Changes In Prolactin Concentrations Research Articles

Myo-Inositol Potentiates the Inhibitory Effect of Metformin on Prolactin Levels

Introduction: Metformin was found to reduce elevated levels of anterior pituitary hormones. Its thyrotropin-lowering effect was more pronounced in individuals receiving myo-inositol. The aim of the present study was to investigate whether the concomitant supplementation of myo-inositol determines the impact of metformin on prolactin levels. Methods: The study population consisted of two groups of women with mild-to-moderate hyperprolactinemia. Group 1 included 24 individuals receiving myo-inositol preparations (2 g daily for at least 6 months), while 24 inositol-naïve women belonged to group 2. Both groups were matched for age, insulin sensitivity, and prolactin concentration. For the following 6 months, all women were treated with metformin (1.7 daily). Plasma glucose levels, the homeostatic model assessment of insulin resistance ratio (HOMA-IR), glycated hemoglobin, as well as plasma levels of total prolactin, monomeric prolactin, thyrotropin, free thyroid hormones, adrenocorticotropic hormone, and insulin-like growth factor-1 were measured at baseline and after 6 months of metformin treatment. Results: Metformin reduced plasma glucose, HOMA-IR, and glycated hemoglobin in both study groups, but this effect was more pronounced in group 1 than group 2. Treatment-induced changes in total and monomeric prolactin levels were significant only in group 1. There were no differences between follow-up and baseline values of thyrotropin, free thyroxine, free tri-iodothyronine, adrenocorticotropic hormone, and insulin-like growth factor-1. Treatment-induced changes in prolactin concentration correlated with baseline prolactin levels, baseline values of HOMA-IR, and the impact of treatment on HOMA-IR. Discussion: The obtained results suggest that myo-inositol supplementation potentiates the inhibitory effect of metformin on prolactin levels in women with hyperprolactinemia.

MON-304 Prolactin as a Surrogate Marker to Predict Long Term Postoperative Hypopituitarism After Transsphenoidal Resection of Pituitary Adenomas

Transsphenoidal surgery (TSS) is the first line treatment for pituitary adenoma. A well-known complication of TSS is hypopituitarism with a reported risk of 5-25% after resection of pituitary adenomas. A decrease in postoperative prolactin concentration was shown to be associated with postoperative hypopituitarism in a previous report. We hypothesized that in addition to clinical factors (preoperative hypofunction and adenoma size), biochemical factors (change in prolactin concentration and immediate post-operative hypofunction) can aid in predicting long term hypopituitarism as defined as ≥1 biochemically confirmed hypofunctioning pituitary axes 3 years after resection. A retrospective analysis of all patients undergoing TSS for both functioning and non-functioning pituitary adenomas at a tertiary center from January 2013 through December 2015 was performed. Prolactinomas were excluded. Of the 75 patients included, 21.3% (n=16) had at least one pituitary axis requiring replacement at 3 years post operatively. Mean age at presentation was 55 ± 16 years, 55% were female and 81% were Caucasian. Mean adenoma size was no different between normal pituitary function and hypopituitary groups (24.0 ± 11.9 mm versus 25.3 ± 10, p=0.7). Factors associated with long term hypopituitarism were older age (mean age 64 ± 4 years versus 53 ± 2 years, p = 0.02), preoperative secondary adrenal insufficiency (AM cortisol 6.4 ± 3.7 vs 12.0 ± 6.5 µg/dL; p = 0.03), preoperative secondary hypothyroidism (0.8 ± 0.2 vs 12.0 ± 6.5 ng/dL; p < 0.01), low immediate postoperative cortisol (5.3±3.1 vs 26.1±18.3 µg/d; p<0.01), and persistence of adrenal insufficiency (10.7% vs 2.7%; p<0.01) and secondary hypothyroidism (13.3% vs 5.3%; p<0.01) at 3 months. Change in prolactin concentration from preoperative to postoperative day 1-7 was not significantly different between groups (p=0.09) due to the higher variability in the hypopituitary group (median 0.2 ng/mL, IQR -0.5 - 0.8 ng/mL) compared to the normal pituitary function group (median 0.7 ng/mL, IQR 0.5-0.8 ng/mL). Adenoma size, optic chiasm and cavernous sinus involvement were not associated with long term hypopituitarism. In patients who developed postoperative hypopituitarism, there was a higher frequency of adenoma persistence or recurrence (20% vs 47%). There was a high rate of patients lost to follow up (56%). Older age, the presence of preoperative secondary adrenal insufficiency and hypothyroidism, and low day 1-7 postoperative cortisol concentration are factors that can be used to deem a patient high risk for future hypopituitarism. These patients should have close follow up with continued screening postoperatively. Contrary to prior reports, adenoma size and parasellar involvement were not associated which may be suggestive of surgical expertise. Prolactin concentrations proved not to be a good surrogate marker to predict long term hypopituitarism.

