Pituitary Prolactin Content Research Articles

Influence of adrenocorticotropin and adrenalectomy on gonadotropin secretion in immature rats.

We examined the effects and mechanisms of action of ACTH and ACTH fragments on gonadotropin secretion in immature rats. ACTH administered by daily injection or continuous infusion (osmotic minipumps) attenuated the postcastration rise in serum LH. Pituitary LH concentration was either unchanged or increased in ACTH-treated rats and pituitary sensitivity to gonadotropin-releasing hormone (GnRH) was reduced by ACTH treatment. A fragment of ACTH (ACTH 4-10), which is less steroidogenic, did not alter levels of serum LH, and ACTH did not reduce LH secretion in adrenalectomized castrates. Serum and pituitary concentrations of prolactin were normal in ACTH-treated animals. These studies demonstrate that the suppression of gonadotropin secretion by ACTH is mediated by the adrenal gland. This mechanism causes a decreased pituitary sensitivity to GnRH, but LH synthesis does not appear to be affected. Prolactin does not play a role in this mechanism.

Delta-9-tetrahydrocannabinol: its effect on hypothalamo-pituitary system in male rats.

Subcutaneous administration of delta-9-tetrahydrocannabinol (delta 9-THC) in adult male rats caused a decrease in serum luteinizing hormone (LH) levels with unchanged serum prolactin, pituitary LH and pituitary prolactin content. Response of pituitary to in vitro gonadotropin releasing hormone (GnRH) remained unaltered while the response to in vivo GnRH treatment was markedly increased with the drug indicating the pituitary to be functionally normal. Differences in the in vitro and in vivo response could be due to the endogenous steroid levels. The hypothalamic LH-RH content concommitantly increased. Delta-9-tetrahydrocannabinol may inhibit the release of luteinizing hormone releasing hormone (LHRH).

Hamster prolactin: physiological changes in blood and pituitary concentrations as measured by a homologous radioimmunoassay.

A specific and sensitive homologous radioimmunoassay (RIA) for determination of hamster prolactin is described and compared to heterologous hamster prolactin RIA and to the homologous and heterologous RIAs for rat prolactin. With this method, we have determined that, in the golden hamster, diurnal plasma prolactin fluctuations have a mean interpeak interval of 1.5 h, that serum prolactin concentrations are influenced by day length, by ether vapors, by animal's gender, and by refeeding following a fast but not by neurosurgical procedures which increase somatic growth and serum GH concentration in adult hamsters. Variations in day length influenced pituitary prolactin content and concentration, and pituitary removal abolished prolactin secretory responses to ether stress. A heterologous RIA for hamster prolactin which utilizes radioiodinated rat prolactin and rabbit antihamster prolactin serum (RK1-15) represents the most advantageous method for the measurement of hamster prolactin because of its high sensitivity (0.14 ng/ml), high antiserum binding to iodinated rat prolactin, and the ability to measure both hamster and rat prolactin.

Plasma and pituitary concentrations of LH, FSH and prolactin after injection of GnRH in aged female C57BL/6 mice

Plasma and pituitary concentrations of LH, FSH and prolactin (Prl) were compared by radioimmunoassay (RIA) in young mature (2–4 monthold) and aged (16–22 month-old) female C57BL/6 mice, following various experiments with IP injections of GnRH. Unanesthetized mice were bled by cardiac puncture either (1) at various time intervals following a single injection of 25 ng GnRH, (2) after several injections of 25 ng GnRH, or (3) after receiving excessively large doses of GnRH. From the RIA of plasma and pituitary concentrations of LH, it appeared that the pituitaries of aged mice were, in general, capable of responding to GnRH treatment, only to a lesser degree than that of the younger females. The exception was that the pituitaries of aged mice that were subjected to unusually high doses of GnRH continued to secrete higher levels of LH, whereas the response of the pituitaries in younger mice plateaued after receiving 25 ng GnRH. Plasma and pituitary concentrations of FSH and Prl remained fairly constant when aged GnRH-treated females were compared with aged controls. This was also true when FSH and Prl concentrations in the younger mice were compared with their controls, except for significantly higher plasma FSH and significantly lower pituitary FSH following several injections of GnRH. When the hormonal concentrations of the young and aged groups were compared in the various experiments, the older mice consistently exhibited higher levels of gonadotropin and lower levels of prolactin than those of the younger mice. In a separate experiment, in which a radioreceptor assay (RRA) was used to quantitate plasma LH in GnRH-treated mice, both age groups were found to have lower concentrations of LH ( p<0.05) than those obtained by RIA from the same animals. The RRA to RIA ratio, however, was 0.84 for 2–4 month-old and 0.57 for 16–22 month-old mice. These studies suggest that the anterior pituitary of the aged mouse is less sensitive to GnRH stimulation.

