treated both free-living and captive males with implants that were either empty (C-males, controls) or packed with T (T-males, experimentals). Timing of implant varied and was designed to mimic natural peak breeding levels except that peaks were either prolonged or premature. We bled the birds at recapture and analyzed their plasma, and that of their female mates, for T and corticosterone (B). We also measured body mass and fat score in free-living T- and C-males. In the field, T-implants elevated T and kept it elevated for at least a month. Experimental males also had higher B than controls. In captives, the effect of the implants on plasma T was detectable within 24 hr. B in captive T-males was again higher than in captive C-males. In females, neither T nor B differed between mates of T- and C-males. T-males implanted in early spring lost more mass between implant and recapture in late spring than did controls and also had lower fat scores when recaptured. When implants were inserted in summer, treatment did not influence mass. Elevated T in early spring apparently hastened the transition from the winter to the breeding mode of fat storage. We suggest that prolonged elevation of testosterone might be selected against because of the association between T and B. Premature elevation of T might be costly because of the resultant loss of mass and fat reserves, which could lead to mortality when spring snowstorms prevent access to food.

Adipose Tissue↗