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PubMed1979

Prolactin-secreting pituitary adenomas: prolactin dynamics before and after transsphenoidal surgery.

Twenty women with hyperprolactinaemia secondary to a pituitary adenoma were studied before and after selective transsphenoidal removal of the tumour. Pre-operatively, thyrotrophin-releasing hormone (TRH) (200 micrograms iv) and metoclopramide (MCP) (10 mg po) did not produce a positive PRL response in the tumour patients. By contrast, 14 post-partum lactating women, who were used as controls, exhibited a positive response to MCP administration. Methergoline (4 mg po) was shown to decrease serum PRL levels in 8 normal subjects, in 6 puerperal women, and 9 of 10 tumour patients. Bromoergocriptine (CB-154, 2.5 mg po) decreased serum PRL levels in 10 tumour patients. Following transsphenoidal removal of the adenoma serum PRL levels were reduced in all patients, and returned to normal in 14 patients. Prognostics for completely normalizing PRL secretion after transsphenoidal surgery is bettery when initial serum PRL levels are below 200 ng/ml. After surgery all hyperprolactinaemic patients failed to show a positive PRL response to TRH and MCP. Nine normoprolactinaemic patients had a positive response to both stimuli while 3 patients failed to show a positive response immediately following surgery. Long-term studies, however, showed that a positive PRL response was obtained in all patients tested 8-14 months after treatment. A positive PRL response to methergoline and bromocriptine was observed post-operatively in the patients tested regardless of their basal PRL level. Data from this study indicate that surgically proven PRL-secreting adenomas are invariably associated with negative PRL responses to TRH and MCP. The normalization of the prolactin regulation after surgery points toward the intrapituitary localization of the lesion associated with PRL-secreting adenomas.

Adenoma↗

PubMed1985

Prolactin secretion by mixed ACTH-prolactin pituitary adenoma cells in culture.

To characterize the functional aspect of prolactin (Prl) cells coexisting with corticotroph adenomas, pituitary adenoma cells obtained from a patient with Cushing's disease and a patient with Nelson's syndrome, who were associated with hyperprolactinaemia, were cultured in monolayer and their Prl responses to various secretagogues were compared with those of prolactinoma cells in culture. Immunohistochemistry performed in one of these two adenomas demonstrated the presence of Prl-containing cells in addition to ACTH cells. When ACTH-Prl adenoma cells were exposed to ovine corticotrophin-releasing factor (CRF), a dose-dependent increase in both ACTH and Prl secretion was observed, which was blocked by coincubation with hydrocortisone. In contrast, no stimulatory effect of CRF on Prl release was observed in all of the experiments using prolactinoma cells. Thyrotrophin-releasing hormone, which consistently stimulated Prl secretion in ACTH-Prl adenomas, was effective in triggering Prl release in only 25% of the prolactinomas. Exposure of the cultured cells to lysine vasopressin, growth hormone-releasing factor and vasoactive intestinal peptide resulted in an increase in ACTH and Prl secretion in one ACTH-Prl adenoma, however, none of the prolactinomas responded to these stimuli to secrete Prl. Dopamine and somatostatin, on the other hand, uniformly suppressed Prl secretion from ACTH-Prl adenomas as well as from prolactinoma cells. These results suggest that the mode of Prl secretion by mixed ACTH-Prl pituitary adenomas is not identical to that by pure prolactinomas and is, at least in part, common to that of ACTh secretion.

Adenoma↗

PubMed1985

Correlation between the number of thyroliberin binding sites, the tumour size and the plasma prolactin level in human prolactin-secreting adenomas.

Basal plasma prolactin (Prl) level, tumour size and [3H]thyroliberin (TRH) binding to tumour membranes were studied in 18 patients bearing Prl-secreting adenomas. Big tumours (grade III) were associated with high plasma Prl levels (median value: 1929 (range: 207-3570) ng/ml) and possessed numerous membrane TRH receptors (median value: 508 (range: 0-1200) fmol/mg of protein). By contrast, smaller tumours (grade II and I) were associated with lower plasma Prl levels (median values: 1085 (range: 40-1890) and 295 (range: 98-788) ng/ml, respectively) and possessed fewer membrane TRH receptors (median values 122 (range: 11-328) and 13 (range: 0-52) fmol/mg of protein, respectively). A direct positive correlation was demonstrated between the plasma Prl level and the number of [3H]TRH binding sites (rho: 0.729 P less than 0.001). That the higher number of TRH receptors is associated with the largest tumours may be of importance in hyperprolactinaemia and should be taken in account when speculating on the pathogenesis of human Prl-secreting adenomas.

