Plasma Plasma Prolactin Levels Research Articles

Effects of age and reproductive experience on the distribution of prolactin and growth hormone secreting cells in the anterior pituitary of a passerine

Plasma prolactin (PRL) is released from lactotrophs in the anterior pituitary. As plasma PRL levels rise during incubation in domestic fowl, the number of lactotrophs (PRL-immunoreactive, PRL-IR cells) increases while the number of growth hormone secreting cells, somatotrophs (GH-IR cells), declines. We measured plasma PRL levels using radioimmunoassay (RIA) and examined the distribution of lactotrophs and somatotrophs in the anterior pituitary of breeding and nonbreeding zebra finches of known ages with and without prior breeding experience using fluorescent immunohistochemistry (IHC). Plasma PRL levels were higher in breeding than in nonbreeding birds, regardless of age, sex, or previous breeding history. PRL-IR cells were localized primarily, but not exclusively, to the cephalic aspect of the anterior pituitary (AP) and along the ventral margin. Birds with prior reproductive experience had more PRL-IR cells than birds with no prior reproductive experience and breeders had slightly higher PRL-IR cell counts than did nonbreeders, but there was no correlation between the number of PRL-IR cells and plasma PRL levels. GH-IR cells were concentrated in the caudal aspect of the AP with some cells in the cephalic lobe, but numbers did not differ between any of the groups studied. An increase in PRL-IR cells corresponded with an increase in GH-IR cells. An increase in lactotroph number with reproductive experience in zebra finches may facilitate future reproductive events by allowing for more robust PRL secretion and increased reproductive success.

Neuroendocrine regulation of rearing behavior in the native Thai hen

Vasoactive intestinal peptide (VIP) is the avian prolactin releasing factor and changes in the concentrations of plasma prolactin (PRL) are found during the avian reproductive cycle. This study investigated the changes in the VIP/PRL system of native Thai hens rearing their young as compared to hens deprived of rearing their chicks. The number of VIP-immunoreactive (VIP-ir) neurons in the Nucleus inferioris hypothalami (IH) and Nucleus infundibuli hypothalami (IN) of hens rearing chicks (R) were compared with those of non-rearing chicks (NR). Plasma PRL levels were determined by enzyme-linked immunosorbent assay. The localization and number of VIP-ir neurons were determined by immunohistochemistry. The numbers of VIP-ir neurons in the IH–IN areas were high in the R hens, whereas the number of VIP-ir neurons decreased in the NR hens as compared to their respective R hens. During the rearing period, changes in the VIP-ir neurons within the IH–IN were correlated with plasma PRL levels. The results of the present study indicate for the first time that the VIP/PRL system plays a role in neuroendocrine reorganization to establish maternal behavior in native Thai chickens. The VIP/PRL system functions not only as a well established key regulator of incubation behavior, but is also involved in the regulation of rearing behavior. It is possible that VIP and the decline in the number of VIP-ir neurons and in turn VIPergic activity and the decrease in PRL levels are related to their contribution to rearing behavior of this non-seasonal breeding, equatorial precocial species.

Research in influence of patient-controlled analgesia on incidence of postpartum depression after cesarean section

Objective To explore the influence of patient-controlled epidural analgesia(PCEA) on incidence of postpartum depression after cesarean section. Methods 256 cases of singleton term primary cesarean delivery were randomly divided into the study group( 130 cases)and the control group( 126 cases).The study group retained analgesia pump connected with epidural catheter,analgesic liquid was injected.In the control group,epidural catheter was removed,and was given intramuscular injection of pethidine hydrochloride 100 mg 4～6 h after operation,repeated 6 h later,total dosage was 200 mg.Postoperative observation time was 48h.Plasma prolactin(PRL) concentration was determined by radioimmunoassay in prenatal,postnatal 24 h and 48 h.Edinburgh postnatal depression scale (EPDS) was used to assess depression state 6 weeks postpartum in the two groups.The incidence of postpartum depression was compared between two groups. Results The plasma PRL level in the study group was significantly higher than the control group 24 h,48 h postpartum.The incidence rate of depression in the study group was 6.15％,while was 16.67％ in the control group,the differences were statistically significant. Conclusions The application of PCEA after cesarean section can significantly reduce the incidence of postpartum depression,and has very important practical significance in preventing the incidence of postpartum depression. Key words: Patient-controlled analgesia; Cesarean section; Postpartum; Depression

