Abnormal regulation of prolactin secretion after successful surgery for prolactin-secreting pituitary tumours

Dopamine, the dopamine D2 receptor and pituitary tumours

Dopamine plays an important role in the hypothalamic-pituitary axis where its major effects are to inhibit pituitary hormone secretion and cell division. Chronic dopamine deficiency has been postulated as a cause of pituitary tumour formation and several lines of evidence exist to suggest that a functional deficiency may develop as a result of defective dopamine receptor action. The available data suggest that a number of sites in the dopamine-D2 receptor-second messenger pathways may be implicated. These abnormalities are reflected in the variety of responses to dopamine and its agonists which have been observed in pituitary tumours both in the clinical situation and in cultured cells in vitro. Whilst it seems likely that the primary defect in pituitary tumour formation lies within the pituitary itself, the role of hypothalamic factors in facilitating tumour growth remains to be explored. Further studies of the dopamine receptor and its function will be of value not only in pathophysiological studies of human pituitary adenomas, but also in the development of new pharmacological agents to treat patients with these tumours.

Enlarged adenomectomy for enclosed prolactinomas: a preliminary study of 26 cases

Preliminary results obtained from 26 cases of prolactinomas less than 20 mm in diameter after treatment by enlarged adenomectomy are described. The operation consisted in removal of the adenoma, a layer of normal pituitary at the outer edge of the tumour and the pituitary capsule in contact with the sellar meninges. 24 women and 2 men were involved whose prolactin levels (PRL) were less than 200 ng/ml. All presented abnormal PRL responses to Thyrotropin releasing hormone (TRH) and Metoclopramide (MCP) tests and an absence of a nocturnal rise in the sleep cycle study. Postoperatively, three patients developed transitory diabetes insipidus and five transitory adrenal insufficiency. Gonadotropin reserve was always found normal. All 24 women resumed normal menstrual cycles and two became pregnant within one year. From a serological viewpoint, after surgery 100% of patients were found to be normal for levels of prolactin but only 85% turned to normal dynamic tests. The results of this small series of enlarged adenomectomies seem better than those obtained using selective adenomectomy, but must be confirmed with time.

Gradual recovery of lactotroph responsiveness to dynamic stimulation following surgical removal of prolactinomas: long-term follow-up studies

Prolactin-secreting pituitary adenomas were selectively removed through a transsphenoidal approach from 120 women. Basal serum PRL levels (measured one to six months after surgery) were normal in 96 patients and decreased appreciably but not to normal in the remaining 24 patients. Dynamics of PRL secretion were studied at three to four months in 81 patients who had normal basal PRL level. Two different patterns of response to provocative stimuli were noted in these patients. In one group (group I, n = 65), patients had greater than 100% rise in serum PRL following TRH or perphenazine (Pz) administration. However, when analyzed as a group, the mean +/- SEM incremental responses (delta PRL) to TRH and Pz in these patients (29.9 +/- 1.9, 20.4 +/- 1.5 ng/mL) were significantly less (P less than 0.005 and P less than 0.001) than those of normal women (38.8 +/- 5, 33 +/- 5 ng/mL, respectively). Nineteen of these patients were restudied 12 to 72 months after surgery. The responses to provocative stimulation at that time were improved and similar to normal women. In contrast, in the second group (n = 16) of patients (group II), the responses to stimulation with the same agents were blunted or absent and remained so during subsequent studies. Recurrence of the hyperprolactinemia was noted in 11 of the 16 patients in group II and in only two of 65 patients in group I. The daily serum PRL levels in the immediate postoperative period were higher in patients from group II than those from group I. We conclude that transsphenoidal surgery is an optimal form of therapy for patients with PRL-secreting adenomas.(ABSTRACT TRUNCATED AT 250 WORDS)

