Disorders of prolactin and growth hormone secretion

Severe hypersomnolence after pituitary/hypothalamic surgery in adolescents: clinical characteristics and potential mechanisms

OBJECTIVES

After resection of hypothalamic/pituitary tumors, children are at risk for development of hormonal deficiencies, obesity, and hypersomnolence. However, the prevalence and pathophysiology of these complications are unclear. The purpose of this study was to assess the prevalence and severity of hypersomnolence in children after resection of pituitary tumors and to study the potential factors that contribute to this sleepiness if present. We further hypothesized that decrements in orexin levels may contribute to the sleepiness.

METHODS

Six children who underwent hypothalamic/pituitary surgery were identified. Five of these patients and 5 matched control subjects underwent overnight polysomnography followed by a multiple sleep latency test. Children who had a primary sleep disorder (eg, obstructive sleep apnea) underwent treatment and were restudied subsequently (n = 2). Blood levels of pituitary hormones were measured. Blood and cerebrospinal fluid (CSF) were drawn from 4 patients and 3 control subjects to measure orexin levels.

RESULTS

Endocrine control was appropriate in all children. Although patients had longer sleep duration but similar sleep efficiency than control subjects, relatively severe daytime somnolence was present (mean sleep latency: 10.3 +/- 5.3 minutes vs 26.2 +/- 1.1 minute in control subjects). Sleepiness did not correlate with body mass index or age. Furthermore, serum and CSF orexin levels did not differ between patients and control subjects.

CONCLUSIONS

Severe daytime sleepiness is frequent among children who undergo pituitary/hypothalamic surgery and does not seem to result from inappropriate cortisol or thyroxine replacement, disturbed nocturnal sleep, or low levels of orexin in the serum or CSF. We therefore speculate that other, unidentified neurohormonal mechanisms may mediate the excessive sleepiness of these patients.

The pathology of pituitary tumors

The pathologist plays an important role in the distinction of pituitary adenomas from other tumors and tumor-like lesions of the sellar region, and in the accurate morphologic characterization of pitutiary adenomas. A clinicopathologic classification of pituitary adenomas is based on cell differentiation correlated with clinical evidence of hormone secretion; this classification emphasizes clinically relevant features that can offer guidance for patient management. The application of a rational approach to the immunohistochemical analysis of these lesions can be used to evaluate pathogenetic and prognostic markers and to predict responses to specific therapeutic modalities.

High prolactin levels in patients with Cushing's disease without pathological evidence of pituitary adenoma

OBJECTIVE

This study was designed to compare the clinical and biochemical features of patients with Cushing's disease without pathological evidence of pituitary adenoma (n = 11) to those in whom a pituitary ACTH adenoma was documented (n = 11).

DESIGN

The clinical and biochemical features of 11 patients with Cushing's disease without pathological evidence of pituitary adenomas were compared to 11 subjects with ACTH-secreting adenomas. The patients underwent transsphenoidal microsurgery between 1979 and 1989. During surgery, when an adenoma was not visualized, a partial hypophysectomy of the central mucoid wedge was performed.

MEASUREMENTS

Cushing's disease was established by the clinical features of hypercortisolism and the high levels of 24-hour free urinary cortisol with no suppression in response to low, but with suppression in response to high, doses of dexamethasone. Basal and post TRH-GnRH plasma prolactin, FSH and LH levels were assessed in each patient before transsphenoidal microsurgery.

RESULTS

Similar results were observed in patients with and without ACTH-secreting adenomas regarding cure rate, and free urinary cortisol levels both basal and after 2 days of dexamethasone, 8 mg daily. After surgery, plasma cortisol levels in cured patients were lower in subjects with ACTH-secreting adenomas than in those without pituitary tumours (P < 0.05). Areas under the curve of PRL (P < 0.002) and LH (P < 0.04) were significantly higher in patients without pituitary adenoma after TRH-GnRH administration. Compared to controls, the peak prolactin level after TRH-GnRH administration was higher in patients without pituitary adenoma (P < 0.005) and lower in those with ACTH adenoma (P < 0.005). Furthermore, a peak prolactin level equal to or greater than 1410 mU/l during the TRH-GnRH test was found in 11/11 patients without ACTH adenoma and 3/11 patients in the other group (P < 0.001), while the CT-scan findings were suggestive of pituitary adenoma in six patients of each group.

CONCLUSION

This study suggests that patients with Cushing's disease without pituitary adenomas can be distinguished from those with ACTH-secreting adenomas by their high prolactin levels after TRH-GnRH administration.