Dose‐dependent effects of olanzapine on QT intervals and plasma prolactin levels in Japanese patients with stable schizophrenia

There have been few reports regarding olanzapine (OLZ)-related QT prolongation and hyperprolactinemia. This study evaluated the dose-dependent effect of OLZ on QT interval and plasma prolactin (PRL) level in a single sample of patients with schizophrenia. Twenty-six subjects treated with varying starting doses of OLZ were enrolled in the study. Following baseline assessments, which included completion of the Brief Psychiatric Rating Scale (BPRS), measurements of Body Mass Index (BMI), QT interval, electrolytes, fasting plasma glucose, PRL, hemoglobin A1c (HbA1c), total cholesterol (TC), triglyceride (TG), high density lipoprotein (HDL), and low density lipoprotein (LDL), the dose of OLZ was increased for each subject. The same parameters were evaluated following the increased dose treatment. A significant decrease was observed in BPRS score (p = 0.01) following treatment with an increased dose of OLZ. Significant increases were observed in BMI (p = 0.032), QTc (p = 0.031), and plasma PRL level (p = 0.028). The mean values of electrolytes, fasting plasma glucose, HbA1c, TC, TG, HDL and LDL treatment were unchanged by the switch to increased-dose OLZ treatment. We have demonstrated the dose-dependent effect of OLZ on the QT interval and the plasma PRL level of patients with schizophrenia.

Gender differences in the relationship between the risperidone metabolism and the plasma prolactin levels in psychiatric patients

Background Risperidone (RIS) has the highest propensity to elevate plasma prolactin (PRL) levels. While the active metabolite 9-hydroxy-risperidone (9-OH-RIS) plays a predominant role in the efficacy and side effects of RIS, the mechanistic details are still poorly understood. The present study evaluated the gender differences in the relationship between plasma levels of RIS or 9-OH-RIS and PRL. Methods Twenty-one male and 19 female subjects treated with RIS were enrolled in the present series. All patients had been receiving RIS for at least 4 weeks at an average dosage of 4.7 mg/day. Plasma RIS, 9-OH-RIS and PRL levels were measured. Results In the male patients, there was no correlation between the RIS dosage and plasma PRL levels, between plasma RIS levels and PRL levels, or between the plasma 9-OH-RIS levels and PRL levels. In the female patients, there was a significant positive correlation between the plasma 9-OH-RIS levels and PRL levels (rs = 0.456, p = 0.049). There was a trend toward a significant positive correlation between the RIS dosage and plasma PRL levels. There was no correlation between the plasma RIS levels and PRL levels. Conclusion 9-OH-RIS is considered to play a more important role in PRL elevation than RIS, and a gender difference exists in the effect of 9-OH-RIS on PRL level.

Effect of concomitant progesterone administration or the effect of removal of estrogen capsule on changes caused by long-term estrogen treatment in pituitary VIP immunoreactivities

In the anterior pituitary besides the classical tropic hormones, peptides of a small molecular weight are also synthesized. One of them is the vasoactive intestinal polypeptide (VIP). VIP immunoreactivity is readily detected in human and monkey pituitaries; however, in the rat VIP immunoreactive cells were observed in about 50% of intact rats. In estrogen treated rats VIP immunoreactive cells were observed in the anterior pituitary of all animals. In this work, we have examined the effect of long-term sexual steroid treatments on the VIP immunoreactivity of the anterior pituitary using diethylstilbestrol (DES) or progesterone (P) filled capsules. The effectiveness of steroid treatments was tested by the measurement of plasma prolactin (PRL) level and by the appearance of prolactinoma. DES enhanced the plasma PRL level and 5months later it induced prolactinomas, the concomitant P treatment prevented both the elevation of plasma PRL level and the formation of prolactinomas. These results indicated that there was enough steroid in the capsules. There was a positive correlation between the duration of DES influence and the number of VIP immunoreactive cells. Two months after the implantation of DES there was a considerable number of VIP cells in the anterior pituitary, and 5months after implantation the number of VIP cells was greatly increased so as to form a VIP-oma. Concomitant implantation of P prevented the formation of VIP-oma. Two months after the implantation, the DES capsule was removed. Already 2months after removal the number of VIP cells approximated to the control level. It has been concluded that P can prevent the undesired effect of DES not only on the PRL, but on the VIP immunoreactivity as well.

