Development of the sex difference in glandular kallikrein and prolactin levels in the anterior pituitary of the rat

Glandular kallikrein is a major estrogen-induced and dopamine-repressed protein of the rat anterior pituitary that appears to originate from lactotrophs. This study examined the development of glandular kallikrein levels in the anterior pituitary in both female and male rats and compared it to anterior pituitary prolactin. In addition, the development of glandular kallikrein levels in the neurointermediate lobe of the pituitary and the kidney were also examined. During puberty, a dramatic surge in glandular kallikrein occurred in female anterior pituitaries (16- to 20-fold increase) and levels remained elevated thereafter. The dynamics of the increase were biphasic--glandular kallikrein increased between Day 30 and 45, plateaued between Days 45 and 55, and then increased again between Days 55 and 65. Female anterior pituitary prolactin increased 7- to 8-fold during puberty. The rise during puberty was biphasic and was generally synchronized with increases in glandular kallikrein. However, the initial rise was proportionately less than that of glandular kallikrein, and the secondary surge was more dramatic. In contrast to females, anterior pituitary glandular kallikrein remained at low levels in male rats; prolactin levels also remained unchanged through puberty and increased moderately thereafter. Glandular kallikrein in the female neurointermediate lobe remained unchanged through Day 55, almost doubled on Day 60, and returned to prepubertal levels by Day 65; males did not exhibit the transient surge in neurointermediate lobe levels. Starting at age 60 days, renal glandular kallikrein was found to be slightly higher (15-20%) in females than in males.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Changes of lactic dehydrogenase activity and combination of its subunits in rat anterior pituitary during puberty and in maturity, as well as during estrous cycle on the actue effect of estradiol and after castration

LDH activity in the female rat anterior pituitary increases substantially at the opening of the vagina, after the gradual increase up to the 90st day no important change occurs. During the estrous cycle activity reaches its peak during the estrus, and lowest in ghe proestrus. Molecular organization of the enzyme shows a change only at the opening of the vagina, i. e. a sudden decrease of H/M ratio occurs, value of which does not change during the estrous cycle. Pituitary LDH activity and subunit ratio in males remains constant during life. LDH activity excess in mature female rat pituitary, being about the double as compared to males, develops at the age of about three months, the difference in H/M ratio however is manifest already during puberty. Anterior pituitary LDH activity and structure of the enzyme are affected by sexual hormones, primarily by estradiol, under physiological conditions, too. After ovariectomy LDH activity decreases gradually. The value before the opening of the vagina to be considered as basal level, develops in the 4th postoperative week. H/M ratio decreases by 20 per cent one week after the operation and shows no change thereafter. Orchidectomy involves but a minor activity and H/M ratio decrease. Experimental findings on activity and subunit ratio are related presumably to prolactin cells and suggest that sexual hormone feedback effects in addition to polypeptide production pituitary metabolism.     

Ontogenesis of enkephalin and humoral endorphin in the rat brain

Radioimmunoassay and column chromatography techniques were used to study the postnatal development of two different opioid ligands, humoral endorphin and enkephalin in the rat brain. Similar patterns were observed for both male and female animals during the period examined (from birth to the seventh week of life). Humoral endorphin content of the developing rat brain was found to increase in parallel to enkephalin, exhibiting a ‘lag’ period of 2 weeks. The most dramatic increase in opioid levels was detected during the third week of life; this stage was followed by a gradual change up to the adult levels.     

