Hyperprolactinemia-induced precocious puberty: studies on the mechanism(s) by which prolactin enhances ovarian progesterone responsiveness to gonadotropins in prepubertal rats

Spontaneous ovarian hyperstimulation syndrome in a pregnant woman with hypothyroidism: a case report

Objective

To study a rare case of spontaneous ovarian hyperstimulation syndrome in a naturally conceived pregnancy associated with overt hypothyroidism.

Design

Case report.

Setting

Endocrinology private practice.

Patient(s)

A 32-year-old woman who was 13 weeks pregnant with bilaterally enlarged ovaries presumed to be secondary to hypothyroidism.

Intervention(s)

Administration of levothyroxine and titration of the dose.

Main Outcome Measure(s)

Regression of signs and symptoms of spontaneous ovarian hyperstimulation syndrome after 12 weeks of therapy.

Result(s)

The patient was diagnosed with severe hypothyroidism, as confirmed by her elevated thyroid-stimulating hormone level. Ultrasound evaluation revealed ovarian enlargement secondary to multiple contiguous cysts with anechoic content. The patient was administered levothyroxine 175 μg/day. Results of hormonal studies demonstrated thyroid function normality at week 12 after treatment. Incomplete regression of ovarian cysts was also noticed within this period. At week 37, the patient developed preeclampsia, and cesarean delivery was recommended. An 8-month postpartum ultrasound evaluation revealed complete regression of the cysts.

Conclusion(s)

Spontaneous ovarian hyperstimulation syndrome secondary to hypothyroidism may be the cause of ovarian enlargement, and levothyroxine replacement seems an appropriate primary therapeutic option. Proper endocrinological assessment of patients is recommended as it may avoid unfavorable outcomes.

Van Wyk-Grumbach Syndrome with Kocher-Debré-Sémélaigne Syndrome: Case Report of a Rare Association

BACKGROUND

Van Wyk-Grumbach syndrome (VWGS) is a rare presentation of juvenile hypothyroidism which manifests in females as chronic autoimmune hypothyroidism, isosexual pseudoprecocious puberty, and multicystic ovaries. It uniquely presents with short stature and delayed bone age unlike other causes of precocious puberty. Kocher-Debré-Sémélaigne (KDSS) is a rare presentation of juvenile hypothyroidism manifesting as calf muscle pseudohypertrophy, delayed contraction and relaxation of reflexes, and percussion myxedema.

OBJECTIVES

To diagnose the rare association of VWGS and KDSS and to conduct a follow-up of the patient on replacement therapy.

METHODS

We present a case of a 9-year-old female child who presented to the endocrine department with complaints of intermittent vaginal bleeding, short stature, and difficulty in walking. On evaluation she was found to be having autoimmune hypothyroidism, FSH-dominated isosexual pseudoprecocious puberty, delayed bone age, secondary pituitary macroadenoma, delayed relaxation of deep tendon reflexes, and pseudohypertrophy of calf muscles. The diagnosis of VWGS associated with KDSS was made. The patient was initially put on 25 μg thyroxine replacement, which was titrated accordingly, and was followed up after 6 months and 1 year.

RESULTS

All the features of the syndrome improved after 12 months of adequate thyroxine replacement.

CONCLUSIONS

VWGS and KDSS are rare presentations of juvenile hypothyroidism, and their association is even rarer. Early diagnosis and prompt replacement therapy can avoid unnecessary investigations and surgical interventions.

Asymmetrical Ovarian Enlargement: Caught Timely Before the Cut!

BACKGROUND

Van Wyk-Grumbach syndrome is a rare complication of prolonged untreated primary hypothyroidism characterized by precocious puberty and enlarged multicystic ovaries. High index of suspicion and timely diagnosis can prevent unnecessary surgical procedures because this condition can be reversed with thyroid hormone supplementation.

CASE

A 12-year-old girl underwent abdominal ultrasonography for recurrent abdominal pain, which showed bilateral asymmetrical enlargement of ovaries. Ovarian tumor markers were negative. Subsequent evaluation revealed severe hypothyroidism. Patient was started on levothyroxine and both ovaries showed regression to normal volume within 1 year of normalizing thyroid function tests.

SUMMARY AND CONCLUSION

Prompt and adequate medical management with levothyroxine can completely reverse ovarian enlargement associated with hypothyroidism.

Van Wyk and Grumbach syndrome: an unusual form of precocious puberty

An 8-year-old girl presented with precocious menstruation and growth delay. Laboratory data revealed hypothyroidism and an X-ray of the wrist showed a delayed bone age. The Van Wyk and Grumbach syndrome (VWGS) was diagnosed and thyroid replacement was started with resolution of the symptoms. The association of precocious puberty and/or polycystic ovaries, delayed bone age and hypothyroidism is known as the Van Wyk and Grumbach syndrome. Clinically this syndrome is a diagnostic challenge because hypothyroidism usually leads to pubertal and growth delay, whereas in case of VWGS hypothyroidism it leads to growth delay and precocious puberty. The pathophysiology of VWGS is not yet clear, but the most accepted theory states that the high concentrations of TSH are sufficient to cause activation of the FSH receptor and produce gonadal enlargement. Thyroid replacement therapy results in a resolution of all signs and symptoms. For this reason, conservative management of the ovarian masses is advocated. Our case is unique as this girl did not have breast development or multicystic ovaries (as the other cases in the literature). This may be due to an early recognition and relatively low TSH levels in comparison to other cases.

Characteristics of girls with pituitary hyperplasia and sexual precocity secondary to primary hypothyroidism

AIM

To investigate the different characteristics of girls with pituitary hyperplasia secondary to primary hypothyroidism (PPH), with and without sexual precocity.

METHODS

Pituitary hyperplasia secondary to primary hypothyroidism girls were divided into two groups: group A, with sexual precocity (n = 8), and group B, without sexual precocity (n = 14). The following values were measured before and after 3 months levothyroxine therapy: free triiodothyronine (FT3 ), free thyroxine (FT4 ), thyrotropin (TSH), follicle-stimulating hormone (FSH), luteinising hormone (LH), prolactin (PRL), estradiol (E2 ), testosterone (T), pituitary height, uterine volume (UV), ovarian volume (OV) and follicular diameter (FD).

