Endocrine correlates of parental care in an Antarctic winter breeding seabird, the emperor penguin, Aptenodytes forsteri

Plasma levels of luteinizing hormone (LH) and prolactin associated with parental behavior were measured in the Antarctic winter breeding emperor penguin, Aptenodytes forsteri. Males exclusively incubate the egg while females exclusively brood the nonhomeothermic young; both sexes alternate in rearing the homeothermic young. Birds were sampled on arrival from the sea through egg laying, incubation, and brooding. All parent birds lost their chicks at the end of the brooding period due to harsh weather but sampling continued. In females, LH titers dropped after egg laying but levels were restored when the birds returned from the sea to brood the chicks and were not depressed by high prolactin levels. Plasma prolactin remained low in males captured on arrival and kept until the free-living males finished incubation. In breeders, prolactin secretion increased during the prelaying period when day length decreased. Prolactin levels stayed elevated in males during incubation and in brooding females returning after a 2-month absence at sea. Prolactin values were higher in brooding females than in males ending incubation or returning in late brooding. These levels did not drop after chick loss, and the sexual difference in prolactin values was maintained after breeding failure. In emperor penguins, increased prolactin secretion appears to be triggered around the time of egg laying and continues, driven by an endogenous mechanism, through incubation and brooding until rearing is completed. Prolactin secretion independent of external stimuli may have evolved in pelagic seabirds to maintain parental care despite long absences at sea from the breeding colony.     

Prolactin's mediative role in male parenting in parentally experienced marmosets (Callithrix jacchus)

Prolactin has been implicated in promoting paternal care behaviors but little evidence of causality has been found to date except for birds and fish. This study was designed to examine the possible causal relationships between prolactin and male parenting behaviors, reproductive hormones, and physical changes in cooperatively breeding common marmosets, Callithrix jacchus. Fifteen parentally experienced fathers were studied over three consecutive infant care periods during two weeks prior and three weeks following their mates' parturition under three-treatment conditions: normal control pregnancy, decreased prolactin and elevated prolactin. The treatments significantly altered the serum prolactin levels in the fathers. Using three methods of determining a father's level of parental care: infant carrying, family effort and responsiveness to infant stimulus tests, we found that only the male response to infant stimuli was altered by the hormone treatments. Lowering prolactin significantly reduced male responsiveness to infant stimuli but elevating prolactin showed the same effect. Hormonal sampling indicated that testosterone levels showed an inverse relationship to prolactin levels during a normal peripartum period and prolactin treatment reduced this relationship. Prepartum estradiol levels were significantly elevated during the lowered prolactin treatment and estradiol was significantly lowered postpartum with the elevated prolactin treatment. Father's weight decreased significantly by the third week of infant care during the normal treatment. Males in the elevated prolactin treatment lost little or no weight from prepartum while in the lowered prolactin treatment showed the most weight loss. The present findings did not distinguish a direct causal relationship of prolactin on behavior in experienced fathers but did find an interaction with other hormones and weight gain.     

Differences in prolactin levels between three alternative male reproductive tactics in striped mice (Rhabdomys pumilio)

In male fishes, birds and mammals, increased prolactin secretion is thought to play a role in species showing paternal behaviours. This hypothesis was investigated in the striped mouse (Rhabdomys pumilio). This paper compares serum prolactin levels in 71 free-living male striped mice following three different reproductive tactics: (i) paternal group-living breeders, (ii) alloparental philopatric group-living males, and (iii) roaming non-paternal solitary males. Prolactin levels of breeding males were significantly higher than that of roamers. Alloparental philopatric males had low prolactin levels, which concur with studies of cooperatively breeding mammals, but contrasts with studies of cooperatively breeding birds. Both breeding males and females showed a decrease in prolactin levels after the breeding season, but not alloparental philopatric males. Prolactin levels were correlated with neither corticosterone levels nor age. These results are in agreement with the hypothesis that prolactin is one proximate mechanism of male reproductive tactics, possibly regulating differences in male parental care.     

