Effect of the GABAA agonist muscimol on prolactin secretion from human prolactin-secreting adenomas and GH3 rat pituitary tumour cells.

The effect of muscimol, a specific potent GABAA receptor agonist, on prolactin release from human prolactin-secreting tissue was investigated using a perifusion system. Perifusion studies on normal rat anterior pituitary tissue, which has identical GABA receptors to those found in normal human pituitary glands, show that muscimol has a specific biphasic effect on prolactin release. This is characterized by an initial transient stimulation (222.3 +/- 21.6% of basal) lasting for 5-10 min followed by a more prolonged inhibitory phase (63.9 +/- 3.1% inhibition of basal). Five human prolactin-secreting adenomas were studied, and in none of the tumours could a biphasic response be demonstrated. One of the prolactin-secreting adenomas had a blunted inhibitory response, but the other 4 showed no inhibitory effect of muscimol on prolactin release. Muscimol had no significant effect on basal or thyrotropin-releasing-hormone (TRH)-stimulated prolactin secretion from GH3 rat pituitary tumour cells. These studies suggest that the GABAergic effect on prolactin secretion is absent or altered in both rat and human prolactin-secreting tumour cells.     

Transforming DNA sequences present in human prolactin-secreting pituitary tumors.

Five human PRL-secreting pituitary tumors were tested for the presence of DNA-transforming sequences. After calcium phosphate transfection to NIH-3T3 mouse fibroblast cells, DNA samples derived from two prolactinomas induced foci of morphologically transformed cells which subsequently grew in soft agar. After retransfection of transformant DNA, resulting secondary transformants elicited rapidly growing solid tumors in nude mice. Southern analysis of transformant DNA revealed the integration of Alu-positive human DNA sequences into the mouse fibroblast NIH-3T3 cells, as judged by hybridization to a Blur-8 probe. The Alu signal became increasingly more difficult to detect with the multiple passaging (greater than 20) of transformant cells in culture. Alu polymerase chain reaction (PCR) was, therefore, used to selectively amplify human DNA sequences from the NIH-3T3 rodent background. PCR using a human Alu-specific primer resulted in amplification of an Alu-containing DNA region within these transformants. The transformant DNA did not hybridize to human genomic probes for genes known to evoke focus formation in this assay, including H-ras, K-ras, N-ras, trk, ret, ros, or met. Further identification of the Alu-containing region revealed that it contained sequences from the human hst gene, a member of the fibroblast growth factor family. The presence of human hst was demonstrated by strong hybridization to a 40-mer oligonucleotide probe to the second exon of hst, by amplification of this region with human hst-nested amplimers within the first and second introns, and finally by direct sequencing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dysregulation of circadian rhythms following prolactin-secreting pituitary microadenoma

A patient who developed an irregular sleep-wake pattern following prolactin-secreting pituitary microadenoma is described. The patient reported difficulties in sleep onset and awakening at the desired time, which caused major dysfunction in his daily life activities. Despite these difficulties, the sleep-related complaints of the patient remained unrecognized for as long as three yrs. Statistical analyses of the patient's rest-activity patterns revealed that the disruption of the sleep-wake circadian rhythm originated from a disharmony between ultradian (semicircadian) and circadian components. The circadian component displayed shorter than 24 h periodicity most of the time, but the semicircadian component fluctuated between longer and shorter than 12 h periods. Additionally, desynchrony in terms of period length was found in the tentative analyses of the rest-activity pattern, salivary melatonin, and oral temperature. While the salivary melatonin time series data could be characterized by a best-fit cosine curve of 24 h, the time series data of oral temperature was more compatible with 28 h best-fit curve. The rest-activity cycle during the simultaneous measurements, however, was best approximated by a best-fit curve of 21 h. The dysregulation of circadian rhythms occurred concomitantly, but not beforehand, with the onset of pituitary disease, thus suggesting an association between the two phenomena. This association may have interesting implications to the modeling of the circadian time-keeping system. This case also highlights the need to raise the awareness to circadian rhythm sleep disorders and to consider disruptions of sleep-wake cycle in patients with pituitary adenoma.     