Postgraze assessment of toxicosis symptoms for steers grazed on toxic endophyte-infected tall fescue pasture1,2

A 2-yr pen experiment was conducted using 12 different crossbred Angus steers each year to determine if short-term changes in prolactin concentrations, body temperature, and vasoconstriction reflect recovery from fescue toxicosis after steers that previously grazed toxic endophyte (Neotyphodium coenophialum)-infected Kentucky 31 tall fescue [Lolium arundinaceum (Schreb.) Darbysh] are placed on nontoxic feed. Groups of 6 steers from toxic endophyte-infected and endophyte-free tall fescue grazing treatments were blocked by BW for assignment to pens as a randomized complete block design with 2 replications. Two environments were implemented by initiating the experiment on 18 August in yr 1 and on 8 September in yr 2 for durations of 30 and 21 d, respectively. Rectal temperatures were recorded, jugular blood was collected for assaying serum prolactin, and cross sections of the caudal artery were ultrasonically imaged at selected time points to evaluate temporal changes in the response variables. Rectal temperatures in steers on the toxic endophyte pasture treatment declined (P < 0.05) linearly over time in yr 1 and 2 and were similar (P > 0.10) to those on endophyte-free treatment on d 30 in yr 1 and by d 15 in yr 2. Prolactin concentrations in steers on the toxic endophyte pasture treatment showed curvilinear increases (P < 0.05) over time and were similar (P > 0.10) to steers on the endophyte-free treatment by d 15 in yr 1 and by d 10 in yr 2. Luminal areas of the caudal artery in toxic endophyte steers were less (P < 0.05) than those in endophyte-free steers across all dates in both years. Results indicated that rectal temperatures in steers after they are removed from toxic fescue may decrease over time, but temporal changes in rectal temperatures could be affected more by prevailing ambient temperatures than by actual mitigation of fescue toxicosis. Prolactin concentrations in steers after they are removed from toxic endophyte tall fescue can increase and stabilize in less than 2 wk, but alkaloid-induced vasoconstriction that causes a vulnerability to severe heat stress is not alleviated within 30 d.

Serotonergic Function and Treatment of Behavioral and Psychological Symptoms of Frontotemporal Dementia

The purposes of this study were first, to evaluate the effectiveness of citalopram in treating behavioral disturbances in frontotemporal dementia (FTD) subjects and second, to determine whether an association exists between serotonergic function, as determined by a neuroendocrine challenge, and treatment response. Single-dose citalopram (30 mg per os) challenge followed by a 6-week open-label study. Outpatients referred to memory clinics. Fifteen patients suffering from FTD with severe behavioral and psychological symptoms of dementia. Following citalopram challenge, all patients were treated with citalopram titrated to a target dose of 40 mg once daily. Behavioral disturbances, using the Neuropsychiatric Inventory (NPI) (primary outcome) and Frontal Behavioural Inventory (secondary outcome), were assessed. Change in prolactin concentration following citalopram challenge was used as an index of central serotonergic response. Citalopram treatment was effective in treating behavioral symptoms, with significant decreases in NPI total score (F[2, 28] = 6.644, p = 0.004), disinhibition (F[2, 28] = 4.030, p = 0.029), irritability (F[2, 28] = 7.497, p = 0.003) and depression (F[2, 28] = 3.467, p = 0.045) scores over the 6 weeks. Significant improvement in Frontal Behavioural Inventory scores suggested that citalopram was also effective in the treatment ofbehaviors specific to FTD. A lower change score in concentration of prolactin was significantly positively correlated with greater improvement in the total NPI score from baseline to endpoint (r = 0.687, p = 0.005). A blunted response to a citalopram challenge, implying a dysfunctional serotonergic system, predicted a more positive treatment outcome. The results suggest that despite the endogenous serotonin deficiency of FTD, citalopram treatment may be effective in targeting the behavioral disturbances characteristic of FTD.