Role of Ammonia and Nitric Oxide in the Decrease in Plasma Prolactin Levels in Prehepatic Portal Hypertensive Male Rats

Objectives: Since very little is known about neuroendocrine changes that occur in portal-systemic hepatic encephalopathy, we studied plasma prolactin (PRL) levels and the involvement of hyperammonemia, nitric oxide (NO) and dopaminergic and adrenergic systems in the control of this hormone secretion in a male rat model of prehepatic portal hypertension (PH). Methods: We conducted in vivo studies to determine plasma ammonia and PRL levels. Dopamine (DA), dihydroxyphenylacetic acid (DOPAC), epinephrine and norepinephrine content in medial basal hypothalamus (MBH) and anterior pituitary (AP) were measured. In addition, NO synthase (NOS) activity and protein expression were evaluated in APs. In in vitro studies, the APs from intact rats were incubated with different doses of ammonia and PRL secretion was determined. In ex vivo studies, the APs from normal and PH rats were incubated in the presence of ammonia and/or a NOS inhibitor, N^G-nitro-L-arginine-methyl ester (L-NAME) and PRL secretion was determined. Results: PH rats had a significant increase in plasma ammonia levels (p < 0.001) and a decrease in plasma PRL levels (p < 0.05). Neither DA nor DOPAC content or DOPAC/DA ratios were modified in both MBH and APs; however, we observed a significant increase in norepinephrine content in both MBH and AP (p < 0.001 and p < 0.05, respectively) and a significant increase in epinephrine in APs (p < 0.001). Moreover, PH produced an increase in NOS activity (p < 0.01) and NOS protein expression (p < 0.0001) in APs. The ammonia (100 µM) significantly reduced PRL secretion from APs in vitro (p < 0.05). The presence of L-NAME, an inhibitor of NOS, abrogated the inhibitory effect of ammonia on PRL secretion from APs from control and PH rats. Conclusions: We found that plasma PRL levels were decreased in PH rats probably due to the high ammonia levels. The central noradrenergic system could also mediate this decrease. Also, the increase in NOS activity and/or content in AP induced NO production that directly inhibited PRL secretion from the AP, without the participation of the dopaminergic system.

Are IGFII and CDK4 useful immunohistochemical markers for malignancy in adrenocortical neoplasms?

Plasma prolactin (PRL) is released from lactotrophs in the anterior pituitary. As plasma PRL levels rise during incubation in domestic fowl, the number of lactotrophs (PRL-immunoreactive, PRL-IR cells) increases while the number of growth hormone secreting cells, somatotrophs (GH-IR cells), declines. We measured plasma PRL levels using radioimmunoassay (RIA) and examined the distribution of lactotrophs and somatotrophs in the anterior pituitary of breeding and nonbreeding zebra finches of known ages with and without prior breeding experience using fluorescent immunohistochemistry (IHC). Plasma PRL levels were higher in breeding than in nonbreeding birds, regardless of age, sex, or previous breeding history. PRL-IR cells were localized primarily, but not exclusively, to the cephalic aspect of the anterior pituitary (AP) and along the ventral margin. Birds with prior reproductive experience had more PRL-IR cells than birds with no prior reproductive experience and breeders had slightly higher PRL-IR cell counts than did nonbreeders, but there was no correlation between the number of PRL-IR cells and plasma PRL levels. GH-IR cells were concentrated in the caudal aspect of the AP with some cells in the cephalic lobe, but numbers did not differ between any of the groups studied. An increase in PRL-IR cells corresponded with an increase in GH-IR cells. An increase in lactotroph number with reproductive experience in zebra finches may facilitate future reproductive events by allowing for more robust PRL secretion and increased reproductive success.