Presence of high affinity dopamine receptors in estrone-induced, prolactin-secreting rat pituitary adenomas: a model for human prolactinomas

Adenomatous cells obtained from a pituitary tumor induced in Fisher 344/Lis rats by the subcutaneous implantation of estrone (E1) were found to secrete large amounts of prolactin (PRL). The secretion of PRL was stimulated by thyrotropin-releasing hormone (TRH) and low concentrations of dopamine (DA), while micromolar concentrations of DA were inhibitory. High affinity binding sites for 3H-spiroperidol (3H-SPIR) were found to be present on the cells and to conform to the criteria of dopaminergic receptors. An adenylate cyclase (AC) present in the cells could be activated by a guanyl nucleotide and was inhibited by DA in the presence of guanosine 5'-triphosphate (GTP). Fractionation of the adenomatous cells by Percoll gradients identified two groups of cells capable of secreting PRL and bearing 3H-SPIR binding sites. These data indicate that this rat pituitary adenoma may be a model for human prolactinomas that might be utilized for the study of the mechanism of action of dopaminergic drugs.     

Intermediate filament expression in pituitary adenomas.

Seventy-five formalin-fixed and 18 alcohol-fixed pituitary adenomas were studied immunohistochemically using antibodies to keratin, vimentin, neurofilaments (NFs), glial fibrillary acidic protein, desmin, actin, S-100 protein and a variety of pituitary hormones. The pituitary adenoma cells were positive for keratin, vimentin and NFs (68 kDa and 160 kDa) and in a few instances there was co-expression of these three types of intermediate filaments (IMFs). The pattern of keratin-specific staining showed diffuse cytoplasmic or patchy paranuclear reactivity and of NF- or vimentin-specific staining showed fibrillar or patchy paranuclear reactivity. The patchy staining seemed to decorate the fibrous body. There was no correlation between the distribution of IMFs and pituitary hormones in pituitary adenomas except that melanocyte-stimulating-hormone-positive reactivity was limited to the NF-positive adenomas. The pattern of IMF staining did not depend on hormone production in adenomas.     

Galanin in pituitary adenomas

Tumor galanin content was measured in extracts from human pituitary adenomas using a specific RIA method for monitoring human galanin. Twenty-two out of twenty-four tumors contained galanin with notably high levels in corticotroph adenomas, varying levels in clinically inactive tumors, and low levels in GH secreting adenomas. Tumor galanin and ACTH contents were closely correlated in all tumors. In four young patients with microadenomas and highly active Mb Cushing tumor galanin was inversely related to tumor volume. The molecular form of tumor galanin, studied with reverse-phase HPLC, was homogeneous with the majority of tumor galanin coeluting with standard human galanin. In the tumors analysed with in situ hybridization there was a good correlation between galanin peptide levels and galanin mRNA expression. In some tumors galanin mRNA and POMC levels coexisted, in others they were essentially in different cell populations. Levels of plasma galanin-LI were not related to tumor galanin concentration, and galanin levels were in the same range in sinus petrosus close to the pituitary venous drainage as in peripheral blood. Corticotrophin releasing hormone injections in two patients caused ACTH, but no detectable galanin release into sinus petrosus. Our results demonstrate that corticotroph, but not GH adenomas, express high levels of galanin, in addition to ACTH, and that in some tumors both polypeptides are synthesised in the same cell population. However, galanin levels in plasma were not influenced by the tumor galanin content.     

Annulate lamellae in adenomas of human pituitary glands.

Twelve nontumorous adenohypophyses and 36 various pituitary adenomas, removed by surgery, have been investigated by electron microscopy in order to shed some light on annulate lamellae, primarily on their ultrastructural features, incidence, origin, fate and functional significance. No annulate lamellae were found in the nontumorous adenohypophyses and in 33 pituitary adenomas. They were, however, detected in two adenomas consisting of undifferentiated cells and one adenoma composed of sparsely granulated prolactin cells indicating that these unique membrane configurations cannot be regarded as an exceedingly rare finding and, furthermore, that they may be disclosed not only in undifferentiated but occasionally in highly differentiated cells. Annulate lamellae may arise from endoplasmic reticulum and/or nuclear envelope and consist of arrays of smooth walled double membrane sheets exhibiting regularly spaced interruptions as well as continuities with the endoplasmic reticulum. No relationship was established between annulate lamellae and adenohypophysial secretory activity. Our findings seem to be consistent with the view that annulate lamellae are present in those cells which have the tendency to proliferate.     