RESULTS

Thyrotropin, FSH, PRL, E2 , T, pituitary height, UV, OV and FD were higher in group A than group B (all p < 0.05); FT3 , FT4 and LH levels were not different (all p > 0.05). In all of the PPH girls, pituitary height was correlated with FT3 , FT4 and PRL (r = -0.545, p = 0.009, r = -0.567, p = 0.006 and r = 0.666, p = 0.001, respectively). PRL was positively correlated with UV, FD and FSH (r = 0.581, p = 0.005, r = 0.482, p = 0.031 and r = 0.667, p = 0.001, respectively), and FSH was positively correlated with OV (r = 0.522, p = 0.013). These abnormalities regressed after therapy.

CONCLUSION

Pituitary hyperplasia secondary to primary hypothyroidism girls with sexual precocity have increased plasma TSH, FSH, PRL, E2 and T levels, pituitary height and uterine, ovarian and follicular size.

Spinal muscular atrophy: from gene discovery to clinical trials

Spinal muscular atrophy (SMA) is a common neuromuscular disorder with autosomal recessive inheritance, resulting in the degeneration of motor neurons. The incidence of the disease has been estimated at 1 in 6000-10,000 newborns with a carrier frequency of 1 in 40-60. SMA is caused by mutations of the SMN1 gene, located on chromosome 5q13. The gene product, survival motor neuron (SMN) plays critical roles in a variety of cellular activities. SMN2, a homologue of SMN1, is retained in all SMA patients and generates low levels of SMN, but does not compensate for the mutated SMN1. Genetic analysis demonstrates the presence of homozygous deletion of SMN1 in most patients, and allows screening of heterozygous carriers in affected families. Considering high incidence of carrier frequency in SMA, population-wide newborn and carrier screening has been proposed. Although no effective treatment is currently available, some treatment strategies have already been developed based on the molecular pathophysiology of this disease. Current treatment strategies can be classified into three major groups: SMN2-targeting, SMN1-introduction, and non-SMN targeting. Here, we provide a comprehensive and up-to-date review integrating advances in molecular pathophysiology and diagnostic testing with therapeutic developments for this disease including promising candidates from recent clinical trials.

An unusual presentation of acquired hypothyroidism: the Van Wyk-Grumbach syndrome

The association in young females of long-standing primary hypothyroidism, isosexual precocious pseudopuberty and multicystic enlarged ovaries was first described in 1960 by Van Wyk and Grumbach. Since then, sporadic case reports have contributed to clarifying the key features of this syndrome. The unique elements that lead to this diagnosis are FSH-dominated sexual precocity combined with a delayed bone age in the presence of hypothyroidism. It is important to recognise this syndrome because initiating simple thyroid hormone replacement completely resolves symptoms and hormone abnormalities, avoiding unnecessary investigations for malignancies or surgical intervention. We describe an 8-year-old girl with autoimmune thyroiditis and severe long-standing hypothyroidism presenting with the clinical features of Van Wyk-Grumbach syndrome, a secondary TSH-secreting adenoma and hyperprolactinaemia. In addition, this girl presented with microcytic anaemia, elevated erythrocyte sedimentation rate (ESR) and two unusual features - a newly developed streaky hyperpigmented skin lesion and parathyroid hormone suppression despite vitamin D deficiency. Thyroxine replacement normalised all hormone abnormalities and shrunk the pituitary adenoma within 9 months, but the new skin lesion persisted. We review the literature and explore the pathophysiology of known and new features that give rise to speculation indicating stimulation of the FSH G protein-coupled receptor by excessive TSH, but LH suppression by hyperprolactinaemia.

Delayed puberty in spontaneously hypertensive rats involves a primary ovarian failure independent of the hypothalamic KiSS-1/GPR54/GnRH system

Spontaneously hypertensive (SH) rats, extensively used as experimental models of essential human hypertension, display important alterations in the neuroendocrine reproductive axis, which manifest as markedly delayed puberty onset in females but whose basis remains largely unknown. We analyze herein in female SH rats: 1) possible alterations in the expression and function of KiSS-1/GPR54 and GnRH/GnRH-receptor systems, 2) the integrity of feedback mechanisms governing the hypothalamic-pituitary-ovarian axis, and 3) the control of ovarian function by gonadotropins. Our data demonstrate that, despite overtly delayed puberty, no significant decrease in hypothalamic KiSS-1, GPR54, or GnRH mRNA levels was detected in this strain. Likewise, in vivo gonadotropin responses to ovariectomy and systemic kisspeptin-10 or GnRH administration, as well as in vitro gonadotropin responses to GnRH, were fully preserved in SH rats. Moreover, circulating LH levels were grossly conserved during prepubertal maturation, whereas FSH levels were even enhanced from d 20 postpartum onwards. In striking contrast, ovarian weight and hormone (progesterone and testosterone) responses to human chorionic gonadotropin (CG) in vitro were profoundly decreased in SH rats, with impaired follicular development and delayed ovulation at puberty. Such reduced hormonal responses to human CG could not be attributed to changes in LH/CG or FSH-receptor mRNA expression but might be linked to blunted P450scc, 3beta-hydroxy steroid dehydrogenase, and aromatase mRNA levels in ovaries from SH rats. In conclusion, our results indicate that the expression and function of KiSS-1/GPR54 and GnRH/GnRH-receptor systems is normal in SH rats, whereas ovarian development, steroidogenesis, and responsiveness to gonadotropins are strongly compromised.

Ovarian tumor in a 12-year old female with severe hypothyroidism: A case of Van Wyk and Grumbach syndrome

We report a 12-year-old female presenting with an abdominal tumor. Diagnostic workup revealed giant bilateral ovarian cysts, severe hypothyroidism as well as an elevation of CA 125. We refrained from ovariectomy, which would be necessary for a malignant tumor, in view of an evident Van Wyk and Grumbach syndrome. The patient promptly responded to L-thyroxine with complete regression of all symptoms. Hypothyroidism should be considered in the evaluation of ovarian cysts. Although the Van Wyk and Grumbach syndrome is rare, it is crucial to rule it out in order to avoid unnecessary ovarian surgery when thyroid replacement is completely sufficient.