Plasma prolactin variations and onset of ovarian activity in lactating anestrous goats given melatonin

This experiment was carried out in order to investigate the effects of melatonin treatment on prolactin plasma levels and the onset of cyclicity in anestrous goats. Fifty lactating goats were treated daily with 2.5 mg melatonin (i.m.) from 6 June to 18 September and fifty goats served as a control. The progesterone and prolactin plasma concentrations were determined by radioimmunoassays on blood samples collected once a week until the end of September. The onset of ovarian activity (monitored by the plasma progesterone determination) was advanced in the melatonin-treated does by about one week compared with the controls. Prolactin plasma levels decreased in the control animals from the highest concentrations observed in June to the lowest near the end of the experiment. In the melatonin-treated goats, the prolactin plasma levels dropped after the beginning of the treatment and remained significantly lower than those of the untreated does for about two months; from then onwards, no differences were observed between the two groups until the end of the experiment.     

Plasma gonadotropin,prolactin levels and hypothalamic tyrosine hydroxylase activity in rats during estrous cycle,after overiectomy and after blockade of catecholamine biosynthesis

Plasma gonadotropin, prolactin levels and hypothalamic tyrosine hydroxylase activity were evaluated at 0900, 1200 and 1700 h during diestrus, proestrus and estrus, ovariectomized and after systemic administration of reserpine or α-methyl p-tyrosine, which interfere with catecholamine biosynthesis, in rats. Gonadotropin and prolactin levels showed peak values during the afternoon of proestrus, while hypothalamic tyrosine hydroxylase activity was markedly lowered at 1200 on proestrus. Gonadotropin levels were slightly lowered whereas prolactin concentrations and hypothalamic tyrosine hydroxylase activity were significantly increased by reserpine. Depletion of hypothalamic dopamine by reserpine apparently resulted in significant elevation of prolactin levels which inturn induce tyrosine hydroxylase. Gonadotropin levels and hypothalamic tyrosine hydroxylase activity were significantly suppressed after the administration of α-methyl p-tyrosine. Prolactin levels, however, were elevated significantly. These results indicate that catecholamines are involved in the control of gonadotropin and prolactin release during estrous cycle and inhibition of catecholamines biosynthesis by α-methyl p-tyrosine could result in suppression of gonadotropin levels, whereas removal of tonic inhibition of hypothalamic dopamine by α-methyl-p-tyrosine elevate prolactin levels.     

Circadian and circannual rhythms of LH, FSH, testosterone (T), prolactin, cortisol, T3 and T4 in plasma of mature, male white-tailed deer

Circadian and circannual rhythm of plasma LH, FSH, testosterone (T), prolactin, cortisol, triiodothyronine (T3) and thyroxine (T4) were investigated in two mature male white-tailed deer. No circadian rhythms were detected. Seasonal levels of LH and FSH were reached in September and October; troughs occur in May and June. Maximal T values were detected in November and December (the time of the rut); minimal levels occur between February and July. Prolactin peaked in May and June; minimal levels were detected between October and February. T3 exhibited two maxima; the first in the May-June period, the second in the September-October period. T4 showed no recognizable circannual rhythm. Cortisol levels were found to be much higher during cold months (December-April) than during the rest of the year. The least variable circadian levels were that of FSH and prolactin, with LH, T4, T3, cortisol and testosterone following in descending order. Cannulation stress might have some effect on the levels of testosterone, LH and cortisol. Correlation between LH and testosterone levels were detected mainly during sexually active periods.     

