Distinctive features of prolactin secretion in acromegalic patients with hyperprolactinaemia

Epidemiology of acromegaly

Acromegaly is a consequence of chronic growth hormone (GH) excess, due in the majority of cases to a GH-secreting pituitary adenoma, and occurring with a population prevalence of 60 per million and an incidence of 3-4 per million per year. Males and females appear to be equally affected with an average age of presentation of 44 years. Younger patients may have more aggressive tumours and higher GH concentrations. There is co-existent hyperprolactinaemia in about one third of cases, and a variable proportion of [figure: see text] tumours appear to have activating mutations of the gsp gene or other genetic abnormalities. Acute complications such as carpal tunnel syndrome, sweating and obstructive sleep apnoea are usually readily reversible with treatment of the condition, but chronic complications such as hypertension, diabetes and heart disease are less readily corrected and post-treatment GH levels of < 2.5 ug/L (5 mU/L) are needed to achieve the prevalence found in the general community. Such 'curative' levels of GH are achieved in only about 50% of patients with current therapies, and as a result there is an ongoing excess of patients with chronic complications of acromegaly leading to increased morbidity and mortality from the disorder, with observed-to-expected mortality ratios ranging from 1.6-3.3 and only approaching unity in those with growth hormone levels < 2.5 ug/L following treatment. Prognostic factors include in some studies the presence of diabetes and [table: see text] hypertension prior to diagnosis as well as measures of exposure to excessive growth hormone derived from the product of preoperative serum GH and the time from first symptoms to treatment. Overall, however, the most important prognostic variable appears to be the serum GH concentration achieved by treatment, with an increasing consensus that this needs to be < 2.5 ug/L (5 mU/L) to achieve cure of the condition.

Pituitary tumors: surgical and medical management

The pituitary gland has been termed the 'master gland' because of the myriad of hormones that emanate from it that are vital for normal homeostasis as well as growth and development. Primary tumors of this region are frequent and account for up to 10% of intracranial tumors. Pituitary tumors are monoclonal in origin, and may arise from any of the different cell types of the pituitary gland. Hence, these tumors may be manifest by their hormonal secretions. This may lead to profound and striking physiological changes attributable, for example, to prolactin, growth hormone, or ACTH excess. The central location of the pituitary gland also leads to characteristic compressive symptoms. This review will explore the clinical presentations of growth hormone, ACTH, and prolactin secreting tumors as well as the non-secreting pituitary tumors. Advances in neuroimaging and neuropharmacology have resulted in changes in our treatment of these tumors. Treatment modalities including surgical, medical, and radiation therapy will be addressed. The treatment of choice is dictated by the type of tumor and the nature of the excessive hormonal expression. Outcomes and efficacy of treatment are discussed.

Novel features of tumors that secrete both growth hormone and prolactin in acromegaly

The most prominent previously reported clinical features of growth hormone (GH) and prolactin (PRL)-secreting pituitary adenomas associated with acromegaly have included the high incidence of galactorrhea in women and a generally more favorable response to dopamine agonist therapy. The authors analyzed a consecutive series of 62 acromegalic patients treated with transsphenoidal microsurgery. GH-PRL tumors were found in 30% of the patients. There was a significant difference in sex distribution between acromegalics with the GH-PRL tumor subtype and all other acromegalics. Women represented 73% of the GH-PRL immunostain subtype, as compared with the overall sex distribution of 33 women (53%) and 29 men (47%) for the entire series of acromegalic patients. Individuals with the GH-PRL subtype had significantly higher postoperative GH levels than those with the GH subtype, and significantly higher postoperative GH levels when compared with all other acromegalics with a variety of immunostain subtypes. Linear regression analysis of the pre- and postoperative GH data revealed that the increased postoperative GH levels in the GH-PRL immunostain subtype were independent of the invasiveness of the tumor and of sex of the subject. When the same linear regression technique was used, lower preoperative levels of thyroxine and thyroid-stimulating hormone were observed in the GH-PRL subtype. These data suggest inherent differences characteristic of tumors that secrete both growth hormone and prolactin.

Acromegaly: an epidemiological study

Although morbility and mortality in acromegaly are higher than in the general population, there have been very few previous epidemiological studies. This study tries to answer "why". Seventy-four patients affected by acromegaly in Vizcaya (Spain) between 1970 and 1989 were considered for an epidemiological study. The prevalence of known cases at the end of 1989 was 60 per million inhabitants. The average incidence of newly diagnosed cases was 3.1 per million people per year. Unexpectedly, acromegaly was more frequent in women (n = 48) than in men (n = 26), with a ratio of 1.8:1. Mean age at diagnosis was significantly higher in women (46.1 +/- 2.2 yr) than in men (39.5 +/- 2.2 yr) (p < 0.05) There was a positive correlation between age at diagnosis and the estimated duration of the disease (r = 0.56, p < 0.05) and a negative one between age and basal GH serum levels (r = -0.52 p < 0.002). The age at diagnosis was significantly higher in patients with invasive tumors (grade III and IV) than in those with enclosed tumors (grade I and II) (47.7 +/- 1.8 vs 40.1 +/- 3.3 p < 0.05). In general, mortality was higher than the expected for the control population (standardized mortality ratio, SMR = 3.2, 95% confidence interval. Cl = 1.55-5.93). However, mortality was higher in men (SMR = 7, 95% Cl = 2.81-14.4) but not in women (SMR = 1.4 95% Cl = 0.29-4.17).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin presents in all pituitary tumors of acromegalic patients

Twenty-two consecutive cases of adenoma in acromegalic patients were studied immunohistochemically. All the tumors contained prolactin (PRL)-reactive cells (3% to 53% of the total number of tumor cells) as well as growth hormone (GH)-reactive cells (4% to 74% of the total number of tumor cells). All acromegalic cases studied were thus plurihormonal adenomas containing GH and PRL; no pure GH cell adenoma was present. Twenty cases were further examined at the ultrastructural level in conjunction with postembedding double-labeling immunoelectron microscopy; 15 of these cases were diagnosed as mixed GH cell-PRL cell adenomas. The previously diagnosed pure GH cell adenomas possibly may have contained PRL cells and thus should be considered as mixed GH cell-PRL cell adenomas. Mammosomatotroph adenomas were rare in this series. Double-labeling immunoelectron microscopy, using protein A gold particles of two different sizes, greatly facilitated the distinction among GH, PRL, and mammosomatotroph cells.