Induction of reproductive function in anestrous mares using a dopamine antagonist

We investigated the role of dopamine in the regulation of seasonal reproductive activity in mares. Nine seasonal anestrous mares, maintained under a natural photoperiod, were treated daily with a dopamine D2 antagonist, [-]-sulpiride (200 mg/mare, im), beginning February 5 (day of year = 36) until the first ovulation of the year or for a maximum of 58. Nine untreated anestrous mares were maintained under the same conditions. The ovaries were examined by ultrasonography twice a week, and blood was collected three times a week for progesterone, LH, FSH and prolactin determinations. Mean day of first ovulation was significantly advanced for [-]-sulpiride-treated mares than control mares (mean day of year +/- SEM = 77.3 +/- 7.9 and 110.0 +/- 6.8, respectively; P < 0.01). Eight mares ovulated during [-]-sulpiride treatment while one mare failed to ovulate. Ovulation occurred 91 d after the start of treatment or on Day 127. All mares continued to have normal estrous cycles after the first ovulation. First cycle length and luteal progesterone concentrations did not differ between [-]-sulpiride-treated and control mares. Plasma prolactin concentrations were significantly increased at 2 and 9 h after [-]-sulpiride administration (P < 0.05), and had returned to basal levels by 24 h. At the time of the LH surge associated with the first ovulation, mean LH and FSH secretion was significantly higher in [-]-sulpiride-treated mares than in control mares (P < 0.05). These results suggest that dopamine plays a role in the control of reproductive seasonality in mares and exerts a tonic inhibition on reproductive activity during the anovulatory season.

Neuroendocrine regulation of prolactin secretion in adult female rhesus monkeys during different phases of the menstrual cycle: role of neuroexcitatory amino acid (NMA)

The present study attempts to examine the role of N-methyl-D, L-aspartate (NMDA) receptors in the central regulation of prolactin (PRL) secretion, which may be involved in ovarian function and its alteration by glutamate in various phases of the menstrual cycle of female rhesus monkeys (Macaca mulatta). The results suggest that the glutaminergic component of the control system, which governs PRL secretion by utilizing NMDA receptors, may have an important role in regulating changes in PRL secretion. The response of PRL during the luteal phase of the cycle was different from that observed in follicular and menstrual phases. Steroids may influence the NMDA-dependent drive to release PRL. N-methyl-D-aspartic acid (NMA) involvement in the regulation of PRL secretion may occur through activation of the PRL-stimulating system depending on the physiological state or steroidal milieu. It is possible, therefore, that the NMA-induced release of PRL-releasing factors (PRF) and PRL are enhanced in the presence of ovarian feedback.

The effect of administering a dopamine agonist (Cabergoline) on follicular and luteal development during pro-estrus and estrus in the female greyhound

To study the effect of the dopamine agonist Cabergoline, on ovarian activity in the female dog during pro-estrus and estrus, 6 greyhounds were treated with 5 microg/kg per os of Cabergoline for 20 days beginning on the first day of pro-estrus; 6 animals were left untreated (controls). Ovarian morphology was determined by ultrasound examination once a day during pro-estrus and twice a day during estrus. Follicles were divided into three classes on the basis of their diameter: F1 (<3mm), F2 (3-6mm) and F3 (>6mm). The presence and diameters of post-ovulatory follicles (F-POST) and corpora lutea (CL) were also recorded. Blood samples were taken once a day during pro-estrus and twice a day during estrus. The plasma was assayed for LH, prolactin and progesterone by radioimmunoassay. There were no differences between Cabergoline-treated and control dogs in the duration of pro-estrus or estrus. There was a progressive increase in follicle diameter from the start of pro-estrus when follicles were mainly class F1 to the day of estrus when follicles were mainly class F3. Three days after the start of estrus, the first F-POST follicles were detected. This pattern of development continued and on day 5 the first CLs were detected. By day 9, only CLs were detected. The peak of pre-ovulatory LH was within 3 days of estrus and ovulation was detected in all animals within 3 days of the LH peak. There were no differences in LH concentrations between groups. Plasma prolactin levels varied between animals and were reduced in treated dogs, however, this was not statistically significant (P=0.12). Plasma progesterone levels were below 1.0 ng/ml before the LH surge and thereafter gradually increased. There were no differences in plasma progesterone concentrations between treated and control dogs. In conclusion these results show that the administration of the dopamine agonist Cabergoline during pro-estrus and estrus did not affect the duration of pro-estrus or estrus or the pattern of follicular and luteal development in female dogs.

Anoestrus in the Dog: a Fascinating Story

In the bitch, progression from early to late anoestrus is characterized by a higher amplitude and a larger number of gonadotrophin-releasing hormone (GnRH) pulses generated by the hypothalamus, an increase in the sensitivity of the pituitary to GnRH, and an increase in ovarian responsiveness to gonadotrophins. An increase in basal plasma follicle-stimulating hormone (FSH) concentration is a critical event required for initiation of folliculogenesis. A period of increased luteinizing hormone pulsatility has been reported shortly before the onset of pro-oestrus. Apart from these changes in the hypothalamic-pituitary-ovarian axis, there is also involvement of dopaminergic influences in the initiation of a new follicular phase in the bitch. Administration of the dopamine-agonists bromocriptine and cabergoline shortens the anoestrus and is associated with a decrease in the plasma prolactin concentration, suggesting that the shortened anoestrus is the result of suppression of prolactin secretion. Yet, the anoestrus is not shortened in bitches treated with metergoline, a drug, which in a low dosage lowers the plasma prolactin concentration via a serotonin-antagonistic pathway. In addition, under physiological conditions low plasma prolactin concentrations are found during the entire anoestrus. Furthermore, a low dosage of bromocriptine, insufficient to cause a decrease in the plasma prolactin concentration, prematurely induces folliculogenesis. These observations indicate that not the decrease in the plasma prolactin concentration, but another dopamine-agonistic influence plays a critical role in the transition to a new follicular phase. The dopamine-agonist induced shortening of the anoestrus is associated with a rapid rise in the basal plasma FSH concentration, similar to what is observed during the physiological late anoestrus. This observation underlines the importance of an increase in the circulating plasma FSH concentration in the initiation of folliculogenesis in the bitch.