Modulation of gonadotrophin and prolacrin secretion by daylength and breeding behaviour in free-living starlings, Sturnus vulgaris

Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured by radioimmunoassay in plasma samples collected from free-living starlings, Sturnus vulgaris , trapped in nest-boxes. By leaving some nest-boxes undisturbed, and repeatedly destroying nests in others, birds from a single-brooded population were trapped whilst nest-building, incubating or feeding nestlings, at different times throughout the normal breeding season. In both males and females trapped whilst nest-building, plasma LH and prolactin levels increased progressively from mid March until late May. In females sampled during incubation, LH and FSH levels were high throughout May but decreased in early June. Prolactin levels were highest in late May. In both males and females trapped during mid May, LH levels were highest in these birds which were nest-building at this time and lowest in those feeding nestlings, FSH did not change significantly, and prolactin was low in those birds which were nest-building and high in those incubating or feeding nestlings. In female starlings from a double-brooded population, levels of LH and FSH were much lower whilst feeding the second brood than when feeding the first brood, whereas prolactin levels were similar. The results suggest that incubation and feeding behaviour inhibit the increase in LH secretion caused by increasing daylength, but stimulate prolactin secretion in excess of that caused by increasing daylength.     

Modulation of prolactin but not corticosterone responses to stress in relation to parental effort in a long-lived bird

We tested the hypothesis that parental effort modulates the magnitude of corticosterone and prolactin responses to stress in a long-lived bird, the Black-legged kittiwake (Rissa tridactyla). To do so, we compared corticosterone and prolactin responses to capture/restraint stress between chick-rearing birds and failed breeders (no parental effort). We predicted that (1) the increase in plasma corticosterone levels in response to stress should be lower in chick-rearing birds, (2) the decrease in plasma prolactin levels in response to stress should be lower in chick-rearing birds, and (3) as both sexes care for the chick, there should be no sex difference in the hormonal response to stress. Baseline plasma corticosterone and prolactin levels were higher in chick-rearing birds and were not influenced by body condition. Failed breeders were in better condition than chick-rearing individuals. Corticosterone response to stress was unaffected by parental effort as both chick-rearing and failed birds exhibited a robust corticosterone increase. Prolactin response to stress was however clearly influenced by parental effort: chick-rearing birds showed a modest 9% prolactin decrease whereas in failed birds prolactin concentrations fell by 41%. Body condition did not influence hormonal responses to stress. When facing stressful condition, breeding kittiwakes attenuate their prolactin response to stress while enhancing their secretion of corticosterone. Increasing corticosterone secretion triggers foraging efforts and diminishes nest attendance whereas an attenuation of prolactin response to stress maintains parental behavior. We suggest that this hormonal mechanism facilitates a flexible time-budget that has been interpreted as a buffer against environmental variability.     

Plasma levels of prolactin and gonadal steroids in relation to multiple-brooding and renesting in free-living populations of the song sparrow, Melospiza melodia

Plasma levels of testosterone (T), estradiol (E2), and prolactin were measured in samples collected from free-living song sparrows, Melospiza melodia. In males, plasma levels of T were elevated early in the season when territories were established and when females laid the first clutch of eggs. Thereafter, T levels declined and remained low throughout the remainder of the breeding cycle. However, if the first brood was lost to a predator, or by experimental removal of the nest, plasma levels of T increased as renesting, to replace the clutch, occurred. Circulating levels of prolactin in males began to rise during the egg-laying stage of the first brood, reached a maximum toward the end of the incubation stage, remained elevated until breeding was terminated, and then declined throughout the moulting stage to basal values in October. Prolactin levels remained high throughout the breeding season irrespective of whether a brood was raised successfully or whether the nest was lost and renesting occurred. In females, plasma levels of E2 were elevated prior to the egg-laying stage for each brood as is typical of multiple-brooded species. However, prolactin titers rose dramatically during egg-laying for the first clutch (slightly higher than in males) and were maximal by onset of incubation. Only females of this species incubate, although males do feed young. As in males, plasma prolactin in females remained high between broods and during experimentally induced renesting, and then declined to basal by the end of the moult stage in October. These data suggest that there are no differences in the temporal patterns of prolactin concentrations in blood between multiple-brooding and renesting. In a separate experiment, captive male song sparrows were transferred from a short day to artificial long days (18L 6D) and a control group was maintained on 9L 15D. In the long-day group, prolactin levels rose abruptly over the first 20 days, as the testes developed, and remained high well into postnuptial moult after the gonads had regressed. Prolactin remained basal in the control group. These data suggest that the temporal pattern of circulating prolactin levels throughout the breeding season is regulated at least partly by changing photoperiod. However, nonphotoperiodic factors are also important since photoperiodically induced increases in prolactin are significantly less than those seen in free-living individuals. These differences may be related to parental behavior.     