Late recurrence of surgically removed prolactinomas

The authors observed the clinical course of 24 women with surgically removed prolactinomas for a mean postoperative interval of 62 months. The frequency of late tumor recurrence and probable factors responsible for the recurrence were investigated. Hyperprolactinemia recurred in 4 of 13 patients with microadenomas (31%) 3 to 9 months after removal. In the macroadenoma group, relapse of hyperprolactinemia occurred in 10 of 11 patients (91%), an average of 26 months after the initial postoperative return to normal prolactin levels. Return of hyperprolactinemia was accompanied by radiologic evidence of tumor recurrence in all patients with macroadenoma, and in one patient with microadenoma. Of 12 tumors in which adjacent dura was available for histopathologic examination, 7 showed dural invasion. Although these seven patients had significantly higher preoperative levels of serum prolactin than the five without dural invasion, there was no significant relation between dural involvement and tumor recurrence. The probabilities of tumor recurring from multifocal adenoma or paraadenomatous lactotrope hyperplasia could not be assessed using our surgical material. The most plausible reason for the high recurrence rate of prolactinomas after apparent surgical cure, in the absence of defined anatomic abnormalities within the pituitary, is a functional abnormality of hypothalamic-pituitary control resulting from a primary hypothalamic disorder.

Long-term bromocriptine therapy may restore the inhibitory control of prolactin release in some patients with pathological hyperprolactinemia

While bromocriptine is effective in controlling hyperprolactinemia, it is not known if bromocriptine therapy can restore the abnormal regulation of prolactin (PRL) release found in patients with pathological hyperprolactinemia. We report 15 hyperprolactinemic patients treated for a mean duration of 5.5 +/- 0.6 years (mean +/- SE) in whom stimulation tests to assess PRL control mechanisms [thyrotropin releasing hormone (TRH) and metoclopramide] were performed before and at least one month after withdrawal of bromocriptine therapy. The basal PRL level after withdrawal of bromocriptine therapy was significantly lower (p less than 0.001) than that before therapy. All patients had blunted PRL stimulatory responses to TRH and metoclopramide (% delta 16.0 +/- 5.6%) before treatment. After withdrawal of bromocriptine, PRL responses to stimulatory tests were significantly improved in seven patients (termed 'responders', % delta 376 +/- 55%) but remained unchanged in eight patients (termed 'non-responders', % delta 9.2 +/- 3.0%). Basal PRL levels were significantly lower (p less than 0.01) in responders (290 +/- 35 mIU/l) than in non-responders (10360 +/- 6790 mIU/l). Four of the responders have maintained normoprolactinemia and normal stimulated PRL responses for 15 months to three years following cessation of bromocriptine therapy and appear to be in remission. Favourable factors amongst the responders were the female sex, absence of a macroadenoma, and a pre-treatment PRL level below 3000 mlU/l. PRL stimulation tests performed before therapy could not predict which patients would respond. No relationship was found between duration of therapy, or age at presentation, and improvement after bromocriptine.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrinological differentiation of primary hypothalamic and pituitary disease

The paper reviews approaches that can be applied to separating the endocrinological central nervous system (CNS) from pituitary components of neuroendocrine disorders. Major reasons which hamper the differentiation of primary hypothalamic from pituitary diseases are considered. Finally, future strategies suitable for a better accomplishment of this task are mentioned. Theoretically, the combined application of CNS-active compounds and hypothalamic regulatory hormones (RHs) should unravel the hypothalamic or pituitary etiology of the disorder. Until now, the most useful diagnostic application of RHs deals with their use in disease states due to isolated or multiple RH deficiency. Thus, the recent isolation of GRF molecules from human pancreatic tumors holds promise of a better functional characterization of GH deficiency states. The differentiation of the hypothalamic or pituitary origin of the disease in states of pituitary hyperfunction, e.g., acromegaly, or prolactinomas, is influenced by factors such as the development or expression of aberrant pituitary receptors for neurotransmitters and neuropeptides, the persistence of the responsiveness of tumorous pituitary cells to the respective RH, the disrupting effect of the excessively produced pituitary or target gland hormone on hypothalamic function. Future strategies of research in this area may include: 1. the development of sensitive and specific assays for RHs, e.g., GRF, CRF, etc. and RH determinations in biological fluids; 2. the search for non-hypophysiotropic peptides in the cerebrospinal fluid and their evaluation after appropriate stimulation; 3. better functional and clinical characterization of ectopic hormone-producing syndromes, or of psychiatric disorders mimicking neuroendocrine abnormalities from an endocrinological viewpoint (e.g., primary affective disorders v. Cushing's disease; 4. use of neuroactive compounds probing selective aspects of neurotransmitter function and, finally, 5. long-term follow-up studies after adenomectomy.