Sex differences in the long-term effect of preweanling isolation stress on memory retention

Social experiences during development can powerfully modulate later neuroendocrine and behavioral system. In the present study, male and female rat pups experienced daily bouts of social isolation for 6 h per day or control conditions during the third postnatal week. Performance on a 12-arm radial maze with 8 arms consistently baited with food reward was examined in adulthood. During the social isolation, both male and female pups exhibited a significant increase in plasma corticosterone levels. When tested on the radial arm maze as adults, the performance of female rats that had experienced social isolation during development was not affected; however, male rats in the isolation condition initially exhibited impairments in working memory but not reference memory. Despite achieving comparable asymptotic levels of performance on the maze, male rats that experienced social isolation during the third week demonstrated disruption in working memory retention when radial arm maze trials were interrupted after the fourth arm choice. Thus, while male rats that experience social isolation during the third week of life eventually perform comparably to controls on the standard radial arm maze task, their ability to retain information over a delay remains impaired. These findings highlight an important sex difference in the long-term effects of stress during this period of late preweanling development.     

2-bromo-alpha-ergocryptine mesylate (CB-154) inhibits prolactin and luteinizing hormone secretion in the prepubertal female rat

Treatment of immature female rats with 100 micrograms 2-bromo-alpha-ergocryptine mesylate (CB-154) per ml drinking water beginning on Day 30 of age until vaginal opening delayed puberty by 6 days. Rats treated with CB-154 exhibited vaginal opening at 43.3 +/- 0.6 days whereas controls exhibited vaginal opening at 37.9 +/- 0.8 days. Most interestingly, serum levels of luteinizing hormone (LH) and prolactin (PRL) on Days 31-35, determined by a homologous radioimmunoassay were significantly lower in treated rats than in controls. The ovarian concentrations of progesterone (P) and androstenedione (A) were lower in rats treated with CB-154 than in controls; ovarian estradiol (E2) concentrations were low in both groups. Serum levels of P (but not A and E2) were reduced on Days 31-35 of the treatment period. Cessation of the CB-154 treatment on the morning of Day 35 returned the onset of puberty to normal values; steroid and gonadotropin levels also returned to normal values within 2 days after removal of the CB-154 from the drinking water. Near the time of onset of puberty, serum levels of LH in rats treated with CB-154 returned to control values. These data indicate that in the female rat the delay in puberty induced by CB-154 might be due to a reduction in the secretion of LH, especially since the onset of delayed puberty in rats treated with CB-154 correlates with an increase in the serum level of LH. Further studies are needed to elucidate the specific effects of hypoprolactinemia on ovarian function and the onset of puberty in the rat.     

Tissue-specific developmental expression of the kallikrein gene family in the rat

Using a series of gene-specific oligonucleotide probes, we have explored the developmental pattern of expression of six members of the rat kallikrein gene family (PS, S1, S2, S3, K1, and P1) in the submandibular gland (SMG) and kidney of both sexes, the prostate and testis of the male, and the anterior pituitary gland (AP) of the female rat. PS (true kallikrein) mRNA was detected in early neonatal life in the SMG and kidney of both sexes. K1, a second kallikrein gene family member expressed in the adult kidney, had a developmental pattern similar to PS in the kidney. In contrast, tonin (S2), S3, K1, and P1, all of which are expressed in the adult SMG, did not reach detectable SMG mRNA levels until puberty in either the male or female rat. Both S3 and P1, which are expressed in the adult prostate, and the novel P1-like mRNA previously detected in the adult rat testis, first appeared in early puberty. In the female AP, PS mRNA levels were not detected until early puberty and thus exhibited a developmental profile different from that of prolactin. The demonstration that S1, S2, S3, P1, and K1 are not expressed in the SMG or prostate until puberty is consistent with the expression of these genes in these tissues being androgen-regulated; the first appearance of PS mRNA in the female AP in early puberty similarly reflects the estrogen dependence of PS gene expression in this tissue. The presence of PS mRNA levels in the SMG and kidney prior to sexual maturation reflects the androgen independence of PS gene expression and suggests that PS (true kallikrein) may play a constitutive and/or developmental role in SMG or renal physiology.     