Ovulatory activity and plasma prolactin concentrations in wild and domestic ewes exposed to artificial photoperiods between the winter and summer solstices

Mouflon and domestic Manchega sheep differ in the timing of their reproductive season under natural photoperiod (NP) conditions. This study examines whether they also differ in their reproductive responses to artificial photoperiod cues. For this, mouflons (n=24) and ewes (n=24) were exposed between the winter and summer solstices to artificial long days (LD: 16h light/day), to short days (SD) simulated via the use of melatonin implants, or to NP conditions (controls), and their ovulatory activity monitored. The effects of these treatments on annual changes in prolactin concentration were also recorded. In the LD mouflon ewes, the offset and onset (7 March±5 and 2 October±4, respectively) of cyclic ovulatory activity occurred earlier (P<0.001) than in the NP animals (26 April±6 and 20 October±2, respectively), but no differences were seen (P>0.05) between the SD and NP mouflon ewes in either the onset of anoestrus (12 May±6 and 26 April±6, respectively) or the onset of subsequent ovulatory activity (13 October±8 and 20 October±2, respectively); however the duration of the anoestrus period was significantly reduced in the SD. In LD Manchega ewes, the onset of anoestrus was advanced (2 February±5 vs 15 March±11), but ovulatory activity started at the same time as in NP Manchega ewes (16 July±4 vs 5 July±8). In the SD Manchega ewes, two animals showed continuous cyclic ovulatory activity over the course of the experiment while the remainder entered anoestrus two months later (16 May±6, P<0.001) than their NP counterparts. In these SD ewes, the onset of cyclic ovarian activity was very variable. An annual rhythm of plasma prolactin concentration was seen in both the mouflon and Manchega ewes under all three photoperiod conditions. However, the amplitudes of the changes seen in prolactin concentration were smaller in both the LD and SD animals than in the corresponding NP animals (P<0.001). In conclusion, the results show that these two types of Mediterranean sheep differ in their ovulatory response when subjected to artificial photoperiods. The results also suggest that refractoriness to SDs may be the most important physiological mechanism regulating the onset of anoestrus in highly seasonal breeds, but not in less seasonal breeds.

A 12-month moderate-intensity exercise intervention does not alter serum prolactin concentrations

Introduction: Many studies have investigated the immediate impact of physical activity on prolactin concentrations; however, it is currently unclear what impact exercise may have on prolactin concentrations in the long-term, particularly among women. Understanding the role of exercise on prolactin is important because epidemiologic studies have reported increased risks of breast cancer in association with high prolactin concentrations. We investigated whether exercise alters serum prolactin concentrations at two time points within a one-year exercise intervention. Methods: Out of 96 women aged 40–75 years, 47 were randomized to a 12-month regimen of moderate-intensity physical activity and 49 were randomized to the control group. Participants in the exercise group (exercisers) took part in exercise at gym facilities 3 times per week and 3 times per week on their own. Serum prolactin was collected from participants at baseline, 3 and 12 months. Using generalized linear models, we compared the percent change in prolactin concentrations from baseline to the two follow-up time points in the exercisers versus the control group. Results: While we observed the suggestion of differences in the change in serum prolactin concentrations in some subgroups, overall there was no difference in the change in prolactin concentrations between exercisers and controls at 3 months (p=0.57) or 12 months (p=0.42). Conclusion: Our study does not support the hypothesis that long-term exercise influences serum prolactin concentrations.

Annual Changes in Day-length, Temperature, and Circulating Reproductive Hormones in Thoroughbred Stallions and Geldings.