The effect of DL-5-hydroxytryptophan (5-HTP) on plasma prolactin in pituitary stalk sectioned rats.

5-HTP (5 mg/100 g body weight), a precursor of serotonin, was administered intravenously to pituitary stalk sectioned rats. Plasma prolactin levels were initially increased 30 and 60 min after the injection of 5-HTP and thereafter decreased. Pituitary prolactin content was decreased 60 min after the stalk section as compared to those seen following sham operation. The treatment of 5-HTP induced a moderate increase in pituitary prolactin content in the stalk sectioned rats. In order to confirm the complete disconnection of pituitary stalk after the operation, 2.5 micrograms of dopamine hydrochloride was given into the lateral ventricle of stalk sectioned rats. Plasma prolactin did not change following the administration. Our results demonstrate that 5-HTP acts either directly at the pituitary level or via some mechanism yet to be determined.

Changes in FSH, LH and prolactin secretion and ovarian follicular development during lactation in the rat.

To elucidate the factors regulating ovarian follicular development during lactation in the rat, plasma and pituitary levels of FSH, LH and prolactin (PRL) were determined for each day of lactation along with the histological examination of size-distribution of ovarian follicles.Post-partum surges in FSH and LH were observed at 1700 hr on Day 0 of lactation (Day 0=day of parturition). Plasma FSH values were within the range of diestrous levels during Days 1 to 21 whereas pituitary content of FSH exceeded the values of 1400hr of proestrus (the highest level during the estrous cycle) from Day 3 onward. On the other hand, concentrations of plasma LH were generally below the range of diestrous values througout lactation. From Day 1 onward pituitary content of LH increased slowly but did not attain proestrous levels until Day 14. High concentrations of plasma PRL were observed from Day 4 to 10, although the time of suckling stimulus was not controlled. Pituitary content of PRL had abruptly increased by Day 3. Thereafter, high levels were maintained until Day 17, followed by a sudden decline on day 18.After post-partum ovulation, the number of healthy follicles larger than 201 μm in diameter abruptly decreased until Day 6. From Day 3 to 7, a few healthy follicles of 201-400 μm were present, but larger follicles were absent. After Day 8, follicles larger than 401 μm were always present.On the basis of these results it is suggested that during the early stages of lactation, the strong suckling stimulus and the consequent high levels of PRL result in a decreased plasma LH level which is insufficient to cause maturation of the follicles. Ovaries during early stages of lactation, however, were still responsive to exogenous gonadotropins initiating follicular maturation under the influence of normal suckling stimulus and high levels of PRL.

Modulation by dopamine antagonists of DNA synthesis in the pituitary gland of the male rat.

Pituitary DNA synthesis and serum and pituitary concentrations of prolactin were measured in male rats given the dopamine antagonist haloperidol or pimozide, and the dopamine agonist bromocriptine. Increased DNA synthesis was observed 25h after a single injection of haloperidol and on each day of the 5-day period of pimozide administration. Haloperidol and pimozide increased serum prolactin levels. Pituitary prolactin concentrations fell 12h after haloperidol, recovering b6 24h, and 24 and 48h after pimozide, recovering by 72 h. Bromocriptine lowered pituitary DNA synthesis and serum prolactin levels and induced a transient rise in pituitary prolactin concentrations. The results indicate that dopamine agonists and antagonists modulate DNA synthesis in the pituitary gland of the rat.

Seasonal changes in prolactin and growth hormone cells in the hypophyses of white-tailed deer (Odocoileus virginianus borealis) studied by light microscopic immunocytochemistry and radioimmunoassay.