Ovarian cysts in young girls with hypothyroidism: follow-up and effect of treatment

Ovarian cysts have been reported in girls with longstanding uncompensated primary hypothyroidism. Restoration of euthyroid state has been associated with resolution of these cysts; long-term follow-up of these patients is however lacking. We evaluated the outcome in ten girls with ovarian cysts and hypothyroidism managed at our hospital with special emphasis on subsequent pubertal development and ovarian imaging. Patients were diagnosed at the age of 8.6 +/- 2.3 years (mean +/- SD) with severe uncompensated primary hypothyroidism (TSH levels >100 mIU/l in all; 509.3 +/- 651 mIU/l) and growth retardation (height SDS -4.1 +/- 1.8). Nine girls had vaginal bleeding at diagnosis; five also had thelarche. LH and FSH levels were prepubertal in all patients. Ovarian cysts were bilateral in eight girls (80%); internal septation was noted in six. Thyroxine replacement (4.1 +/- 0.7 microg/kg/day) led to normalization of TSH levels with reversal of pubertal changes and regression of ovarian cysts in all patients 2.2 +/- 1.0 months after treatment. At last follow-up 3.5 +/- 2.6 years after initiation of treatment at the age of 12.0 +/- 2.3 years, all patients had normal ovarian size in ultrasound evaluation with six girls progressing to normal puberty. Our study emphasizes the need to exclude hypothyroidism in young girls with ovarian cysts. Identification of hypothyroidism in these girls obviates the need for extensive investigations.

Cellular localization and changes in expression of prolactin receptor isoforms in sheep ovary throughout the estrous cycle

The actions of prolactin (PRL) on target cells depend on the type of prolactin receptor (PRLr) predominantly expressed, particularly whether the long PRLr isoform is expressed. The aims of this study were to determine the cellular localization and the changes in expression of long and short PRLr isoforms in sheep ovary throughout the estrous cycle. Long and short PRLrs were localized mostly in the same ovarian cells. Maximum signal intensity, particularly for long PRLrs, was found in stromal cells surrounding primordial and primary follicles, and, for both PRLrs, in granulosa cells of preantral follicles and in luteal cells. Moderate signal intensity for PRLrs was found in theca cells of preantral to ovulatory follicles, and in granulosa cells of antral follicles up to the gonadotropin-dependent stage. Decreasing immunoreactivity to PRLrs was found in granulosa cells of gonadotropin-dependent to ovulatory follicles. For long PRLrs in particular, no signal was found in mural granulosa cells of gonadotropin-dependent follicles; for both isoforms, no signal was found in most granulosa cells of ovulatory follicles. In primordial to gonadotropin-dependent follicles, cellular localization of PRLr was similar on days 0, 10 and 15 of the cycle. Oocytes consistently showed positive immunostaining for PRLrs. Comparative RT-PCR analysis of long and short PRLr expression showed that the short isoform is evenly expressed throughout the estrous cycle, whereas the expression of the long form increases at the time of estrus and decreases at mid-luteal phase and at the onset of the follicular phase. Expression of long PRLrs was greater than that of short PRLrs on day 0 of cycle; expression of both isoforms was similar on day 10 and on day 15, long PRLrs expression was lower than that of short PRLrs. Our results indicate that in sheep ovary, the maximum responsiveness to PRL might occur during the preovulatory phase of the estrous cycle.

Low doses of bromocriptine shorten the interestrous interval in the bitch without lowering plasma prolactin concentration

In order to investigate the effect of different doses of bromocriptine on plasma prolactin concentration and the interestrous interval, beagle bitches were treated twice daily with 5 microg (5-group), 20 microg (20-group), or 50 microg (50-group) bromocriptine per kg body weight orally, starting 28 days after ovulation. In the 5-group, the difference between the mean plasma prolactin concentration before and that during bromocriptine treatment was not significant. In contrast, mean plasma prolactin concentration decreased significantly after the start of bromocriptine treatment in the 20- and 50-groups. The mean interestrous interval was significantly shorter in all three groups than in untreated bitches in the same colony. The mean interestrous interval in the 20-group and that in the 50-group were similar, but both were significantly shorter than that in the 5-group. The results of this study indicate that bromocriptine shortens the interestrous interval in the bitch even when the dose is so low that it does not lower plasma prolactin concentration. Induction of estrus in the bitch by bromocriptine therefore involves a mechanism other than via the lowering of plasma prolactin concentration. Furthermore, this study shows that the extent of shortening of the interestrous interval by bromocriptine is dose dependent.

Polycystic ovaries, precocious puberty and acquired hypothyroidism: The Van Wyk and Grumbach syndrome

Long-standing acquired hypothyroidism can rarely be associated with precocious puberty and polycystic ovaries. The authors report such a case, which responded to the simple replacement of thyroid hormone. It is important to look for hypothyroidism in girls with ovarian masses and precocious puberty to avoid surgery on the ovaries.

Effect of prenatal melatonin exposure on gonadotropins and prolactin secretion in male and female rat pups

We evaluated whether melatonin administration to pregnant rats during the final week of pregnancy affects prepubertal secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin in offspring. Melatonin was administered in the drinking water from day 14 to delivery. LH, FSH and prolactin concentrations were determined in plasma sampled from offspring between 5 and 30 days in the dark portion of the diurnal cycle. Administration of 2 or 20 microg/ml melatonin did not affect LH or FSH in male or female offspring. The 20-microg/ml dose caused a significant increase in prolactin in males and females at day 15. In contrast, melatonin, 2 or 20 microg/ml, decreased prolactin at days 25 and 30 in females and day 25 in males. Thus, prenatal melatonin exposure alters prolactin secretion, but not that of LH and FSH in infantile and prepubertal male and female rats.

Activation of AMPA receptors inhibits prolactin and estradiol secretion and delays the onset of puberty in female rats

Previous experiments have evidenced the neuroendocrine role of AMPA receptors. Present studies were carried out to obtain information on the role of these receptors in the control of the onset of puberty. To this end, female rats were i.c.v. injected with vehicle or AMPA (agonist of AMPA receptors: 0.1 or 0.5 nmol/day) between 26 and 30 days (Experiment 1), or 30 and 34 days (Experiment 2) of age. Serum concentrations of PRL, LH and estradiol were measured before drug administration, 10 min after the last injection, at vaginal opening (VO) and at first estrus (FE) presentation. In both experiments, AMPA administration inhibited PRL and estradiol secretion without affecting LH release. When AMPA was administered between 26 and 30 days a significant delay in the day of vaginal opening was observed. These results confirmed the inhibitory effect of AMPA on PRL secretion and suggests a role of AMPA receptors in the control of puberty onset.