Changes in follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, immunoreactive(ir)-inhibin, testosterone, estradiol-17β, and insulin-like growth factor (IGF)-I in Thoroughbred stallions along with changes in prolactin secretion in geldings were studied. The correlations of day-length with changes in the concentrations of these hormones were also studied. Five stallions and thirteen geldings were employed to draw blood samples in monthly basis and radioimmunoassay was performed to measure these hormones. All hormones showed a seasonal pattern, the levels being highest during the breeding season and lowest during the winter months. Most of the hormones were at their highest concentration during the month of April, the mid of spring in northern hemisphere. The concentration of circulating IGF-I also demonstrated seasonality, the peak lying on the month of April. The plasma concentration of prolactin also increased during the breeding season. This phenomenon was similar both in stallions and geldings although geldings had lower concentration than that of stallions. The changes in concentration of prolactin in stallions and geldings correlated more towards the day-length than towards the temperature. These results clearly indicate the seasonality of pituitary and gonadal hormones of Thoroughbred stallions, the activity being highest during the month of April and May of the breeding season.

Effect of a 12-Month Randomized Clinical Trial of Exercise on Serum Prolactin Concentrations in Postmenopausal Women

Prolactin is associated with an increased risk of postmenopausal breast cancer; however, few modifiable factors are known to reduce prolactin concentrations. Therefore, we examined the effect of a 12-month moderate-intensity exercise intervention on serum prolactin concentrations as a secondary end point (primary end points were estrogens and androgens). We randomly assigned 173 postmenopausal women who were sedentary, overweight (body mass index >24 kg/m(2), body fat >33%), ages 50 to 75 years, and not using hormone therapy to an exercise intervention or stretching control group. The intervention was facility- and home-based (45 min, 5 days/wk moderate-intensity sports/recreational exercise). One hundred and seventy (98%) women completed the study. Prolactin concentrations were similar at baseline (P = 0.25, geometric mean exercisers = 6.9 and controls = 7.5 ng/mL). Overall, the intervention was not associated with changes in prolactin concentrations between exercisers and controls at 3 months (P = 0.46) or 12 months (P = 0.29). The intervention effect did not vary by baseline age, body mass index, parity, or change in percent body fat during the intervention. Among exercisers, there was a significant difference in prolactin concentrations by change in fitness (VO(2)max) between baseline and 12 months. Exercisers whose VO(2)max changed by <5% had a 5% increase in prolactin concentrations, whereas those who increased their VO(2)max by 5% to 15% and >15% had a 11% (P = 0.03) and 7% (P = 0.01) decrease in prolactin concentrations, respectively. Although the exercise intervention had little effect on prolactin concentrations overall, increasing physical fitness was associated with reduced prolactin concentrations among postmenopausal women.

Control of molt in birds: Association with prolactin and gonadal regression in starlings

Despite the importance of molt to birds, very little is known about its environmental or physiological control. In starlings Sturnus vulgaris, and other species, under both natural conditions and experimental regimes, gonadal regression coincides with peak prolactin secretion. The prebasic molt starts at the same time. The aim of this series of experiments was to keep starlings on photo-schedules that would challenge the normally close relationship between gonadal regression and molt, to determine how closely the start of molt is associated with gonadal regression and/or associated changes in prolactin concentrations. In one series of experiments, photosensitive starlings were moved from a short photoperiod, 8 h light per day (8L), to 13 or 18L, and from 13 to 18L or 13 to 8L during testicular maturation. Later, photorefractory birds under 13L that had finished molting were moved to 18L. In another series of experiments, photorefractory starlings were moved from 18 to 8L for 7 weeks, 4 weeks, 2 weeks, 1 week, 3 days, 1 day, or 0 days, before being returned to 18L. There was no consistent relationship between photoperiod, or the increase in photoperiod, and the timing of the start of molt. Nor was there a consistent relationship with gonadal regression and the start of molt–molt could be triggered in the absence of a gonadal cycle. However, there was always an association between the start of molt and prolactin. In all cases where molt was induced, there had been an earlier increase in prolactin. However, the timing of molt was related to the time of peak prolactin, not the magnitude of that peak. This relationship between peak prolactin and the start of molt could explain the normally close relationship between the end of breeding activity and the start of molt.