The inability of dynamic tests of prolactin and TSH secretion to differentiate between tumorous and non-tumorous hyperprolactinemia

Certain hyperprolactinemic patients have an obvious pituitary tumor while others with normal pituitary radiology may or may not harbor a pituitary microadenoma. A variety of biochemical tests have been proposed to distinguish between those with and those without pituitary tumors. The aims of this study were: firstly to examine these tests to assess their efficacy in differentiating between patients with radiologically-demonstrated pituitary tumors and normal controls; and secondly to establish if those hyperprolactinemic patients with normal radiology formed two distinct groups biochemically as might be expected if some did and some did not have tumors. The prolactin (PRL) and thyroid stimulating hormone (TSH) response to domperidone and the PRL response to TRH and insulin-induced hypoglycemia have thus been examined in hyperprolactinemic subjects with and without radiological evidence of an adenoma and in normal controls. The basal serum PRL was similar in patients with and without radiological evidence of a pituitary adenoma. The serum PRL response to all stimuli studied, expressed as a percentage of initial values, was blunted in patients with known pituitary tumors with total separation from values in control subjects. Results for patients with normal pituitary radiology were similar to those for patients with tumors with minimal overlap with controls. The peak TSH increment after domperidone was exaggerated in patients with known tumors, but overlap with control values was observed in 25%. In patients with normal radiology the peak TSH increment after domperidone was similarly increased but again overlap with control values occurred in 28%. Cluster analysis showed no evidence of two subgroups of response with in the hyperprolactinemic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect rates of different modalities for treatment of prolactin adenomas

Results of treatment of 963 patients with prolactin adenomas described in the literature were reviewed. The patient population was stratified into four subgroups: women and men with serum prolactin levels above and below 100 ng/ml for each of the treatment modalities: transsphenoidal surgery, bromocriptine, heavy ion radiation, conventional radiation, and transsphenoidal surgery plus conventional radiation. The five largest series within each subgroup were included. Success rates and recurrence rates were calculated for: (1) reduction of tumor size, (2) normalization of serum prolactin levels, and (3) normalization of other pituitary functions. Complication rates were calculated for procedural impairment of other pituitary functions. Transsphenoidal surgery was found to be the most effective treatment for lasting control, and bromocriptine for temporary control, of prolactin adenomas. Recurrent adenomas were most effectively treated by transsphenoidal surgery if serum prolactin levels were below 100 ng/ml. If serum prolactin levels were above 100 ng/ml, bromocriptine was the most effective treatment. Heavy ion radiation, with success rates comparable to those of transsphenoidal surgery and bromocriptine, but with lower recurrence rates, may eventually prove the most effective treatment of all.

Variation of serum prolactin-releasing activity in women with the galactorrhea-amenorrhea syndrome after bromocriptine treatment

Serum methanol extracts were obtained from nine women with the galactorrhea-amenorrhea syndrome, 24 pregnant women in the third trimester, and 18 normal men and women. The serum extract released prolactin (PRL) in significant amounts from rat anterior pituitary in vitro. The extracts from patients with galactorrhea-amenorrhea released PRL in large quantities. A significant positive correlation was observed between the PRL-releasing activity and serum PRL levels in individual samples from the pregnant women and normal subjects but not from the patients with galactorrhea-amenorrhea. Bromocriptine therapy suppressed serum PRL levels of five patients without tumors but increased the PRL-releasing activity in three out of five patients after treatment for 1 or 2 months. Apparently hypothalamic regulation of PRL secretion was disrupted in these three patients after bromocriptine therapy.