Postnatal profile of plasma leptin concentrations in male and female rats: relation with the maturation of the pituitary-gonadal axis

Leptin, the ob gene product, has been implicated in the initiation of puberty in mice and humans. However, it is not yet clear whether leptin also plays a pivotal role in promoting sexual maturation in rats. Based on the assumption that circulating leptin levels would increase during the peripubertal period if this hormone triggers puberty, we examined the developmental profile of plasma leptin from neonatal (day 1) through adult (day 85) age in both male and female rats and simultaneously monitored several important indices of pituitary-gonadal function. A significant elevation of plasma leptin during the peripubertal period was not observed in either male or female rats. Although this finding may not support leptin as a humoral factor triggering puberty, we observed a rise in leptin in both sexes from the second postnatal week, which clearly preceded the first significant elevations of luteinizing hormone and gonadal steroids. Therefore, it is still possible that leptin may play a role in promoting sexual maturation in rats of both sexes already from an early postnatal period. It seems that the role for leptin in sexual development is permissive, but not decisive, in rats.     

Modulation of prolactin binding sites in vitro by membrane fluidizers. IV. Differential effects on plasma membrane and Golgi fractions of male prostate and female liver in the rat

In vitro treatment of crude particulate fractions of male rat ventral prostate and female rat liver with membrane fluidizers (aliphatic alcohols) has been previously reported by us to increase prolactin (PRL) receptor levels, presumably by unmasking cryptic prolactin receptors. The objective of this study was to determine if similar in vitro treatment of purified plasma membrane- and Golgi-rich fractions of male rat prostate and female rat liver with ethanol produced differential effects on prolactin binding in these two subcellular fractions. The degree of fluidization was monitored by a fluorescence polarization method using 1,6-diphenylhexatriene. 125I-PRL specific binding to Golgi-rich fractions of male ventral prostate and female liver was approximately 4-fold higher than that observed in plasma membrane-rich fractions. The microviscosity parameter, inversely related to lipid fluidity, was consistently lower in Golgi-rich fractions than that in plasma membrane-rich fractions in both prostate and liver. In vitro ethanol treatment of prostatic and hepatic plasma membrane fractions produced a dose-related increase and then decline in prolactin binding and a maximal (60-75%) increase in prolactin binding was observed at 4.8% and 2.0% ethanol in prostatic and hepatic membranes, respectively. This in vitro treatment also produced a significant increase in apparent lipid fluidity of plasma membrane-rich fractions of prostate gland and liver. However, similar in vitro ethanol treatment of Golgi fractions of both prostate gland and liver exhibited little increase in prolactin binding without changing microviscosity. Our observations are consistent with the direct relationship between membrane fluidity and prolactin receptor levels. The changes in prostatic and hepatic plasma membrane fractions following in vitro ethanol treatment suggest that prolactin receptors located on the plasma membranes may be modulated (via membrane lipid microviscosity changes) in vivo to a greater extent by various physiological agents than those located within the Golgi fraction.     

Time course of the insensitivity of prolactin release to morphine administration in the lactating female rat

The effect of morphine on circulating levels of prolactin and growth hormone (GH) in the lactating female model was determined at various time intervals following the termination of suckling. Morphine administration did not produce an increase in prolactin levels when dams remained suckling. Four days after suckling was terminated, 50% of the dams tested showed a morphine induced prolactin increase. The prolactin secretory response to morphine gradually returned in dams, so that after 8 days of non-suckling, all animals tested showed a morphine induced prolactin increase. Consistent with the lack of prolactin stimulation, the tuberoinfundibular dopaminergic (TIDA) neurons, were insensitive to the morphine induced inhibition of activity during lactation. In contrast, circulating levels of GH were increased in these dams following morphine administration. These results suggest that the lactating female rat is insensitive to the mu mediated stimulation of prolactin release while suckling. However, sensitivity begins to return following at least 4 days of non-suckling.     