Numerous investigators have shown a relationship between basal serum prolactin (PRL) levels and photoperiod in domestic ungulates, and we have shown recently that a similar seasonal baseline serum PRL profile exists in both sexes of a captive but free-breeding population of white-tailed deer. In order to localize and describe the distribution and possible seasonal changes of PRL and growth hormone (GH) cells in the adenohypophyses of deer, we have used antisera raised against ovine PRL and bovine GH and the unlabeled antibody enzyme technique, in conjunction with point counting morphometry. In addition, we have measured seasonal changes in pituitary PRL concentrations in this same population, using a heterologous application of a recently developed homologous radioimmunoassay (RIA) for ovine PRL. Our results show that GH and PRL cells comprise two morphologically separate and immunologically distinct populations. Growth hormone cells were distributed evenly throughout the gland, except in the zona tuberalis, and males had a slightly greater volume density of immunoreactive GH than females; however, there were no differences between sexes in the average size of these cells, and little seasonal change was observed in these cell populations. In contrast to GH cells, the volume density of PRL cells, the size of PRL cells, and the pituitary concentration of RIA--measurable PRL all showed marked seasonal changes in deer of both sexes. These changes were well correlated with one another and with previously reported changes in basal serum levels (in these animals), in that they all reached zenith during midsummer, and nadir in midwinter. Our results demonstrate the necessity of reporting the time of year and latitude (to specify photoperiod) in studies concerning PRL cell physiology, particularly when dealing with any wild animal population.

Effects of ageing and gonadal steroid hormones on prolactin concentrations in the anterior pituitary of the chicken.

1. Effects of ageing and gonadal steroid hormones on pituitary prolactin (PRL) concentration in the chicken were investigated. 2. No difference was found in the qualitative electrophoretic patterns of the anterior pituitary homogenates at different ages and between the sexes. 3. Pituitary PRL concentrations in males were generally higher than in females. 4. Pituitary PRL concentrations in castrated immature cockerels were higher than in intact birds, while PRL concentration was depressed by the injection of testosterone propionate or oestradiol benzoate. 5. Prolactin concentration in intact immature cockerels was decreased by daily injection of testosterone or oestradiol for 3 weeks but not by injection of the hormones for 1 week.

Circadian rhythm of circulating corticosterone and prolactin levels in spontaneously hypertensive rats

Circulating levels of corticosterone and prolactin were measured by radioimmunoassay at hourly intervals during a 24 h period to establish the diurnal rhythm of these hormones in spontaneously hypertensive rats (SHR). Corticosterone levels exhibited a distinct circadian variation with concentrations reaching a zenith at 2000 h and a nadir at 1200 h in male and female SHR. Corticosterone levels in females were consistently greater than males. Circulating prolactin levels were greater during the light h than dark in the female; the opposite occurred in males. Measurement of pituitary prolactin content tended to be low when serum prolactin levels were high and vice versa. The circadian rhythm of circulating corticosterone and prolactin in the hypertensive SHR was found to be similar to the day-night patterns established for normotensive rats. However, these measurements were made under quiescent conditions. It is suggested that because SHR are hyper-responsive to stress and because corticosterone and prolactin have synchronous effects on stress-induced adrenal steroidogenesis, further investigation of prolactin and corticosterone may reveal a participatory role of these hormones in the pathogenesis of the genetically-programmed hypertension of SHR.

Studies of the neural mechanisms by which hypothyroidism decreases prolactin secretion in the rat

These studies report that chronic hypothyroidism in the rat is accompanied by decreased serum prolactin. An investigation of those mechanisms by which hypothyroidism decreases prolactin secretion revealed the following findings: (1) activation of tyrosine hydroxylase in the median eminence (ME) and increase in the turnover-rate of dopamine (DA) in the ME; (2) a decreased content and in vitro release of prolactin by pituitaries from hypothyroid rats; (3) decreased [ 3H]spiroperidol binding to pituitary homogenates obtained from hypothyroid rats, and (4) normal increase of serum prolactin following administration of haloperidol. Comparison of the effects of hypothyroidism on dopaminergic terminals of the striatum with those of the ME was made and the following tentative conclusions proposed. Hypothyroidism presumably increases the release of DA into the pituitary portal system. A deficiency of thyroid hormone desensitizes the pituitary lactrotrope to inhibition by DA, decreases the total pituitary prolactin content and presumably also reduces the peripheral catabolism of prolactin. The overall net effect of hypothyroidism is therefore, a decrease in serum prolactin levels which can increase normally following haloperidol. The mechanism by which a deficiency of thyroid hormone alters the function of the tuberoinfundibular and striatal dopaminergic systems is unknown.

Plasma and pituitary concentrations of LH, FSH and prolactin in aged female C57BL/6 mice.