Steady-State Pharmacokinetics of a New Antipsychotic Agent Perospirone and Its Active Metabolite, and Its Relationship with Prolactin Response

The authors investigated steady-state pharmacokinetics of perospirone and its active metabolite hydroxyperospirone (ID-15036) and its prolactin response in 10 schizophrenic patients receiving 16 mg twice daily. Plasma concentrations of perospirone, hydroxyperospirone, and prolactin were monitored just before and up to 12 hours after the dosing. Thereafter, the dose was decreased to 8 mg twice daily in 8 patients, and drug concentrations were determined. The geometric means of peak concentration (Css(max)), time to Css(max) (tmax), area under the plasma concentration-time curve from 0 to 12 hours [AUC (0-12)], and elimination half-life at steady state were 8.8 ng/mL, 0.8 hours, 22.0 ng x h/mL, and 1.9 hours, respectively, for perospirone, and those of Css(max), tmax, and AUC (0-12) for hydroxyperospirone were 29.4 ng/mL, 1.1 hours, and 133.7 ng x h/mL, respectively. There were no differences in dose-normalized Css(max) or AUC (0-12) perospirone and hydroxyperospirone between 16 mg/day and 32 mg/day of perospirone. Changes in prolactin concentration from 1 to 2 hours after the dosing were parallel with drug concentrations, and almost normal ranges of prolactin concentration were observed before the morning dose despite steady state. The current study indicated that perospirone is rapidly absorbed and rapidly eliminated, which influences the prolactin response. The active metabolite hydroxyperospirone may play an important role in the antipsychotic effect because the plasma concentration of this metabolite is higher than that of the parent compound.

Central Serotonergic Activity is Related to the Aggressive Behaviors of Alzheimer's Disease

The clinical correlates of reduced serotonin (5-HT) in Alzheimer's disease (AD) remain unknown. The hypothesis of this study was that altered central serotonergic activity is related to aggression in AD. Twenty-two institutionalized, nondepressed elderly (12 M/10 F, mean age ± SD: 82.2 ± 6.4) with probable AD, severe cognitive impairment (MMSE = 4.1 ± 4.7) and significant behavioral disturbance (Neuropsychiatric Inventory (NPI) score ⩾ 8) were studied. The prolactin (PRL) response to d,l-fenfluramine (60 mg p.o.) was used as an index of central serotonergic function. The NPI aggression score, NPI irritability score, and Behavioral Pathology in AD aggression score were positively correlated to prolactin concentrations following fenfluramine challenge (rS = .61, p = .003; rS = .53, p = .012; and rS = .47, p = .029 respectively). In addition, aggressive patients showed a greater mean PRL increase (% baseline) (215 ± 60, n = 11) than nonaggressive subjects (123 ± 54, n = 11) (p = .01, 2-tailed t-test). The change in PRL concentration depended on level of cognitive impairment (p = .0004) and the gender x aggression interaction (p = .015) with the overall regression model accounting for 74% of the variance (r = 0.86, F = 11.9, p = .0001). Female aggressive subjects with less cognitive impairment had the largest response to fenfluramine challenge. These results suggest a complex link between aggression in AD and central serotonergic dysfunction having interactions with gender and cognitive impairment.

Single oral dose kinetics of zotepine and its relationship to prolactin response and side effects.

The authors investigated the single oral dose kinetics of zotepine and its relationship with prolactin response and side effects in 14 healthy male volunteers. Each subject took a single oral 25-mg dose of zotepine, and plasma concentrations of zotepine, prolactin, and their side effects were monitored up to 36 hours after dosing. The means +/- SD of the time of maximal plasma concentration (tmax), the apparent oral clearance, the apparent volume of distribution, and the elimination half-life (t1/2) were 3.8 +/- 1.2 hours, 4.6 +/- 4.2 1/h.kg, 109.0 +/- 59.0 1/kg, and 21.0 +/- 8.9 hours, respectively. The change in prolactin concentrations and side effect scores were parallel with that of drug concentrations, although no significant correlation was found between these three parameters at any time-point. The current results clearly indicate that the tmax and t1/2 of zotepine are much longer than those previously reported, which are reflected in the changes in prolactin concentrations and side effect scores.

Multiple fixed doses of “Seroquel” (quetiapine) in patients with acute exacerbation of schizophrenia: A comparison with haloperidol and placebo