Prolactin levels of fathers and helpers related to alloparental care in common marmosets, Callithrix jacchus

Previous studies have suggested that prolactin may play a role in regulating allocare behaviour in cotton-top tamarins, Saguinus oedipus. In this study, we investigate the prolactin profile of 3 groups of captive common marmosets, Callithrix jacchus. Carrying behaviour in this species was observed after parturition. Prolactin assays of blood samples of both fathers and helpers (sub-adult non-fathers) in 3 family groups were taken for 8 weeks before and after birth of the infants. The after-birth condition was divided into 2 groups: carrying and non-carrying animals. The results suggest a relationship between prolactin levels and allocare behaviour, with carrying behaviour being associated with increased prolactin in both fathers and helpers. This suggests that extra prolactin is produced in response to physical contact, and may be associated with carrying behaviour. Also, prolactin production may be related to learning parental skills in Neotropical primates.     

Effects of melatonin treatment on the onset of ovarian activity,reproductive parameters and PRL plasma levels of immature ewes

The aims of this study were to investigate the effect of chronic treatment with melatonin on prolactin plasma profiles, the onset of ovarian activity and the fertility of immature ewes. Beginning in late June, 30 maiden ewes were administered 2.5 mg melatonin (i.m.) daily until mid-September. Progesterone and prolactin plasma concentrations were determined by validated radioimmunoassays on samples collected every 5 days from 17 June until 31 October. Prolactin (PRL) plasma concentrations in the control animals were highest at the beginning of the experiment and lowest towards its conclusion. In melatonin-treated ewes, PRL levels dropped just after treatment began and were similar to those observed in the control animals at the end of the experimental period. The ovarian activity was advanced by approximately one month by the administration of melatonin, while the mean date of lambings was advanced by about two weeks compared with the controls. Fertility in the treated animals was very similar to that of the controls; the prolificacy (lambs/pregnant ewe) was 2 in the treated and 1.62 in the control ewes.     

Hormones associated with non-maternal infant care: a review of mammalian and avian studies

Hormonal changes during non-maternal infant care have been demonstrated in many cooperatively breeding bird species, some monogamous rodents and two species of New World primates. Coevolution of hormones and social traits may have provided for the different breeding systems that occur today. Several hormones have been shown to covary with the breeding systems of vertebrates. Elevated levels of the hormone prolactin with male parenting behaviours are common to many birds, rodents and the callitrichid monkeys Callithrix jacchus and Saguinus oedipus. In birds, prolactin may be elevated in both male and female breeders during various stages of nest building, egg laying, incubating and feeding of young. Testosterone levels appear to have an inverse relationship to prolactin levels during infant care in birds and rodents, but this relationship has not been examined for primates. In cooperatively breeding birds, helpers who remain at the nest also have elevated levels of prolactin when displaying parental care behaviours. Prolactin levels are elevated in helper callitrichid monkeys during the postpartum period. Monogamous male rodents demonstrate elevated prolactin levels with parental care behaviour but, in contrast to the birds, the mechanisms mediating prolactin increase appear to differ for male and female rodents. Two factors may influence male parental behaviours and hormonal changes: stimuli from the pregnant female and stimuli from the newborn pups; whereas maternal behaviours are influenced by the maternal hormones of the female and the pup stimuli. An experiential factor may also influence male parental behaviours. Neuropeptides such as oxytocin and vasopressin appear to be involved in male rodent parental care and there may be an interaction between a series of hormones and neurosecretions and stimuli from mates and pups. Studies of Saguinus oedipus, the cotton-top tamarin, suggest that prolactin levels are responsive to stimuli from contact with infants and the level of infant care experience influences the levels of prolactin with male infant care. Father tamarins also have elevated levels of prolactin before the birth of infants suggesting that cues from the pregnant female are important. Prolactin's role in parental care may have evolved from prolactin's role in other reproductive functions. Hormonal regulation of non-maternal care may occur due to a complex interaction of many hormones and neurotransmitters. Studies described here should provide the impetus for further work on parental care hormones in a wide variety of primates.     