Adenoma↗

PubMed1985

Lack of plasma prolactin response to intravenously injected vasoactive intestinal polypeptide in patients with prolactin-secreting adenoma.

The effect of an iv bolus injection of 1 microgram/kg body weight of vasoactive intestinal polypeptide (VIP) on plasma prolactin (Prl) levels was tested in 13 normal volunteers and 15 patients with hyperprolactinaemia of various aetiology: 9 with Prl-producing pituitary tumours (6 prolactinoma, 3 mixed pituitary adenoma, secreting Prl and growth hormone (GH)), 6 with hyperprolactinaemia secondary to a hypothalamic lesion (4 craniopharyngioma, 1 hypothalamic germinoma, 1 meningoencephalitis). In the normal subjects, an iv injection of VIP caused a prompt increase in plasma Prl with peaks 2- to 3-fold greater than the basal values. On the other hand, none of the 9 patients with a Prl producing pituitary tumour showed any obvious Prl rise after VIP irrespective of a marked difference in their basal Prl levels. Lack of a Prl response to VIP was also found in the 2 patients with hypothalamic lesions (1 craniopharyngioma, 1 hypothalamic germinoma) whose basal Prl concentration was higher than 100 ng/ml. However, in the remaining 4 patients with hypothalamic lesions whose basal Prl concentration was less than 100 ng/ml, VIP injection resulted in a stimulation of the Prl secretion with a maximal net increment of 11.3 +/- 3.8 ng/ml, which is not different statistically form that (16.3 +/- 3.3 ng/ml) in the normal subjects, but significantly higher than that (-2.3 +/- 2.7 ng/ml) in the 4 patients with Prl-secreting adenoma and a basal Prl concentration of less than 100 ng/ml. These results indicate that the VIP test may be a useful diagnostic tool for discriminating a Prl-producing tumour from a hypothalamic lesion in patients with mild hyperprolactinaemia.

Adenoma↗

PubMed1993

Different responses in little and bigbig prolactin to metoclopramide in subjects with hyperprolactinemia due to 150-170 kD (bigbig) prolactin.

We have studied in vivo induction of serum prolactin (PRL) levels in four females and one male, and regulation of PRL in the menstrual cycle in three females all with hyperprolactinemia with large amounts (72-92%) of bigbig PRL (MW 150-170 kD). Metoclopramide (MTC) iv induced a 4-29-fold increase in little PRL (25 kD PRL) at 30 min, while the increase in 150-170 kD PRL was 1.1-2.2-fold. The maximal response in 150-170 kD PRL was seen after 2-6 h, and the decrease after the maximal PRL values for 150-170 kD PRL was delayed compared to the decrease in 25 kD PRL. The different kinetics for 25 kD PRL and 150-170 kD PRL was responsible for the prolonged increase in total PRL seen in the subjects with large amounts of 150-170 kD PRL compared to the controls. The percentage of 150-170 kD PRL decreased to 29-60% at 30 min and returned to unstimulated values after 6-24 h. In contrast, prolonged stimulation of PRL secretion, as in the luteal phase, did not change the percentage of 150-170 kD PRL. In a male subject secreting large amounts of 150-170 kD PRL the increase in PRL after MTC was less, while the temporal changes in the 25 kD PRL levels were almost the same as in the females.

Adult↗

PubMed1993

Detection of growth hormone, prolactin and human beta-chorionic gonadotropin mRNA in growth hormone-secreting pituitary adenomas and in prolactin-secreting pituitary adenomas by in situ hybridization using a non-isotopic detection method.

A non-isotopic in situ hybridization method with digoxigenin-labelled probes was used to examine growth hormone (GH), prolactin (PRL) and human beta-chorionic gonadotropin (beta-hCG(LH)) gene expression in 63 pituitary tumours in acromegaly and 20 adenomas in hyperprolactinaemia. hCG and LH were detected simultaneously because of the extensive homology (more than 90%) of their mRNA sequences (1). A comparison with former results obtained with 35S-labelled probes shows the value of the easier and faster non-isotopic method. Additionally, immunohistochemical data are included to give even more evidence for the synthesis of the respective hormones by the tumour cells. In all 63 adenomas in acromegaly, GH mRNA was revealed in 59 PRL mRNA and in 36 beta-hCG(LH) mRNA. A positive immunostaining for GH was found in all, for PRL in 40, and for beta-hCG(LH) in 34 adenomas. The comparison of the two in situ hybridization methods revealed no differences concerning GH mRNA detection, but not all tumours positive after non-isotopic PRL and beta-hCG(LH) mRNA detection showed signals with the radioactive method. Referring to the 20 PRL-secreting adenomas, PRL gene expression was demonstrable in all, GH mRNA in 12, and beta-hCG(LH) mRNA in 2 cases. Comparing the positive results of immunohistochemistry with those of in situ hybridization, correspondence was found in 19 cases for PRL, in 5 cases for GH and in no case for beta-hCG(LH).