Plasma and pituitary concentrations of LH, FSH and prolactin were determined by radioimmunoassay in 2-month-old (young) and 16-20-month-old (old) C56BL/6 mice. There were no statistical differences in hormonal levels between aged females in oestrus (those exhibiting a copulatory plug) and those in constant dioestrus. In the old females plasma levels of LH (P < 0.002) and FSH (P < 0.001) were significantly elevated, while levels of prolactin (P < 0.001) were significantly depressed when compared with those from young animals. Pituitary homogenates from old females also contained more gonadotrophins (P < 0.001) and less prolactin (P < 0.001) than those of the young females. A radioreceptor assay utilizing a plasma membrane of luteinized rat or mouse ovaries indicated that LH from 2-month-old animals bound better to ovarian receptors (P < 0.05) than did LH from old mice, although radioimmunoassay of the same samples gave higher (P < 0.01) plasma LH levels for the old mice. Since the radioreceptor assay is considered to be a more sensitive test for biologically active LH, the results from these two types of assays suggest that there may be an alteration in the mouse LH molecule with age.

Plasma and pituitary concentrations of LH, FSH and prolactin in aged superovulated C57BL/6, CD-1 and B6D2F 1 mice

Plasma and pituitary concentrations of LH, FSH and prolactin in aged superovulated C57BL/6, CD-1 and B6D2F 1 mice

Does pinealectomy, anopsia or exposure to constant darkness affect pituitary prolactin levels in the goldfish,Carassius auratus L.?

The ef fects of exposure to constant darkness, anopsia and pinealectomy on pituitary prolactin levels in the goldfish were examined. Determination of prolactin was made in a polyacrylamide microelectrophoretic system coupled with densitometry. Neither pinealectomy nor anopsia had an effect on pituitary prolactin content in the fall. Exposure to constant darkness in the fall was without obvious effect, whereas such treatment in the spring resulted in significantly elevated pituitary prolactin content. Pinealectomy in the spring did not alter pituitary content, suggesting that the response to constant darkness is independent of the pineal organ, perhaps involving retinal or extra-retinal photoreception.

Serum and pituitary concentrations of growth hormone and prolactin in pygmy mice.

SummaryBasal levels of GH and PRL in the serum and pituitary gland of normal (Pg/ Pg) and pygmy (pg/pg) (VY X C3H) F-l hybrid mice were measured by homologous radioimmunoassays. The serum concentrations of GH and PRL in pygmy mice at approximately 90 days of age were found to be no different from those in corresponding normal controls. The pituitary concentrations of the two hormones, however, were substantially subnormal in pygmy mice. Perphena-zine injection failed to stimulate PRL release by pygmy (pg/pg) pituitaries, in contrast to the marked increase in serum PRL levels of the normal Pg/Pg mice. Daily administration of 100 μg of ovine PRL for 8 weeks produced none or very little increase in the body weight of pygmy mice. These results suggest that the pg mutation induces a multifaceted change affecting the synthesis, release, and function of growth hormone and prolactin.The ovine PRL used in these studies was supplied by the Pituitary Hormone Distribution Program of the National Institute of Arthriti...

Hypothalamic monoamine oxidase, a component in the serotonergic control of pituitary prolactin content in Carassius auratus L.

The role of the enzyme monoamine oxidase (MAO) was examined with regard to the control of pituitary prolactin content in the goldfish. Inhibition of MAO by means of intraperitoneal injection of pargyline resulted in significantly elevated brain serotonin content. Concomitantly, pituitary prolactin stores were also significantly elevated. Time-course and dose-response experiments revealed that pargyline at doses ≥25 mg/kg completely inhibited MAO and significantly increased brain serotonin and pituitary prolactin content within 12 hr. It is concluded that the enzyme MAO may be a significant component of the monoaminergic system of the goldfish, serving to modulate the serotonergic inputs to centers involved in the control of pituitary prolactin secretion.

Indomethacin fails to alter basal or phenothiazine-induced prolactin concentrations in man.