Seasonal changes in the concentration of plasma prolactin in the migratory Canada goose (Branta canadensis interior)

• 1.1. Seasonal changes in the plasma prolactin level of the migratory Canada goose breeding in the Canadian subarctic region (Fort Churchill, Manitoba) and wintering in the southern USA (Swan Lake Refuge, Missouri) were studied.
• 2.2. Peak prolactin level was observed in geese collected at Missouri in October, immediately after Fall migration (Fall postmigratory period). This was significantly higher than that in September (Fall premigratory period), July (moulting period) and March (Spring premigratory period).
• 3.3. Prolactin levels in May (Spring postmigratory period) and June (incubating period) did not differ significantly from that of any other period.

     

Hormonal changes related to paternal and alloparental care in common marmosets (Callithrix jacchus)

The physiological mechanisms of parental and alloparental care in cooperatively breeding nonhuman primate species such as the common marmoset (Callithrix jacchus) are poorly known. In this study, we examined prolactin and cortisol plasma levels of fathers and older offspring of both sexes, with and without previous experience in infant carrying, around parturition and during infant carrying. Blood samples were collected from fathers and older offspring and prolactin and cortisol were measured by RIA and EIA, respectively. Prolactin levels of both caretakers were not influenced by infant's birth, previous experience or proximity to parturition. However, prolactin levels increased in both caretakers while in physical contact with infants and also with the number of infants being carried in older offspring. These findings suggest that increased prolactin seems to be mainly due to physical effort rather than a physiological trigger of paternal and alloparental care in common marmosets. Cortisol levels were higher for experienced fathers shortly before parturition which could act to reinforce affiliative bonds between breeding males and females at this time or in the ability of males to detect the proximity of the parturition or both.     

The effects of immersion and exercise on prolactin during pregnancy

Prolactin is an important hormone during pregnancy, affecting mother, fetus, and amniotic fluid volume. Immersion is known to affect prolactin levels significantly. To determine the effect of immersion and exercise on the prolactin response during pregnancy, we examined serum prolactin levels at 15, 25, and 35 weeks' gestation and 10 weeks post partum. Twelve women completed 20 min land rest, 20 min immersion in 30 degrees C water to the xiphoid, and 20 min exercise in the water at 60% VO2max. Resting prolactin levels were 1.91 +/- 0.32, 4.55 +/- 0.5, and 5.85 +/- 0.27 nmol.l-1 +/- standard error of the mean at 15, 25, and 35 weeks' gestation, respectively. Postpartum lactating women had a resting mean prolactin level of 3.95 +/- 1.6 versus 0.22 +/- 0.4 nmol.l-1 in non-lactating women. Prolactin levels declined significantly during immersion even after correction for dilution by plasma volume shifts. The immersion response was inversely related to the duration of pregnancy with 29%, 22%, and 12% drops during 15-, 25- and 35-week trials, respectively. Compared to rest, exercise prolactin levels remained depressed during the 15th and 25th week trials. We hypothesize that immersion in water caused prolactin levels to decline.     