Acromegaly↗

PubMed1994

Pulsatile thyrotropin and prolactin secretion in a patient with a mixed thyrotropin- and prolactin-secreting pituitary adenoma.

The circadian and pulsatile thyrotropin (TSH) and prolactin (PRL) release was investigated in a patient with slight hyperthyroidism due to a mixed TSH- and PRL-secreting pituitary adenoma. Blood was withdrawn every 10 min for 24 h (before and after medical treatment); pulse characteristics were analyzed by Desade and Cluster programs (values as mean +/- SD). The inappropriately high mean 24-h TSH concentration of 3.55 +/- 0.31 mU/l was associated with a higher mean 24-h TSH pulse amplitude but unaltered mean 24-h TSH pulse frequency relative to healthy controls. The nocturnal TSH surge (absolute surge 0.5 mU/l, relative surge 16%) was low, related to a loss of the usual nocturnal increase of TSH pulse amplitude and TSH pulse frequency. Chronic treatment with octreotide resulted in a modest clinical and biochemical improvement of the hyperthyroid state; addition of bromocriptine at a later stage had no further beneficial effect. At the end of the follow-up period the mean 24-h TSH paradoxically had increased to 5.33 +/- 0.81 mU/l. The nocturnal TSH surge also increased (absolute surge 1.9 mU/l, relative surge 42%), but circadian changes in TSH pulsatility remained absent. In the untreated period the increased mean 24-h PRL concentration of 234 +/- 24 micrograms/l was associated with an increased mean 24-h PRL amplitude, whereas the 24-h PRL pulse frequency (N = 4) was lower relative to controls. No circadian PRL rhythm was present. After octreotide and bromocriptine treatment the mean 24-h PRL concentration and mean 24-h PRL pulse amplitude were unchanged, but a clear nocturnal increase of PRL now was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗

PubMed1991

Pituitary prolactin concentrations associated with daily prolactin surges in pseudopregnant rats.

During pseudopregnancy (PSP) two surges of prolactin (PRL) secretion from the pituitary are observed, the nocturnal surge at dawn and the diurnal surge in the evening. An attempt was made to clarify the correlation between changes in serum and pituitary PRL concentrations on day 5-6 of PSP. During the nocturnal surge, pituitary PRL concentration decreased significantly from 0000 hr to 0300-0600 hr. On the other hand, the high pituitary PRL concentration remained unchanged during the diurnal surge from 1200 hr to 1800 hr. These findings suggest that the nocturnal and diurnal PRL surges are regulated by separate controlling mechanisms.

Animals↗

PubMed1982

The autonomy of prolactin secretion in patients with prolactin producing tumor.

To examine the responsiveness of prolactin (PRL) secretion in patients with PRL-producing tumor (PRL-noma), TRH (500 micrograms), arginine (0.5 g/kg, b. wt.), and sulpiride (100 mg) were administered to 13 patients with PRL-noma. Seven of these patients responded to TRH or other agents with an increase in their plasma PRL levels of 50% or more above the basal values (categorized as Group I). The remaining six patients, however, showed no response to any of these agents (categorized as Group II). After the administration of L-dopa (500 mg, p.o.), Group I patients showed significantly greater decreases in plasma PRL (-68.9 +/- 6.6%) from the basal value than did Group II (-37.4 +/- 8.6%; p less than 0.02). The mean basal PRL levels were higher in Group II than in Group I, although these differences failed to reach statistical significance. Moreover, there were no differences in age, sellar volume, or the presence of bitemporal hemianopsia between the two groups of patients. It is concluded that there are two patterns of PRL-secretory responses to pharmacological stimuli in patients with PRL-noma. The differences between the two patterns might be characterized by the properties of the lactotroph cells themselves rather than by the relation of these cells to the hypothalamus.

Adult↗

PubMed2003

Alternative splicing to exon 11 of human prolactin receptor gene results in multiple isoforms including a secreted prolactin-binding protein.