Blunted fenfluramine-evoked prolactin secretion in hypertensive rats.

Plasma prolactin (PRL) levels after acute administration of fenfluramine (FEN) have been used as a probe of brain serotonin activity. FEN-evoked increases in PRL levels inversely correlate with arterial blood pressure (ABP) in humans (Muldoon et al. Hypertension. 1998;32:972-975), thereby suggesting that brain serotonin activity may be reduced in hypertension. The present study sought to determine whether the relation between FEN-evoked PRL levels and ABP was present in two rat models of hypertension. Experiments were performed in awake male rats that were instrumented with femoral arterial and venous catheters 2 days before experiments. FEN (3.0 mg/kg IV) significantly increased plasma PRL levels in both spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY); however, FEN-evoked PRL levels were significantly lower in SHR compared with WKY, though baseline levels were similar between strains. Similar results were obtained in rats with chronic hypertension produced by figure-8 renal wrap plus contralateral nephrectomy. In contrast, the increase in PRL levels evoked by the serotonin receptor agonist m-CPP or the dopamine receptor antagonist eticlopride did not differ between SHR and WKY, indicating that PRL secretion is not generally blunted in chronic hypertensive rats. Furthermore, FEN-evoked PRL levels were not attenuated in rats made acutely hypertensive by an infusion of the alpha-adrenergic agonist phenylephrine. Thus, the present findings are consistent with the human data and suggest that chronic hypertension is associated with a presynaptic alteration in brain serotonin function.

Transcriptional changes in hypothalamic vasoactive intestinal peptide during a photo-induced reproductive cycle in the turkey.

To characterize further vasoactive intestinal peptide (VIP) as the prolactin-releasing factor in avian species, the present study examined hypothalamic VIP transcription and plasma prolactin (PRL) levels during the turkey reproductive cycle. The contribution of transcription to hypothalamic VIP mRNA steady-state levels and VIP content in response to gonadal stimulating photoperiod was also investigated. Nuclear run-on transcription assays were performed using nuclei isolated from hypothalami. Cytoplasmic VIP mRNA levels, and VIP content in the median eminence and plasma PRL levels were determined by Northern blot analysis and radioimmunoassays respectively. The alterations in VIP transcription mirrored the changes in cytoplasmic VIP mRNA and VIP content during the reproductive stages. VIP transcription, cytoplasmic VIP mRNA level and VIP content were lowest in non-photostimulated birds, higher (P<0.05) in laying hens, and greatest (P<0.05) in incubating birds. These increases paralleled the changes in circulating plasma PRL levels. Changes in VIP transcription (P>0.05) were not observed during the transition from incubation to photorefractoriness, even though there was a sharp decline in circulating plasma PRL levels (P<0.05). Following photostimulation, VIP transcription, cytoplasmic VIP mRNA levels, and VIP content increased as the hens progressed towards sexual maturity (P<0.05), and these increases were correlated with an increased plasma PRL level. These results suggest that VIP is regulated in large part at the transcriptional level during the turkey reproductive cycle and that this transcriptional regulation is coupled to the photo-induced increase in PRL secretion.

Exogenous Oxytocin Attenuates Suckling-Induced Prolactin Release but Not Maternal or Infant Behavior in Lactating Rats