Appearance of a nocturnal peak of leptin secretion in the pubertal rat

Whether leptin is involved in the timing of puberty remains highly controversial in the rat. Daytime leptin secretion shows little change during the transition into adulthood. Because leptin exhibits a diurnal variation in the adult, it is possible that the ontogeny of such a rhythm provides important information for the timing of puberty. To begin to evaluate this hypothesis, we determined the development of the diurnal leptin secretion in the rat. The young females were raised in a light-controlled environment (12L, 0700 h light on). A cannula was placed in the right atrium on the previous day, and blood samples were collected every 4 h on Days 21, 24, 28, 32, 36 (1 day after vaginal opening), and 48 (adult, diestrus of estrous cycle). In addition to vaginal opening, plasma prolactin levels were determined as an endocrine index of puberty. Changes in food intake were monitored because nocturnal food intake has been considered to be a synchronizer for the leptin rhythm. This pattern of food intake was clearly evident throughout the ages studied. By contrast, there was no leptin rhythm at 21 and 24 days of age. Beginning at 28 days, leptin secretion exhibited a significant nocturnal peak (2300 h); this nocturnal peak increased in amplitude at 32 and 36 days and was still apparent in the cycling adult at Day 48. Plasma prolactin did not exhibit a diurnal rhythm but it increased from Days 32 to 48. The present findings indicate that in the rat, both the appearance of the nocturnal leptin rhythm and the nocturnal increase in circulating leptin levels during development carry information for timing the onset of puberty.     

Regulation of the female rat estrous cycle by a neural cell-specific epidermal growth factor-like repeat domain containing protein,NELL2

NELL2, a protein containing epidermal growth factor-like repeat domains, is predominantly expressed in the nervous system. In the mammalian brain, NELL2 expression is mostly neuronal. Previously we found that NELL2 is involved in the onset of female puberty by regulating the release of gonadotropin-releasing hormone (GnRH), and in normal male sexual behavior by controlling the development of the sexually dimorphic nucleus of the preoptic area (POA). In this study we investigated the effect of NELL2 on the female rat estrous cycle. NELL2 expression in the POA was highest during the proestrous phase. NELL2 mRNA levels in the POA were increased by estrogen treatment in ovariectomized female rats. Blocking NELL2 synthesis in the female rat hypothalamus decreased the expression of kisspeptin 1, an important regulator of the GnRH neuronal apparatus, and resulted in disruption of the estrous cycle at the diestrous phase. These results indicate that NELL2 is involved in the maintenance of the normal female reproductive cycle in mammals.     

Prolactin levels during the periparturitional period in the biparental cotton-top tamarin (Saguinus oedipus): interactions with gender, androgen levels, and parenting

Unlike biparental bird and rodent species, mating and parenting occur simultaneously in cotton-top tamarins, Saguinus oedipus, providing a unique model for examining endocrine interactions. This study was designed to determine the relationship of prolactin to testicular androgens during parenting and mating. Specifically we examined (1) the patterns of postpartum prolactin excretion in male and female tamarins with and without infant survival; (2) the relationship between androgen and prolactin levels during the periparturitional period in male tamarins; and (3) male hormonal response to the postpartum mating that occurs simultaneously with paternal care. All females showed an elevation in prolactin during the first week postpartum and when infants died, female prolactin levels decreased significantly. Infant survival during the first 15 days did not influence male levels of prolactin, cortisol, or the testicular androgens testosterone and dihydrotestosterone (DHT). Prolactin did not show an inverse relationship with any of the androgens (testosterone, DHT) studied during the postpartum period. No significant differences in hormones were found between prepartum levels and the first, second, and third 5-day blocks postpartum for all 10 males. Males who had infant-care experience showed an increase in testosterone during the first 5 days postpartum and prolactin levels correlated with the number of previous births a male had experienced. However, the most significant changes in testosterone occurred in males whose mates ovulated during the first 15 days following birth in contrast to males whose mates ovulated later than 15 days. These results indicate that unlike females, male tamarins are not showing hormonal changes in response to infants. Urinary androgens did not show an inverse relationship to prolactin in male tamarins, but were elevated concurrent with the female's fertile period.     