Prolactin responses to infant cues in men and women: effects of parental experience and recent infant contact

We used a longitudinal design to test whether parental experience differentially affects the development of prolactin responses to infant cues in men and women. Couples provided two blood samples at three tests, one test just before their babies were born, and two tests during the early postnatal period (n=21). Nine couples repeated the tests near the birth of their second babies. In the 30 min between the two samples, couples listened to recorded infant cries at the prenatal test and held their baby (fathers) or a doll (mothers) at the postnatal tests. Blood samples were analyzed for prolactin concentrations. Prolactin values were then related to sex and parity differences as well as to questionnaire data concerning emotional responses to infant cries and previous infant contact. We found that (1) prior to the birth of both the first and second babies, women's prolactin concentrations increased after exposure to infant stimuli, whereas men's prolactin concentrations decreased; postnatal sex differences varied with parity; (2) women's prolactin reactivity did not change significantly with parental experience; (3) the same men's prolactin concentrations decreased after holding their first newborns but increased after holding their second newborns; this change was not gradual or permanent; (4) men reporting concern after hearing recorded infant cries showed a different postnatal pattern of prolactin change after holding their babies than men not reporting concern; and (5) men who had little contact with their babies just prior to testing had a more positive prolactin response than men who had recently held their babies for longer periods. Although parental experience appears to affect men's prolactin responses, differences in reactivity were also related to patterns of recent infant contact and individual differences in responses to infant cues.     

Prolactin Concentrations in Patients with Breast Cancer

Basal prolactin levels were measured before operation in 113 patients undergoing surgery for a lump in the breast. Prolactin concentrations were not significantly higher in those patients with breast cancer than in those with benign lumps. Prolactin concentrations were, however, found to be higher in premenopausal women than in postmenopausal ones, regardless of tumour histology.     

Prolactin enhances production of interferon-gamma,interleukin-12, and interleukin-10, but not of tumor necrosis factor-alpha,in a stimulus-specific manner

Prolactin, an anterior pituitary hormone, has been shown to have a role in immunomodulation. Some reports have shown the importance of prolactin in activating lymphocytes and macrophages, while in hyperprolactinemia patients, prolactin was found to decrease lymphocyte activation and natural killer function. In the present work, at physiological (15ng/ml) and stress-induced levels (30ng/ml) of prolactin, interferon-gamma (IFN-gamma) and interleukin (IL)-12 p70 levels, but not of IL-10 and tumor necrosis factor-alpha (TNF-alpha), increased significantly (p<0.05-0.006) in phytohemeagglutinin (PHA)+lipopolysaccharide (LPS)-stimulated whole blood. However, no such effect was observed at high concentrations of prolactin (100-300ng/ml). In addition, 15ng/ml of prolactin reversed hydrocortisone suppressive effect on IFN-gamma, IL-12 p70, and IL-10 production in PHA+LPS-stimulated whole blood. On the other hand, in LPS-stimulated whole blood, prolactin enhanced significantly (p=0.027) the production levels of IL-10, but not of IFN-gamma, IL-12 p70, and TNF-alpha, in non-concentration-dependent manner. These results suggest that prolactin modulates cytokine response during antigenic response, and this modulation is stimulus specific.     

Effects of hypophysectomy and thyroidectomy on salt balance in the plethodontid salamanders,Desmognathus fuscus andDesmognathus monticola

Summary Hypophysectomy significantly reduced serum sodium levels inDesmognathus fuscus andD. monticola. Prolactin, corticosterone or aldosterone replacement failed to restore serum sodium to control levels. Hypophysectomy also led to decreases in in vitro integumental potential difference and shortcircuit current, which were not restored to control levels by prolactin or corticosterone. Thyroidectomy significantly reduced the level of serum sodium inD. monticola, but it increased in vitro potential difference and short-circuit current. Thyroxine treatment of either hypophysectomized or thyroidectomizedD. monticola completely restored serum sodium, potential difference and short-circuite current to control levels.