The influence of exogenous oxytocin (OT) on maternal and infant behavior over 60 min of suckling, which followed 6 h of isolation, was investigated on Day 12 of lactation in rats. Mothers administered 1 IU of OT or saline through an indwelling atrial catheter and their litters indicated a similar nursing and suckling pattern, which was estimated by the crouching time of the mothers and the number of stretch reactions performed by the litters during a suckling period. To assess the alteration of the suckling intensity by OT administration, the plasma prolactin (PRL) level was determined by an Nb 2 lymphoma cell bioassay. In the control group, the plasma PRL level increased and reached a peak at 45 min after the onset of suckling in 60% of the animals. The suckling-induced PRL release was completely inhibited and/or markedly delayed by OT administration. The difference in body weight of the litters before and after a suckling period was estimated as an index of the amount of milk suckled by the litters. There was no difference in the amount of milk between the control and OT-treated groups during a 60-min suckling period. However, it was significantly greater in the OT-treated group during the first 20 min of the suckling period. These results indicate that a dose of OT is a factor in the attenuation of the intensity of suckling done by the pups, whereas the nursing and suckling behavior is not influenced by OT administration.

Circulating prolactin levels at the end of the photophase and the end of the scotophase throughout the reproductive cycle of the turkey hen

Plasma prolactin (PRL) levels rise following long daily photostimulation and increase dramatically at the onset of incubation behavior. Previous work has shown that a daily rhythm in PRL secretion may occur, with the lowest PRL levels found prior to lights out and the highest levels found prior to lights on. It has been suggested that an early event in the onset of incubation behavior may be an increase in nocturnal PRL levels. A retrospective study was conducted to contrast the morning and evening PRL secretion patterns at weekly intervals throughout the reproductive cycle in birds that exhibited: 1) incubation behavior; 2) high egg production and low nesting frequency for the last 16 wk of a 21-wk reproductive cycle; 3) high egg production while nesting frequently; or 4) photorefractoriness (defined by a cessation of egg production without incubation behavior). All hens showed an increase in PRL levels following photostimulation. When day and night PRL levels for each hen were compared over the entire reproductive cycle, more than 50% of those studied had significantly higher PRL levels at the end of the scotophase than at the end of the photophase. Circulating PRL levels increased greatly with the onset of incubation behavior, but morning and evening PRL levels changed in parallel. Good layers had moderate PRL levels throughout egg production, but PRL levels did not differ among laying hens with high or low nesting frequency. Plasma PRL levels declined to low levels in photorefractory hens. These results show that daytime PRL measurements accurately reflect reproductive state, and that moderate PRL levels seem consistent with optimum egg production.

Analysis of Pituitary Prolactin and Adrenocortical Response to Ether, Formalin or Restraint in Lactating Rats: Rise in Corticosterone, but No Increase in Plasma Prolactin Levels after Exposure to Stress

It is well established that stress causes a rise in plasma prolactin (PRL) levels of male or cycling female rats. In lactating animals, the pituitary PRL response to stress is not well understood. Therefore, the purpose of the present study was to analyze this question in lactating rats having low or elevated prestress plasma PRL levels. The animals were exposed to ether, formalin or restraint, and plasma PRL and corticosterone levels were determined. In mothers continually together with their pups, plasma PRL levels decreased significantly after exposure to ether vapor or injection of formalin under the skin. At the same time, both agents caused a significant rise in blood corticosterone concentrations. Lactating rats isolated for 4 h had very low levels of PRL before application of stress. However, neither formalin nor restraint caused any elevation in their plasma PRL levels although both interventions increased blood corticosterone concentrations. Lactating mothers receiving formalin after a 30-min suckling stimulus preceded by 4 h isolation did not show appreciable changes in pituitary PRL secretion following the administration of formalin. For information on the mechanism of the effect of stress on PRL, lactating rats were pretreated with the dopamine receptor antagonist domperidone (injecting 80 micrograms/kg body weight) or were adrenalectomized 7 days prior to exposure to stress. The very high levels of PRL caused by domperidone decreased markedly in animals subjected to restraint stress. Administration of formalin to adrenalectomized lactating rats continually together with their litter caused a slight immediate decrease, followed by a transitory elevation and a subsequent small second decrease in blood PRL concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Sexually dimorphic effects of aging on tuberoinfundibular dopaminergic neurons and lactotropes of rats