Endocrine and autocrine prolactin (PRL) exerts effects on normal breast and breast cancer cells, and high serum PRL is a poor prognostic factor for colorectal cancer. Here we tested the hypothesis that short isoforms of the PRL receptor (PRLR) in human tissue regulate the actions of PRL in cancer. Using 3' RACE we isolated five splice variants of the human PRLR (hPRLR), three of which encode the complete extracellular binding domain. Two of these isoforms, short form 1a (SF1a) and short form 1b (SF1b), possess unique intracellular domains encoded by splicing to exon 11 from exons 10 and 9 respectively. A third novel isoform (delta7/11) reflects alternative splicing from exon 7 to exon 11 and encodes a secreted soluble PRL-binding protein. Additional splice variants of SF1b and delta7/11 that lacked exon 4 (delta4-SF1b and delta4-delta7/11) were also identified. Functional analyses indicated that hPRLR-SF1b is a strong dominant-negative to the differentiative function of the PRLR long form while hPRLR-SF1a is a weaker dominant-negative. Differential abundance of SF1a, SF1b and delta7/11 expression was detected in normal breast, colon, placenta, kidney, liver, ovary and pancreas, and breast and colon tumors. Taken together, these data indicate the presence of multiple isoforms of the hPRLR that may function to modulate the endocrine and autocrine effects of PRL in normal human tissue and cancer.

Alternative Splicing↗

PubMed1996

Somatostatin does not inhibit prolactin synthesis in normal male rat pituitary cells but inhibits prolactin synthesis in estradiol-primed pituitary cells.

The effects of somatostatin (SRIF) on prolactin (PRL) synthesis and release were examined in primary cultured pituitary cells derived from normal and estradiol (E2)-primed male rat pituitaries. The cells were continuously incubated in a pulse medium containing [3H]leucine with or without 10(-6) mol/l SRIF for a period of 15, 30, 60, 180 or 360 min. Following incubation, the medium was recovered and the cells were fractionated into cytosolic and granular fractions. PRL was isolated by SDS-PAGE and newly synthesized PRL ([3H]PRL) was identified by coincident peaks of tritium activities and PRL contents. The specific activity (SA, c.p.m./ng), a ratio of [3H]PRL to total PRL, was determined for the granular, cytosolic and medium fractions. In control and SRIF-treated groups of non-primed pituitary cells, SAs of all three fractions significantly increased during the 6-h incubation. Cytosolic and granular SAs showed similar profiles of increasing rate in comparison to control. Medium SAs showed a significantly higher value in the SRIF-treated group than in the control group only at 180 min. These observations indicate that, in the non-primed condition, PRL synthesis is not inhibited by SRIF. Medium SAs in the E2-primed group were significantly higher than SAs in the non-primed control cells during the initial 3 h of incubation, and cytosolic and granular SAs were significantly higher than those of the non-primed control during the 3- to 6-h incubation period. These observations demonstrate that E2 enhances PRL synthesis and secretion of newly synthesized PRL. SRIF treatment of E2-primed lactotrophs resulted in a significant decrease in SAs of all three fractions as compared with those of the E2-primed control. Our results indicate that in normal male rat pituitary cells SRIF does not inhibit PRL synthesis but effectively inhibits PRL synthesis in E2-primed lactotrophs. This suggests that the inhibitory action of SRIF on PRL synthesis is estrogen dependent.

Animals↗

PubMed2001

Administration of unmodified prolactin (U-PRL) and a molecular mimic of phosphorylated prolactin (PP-PRL) during rat pregnancy provides evidence that the U-PRL:PP-PRL ratio is crucial to the normal development of pup tissues.