Control of prolactin secretion

1. Prolactin is a 21,500 Dalton single-chain polypeptide hormone but may occur in 50 kDa and 150 kDa molecular variants. 2. These large PRL variants may be secreted predominantly; this condition is termed "macroprolactinemia". It is characterized by high immunological and normal biological serum levels of prolactin, and lack of clinical symptoms of hyperprolactinemia. 3. The information on PRL is encoded on chromosome 6. Transcription can be enhanced and suppressed by a variety of hormonal factors. 4. PRL is secreted in a pulsatile fashion; it displays a circadian rhythm (with a maximum during sleep) and is stimulated by some amino acids. PRL also responds to mechanical stimulation of the breast. 5. PRL rises during pregnancy, and maintainance of hyperprolactinemia (and, thereby, physiological infertility) is dependent on the frequency and duration of breast feedings. 6. Hypothalamic regulation of prolactin mainly involves tonic inhibition via portal dopamine. The physiological importance of various stimulating factors present in the hypothalamus is still incompletely understood. In particular, there is still no place for TRH in PRL physiology. 7. PRL is released in response to stress; this response may be mediated by opioids. The low-estrogen, low-gonadotropin amenorrhea of endurance-training women is not mediated by prolactin, however. 8. Estrogens stimulate PRL gene transcription via at least two independent mechanisms. There are many clinical examples of this estrogen effect on prolactin serum levels, and also on the growth of prolactinomas. 9. Mild hyperprolactinemia remains an enigma which cannot satisfactorily be resolved by biochemical or radiological testing. The border between "normal" and "elevated" prolactin is ill-defined. The possibility of macroprolactinemia complicates this matter even further. 10. The number of drugs which suppress prolactin by acting on pituitary D2 receptors, and which are useful in the treatment of hyperprolactinemia, continues to increase. In the field of ergot alkaloids, parenteral application appears to be a logical solution to the problem of the high first-pass effect; in addition, this form of treatment is frequently better tolerated than the oral route. 11. Prolactinoma development is presently being studied employing molecular biological techniques; the question of whether tumorigenesis can be attributed to specific defects of gene regulation remains to be answered.

Pharmacology of new hormonal therapies in the treatment of pediatric endocrine disorders

Advances in genetic engineering will make possible treatment of many pediatric endocrine disorders with replacement therapy. Some of these conditions include short stature, precocious puberty, and diabetes mellitus. Although the availability of such hormonal replacement offers new treatment modalities, an understanding of their mechanism of action and pharmacologic characteristics is crucial to maximize their effectiveness while minimizing possible untoward effects. The clinician must evaluate potential risks and benefits as these substances come to market without definitive answers being available as to their long-term effects.

Glycoprotein hormone alpha-subunit and prolactin release by cultured pituitary adenoma cells from acromegalic patients: correlation with GH release

In-vitro data of pituitary adenoma cells from 28 acromegalic patients were evaluated. In addition to GH, PRL was produced by 16 adenomas (57%) and alpha-subunit by 15 adenomas (54%) while there was a significantly higher incidence of tumours producing PRL and alpha-subunit simultaneously. From 26 pituitary adenomas enough cells were obtained in order to perform secretion studies. Percentage basal hormone release (medium: (medium + intracellular hormone)) x 100% of GH and alpha-subunit by 11 adenomas showed a close correlation while such a correlation for GH and PRL was present only in a subgroup of 10 of 13 adenomas. The responses of GH and alpha-subunit release to 10nM SMS201-995, 10nM bromocriptine, 100 nM TRH and 10nM GHRH were closely related in that a response or an absent response of GH release to the four secretagogues was virtually always attended with a response or an absent response respectively of alpha-subunit release. Such a relationship was less evident with respect to the effects of SMS201-995, bromocriptine. TRH and GHRH on GH and PRL release. We conclude that basal and secretagogue-induced alpha-subunit release by cultured pituitary adenoma cells from acromegalic patients closely follows the pattern of GH release while such a relationship for GH and PRL is present only in a subgroup of the adenomas secreting GH and PRL simultaneously.

Mixed growth hormone and prolactin-secreting human pituitary adenomas: a pathologic, immunocytochemical, ultrastructural, and immunoelectron microscopic study

A study of 30 adenomas from patients with signs of growth hormone (GH) and prolactin (PRL) hypersecretion revealed the presence of mammosomatotroph cells (MSC) containing both hormones in all cases. Although the number of immunostained cells varied from case to case, in 14 of 25 tumors, all stained cells were MSC. Nine tumors had the ultrastructural appearance of densely granulated growth hormone adenomas, while 11 cases resembled sparsely granulated growth hormone adenomas with frequent fibrous bodies. Exocytosis was present in six of these 11 cases, a feature unusual for pure growth hormone adenomas. Nine tumors consisted of a mixture of cells with the morphology of GH and PRL cells. In the four cases examined, immunoelectron microscopy using double immunolabeling with protein A-gold particles revealed the presence of secretory granules containing both hormones in some tumor cells recognized as mammosomatotroph cells.