The effect of aging on plasma prolactin (PRL) levels, hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons and pituitary lactotropes was evaluated in prolactinoma-free young (5-month-old) and old (23- to 24-month-old) Long-Evans rats of either sex. The young female rats were in diestrus, the old ones in recurrent pseudo-pregnancy. The tyrosine hydroxylase (TH)-labelled neurons in the arcuate nucleus (AN) and axons in the median eminence (ME) as well as the PRL-labelled lactotropes in the pituitary gland were studied by morphometry and densitometric immunohistochemistry. Further, we investigated the secretory function of isolated lactotropes by reverse hemolytic plaque assay (RHPA) and by cell culture in comparable animal groups. Compared with young animals, the plasma PRL levels of old rats of both sexes were similar or reduced. All morphometric and densitometric measurements of the AN neurons, ME axons (except number) and pituitary lactotropes were comparable in young and old female rats. In old male rats the AN and ME measurements were mostly decreased, while the lactotropes remained almost unchanged. The RHPA generally showed a reduced PRL release from lactotropes of old animals of both sexes. The PRL release from the cultured lactotropes, on the contrary, was greatly increased in old female rats and unchanged in old male rats. Our functional and morphological data suggest that the in vivo function of lactotropes in old prolactinoma-free female and male rats does not seem to be strongly influenced by the mildly reduced TIDA neuron activity, yet emphasize the differences of the aging process in the two sexes

Absence of direct regulation of prolactin cells by estradiol-17β in rainbow trout ( Oncorhynchus mykiss)

The effects of estradiol-17β (E 2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout ( Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17β did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17β effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17β and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary. No labeling was discernible over PRL cells whereas other parts of the pituitary were labeled. Grain counting corroborated this localization. These results indicate that (1) in vivo estradiol-17β treatment did not modify PRL cell activity in rainbow trout, (2) PRL secretion, in this fish species, is not directly regulated by estradiol.

The effects of confinement stress on circulating prolactin levels in rainbow trout (Oncorhynchus mykiss) in fresh water

Rainbow trout were confined for 48 hr, during which time water quality either was allowed to deteriorate (resulting in elevated NH3, elevated free CO2, and reduced dissolved O2) or was maintained at preconfinement levels. Fish were removed and. blood samples taken at 0, 2, 4, 8, 24, and 48 hr after the onset of confinement from both stressed (confined) and unstressed (unconfined) fish. Plasma cortisol and plasma prolactin (PRL) levels were determined using specific RIAs. Chronic confinement of rainbow trout, accompanied by a decline in water quality, resulted in significant elevation of plasma cortisol, maintained for the period of confinement. Plasma PRL levels were significantly lower in stressed fish, by up to 60% relative to control fish, during the first 24 hr of confinement. The stress of confinement alone, in the absence of deterioration in water quality, produced similar results, with the change in prolactin levels being less rapid but more prolonged under these conditions.

G protein modulation by estrogens

Levels of various G protein subunits were assayed by immunoblot and densitometry, using specific antibodies, in anterior pituitaries and striata of female rats exposed to physiological or pharmacological modifications of ovarian hormone levels and, for comparison, in the same tissues of coeval male rats. Treatment of ovariectomized rats with 17β-estradiol 10 μg/rat/day for 5, 10 or 20 days induced a time-dependent rise in plasma prolactin (PRL) levels. While no change in G protein levels was observed in the striatum, estrogen treatment induced a significant reduction of all pituitary G protein levels except those of αil, which remained unchanged, and of αs42, which increased in a time-dependent manner. A highly significant correlation was observed between pituitary αs42 values and plasma PRL levels. During the estrous cycle, pituitary values of αo, αi3 and αs47 were generally lower than those of ovariectomized rats, suggesting the existence of tonic inhibitory influence of circulating ovarian hormones. Pituitary levels of αo, αil and αs42 also showed a significant modulation during the various phases of the estrous cycle, and those of αo, αi3, αs47 and β were significantly lower in female than in male rats. No significant effects of estrous cycle hormone variations or sex differences were observed in the values of striatum G proteins. In conclusion, these data clearly indicate that ovarian hormones, and particularly estrogens, have a significant and specific effect on pituitary G protein levels which may modulate the secretion of pituitary hormones such as PRL.