In order to evaluate the possible role of prostaglandins in pituitary prolactin (PRL) secretion, PRL was serially measured following perphenazine (Trilafon) ingestion in 8 men before and after 5 days of indomethacin administration. Since estrogens have been shown to modulate prolactin secretion in man, serum steroids including estrone (E1), estradiol (E2), progesterone (P) and testosterone (T) were measured before and after indomethacin ingestion. Serum E1, P and T levels were similar during the pre- and post-indomethacin study periods: 56 +/- 4 (1 SEM) vs 48 +/- 5 pg/ml, 298 +/- 28 vs 315 +/- 32 pg/ml, and 8.1 +/- 0.7 vs 8.6 +/- 0.7 ng/ml, respectively. Serum E2 levels were slightly, but significantly, lower following indomethacin treatment at 30 +/- 3 vs 37 +/- 3 pg/ml (p less than .01). Basal serum PRL concentrations were unaffected by indomethacin administration (9 +/- 3 pre- vs 8 +/- 2 ng/ml post-drug treatment). Integrated perphenazine-induced PRL responses were likewise similar during the 2 study periods: 101 +/- 16 ng . hr/ml during the control period and 104 +/- 14 ng . hr/ml following indomethacin. Thus, short-term indomethacin treatment had no effect on basal or perphenazine-stimulated PRL secretion in men.

Hypothalamus-pituitary-thyroid axis interactions with pineal gland in the rat.

We examined in the rat several possible relationships between the pineal gland and the hypothalamus-pituitary-thyroid axis. The pineal gland, the retina, and the hypothalamus exhibited a diurnal rhythm in thyrotropin-releasing hormone (TRH) content with peak values occurring around 1200 h. This rhythm in the hypothalamus was abolished by constant light but was not affected by pinealectomy. Nor did pinealectomy affect hypothalamic TRH content, pituitary content of thyroid-stimulating hormone (TSH) or prolactin; serum levels of (TSH), triiodothyronine (T3), or thyroxine (T4), or serum free-thyroxine index; or free-triiodothyronine index. Melatonin did not affect TSH or prolactin release from the anterior pituitary or TRH release from the hypothalamus in vitro. Isoproterenol did not affect the TRH content of pineal glands in vitro; nor did TRH or T3 affect basal or stimulated activities of serotonin N-acetyltransferase, the presumed controlling enzyme in melatonin production. We found no evidence for significant interactions between the pineal gland and the hypothalamus-pituitary-thyroid axis.

EFFECT OF TREATMENT WITH AN AGONIST OF LUTEINIZING HORMONE RELEASING HORMONE ON EARLY MATURATIONAL CHANGES IN PITUITARY AND TESTICULAR FUNCTION IN THE RAT

Male rats aged 30 days were injected once daily for between 1 and 7 days with 50 ng (D-serine t-butyl6, des-glycine-NH210) luteinizing hormone releasing hormone ethylamide (LH-RH agonist), and pituitary and testicular function were assessed. Treatment for 7 days significantly (P less than 0.02) inhibited maturational increases in the pituitary content and serum concentration of gonadotrophins, testicular luteinizing hormone (LH)-receptor concentration and the testicular capacity to secrete testosterone; the pituitary content and serum concentration of prolactin, the hypothalamic content of LH-RH and testicular weight were unaffected. In rats treated with LH-RH agonist, the initial (2 to 3 days) reduction in testicular LH-receptors and the capacity to secrete testosterone probably resulted from acutely raised levels of LH in the blood, whilst later effects may have resulted from the apparently chronic reduction in serum gonadotrophin levels. The latter may reflect a decrease in pituitary responsiveness to repeated stimulation with LH-RH agonist. Despite the extensive loss of testicular LH-receptors and diminished responsiveness, the concentration of HCG which significantly (P less than 0.05) increased testosterone secretion by the testis in vitro was the same (2 pmol/l) as that for testes from control rats.

Measurements of pituitary prolactin levels in breeding pigeons by crop sac radioreceptor assay

A recently developed assay based on the ability of ovine prolactin to bind to pigeon crop sac receptors was used to measure changes in pituitary prolactin content and concentration in male and female pigeons during the reproductive cycle. Pituitaries were collected from six regularly breeding pairs of pigeons at each of four stages: active nest-building (2–3 days before egg-laying), egg-laying, midincubation, and Day 1 posthatching. In females, prolactin content and concentration declined progressively between nest-building and midincubation but rose to peak levels by Day 1 posthatching. Prolactin levels of males were generally lower than those of females, but the pattern of changes was similar for both sexes. Comparison of these results with the pattern of prolactin-dependent crop sac changes suggests that the decline in pituitary prolactin levels during early incubation reflects the release of the hormone into the circulation. A marked increase in prolactin content was observed in both sexes during the second half of the incubation period, which may function to insure that a sufficient amount of prolactin is available to stimulate the formation of crop “milk” for regurgitation to the newly hatched young.