Clinical and genetic features of familial pituitary adenomas.

Inherited or familial pituitary tumor syndromes such as multiple endocrine neoplasia type 1 and Carney complex provide an important insight into the genetics and molecular pathology of endocrine cancers. Our understanding of these conditions is expanding rapidly due to the identification of the genes and proteins affected and the availability of murine knockout models. The successes achieved to date in understanding multiple endocrine neoplasia type 1 and Carney complex have helped in the identification and study of new inherited pituitary tumor syndromes such as isolated familial somatotropinomas. This review assesses the current status of research into the clinical features, genetics and molecular pathologies of multiple endocrine neoplasia type 1, Carney complex, and isolated familial somatotropinomas, and details ongoing work to delineate familial isolated pituitary adenomas, a potentially new clinical entity.     

Impaired calcium mobilisation in the 7315a prolactin-secreting pituitary tumour

The 7315a tumour secretes prolactin, but is refractory to enhancement of prolactin release by thyrotrophin-releasing hormone (TRH). In order to investigate further this refractoriness of the 7315a tumour cell, we compared cells from the tumour and from the normal pituitary with regard to TRH-enhanced fractional 45Ca2+ efflux and inositol phosphate production. TRH caused a large efflux of calcium from normal pituitary cells, but only mildly enhanced calcium efflux from the tumour cells. In contrast, TRH enhanced total inositol phosphate generation in both groups of cells to a similar degree. We therefore conclude that prolactin release from 7315a tumour cells is refractory to TRH due, at least in part, to impaired mobilisation of intracellular calcium by inositol phosphates.     

垂体催乳素瘤的病因及发病机制的实验研究

应用在同一只雄性ＳＤ大鼠中,保留原位垂体并在肾囊内植入一异体垂体,同时背部埋植装有１７－β－雌二醇（１７－β－ｅｓｔｒａｄｉｏｌ,Ｅ２）的药泵,经Ｅ２在体作用６０￣１２０天后,其原位垂体和异体移植入肾囊的垂体同时形成２垂体催乳素（ｐｒｏｌａｃｔｉｎ,ＰＲＬ）瘤的动物模型,研究ＰＲＬ瘤的发病机制。结果表明,Ｅ２长期作用可诱发原位垂体和远离下丘脑的移植垂体同时形成ＰＲＬ瘤,并伴高ＰＲＬ血症和ＰＲＬ基因     

Dopamine inhibits calcium flux in the 7315a prolactin-secreting pituitary tumour

Cells of the 7315a prolactin-secreting tumour express biochemically normal cell-surface receptors for dopamine. However, dopamine inhibits prolactin release from these cells only when the basal rate of prolactin release is augmented by increasing the intracellular and/or extracellular calcium concentration of the tumour cells. This suggests that dopaminergic modulation of calcium ion flux could have a central physiological role in these neoplastic cells. In 7315a cells we examined the ability of dopamine to regulate 45Ca2+ influx and fractional 45Ca2+ efflux under conditions of enhanced calcium flux using the calcium channel activator, maitotoxin. It was observed that unidirectional calcium influx stimulated by maitotoxin was significantly inhibited by dopamine. Maitotoxin stimulated fractional efflux and prolactin release from the tumour cells and dopamine simultaneously inhibited both processes by a haloperidol-reversible mechanism. Therefore, in 7315a cells dopamine receptor activation is coupled to inhibition of calcium flux as at least one component in the regulation of prolactin release. These cells may provide further opportunity to study intracellular signalling mechanisms that are modulated by dopamine receptor activity.     

Prolactin-secreting pituitary adenomas in males: transsphenoidal microsurgical treatment.

Fifteen male patients with prolactin-secreting pituitary adenomas were studied before and after transsphenoidal microsurgical treatment. Loss of libido and sexual impotence were the most frequent symptoms, being present in 12. Visual defects were present in seven patients, gynecomastia was observed in four and galactorrhea was noted in three. Most of the tumours were large; only one was a microadenoma. Four patients were cured by the operation. In all the other patients the plasma levels of prolactin were significantly lowered and the visual defects corrected or lessened, but sexual impotence was not modified. No important deficiency of the pituitary gland was induced by the operation. The results indicate that in males loss of libido and sexual impotence are frequent and early manifestations of prolactinomas, and that transsphenoidal resection is a safe therapeutic approach.