Prolactin Short-Loop Feedback and Prolactin Inhibition of Luteinizing Hormone Secretion during the Breeding Season and Seasonal Anoestrus in the Ewe

In seasonally breeding mammals, plasma prolactin (PRL) concentrations vary on an annual basis with levels high in summer and low in winter. In this study of the ewe, we determined, first, whether PRL secretion is regulated by short-loop feedback and, second, whether the high summer levels of PRL are due to a change in sensitivity or loss of this feedback loop. Because the high summer levels of PRL coincide with the period of seasonal anoestrus in the ewe and could therefore be involved in the seasonal suppression of gonadotrophins, the effects of intracerebroventricular PRL on pulsatile LH secretion were also determined. Ovary intact ewes received intracerebroventricular injections of ovine PRL (oPRL; 50 micrograms) or anti-PRL serum. From 3 to 13 h after central administration of oPRL, plasma PRL concentrations were significantly reduced compared with the vehicle-treated controls. In contrast, following injection of anti-PRL serum, plasma PRL levels increased significantly. To determine whether there was a seasonal change in sensitivity to PRL feedback, a series of experiments were conducted in July and November when PRL concentrations are high and low, respectively. At each time of year, ovariectomized oestradiol-implanted ewes were injected intracerebroventricularly with 10 and 50 micrograms oPRL with control animals receiving the vehicle. At both times of year there was clear evidence of PRL short-loop feedback with no indication that sensitivity was reduced in the July trial. Luteinizing hormone (LH) pulse frequency, pulse amplitude and mean LH were not affected by intracerebroventricular oPRL at either time of year.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of estradiol and progesterone on rat striatal dopamine uptake sites

Striatal dopamine (DA) uptake sites labelled with [ 3H]GBR-12935 binding were investigated in ovariectomized (OVX) rats acutely treated with 17β-estradiol (E 2) or progesterone (P). One injection of E 2 (100 ng, SC) to OVX rats increased plasma levels of this steroid after 15 min while plasma prolactin (PRL) levels remained unchanged. The E 2 injection left striatal [ 3H]GBR-12935 binding affinity unchanged while the maximum density increased 15 and 30 min after the injection (+ 24% and +18%, respectively). One injection of P (110 μg, SC) to OVX rats increased this steroid plasma level from 15 to 120 min while plasma PRL levels remained unchanged. [ 3H]GBR-12935 binding density and affinity remained unchanged up to 120 min after the injection. Thus, acutely, E 2 but not P, modulated striatal DA uptake sites in OVX rats. The effect of E 2 appeared in coincidence with the peak of this steroid plasma concentration. This increase was rapid and is probably nongenomic and suggests a causal effect relationship as well as a presynaptic site of action of E 2.

Neuroendocrine measures of dopaminergic function in chronic cocaine users

Plasma prolactin (PRL) and growth hormone (GH) levels are determined, in part, by the effects of dopamine (DA) at pituitary and hypothalamic DA receptors, respectively. To determine if chronic cocaine abuse alters dopaminergic activity, basal PRL and GH concentrations were measured in 16 male patients meeting DSM-III-R criteria for cocaine dependence (8 cocaine users and 8 cocaine + alcohol users) and 8 normal controls. In addition, the functional responsivity of DA receptors was assessed in the same group of patients by measuring the change in plasma PRL and GH concentration following the administration of the direct-acting DA agonist, apomorphine (0.01 mg/kg, s.c.) or saline. No difference in basal plasma PRL and GH levels or plasma PRL and GH responses to apomorphine administration was found between the entire group of cocaine patients and normal controls. However, three of the cocaine patients had basal plasma PRL levels that were more than 2.5 SD greater than that of the normal controls, suggesting that some interference of dopaminergic inhibition of PRL secretion might be present in at least some cocaine users. Although baseline plasma PRL levels were elevated in a subgroup of cocaine users, these data do not support the hypothesis that chronic cocaine abuse produces consistent abnormalities in dopaminergic function at the pituitary or hypothalamus.