Ibuprofen fails to increase plasma growth hormone levels in humans

In eight healthy volunteers, basal and arginine-stimulated plasma glucose and growth hormone levels were determined during administration of a placebo and after 3 days of ibuprofen (800 mg four times daily). Ibuprofen had no significant effect on basal or stimulated plasma glucose or growth hormone levels. As is not the case with indomethacin, ibuprofen fails to increase basal and arginine-stimulated plasma growth hormone levels. This suggests that the effect of indomethacin on growth hormone secretion is due to a mechanism unrelated to inhibition of prostaglandin synthesis.

Indomethacin increases plasma growth hormone levels in man

In seven normal volunteers, the basal and arginine-stimulated levels of plasma growth hormone, glucose, glucagon, and free fatty acids and serum insulin was determined during placebo and during indomethacin 25 mg four times daily. Basal plasma growth hormone was higher during indomethacin (5.4 +/- 1 vs 1.7 +/- 2 ng/ml, p less than 0.005), as was the mean integrated response to intravenous arginine (40 +/- 14 vs 6 +/- 4 ng.min/ml, p less than 0.05). Despite lack of effect on plasma glucagon, indomethacin decreased the insulin response to arginine. The fall in free fatty acids during arginine infusion was decreased by indomethacin, which may in part be due to increased plasma growth hormone levels. In view of the many patients treated with indomethacin, the effect on growth hormone may be of clinical importance.

Suprasellar germinoma--occult presentation with hypothalamic failure 18 months before diagnosis

Hormonal evidence of widespread hypothalamic failure, including diabetes insipidus, hyperprolactinaemia, growth failure, hypothyroidism, and adrenal failure, was present in a boy of 14 years. Investigation with computerised axial tomography (CT) and metrizamide encephalography failed to identify any anatomical abnormality at the time of presentation. However, 18 months later papilloedema was noted at which time a suprasellar mass and gross dilatation of the ventricular system were readily identified using CT and a germinoma was subsequently diagnosed and treated. In the light of this experience we recommend that when "idiopathic" hypothalamic failure is diagnosed, imaging procedures, including CT or nuclear magnetic resonance examinations, should be repeated on at least one occasion, after an interval of approximately 6 months.

Evaluation of a commercial immunoenzymometric assay for human prolactin

A commercially available immunoenzymometric assay for human prolactin based on two monoclonal antibodies, one bound to a solid-phase bead and the other conjugated to alkaline phosphatase, was evaluated. The assay had a lower limit of detection of 2 ng/ml and between-batch coefficients of variation of less than 10% for prolactin concentrations in the range 7-152 ng/ml. Assay accuracy as judged by comparison of patient samples analysed by a RIA, assay of quality control samples and recovery experiments, was good. No significant cross-reactivities or interferences were found. The assay is precise, accurate, fast and robust with the advantage of using a non-isotopic label.

Tall stature: a clinical, endocrinological and radiological study

We have studied GH secretory dynamics in 38 (25 F, 13 M) children referred for investigation and treatment of tall stature (Height SD score (SDS) greater than 1.8). Five children had elevated basal GH levels (mean 20.4 mU/l) and a further four had abnormal GH responses to exogenous TRH. Two other children had paradoxical GH responses to oral glucose loading. Although one of these was receiving high dose testosterone to limit final height. All these children were pubertal and did not show concordance between peak GH concentration observed after insulin-induced hypoglycaemia and during stage IV sleep. Twenty-four hour GH profiles revealed increased GH pulse amplitude and area under the pulse during puberty. Morning GH secretion was also regularly observed and it is possible that the paradoxical responses seen by us and reported by others reflect this increased physiological secretion. Pituitary radiology revealed morphological abnormalities suggestive of microadenomata in 17 patients but these were all in late puberty and these changes may be related more to the effects of sex hormones than to somatotroph pathology. 'Abnormal' endocrinology and radiology are seen in tall children in puberty and must be interpreted with caution.

Growth hormone neurosecretory dysfunction

The basis for understanding clinical disorders in the neuroregulation of GH secretion is derived from the complexity of the CNS-hypothalamic-pituitary axis. Studies in animals and humans demonstrate an anatomic, physiological and pharmacological evidence for neurosecretory control over GH secretion including neurohormones (GRH, somatostatin), neurotransmitters (dopaminergic, adrenergic, cholinergic, serotonergic, histaminergic, GABAergic), and neuropeptides (gut hormones, opioids, CRH, TRH, etc). The observation of a defect in the neuroregulatory control of GH secretion in CNS-irradiated humans and animals led to the hypothesis of a disorder in neurosecretion, GHND, as a cause for short stature. We speculate that in this heterogeneous group of children a disruption in the neurotransmitter-neurohormonal functional pathway could modify secretion ultimately expressed as poor growth velocity and short stature.