Five fixed doses of the atypical antipsychotic "Seroquel" (quetiapine) were evaluated to delineate a dose-response relationship, as measured by changes from baseline in Brief Psychiatric Rating Scale (BPRS), Clinical Global Impression (CGI), and Modified Scale for the Assessment of Negative Symptoms (SANS) summary scores, and to compare efficacy and tolerability opposite placebo and haloperidol. Three hundred sixty-one patients from 26 North American centers entered this double-blind, placebo-controlled trial with acute exacerbation of chronic schizophrenia (DSM-III-R). Patients who completed a single-blind, placebo washout phase were randomized to double-blind treatment with quetiapine (75, 150, 300, 600, or 750 mg daily), haloperidol (12 mg daily), or placebo and evaluated weekly for 6 weeks. At end point, significant differences (p < 0.05, analysis of covariance) in adjusted mean changes from baseline were identified between the four highest doses of quetiapine and placebo for BPRS total, BPRS positive-symptom cluster, and CGI Severity of Illness item scores and between quetiapine 300 mg and placebo for SANS summary score. Differences between quetiapine and haloperidol were not significant. Dose-response modeling showed significant linear and quadratic functions of quetiapine dose for all primary efficacy variables. Notably, no significant safety concerns were identified as dose increased. Quetiapine was no different from placebo across the dose range studied regarding incidence of extrapyramidal symptoms or change in prolactin concentrations. Quetiapine is well tolerated and clinically effective in the treatment of schizophrenia. It is both superior to placebo and comparable to haloperidol in reducing positive symptoms at doses ranging from 150 to 750 mg/day and in reducing negative symptoms at a dose of 300 mg/day.

Changes in expression of the prolactin and growth hormone gene during different reproductive stages in the pituitary gland of turkeys.

The changes in levels of prolactin (PRL) and growth hormone (GH) in plasma and the pituitary gland and their transcripts were measured in turkey hens at different physiological stages by radioimmunoassay and dot blot hybridization analysis, respectively. The levels of tPRL mRNA in the pituitary gland increased from those of the immature group to the egg-laying group, reaching a maximum during the incubation and a minimum during the moulting stages. Changes in pituitary levels of PRL and PRL mRNA followed a similar trend and consequently were highly correlated (r2 = 0.83), whereas a significant but lower correlation was observed between circulating and pituitary levels (r2 = 0.62). Less significant changes were measured for tGH mRNA, with maximum and minimum levels measured in the pituitaries of egg-laying and non-laying hens, respectively. These data suggest that although changes in concentration of PRL are correlated with the reproductive stage of the turkey hen, coordinate changes in levels of GH are not.

Determination of canine prolactin by use of a commercial heterologous enzymeimmunoassay kit.

The present study evaluated a commercial heterologous enzymeimmunoassay (EIA) method for the determination of prolactin (PRL) in canine blood plasma and compared the results found with this heterologous method to the PRL concentrations measured by use of a commercial homologous PRL EIA. The heterologous PRL EIA was characterized by intra-assay coefficients of variation (CV %) of 3-5 % for replicate determinations, and inter-assay CV %'s of 5-7 % between means of duplicate determinations. The least detectable concentration was 0.1 microgram/L. A satisfying accuracy was settled by a recovery of added PRL not different from 100 % at varying PRL levels. The cross-reactivity (CR) to canine growth hormone (GH) was 5 %. Both methods outlined equally well the changes in PRL concentrations induced by administration of metoclopramid and bromocriptin; the specificity of both methods was further confirmed by a lack of response to clonidin GH stimulation test. The results achieved with the two methods were not identical despite of identical dose response relations. This difference in test results was, however, considered to be of minor practical importance if locally established reference ranges are used for evaluation of test results.

Regulation of prolactin receptor mRNA expression in peripheral lymphocytes in rats in response to changes in serum concentrations of prolactin.

In the present study we have evaluated the absolute number of the two forms of prolactin (PRL) receptor mRNA in rat peripheral blood lymphocytes and the modulation of receptor mRNA induced by changes in serum levels of endogenous PRL or by administration of ovine PRL. Lymphocytes expressed low levels of both forms of PRL receptor transcripts. Repeated treatments with ovine PRL significantly reduced levels of mRNA encoding the long form PRL receptor, whereas expression was markedly increased by repeated doses of bromocriptine. In contrast, the mRNA level of short form PRL receptor was unchanged by both treatments. The expression of long form transcripts was also markedly decreased in lymphocytes from pituitary-grafted rats. Therefore it appears that in rat peripheral lymphocytes PRL has a negative effect on the expression of its own receptor.