Modulation of testicular lutropin receptors in the developing male rat

In the developing male rat around 40 days of age, the testis appears to contain the maximum amount of lutropin receptors per unit weight. During this period, circulating levels of testosterone markedly increase without the concomitant major surges in lutropin levels. The increased sensitivity and responsiveness of tests to basal levels of circulating lutropin during this period is accompanied by enhanced serum prolactin levels suggesting that this hormone may be involved in this process. The finding that prolactin treatment of pubertal rats for 3 days induced the formation of more testicular lutropin receptors supports the above premise. However, shortterm immunoneutralisation of endogenous prolactin did not significantly alter the specific binding of [ 125 I ]-labelled lutropin to testicular membranes. Interestingly, during development, a close correction exists between receptor occupancy and capacity of the tissue to bind labelled lutropin. The apparent dissociation between serum lutropin levels, on the one hand and tissue occupancy and free receptor contents on the other, suggests that factors other than lutropin (presumably prolactin) are involved in the modulation of the sensitivity and the responsiveness of the testis to lutropin during early development.     

Hormonal Responses of Male Gerbils to Stimuli from Their Mate and Pups

Following copulation and cohabitation with a pregnant female, male gerbils show high levels of parental behavior toward their pups. The initiation of male parental behavior may be the result of neuroendocrine changes induced by cohabiting with the pregnant female or by pup stimuli. Experiment 1 examines the changes in androgen and prolactin levels in male gerbils cohabiting with females over the reproductive cycle. Gerbils were mated and blood samples taken from males for hormone analysis 1, 10, and 20 days after pairing and 3, 10, and 20 days after pups were born. A group of unmated male gerbils served as controls. Plasma prolactin levels of males were elevated throughout the female's pregnancy and lactation periods, but were only statistically significantly higher than those of unmated males 20 days after pups were born. Androgen levels rose during pregnancy and dropped significantly after the birth of the pups. These hormonal changes are similar to those found in males of monogamous birds and differ from those found in males of polygynous rodents such as the rat. Experiment 2 examined the hormonal responses of male and female gerbils to pup replacement after 4 hr of parent–pup separation. Female gerbils showed a significant elevation of prolactin levels 1 hr after pup replacement, but males did not. Males with pups returned showed no difference in androgen levels from males who did not have pups returned. Thus, male gerbils show neuroendocrine changes following long-term cohabitation with their mate and pups, but do not show acute hormone responses to pup removal and replacement. These results indicate that parental males have neuroendocrine changes associated with parental behavior and these differ from the neuroendocrine changes underlying female parental behavior.     

Correlation of hypothalamic LHRH, pituitary LH and plasma LH in developing rats.

Hypothalamic LHRH, pituitary LH and plasma LH levels were measured in rats of both sexes from day 5-60 after birth. The content of hypothalamic LHRH was very high in one-week-old male and female rats. It declined gradually till day 17 in the female rat and sharply on day 10 in the male rat. Subsequently the content of hypothalamic LHRH increased and showed peak values on day 25 in the female rat and on day 45 in the male rat. It decreased markedly at respective times of puberty in both sexes (day 37 in the female rat and day 52-60 in the male rat). Results of the study suggest that maturation of hypothalamo-hypophyseal-axis proceeds in three distinct stages. Observations on days 17, 25 and 37 in the female rat and on days 5, 7, 10 and 22 in the male rat clearly show an inverse relationship between hypothalamic LHRH and plasma LH and a parallel relationship between pituitary and plasma LH. Marked decline in the content of hypothalamic LHRH at respective times of puberty in both sexes indicates that the release of threshold levels of LHRH from the hypothalamus may apparently be the event initiating the pubertal changes in rat.     