Seasonality in mares

In this review, we have attempted to summarize, based on recent data obtained in our laboratory and elsewhere, our current understanding of the regulatory mechanisms of seasonality and discuss the implications with regard to treatment strategies to advance the onset of cyclic reproductive activity in the early spring.

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.

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid activity in the female rat. A focus on the EDSTAC recommendations

In 1996, the US Environmental Protection Agency was given a mandate by Congress to develop a screening program that would evaluate whether variously identified compounds could affect human health by mimicking or interfering with normal endocrine regulatory functions. Toward this end, the Agency chartered the Endocrine Disruptor Screening and Testing Advisory Committee in October of that year that would serve to recommend a series of in vitro and in vivo protocols designed to provide a comprehensive assessment of a chemical's potential endocrine-disrupting activity. A number of these protocols have undergone subsequent modification by EPA, and this review focuses specifically on the revised in vivo screening procedure recommended under the title Research Protocol for Assessment of Pubertal Development and Thyroid Function in Juvenile Female Rats. Background literature has been provided that summarizes what is currently known about pubertal development in the female rat and the influence of various forms of pharmaceutical and toxicological insult on this process and on thyroid activity. Finally, a section is included that discusses technical issues that should be considered if the specified pubertal endpoints are to be measured and successfully evaluated.

Stimulatory role of prolactin on the development of tuberoinfundibular dopaminergic neurones in prepubertal female rats: studies with cysteamine and somatostatin

Cysteamine, a potent depletor of prolactin and somatostatin, was used to determine the role of prolactin and somatostatin in the control of central dopamine neurones in prepubertal rats. Cysteamine (100 mg/kg, i.p., twice daily) was injected for 7, 14 or 21 days in 28-day-old Sprague-Dawley female rats in one study and for 3 days in 35-day-old rats in another. In control rats, the 3, 4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence increased threefold from day 35 to day 49, and serum prolactin concentration increased about 50%. Cysteamine lowered serum prolactin concentrations to 20%, and median eminence DOPAC and dopamine levels to 32-50% of control levels in both studies. The DOPAC levels in the nucleus accumbens and striatum were also lowered, while both DOPAC and dopamine in the paraventricular nucleus and periventricular nucleus (A14) were increased by cysteamine. A single injection of rat prolactin (0.01, 0.1 or 1 mg/kg) significantly increased DOPAC or DOPA levels in the median eminence, nucleus accumbens and striatum, but not in the paraventricular nucleus or A14 at 14 h later in 28-day old female rats or in 40-day-old rats pretreated with cysteamine. In contrast, central injection of somatostatin dose (0.001-1 microg/rat) and time (30-90 min) dependently decreased the DOPAC levels in the median eminence, paraventricular nucleus and A14 and increased those in the nucleus accumbens and striatum of adult female rats. These results indicate that serum prolactin is important for the maturation and maintenance of dopamine systems in the median eminence, nucleus accumbens and striatum, while somatostatin exhibits inhibitory and stimulatory effects on hypothalamic and midbrain dopamine systems, respectively.

Body weight gain induced by antipsychotic drugs: mechanisms and management

Long-term administration of typical and atypical antipsychotic drugs (AP) induces excessive weight gain which afflicts up to 50% of patients, impairs health and interferes with treatment compliance. Basic and clinical research has shown that AP may affect body weight through diverse mechanisms. Increased appetite is probably related to the interaction of AP with neuronal receptors to dopamine, serotonin and histamine. Additional metabolic-endocrine disruption of weight regulation may be related to the effects of AP-induced hyperprolactinaemia on gonadal-adrenal steroids and insulin sensitivity. In humans, programmed physical activity, dietary restriction, anorectic agents, and drugs that counteract hyperprolactinaemia have been shown to be successful in a limited number of studies. Two novel strategies could expand the available therapeutic options. First, in preclinical experiments in female rats the estradiol antagonist/agonist drug tamoxifen or estradiol itself have been shown to completely prevent the obesity provoked by the AP sulpiride, and to induce an endocrine-metabolic milieu that seems to counteract AP-induced obesity. Secondly, it has also been shown that oral antihyperglycaemic agents such as metformin may decrease body weight and counteract insulin resistance and hyperinsulinaemia which is correlated with several metabolic abnormalities in obese subjects. Lastly, estradiol replacement, tamoxifen and/or antihyperglycaemic agents are not devoid of significant side-effects, and these drugs have not been tested in obese psychiatric patients. Therefore, further research is needed before their clinical use may be recommended.

Effects of dehydroepiandrosterone and other sex steroid hormones on mammary carcinogenesis by direct injection of 7,12-dimethylbenz(a) anthracene (DMBA) in hyperprolactinemic female rats

The present study was performed to investigate the effects of dehydroepiandrosterone (DHEA) compared with those of sex steroid hormones on the mammary tumor induced by local injection of 7,12-dimethylbenz(a) anthracene (DMBA) in hyperprolactinemic female rats. Under sustained hyperprolactinemia induced by pimozide (PMZ) from day 21, DMBA was injected locally into the mammary glandular tissues on day 73. Rats were divided into 5 groups as follows; steroid free (DP group), 17 beta-estradiol (DP + E2 group), testosterone (DP + T group), progesterone (DP + Prog group), or dehydroepiandrosterone (DP + DHA group). The growth pattern and histological classification of the tumor in these 5 groups and rats treated only with DMBA (D group) were examined. All of the tumors grew to a size of 10 mm in diameter and after retaining the size for a certain duration, increased the size rapidly again (onset of rapid tumor growth). The period from the day of DMBA administration to that of onset of the rapid tumor growth in DP group was shorter than in D group, and the period in DP + DHA was longer than DP group and longest in steroid-treated groups. The incidence of adenocarcinoma was 2 tumors/16 animals in D group, 9/11 in DP group, 5/11 in DP + Prog group, 2/7 in DP + E2 group, 2/8 in DP + T group, and 0/10 in DP + DHA group. The incidence of adenocarcinoma in each steroid group except in DP + Prog group was lower than in DP group. These results suggest that prolactin (PRL) increases the incidence of adenocarcinoma in the DMBA-induced mammary tumor model, and DHEA especially decreases the incidence of adenocarcinoma.