Modulation of nitric oxide and TNF-ALFA production by rat neutrophils in response to changes in serum concentrations of prolactin

Modulation of nitric oxide and TNF-ALFA production by rat neutrophils in response to changes in serum concentrations of prolactin

Plasma progesterone concentrations and length of the first spontaneous oestrous cycle in pubertal rats

The length of the first spontaneous oestrous cycle in pubertal Wistar-Imamichi strain rats determined by vaginal smears varied from 5 to 18 days. The variation was ascribed to the period (3-16 days) of the stage of vaginal smears consisting of leucocytic cells (L stage). Plasma progesterone concentration and the decidual reaction in the uterus were used as indicators of the function of the corpus luteum and the L stage period was categorized as short, lasting for 3-6 days (average 4 days) with non-functional corpora lutea, or long, lasting 9-16 days (average 12 days) and with functional corpora lutea. Rats with the long L stage showed nocturnal and diurnal prolactin surges, but no daily changes in prolactin values were observed in rats with a short L stage. Daily changes in prolactin concentrations were maintained by the administration of progesterone in rats ovariectomized on Day 6 of the L stage. Plasma progesterone values on Day 6 of the L stage decreased with ergocornine treatment on Days 4 and 5 of the L stage and administration of bovine prolactin restored the level. These results indicate that the L stage observed in the first oestrous cycle is maintained by a positive feedback relation between progesterone and prolactin secretions.

Physiological Significance of the Negative Short-Loop Feedback of Prolactin

The aim of the present study was to evaluate the physiological significance of the rapid, short-loop, negative feedback of prolactin by passive immunization with antiserum to rat prolactin injected into the third cerebral ventricle (3V) of conscious, freely moving intact or castrated male rats. Blood samples for measurement of plasma prolactin concentrations were removed through implanted external jugular catheters. After injection of 3 microliters of undiluted antiserum, plasma levels of prolactin decreased rapidly (within 5 min) to values undetectable by RIA. Further study revealed that this dose of antiprolactin serum had combined with circulating prolactin, thus rendering it undetectable by RIA. To overcome this problem, we repeated the experiment injecting 2 microliters of diluted antiserum (dilution factors 20, 100, 200, 2,000) into the 3V. When compared to values of plasma prolactin in control rats injected with 2 microliters of normal rabbit serum, none of the dilutions of antiserum induced a significant change in prolactin concentrations for as long as 4 h after injection. Since there was no effect of intraventricularly injected antiprolactin serum on basal prolactin secretion, in the next experiment, intact as well as castrated male rats were subjected to ether stress 30 min after intraventricular injection of antiserum (dilution factor 100). The elevation of plasma prolactin which followed ether stress was significantly higher in male rats pretreated with antiprolactin serum than that which occurred in control rats. A similar enhancement of the increase in plasma prolactin following ether stress, but of longer duration, was obtained in castrated rats injected with antiprolactin serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily Changes in Concentrations of Prolactin in Serum of Prepubertal Bulls Exposed to Short- or Long-Day Photoperiods

Early temporal changes in concentrations of prolactin (PRL) in serum after a sudden change in photoperiod and daily responsiveness to PRL-releasing and inhibiting factors were investigated in prepubertal Holstein bull calves exposed to different photoperiods. In calves switched from 8-hr light: 16-hr dark to 16-hr light:8-hr dark, there was no observable change in the daily pattern of serum concentrations of PRL after 1, 2, or 4 days. On the other hand, in animals switched from 16-hr light:8-hr dark to 8-hr light:16-hr dark, there was a consistent increase in serum PRL from 33.4 ng/ml on Day 0 to maximum values of 57.3, 62.7, and 78.9 ng/ml between 14 and 18 hr after onset of light on Days 1, 2, and 4, respectively. Thus, absence of light allowed expression of a daily rhythm in serum concentrations of PRL that persisted for at least 4 days after the photoperiod switch. There were no differences in L-dopa inhibition of PRL release in animals exposed to 16-hr light:8-hr dark at 3 or 15 hr after onset of light. However, thyrotropin-releasing hormone-induced release of PRL was greater 3 hr after onset of light (11 hr after onset of dark) compared with release at 9, 15, and 21 hr after onset of light in animals exposed to 16-hr light:8-hr dark, but not in bulls exposed to 8-hr light:16-hr dark. The results provide evidence that the cue for the putative photosensitive period of PRL secretion in cattle may be more closely associated with onset of dark, not onset of light.