During rat pregnancy initial high concentrations of prolactin (PRL) decline by about day 9, concomitant with an increase in the ratio of unmodified to phosphorylated PRL. The physiological significance of both the decline in total PRL and the change in ratio of the two PRLs is unknown. To test the importance of each, either unmodified PRL (U-PRL) or a molecular mimic of phosphorylated PRL (PP-PRL) were continuously administered to rats throughout pregnancy. A dose of 6 microg/24 h resulted in circulating concentrations of 50 ng/ml of each administered PRL and had little effect on the pregnancy itself. After birth, pups were killed and various tissues examined. In the pup lungs, exposure to additional PP-PRL caused a reduction in epithelial integrity and an increase in apoptosis, whereas exposure to additional U-PRL had beneficial, anti-apoptotic effects. In the heart, PP-PRL caused an apparent developmental delay, whereas U-PRL promoted tissue compaction. In the blood, U-PRL increased the number of mature red blood cells at the expense of white blood cell production. Within the white blood cell population, myelopoiesis was favored at the expense of lymphopoiesis. PP-PRL, in contrast, had a less dramatic influence on the hematopoietic compartment by promoting red blood cell maturation and granulocyte production. In the thymus, exposure to PP-PRL caused accumulation of apoptotic thymocytes in enlarged glands, whereas exposure to U-PRL resulted in smaller thymi. In the spleen, exposure to U-PRL increased cellularity, with the majority of cells belonging to the erythroid series - a finding consistent with increased red blood cells in the circulation. Exposure to PP-PRL was without discernible effect. In all of these tissues, the contrasting effects of the two PRLs indicate that the absolute concentration of PRL is not crucial, but that the ratio of U-PRL to PP-PRL has a profound effect on tissue development. In brown fat, both PRL preparations decreased the number of lipid droplets. This result is therefore probably a consequence of the increase in total PRL. The results of this study attest to the importance of the U-PRL:PP-PRL ratio normally present during pregnancy and have provided clues as to the possible pathogenesis of a variety of neonatal problems.

Animals↗

PubMed1981

Use of active immunization against prolactin to study the influence of prolactin on growth and reproduction in the ram.

An experiment was conducted to determine whether prolactin (PRL) is involved in the maintenance of reproductive tissue weights and body growth in yearling rams. Suppression of circulating PRL was achieved by active antibody production against bovine PRL. Free plasma PRL concentrations in immunized rams were decreased (P less than .05) by 73% after 3 months of treatment and 91% after 10 months of treatment in relation to concentrations in control rams. Average daily gain and final body weight were lower (P less than .05) for rams with suppressed circulating PRL (.042 kg/day and 67.0 kg for treatment rams and .060 kg/day and 72.7 kg for control rams). Although testes weights were 32% lower for the treated rams, antibody treatment did not affect (P greater than .05) the weights of the testes or accessory sex glands. No treatment effect was noted on plasma luteinizing hormone (LH), growth hormone (GH) or thyrotropin (TSH). Seasonal differences were observed in some variables of LH, GH and TSH secretion. Mean baseline LH for all animals was higher (P less than .01) in December than in March, June or September. Overall and baseline concentration of GH and TSh were highest (P less than .01) in December. These data suggest that (1) PRL is involved in body growth of the yearling ram, and (2) PRL may have a role in the maintenance of reproductive tissue weights in the yearling ram.

Animals↗

PubMed1989

Relationships among prolactin binding, prolactin concentrations in plasma and metabolic activity of the porcine mammary gland.

The current studies were designed to investigate relationships among prolactin (PRL) binding, PRL concentrations in plasma and metabolic activity of porcine mammary glands. Preliminary studies revealed specific high-affinity binding of oPRL to porcine mammary gland. Conditions for optimal specific binding were similar to those observed for other species. To address the main objectives of the study, four mammary biopsies and blood samples were obtained from each of four gilts during lactogenesis and lactation (d-11, 4, 21 and 42 of lactation) to measure in vitro rates of metabolic activity, PRL binding to mammary membranes and PRL concentrations in plasma. Metabolic activity, as measured by oxidation of glucose or acetate to CO2 and incorporation into lipid, was low during pregnancy, increased two- to five-fold on d 4, and then paralleled the lactation curve for sows. There were highly significant positive correlations between PRL binding and all measures of mammary metabolism when data from pregnancy and lactation were utilized. Coefficients were positive but generally not statistically significant when lactation data only were utilized. During lactation, significant negative correlations were observed between concentrations of PRL in plasma and PRL binding and between PRL in plasma and mammary metabolic rate. These data provide evidence that binding of PRL to its receptor is an important effector of milk production in sows. Furthermore, oPRL is a suitable ligand to quantify PRL binding to porcine mammary tissue.

Animals↗

PubMedDate not supplied

Partial proteolytic digestion of the mammary prolactin receptor: identification of smaller prolactin binding fragments.

Partial proteolytic digestion of the mammary prolactin (PRL) receptor was used to generate receptor fragments and analyze their immunoreactivity and PRL binding properties. Tryptic digestion of the PRL receptor produced two immunoreactive fragments (Mr approximately 30,000 and approximately 15,000) that reacted with a monoclonal anti-PRL receptor antibody and still specifically bound PRL, while the complete immunoreactive PRL binding unit (Mr approximately 42,000) disappeared. Neither chymotrypsin nor V8 protease were able to generate any immunoreactive receptor fragments. These receptor fragments may represent smaller PRL binding receptor form(s) of biological significance.