Cyclosporine effects on in vitro responsiveness of anterior pituitary hormone release to dopamine and thyrotropin-releasing hormone in young female rats

Endocrine side effects of the immunosuppressive drug cyclosporine (CyA) include changes in anterior pituitary hormone secretion. The aim of the present study was to examine the effects of CyA on the responsiveness of in situ and ectopic anterior pituitary prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) release response to dopamine (DA) and thyrotropin-releasing hormone (TRH) treatment in young female rats, and to evaluate the possible PRL participation in these effects. Thirty day old rats were rendered hyperprolactinemic by transplanting an anterior pituitary gland of a littermate donor, under the kidney capsule, and were then injected with CyA or vehicle for 2 or 8 days. Sham-operated rats were used as controls and treated in the same way. CyA treatment prevented the increase in plasma PRL levels which occurred in controls after pituitary grafting. In vitro basal PRL release of in situ pituitaries from either sham-operated and/or pituitary-grafted animals was decreased by CyA treatment at any point studied. Basal in vitro secretion of GH was only decreased in the in situ pituitaries from grafted animals after 2 days of CyA therapy. The presence of an ectopic pituitary lead to an increase in the in vitro basal LH secretion from in situ pituitaries as compared to those from sham-operated rats. Basal LH release rates were not changed by CyA treatment, although the LH release in vitro did increase in the in situ pituitaries from sham-operated animals treated with the drug for 2 days. DA addition to the incubation media decreased the in vitro release of PRL, GH and LH from the in situ pituitaries of sham-operated and pituitary-grafted animals treated with vehicle. In CyA treated animals, DA decreased in vitro PRL release from the in situ pituitaries of animals, independently of the presence or absence of an ectopic pituitary. Reductions of the in vitro GH and LH release release after DA treatment were higher in the in situ pituitaries from grafted animals on day 8 of CyA or vehicle treatment. TRH increased the in vitro release of the three hormones with differential effects related to the length of the treatment with CyA and/or the presence of an ectopic pituitary. In vitro release of PRL and GH by ectopic pituitaries was inhibited by previous treatment with CyA and this effect was decreased proportional to the duration of the treatment with the drug, while LH secretion was not modified. Addition of DA to the incubation media resulted in a marked reduction of in vitro PRL and GH release, but only at day 8 of vehicle treatment on GH release did DA addition to media further decrease the release of both hormones from ectopic pituitaries from animals treated for 2 or 8 days with the drug, whereas LH secretion was not modified. TRH addition to the incubation media of ectopic pituitaries surprisingly reduced PRL and GH secretion on day 8 of CyA treatment or after surgery. The results of these studies suggest that CyA can act directly at the hypophyseal level modifying pituitary responsiveness to external stimuli. CyA seems to exert its main effects on lactotroph activity while its effects on somatotrophs and gonadotrophs are less.

Precocious puberty in a girl with an hCG-secreting suprasellar immature teratoma. Case report

Although precocious puberty is common in boys with human chorionic gonadotropin (hCG)-secreting brain tumors, it is extremely rare in girls. The authors describe a 6-year-old girl with an hCG-secreting suprasellar immature teratoma who presented with diabetes insipidus, increased intracranial pressure, and precocious puberty. On admission, breast budding was observed. The serum hCG level was 1230 mIU/ml. Both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) remained below detectable levels, even after gonadotropin-releasing hormone stimulation. Serum estrogen and androgen were moderately elevated. After chemotherapy, breast budding disappeared with normalization of serum hCG. It has been believed that hCG does not produce precocious puberty in girls in the absence of FSH, and this has been used as an explanation for the rarity of precocious puberty in girls with hCG-secreting brain tumors. However, it has also been reported that hCG has not only LH activity but also intrinsic, although weak, FSH-like activity. In the present case, this FSH-like activity was considered to have played a role in the development of precocious puberty. It is speculated that a very high level of serum hCG can produce precocious puberty in girls. The rarity of intracranial germ-cell tumors with a high potential of hCG secretion may be one of the reasons why hCG-induced precocious puberty is uncommon in girls.

Serum prolactin and luteinizing hormone levels and the activities of hypothalamic monoamine oxidase A and B and phenylethanolamine-N-methyl transferase are changed during sexual maturation in male rats treated neonatally with melatonin

Male rat pups were given a single dose of melatonin on day 5 of age. On days 30, 45, and 60, prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T) were measured in serum and monoamine oxidase A (MAO A) activity, monoamine oxidase B (MAO B), and phenylethanolamine-N-methyl transferase (PNMT) activity were measured in the hypothalamus. Melatonin administration increased serum PRL levels at all ages studied. Serum LH levels were decreased in the melatonin treated group on day 30, but levels were elevated on days 45 and 60 of age as compared to controls. LH response to luteinizing hormone-releasing hormone (LHRH) only increased in melatonin treated animals at 30 days of age. Serum T levels decreased with melatonin treatment at 30 days of age, but increased on days 45 and 60 of age. T response to human chorionic gonadotropin (hCG) was blunted by melatonin treatment at 30 days of life. Hypothalamic MAO A activity increased, after neonatal melatonin administration, at 30 and 45 days of age and decreased at 60 days of life. Early neonatal melatonin administration increased MAO B and PNMT activities on day 45. These findings suggest that neonatal melatonin administration induces an earlier sexual maturation in male rats, possibly related to PRL, LH, MAO, and PNMT increases.

Ontogenic studies of the neural control of adenohypophyseal hormones in the rat. II. Prolactin

1. Serum prolactin levels are low during the first 20 days of life and gradually increase toward puberty, in both male and female rats. 2. There is an age-related increase in the cell population engaged in prolactin secretion, as well as an increase in the synthesis of prolactin and of the amount of prolactin secreted from individual lactotropes. 3. The gradual increase in prolactin levels in the third week of life is not related to a decrease in dopaminergic inhibition but to an increase in the efficiency of prolactin releasing factors such as estrogen, serotonin, opiates, and posterior pituitary extracts. 4. Prolactin release induced by physiological factors, such as stress, cervical stimulation, or the expression of spontaneous diurnal and nocturnal surges, requires maturational events within the hypothalamic-pituitary axis which are evident at the end of the third week of life. 5. In the female rat the steadily increasing levels of prolactin are involved in the timing of puberty eclosion acting at the ovary and at the brain. 6. In the prepubertal male rat increasing titers of prolactin may be involved in testicular and accessory organ development and may facilitate the actions of luteinizing hormone, follicle stimulating hormone, and testosterone on male sexual organs.