Delay in the age of balano-preputial skinfold cleavage and alterations in serum profiles of testosterone, 5 alpha-androstane-3 alpha,17 beta-diol, and gonadotropins in adult rats treated during puberty with luteinizing hormone releasing hormone

Previous work has shown that chronic treatment of intact, immature male rats with luteinizing hormone releasing hormone (LHRH) decreases sex accessory gland weights and results in retardation of the normal developmental increase in the ratio of serum testosterone (T)/5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) via an apparent enhancement of testicular 5 alpha-reductase or 3 alpha-hydroxysteroid oxidoreductase activities. In the present work, androgen dependent balano-preputial skinfold cleavage was significantly delayed by approximately one week in intact, immature male rats which were treated daily for two weeks with either 1.0 micrograms, 2.5 micrograms or 5.0 micrograms of LHRH during a discrete phase of pubertal development (28-41 days of age). In intact, adult (62 day old) animals which received LHRH treatments during pubertal development, serum T concentrations and sex accessory gland weights were reduced compared to control animal values. Serum 3 alpha-Diol content in the adult rats was either unaltered or increased significantly depending on the LHRH dosage employed during sexual development. Serum luteinizing hormone concentrations were not different between control and LHRH-pretreated adult rats whereas the highest dosage of LHRH employed (5.0 micrograms) during puberty resulted in a significant elevation of adult serum follicle stimulating hormone levels. It is suggested that chronic LHRH treatment of the male rat during puberty results in a perturbation in testicular androgen biosynthetic activities and an impairment of pituitary-testicular hormone feedback mechanisms which persist at least through early adulthood.     

Age-related changes in urinary testosterone levels suggest differences in puberty onset and divergent life history strategies in bonobos and chimpanzees

Research on age-related changes in morphology, social behavior, and cognition suggests that the development of bonobos (Pan paniscus) is delayed in comparison to chimpanzees (Pan troglodytes). However, there is also evidence for earlier reproductive maturation in bonobos. Since developmental changes such as reproductive maturation are induced by a number of endocrine processes, changes in hormone levels are indicators of different developmental stages. Age-related changes in testosterone excretion are an indirect marker for the onset of puberty in human and non-human primates. In this study we investigated patterns of urinary testosterone levels in male and female bonobos and chimpanzees to determine the onset of puberty. In contrast to other studies, we found that both species experience age-related changes in urinary testosterone levels. Older individuals of both sexes had significantly higher urinary testosterone levels than younger individuals, indicating that bonobos and chimpanzees experience juvenile pause. The males of both species showed a similar pattern of age-related changes in urinary testosterone levels, with a sharp increase in levels around the age of eight years. This suggests that species-differences in aggression and male mate competition evolved independently of developmental changes in testosterone levels. Females showed a similar pattern of age-related urinary testosterone increase. However, in female bonobos the onset was about three years earlier than in female chimpanzees. The earlier rise of urinary testosterone levels in female bonobos is in line with reports of their younger age of dispersal, and suggests that female bonobos experience puberty at a younger age than female chimpanzees.     

Differential responsiveness of LH and prolactin to p-tyramine in male and female rats

The effect of p-tyramine, a natural amine which is found in the rat brain in trace amounts, was evaluated for its capacity to influence LH and prolactin secretion in male and female rats under different hormonal conditions. p-Tyramine (40 mg/kg ip) was ineffective in modifying LH levels in either female or male rats which had been gonadectomized for 2 days, but if the animals were injected with 12.5 micrograms of estradiol benzoate (EB) on the day of castration, p-tyramine was able to release LH in female but not in male rats. To evaluate whether early androgenization of brain structures which control LH secretion was involved in the sexual difference observed, p-tyramine was tested in female androgenized rats (200 micrograms of testosterone propionate on the day of birth), and in male rats castrated at birth. The trace amine was ineffective in altering LH levels in both experimental models, even if rats were pretreated with EB as control females. On the other hand, p-tyramine inhibited prolactin secretion in male rats pretreated with EB, and not in similarly treated female rats. The present results suggest that p-tyramine may be involved not only in prolactin regulation as it has been previously shown, but also in LH control, and that the hormonal response to this amine is sexually differentiated in the rat.