Animals↗

PubMed1983

Thyroid stimulating hormone and prolactin secretion: reduced sensitivity to TRH-stimulated prolactin release after midpregnancy in rats.

Prolactin (PRL) and thyroid stimulating hormone (TSH) plasma concentrations were measured during the latter part of the dark period in early and mid-late pregnancy in the rat. On Days 4-5 and 7-8 of pregnancy, plasma PRL concentrations surged between 22:00 and 06:00 hr and TSH values increased between 22:00 and 02:00 hr. While the TSH pattern was maintained during the second-half of pregnancy, surges in PRL release ceased and PRL levels remained at less than 10 ng/ml. The effects of thyrotropin releasing hormone (TRH) administration on PRL and TSH secretion were then measured to determine whether the second-half of pregnancy is associated with a decrease in sensitivity to an agent that can stimulate PRL release. Injection (iv) of cannulated pregnant rats with a low dosage (20 ng) of TRH stimulated a twofold increase in plasma TSH during both early (Days 5-9) and later (Days 14-18) pregnancy but did not change plasma PRL levels. Treatment with a high dosage (2 micrograms) of TRH induced a sixfold rise in plasma TSH during both phases of gestation. The higher dose of TRH also stimulated elevations in plasma PRL during early and mid-late pregnancy; however, both the absolute increase in the amount of PRL in plasma and the percentage increase over baseline levels were greater from Days 5-9 than from Days 14-16 of gestation. These data indicate that the neuroendocrine sensitivity to factors that stimulate PRL secretion changes as pregnancy progresses, and suggest that nocturnal secretion of PRL and TSH during pregnancy may be regulated, in part, by a common trophic factor.

Animals↗

PubMed1983

Early action of prolactin on ornithine decarboxylase activity is not essential for the subsequent actions of prolactin on casein and lipid biosynthesis.

The actions of prolactin (PRL) on casein and lipid biosynthesis in cultured mouse mammary gland explants require the ongoing synthesis of the polyamines. This is supported by the fact that (MGBG) methylglyoxal bis(guanylhydrazone), a drug that inhibits the conversion of putrescine to spermidine, abolishes the effects of PRL on casein and lipid biosynthesis; the inhibitory effects of MGBG are reversed by the addition of spermidine to the culture medium. alpha-Difluoro methyl ornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase activity, reduces the PRL-stimulated ornithine decarboxylase (ODC) activity by more than 95%, and yet does not suppress the effects of PRL on RNA, casein or lipid synthesis. These observations suggest that PRL's early action on ODC activity is not essential for the subsequent actions of PRL on the synthesis of certain of the components of milk.

Acetates↗

PubMed1991

Intrahypothalamic pituitary grafts elevate prolactin in the cerebrospinal fluid and attenuate prolactin release following ether stress.

Anterior pituitary (AP) tissue grafted into the hypothalamus of female rats inhibits the luteotrophic prolactin (PRL) secretion which normally follows mating. Dopamine blockade has been shown to overcome this inhibition, suggesting that the grafts suppress PRL release from the in situ pituitary by the action of graft PRL increasing dopamine activity in the hypothalamus. To examine whether PRL levels in the cerebrospinal fluid (CSF) were elevated by the AP grafts, CSF samples were taken from 5 control rats and 10 rats bearing intrahypothalamic AP grafts. Mean PRL concentrations in the CSF of the control rats were 3.0 +/- 0.8 ng/ml. The grafted rats had significantly higher concentrations of PRL in their CSF, averaging 23.2 +/- 4.2 ng/ml (P less than 0.005). Plasma PRL concentrations were similar in the control and grafted rats. PRL release in response to 5 min of ether stress was examined in 8 control and 11 grafted rats. In control animals, PRL rose from 4.2 +/- 1.5 to 44.7 +/- 9.0 ng/ml following exposure to ether, but the response was significantly attenuated in the grafted rats, peaking at 9.3 +/- 1.4 ng/ml (P less than 0.001). This inhibition of response due to the grafts was evident within 1 week of graft placement. The results confirm that the presence of intrahypothalamic AP grafts led to the accumulation of supranormal PRL concentrations in the CSF. This elevated PRL suppressed pituitary PRL release in response to ether stress, probably by an autoregulatory feedback activation of the inhibitory tuberoinfundibular dopaminergic neurons in the hypothalamus.

Animals↗