Prolactin-dependent seasonal changes in pelage: role of the pineal gland and dopamine

The Siberian hamster displays seasonal changes in pelage that are dependent upon fluctuations in circulating prolactin levels. Pinealectomy prevented the decrease in serum prolactin and molt to the winter pelage displayed by castrated males housed under a short-day photoperiod. A dopaminergic antagonist, pimozide, enhanced prolactin levels in both pinealectomized and sham-operated animals under both long and short photoperiods. In the short-day animals, this effect of pimozide was associated with a prevention of the development of winter pelage. These results indicate that seasonal prolactin levels and related pelage changes are dependent upon the integrity of the pineal gland. However, basal prolactin levels under different photoperiod conditions appear to be only partly regulated by the actions of the dopaminergic system.

Sexual maturation in female rats: hereditary, developmental and environmental aspects

Two physiological components of sexual maturation, vaginal opening and first estrus, apparently evolve similarly in Wistar and Sprague-Dawley rats. However, a bimodal distribution in the frequency of the days of vaginal opening is observed within a given strain, which is less related to heredity than to the timing and type of experiment. In addition, when the modulators of sexual maturation are reviewed, it can be observed that sensitivity to external stimuli can vary even within a strain. For a defined set of breeding conditions, one group of rats can be more susceptible to changes in the lighting regimen and not be affected by controlled stressors, while another group responds more to stress and less to light. The reason for susceptibility to one rather than another environmental factor under similar breeding conditions is not understood. In that context, it is difficult to evaluate the role of heredity when we cannot understand the full impact of the environment, not to mention maternal influence in fetal and early life. Using two lines of psychogenetically selected rats, it was possible to show that they had differences in sexual maturation, which strongly suggested a genetic predisposition. Nevertheless, the question arises as to whether the genetic locus directly affects organs implicated in sexual maturation or whether it acts on some unknown factor which only secondarily modifies sexual maturation. In summary, there is more need to understand the role of the environment, including that of the mother early in fetal and neonatal life. It is suggested that the mechanisms underlying organ growth are set for a given species, while developmental and environmental factors fix the timing of vaginal opening and first ovulation. In the rat, there appear to be two times which are preferred for vaginal opening, given the laboratory conditions that have been used in the last 20 or so years: an early period, at 31-35 days, and a late period, at 36-40 days. An explanation for this dichotomy would be that a combination of parameters (not necessarily always the same) is needed for vaginal opening. These parameters oscillate during sexual maturation with different frequencies, which can achieve resonance to lead to vaginal opening and ovulation only during given periods.

Neonatal melatonin administration advances rat vaginal opening and disrupts estrous cyclicity and estrogen-dependent regulatory mechanisms of luteinizing hormone and prolactin

Melatonin (100 micrograms/rat) was administered to female rats on day 5 of life, 3 hours prior to the onset of darkness or at 12:00 hours. Melatonin administration induced precocious puberty in both cases, as indicated by the advance of the time of the vaginal opening and the appearance of the first estrous smear as compared with controls (P less than 0.01), together with an increase in the number of estrous smears (P less than 0.05) and a reduction in the number of diestrous smears (P less than 0.05). Decreased serum prolactin levels were observed on day 21 of age (P less than 0.05) in melatonin-treated rats with both of the melatonin injection times as compared with controls. No differences were apparent in basal luteinizing hormone (LH) levels either at 30 or at 60 days of age comparing melatonin- and vehicle-treated rats with either of the scheduled melatonin injection times. As to serum follicle-stimulating levels (FSH) levels, there was a marked decrease in circulating FSH levels in melatonin-treated rats in both cases on days 21, 30, and 45 (P less than 0.05) as compared with controls. A marked increase of serum prolactin at both 48 and 55 hours after estradiol benzoate (EB) administration was detected in 30-day-old melatonin-treated rats as compared with controls (P less than 0.05 for both points). Also, an increased responsiveness of prolactin to EB was found on the first day post-administration. At 60 days of age, an increase in prolactin responses to EB was observed on the first day post-administration (31 and 48 hours after, (P less than 0.01), whereas no differences were detected at any other studied time. The LH burst that occurs 31 hours after EB administration in 30-day-old rats was decreased in melatonin-treated animals as compared with controls (P less than 0.05). In 60-day-old melatonin-treated rats, a marked increase in the LH response to EB administration, 31 hours after injection (P less than 0.01), was observed. These data suggest that neonatal melatonin administration in pharmacological amounts induces precocious puberty as measured by vaginal opening and, furthermore, it advances the appearance of the first estrous smear with age-dependent modifications of estrous cyclicity and prolactin and LH responses to EB.

Pituitary-thyroid relationships in hypothyroidism

The pituitary gland is undoubtedly a target for thyroid hormone. It is the tissue with the highest density of T3 receptors and contains Type II T4 5' deiodinase which are involved in the secretion of TSH and other pituitary hormones. In the case of TSH, this knowledge has resulted in a better understanding of a number of conditions such as the adaptation to reduced thyroid reserve, and in an improvement in the way we treat hypothyroidism. But the pituitary being a target tissue for thyroid hormones has additional consequences. A direct effect of T3 on various secretions of the gland has been documented, and in the case of other pituitary hormones, directly or indirectly, thyroid hormone has some effect. T3 has a broad spectrum of metabolic and physiological effects that may, by themselves, account for a large proportion of the variability of the clinical presentation of hypothyroidism. The multiplicity of pituitary hormones and the multiplicative action of these various hormones through their target glands make the pituitary gland another key element in the variability of clinical manifestations of hypothyroidism. While this variability poses a diagnostic challenge in that hypothyroidism should be considered in a large number of conditions, the abnormalities resulting from the lack of thyroid hormone in the pituitary are equally challenging from a therapeutic point of view, since they respond promptly to the correction of the hypothyroidism. We should try to identify and treat those that are both life-threatening and not corrected rapidly by the administration of thyroid hormone.

Sexual differences in the dopaminergic control of luteinizing hormone secretion in the developing rat

The aim of the present study was to compare the effect of haloperidol on the secretion of luteinizing hormone (LH) in male and female immature rats. At 12 days of age, haloperidol significantly released LH in females but not in males. The same results were obtained using sulpiride. The LH-releasing effect of haloperidol diminished with age; in 28-day-old rats it could not be evidenced. The influence of early organization of brain structures controlling LH secretion on this effect was then studied. Neonatally androgenized females failed to respond at 12 days of age and in neonatally castrated males the effect of haloperidol on LH followed the same pattern as in normal females. We conclude that the dopaminergic system plays an important inhibitory role in the control of LH in infantile females and not in males, and that this sexual difference depends on early differentiation of the brain.

Neuroendocrine mechanisms controlling the onset of female puberty

This article describes the major neuroendocrine developments that are associated with the normal onset of puberty in the female rats. Although differences exist between rats and humans with regard to development and function of the reproductive system, there are major basic similarities. This makes the rat a valuable laboratory model in which to evaluate the effects of potentially hazardous substances on normal sexual maturation. A systematic experimental approach is presented to show how the study of reproductive development in the female rat can aid our understanding of the processes by which these substances could disturb normal puberty in the human female.

Effect of neonatal melatonin administration on sexual development in the rat

In order to study the mechanisms by which melatonin modulates sexual development, 5-day-old female Wistar rats have been treated with a single s.c. injection of melatonin, 3 h before the darkness onset. Criteria for sexual development were the age of vaginal opening and the circulating levels of prolactin, LH, FSH and estradiol. Also, pineal melatonin content was measured. There was a precocious puberty (P less than 0.01) in melatonin-treated rats measured by the age of the vaginal opening. An increase in the number of estrous smears over the whole period studied was observed in melatonin-treated animals as compared to controls. Along with these modifications, there was decrease in pineal melatonin content and serum prolactin levels, on day 21 of life (P less than 0.05), with an increase in both parameters on day 30 of age, in melatonin-treated rats as compared to controls, with no modifications at any other time studied. No differences were detected for serum LH levels considering the whole period studied for both groups. There was a faster decrease in plasma FSH levels with age in melatonin-treated animals than in controls. Serum estradiol levels were decreased in the peripubertal period in melatonin-treated rats as compared to controls. All these data suggest that the modifications induced by neonatal melatonin administration on prolactin, FSH and estradiol could be responsible for the precocious puberty shown in this study.

Differential effects of flurothyl- and electro-convulsive shock on sexual maturation and prolactin release in the rat

The effects of single and repeated seizures on luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin secretion and on the onset of sexual maturation in rats are described. In addition, the influence of convulsions generated electrically (electroconvulsive shock, ECS) and chemically (using flurothyl) are compared. Repeated flurothyl convulsions and ECS (one daily convulsion from age 24 days) significantly delay vaginal opening in female rats. The incidence of first ovulation at maturation is reduced to 20% compared with 70-100% for untreated groups. Body and adrenal weights in immature rats are not modified by flurothyl convulsions. Repeated ECS does not influence adrenal weight although somatic growth is inhibited. In an effort to clarify the mechanism of action of convulsions on puberty onset, we examined acute changes in LH, FSH and prolactin secretion and the surge response of LH/FSH to gonadal steroid priming. A single flurothyl convulsion potently inhibits prolactin secretion. In contrast, an ECS acutely stimulates prolactin release in male and female rats. Convulsive seizures do not consistently alter tonic gonadotropin output. However, both flurothyl convulsions and ECS attenuate estradiol benzoate/progesterone-induced LH and FSH surges in ovariectomized rats though this is apparently not mediated by dopamine/prolactin since bromocriptine treatment delays sexual maturation without preventing ovulation at first estrus. Similarly, bromocriptine does not disrupt LH/FSH surges induced by gonadal steroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin secretion in pubertal and adult male subjects

Prolactin, LH and FSH circadian secretion were studied in a group of 20 boys in various pubertal stages and in 13 normal male adults. Prolactin 24-hour integrated concentration was similar in all groups except in stage 2 boys, in which it was significantly higher with respect to stage 3-4 boys. This pattern was observed also for nocturnal, but not for diurnal concentration. As already described by other authors, LH showed and amplified circadian secretion in stage 2 and 3-4 boys, particularly during night time. FSH increase was less evident, and reached the peak 24-hour mean concentration in stage 2 subjects. Our results suggest that during puberty the hypothalamic pituitary system increases its activity not only with regard to gonadotropins but also to prolactin secretion.

The effect of prolactin pretreatment on prostaglandin F2 alpha-associated structural changes in membranes from rat corpora lutea

The ability of prolactin treatment to antagonize the luteolytic effect of prostaglandin F2 alpha (PGF2 alpha) was examined in the rat. Animals were superovulated, treated with PGF2 alpha and various doses of prolactin. Plasma progesterone concentrations were measured to assess luteal function. Microsomes were prepared from ovarian homogenates and examined by wide-angle x-ray diffraction for evidence of structural changes in the cellular membranes during luteolysis. In addition, the concentrations of various lipids were analyzed for alterations in membrane lipid composition. In preparations from control animals, all of the membrane lipid was in the liquid-crystalline phase at body temperature. However, in samples from PGF2 alpha-treated rats, portions of the bilayer underwent a structural alteration from liquid-crystalline to gel phase. This phase transition was not accompanied by significant changes in the relative concentrations of various lipids. Prolactin treatment was effective in inhibiting this membrane breakdown in a dose-dependent manner. These results suggest that PGF2 alpha and prolactin may control luteal function by affecting membrane structure.

Studies on the central effect of prolactin in inducing precocious puberty in the female rat

Implantation of prolactin (PRL) into the median eminence (PRL-ME implants) of 23 day old female rats markedly advanced the onset of puberty, as measured by the age at vaginal opening and at first ovulation. Precocious puberty was preceded by steroidogenic activation of the ovary, as reflected by increases in uterine weight and an enhanced in vitro steroidal responsiveness of the ovary to hCG. The stimulatory effect of PRL-ME implants could not be attributed to alterations in the release of LH, FSH, GH or TSH from the anterior pituitary. Likewise, the PRL effect was neither exerted through the adrenal gland nor involved activation of a direct neural, vagal-mediated influence on the ovary. Furthermore, the effect of PRL-ME implants was not due to a decrease in pituitary secretion of opioid substances, which appear to restrain chronically gonadotropin release during female prepubertal development. These latter experiments also showed that administration of the opioid agonist, morphine, can delay the onset of puberty in the female rat. Although local exposure of the medial basal hypothalamus to high PRL levels is extremely effective in accelerating puberty, the mechanisms by which this effect is exerted remains to be elucidated.