Twenty-four hour melatonin pattern in acromegaly: effect of acute octreotide administration

Alterations in diurnal rhythmicity in patients treated for nonfunctioning pituitary macroadenoma: a controlled study and literature review

OBJECTIVE

Patients treated for nonfunctioning pituitary macroadenomas (NFMAs) have fatigue and alterations in sleep characteristics and sleep-wake rhythmicity frequently. As NFMAs often compress the optic chiasm, these complaints might be related to dysfunction of the adjacent suprachiasmatic nucleus (SCN). We aimed to explore whether indirect indices of SCN functioning are altered in the long term after surgery for NFMAs.

METHODS

We studied 17 NFMA patients in long-term remission after transsphenoidal surgery, receiving adequate and stable hormone replacement for hypopituitarism, and 17 control subjects matched for age, gender, and BMI. Indirect indices of SCN function were assessed from 24-h ambulatory recordings of skin and core body temperatures, blood pressure, and salivary melatonin levels. Altered melatonin secretion was defined as an absence of evening rise, considerable irregularity, or daytime values >3 pg/ml. We additionally studied eight patients treated for craniopharyngioma.

RESULTS

Distal-proximal skin temperature gradient did not differ between NFMAs and control subjects, but proximal skin temperature was decreased during daytime (P=0.006). Core body temperature and non-dipping of blood pressure did not differ, whereas melatonin secretion was often altered in NFMAs (OR 5.3, 95% CI 0.9-30.6). One or more abnormal parameters (≥2.0 SDS of control subjects) were observed during nighttime in 12 NFMA patients and during daytime in seven NFMA patients. Similar patterns were observed in craniopharyngioma patients.

CONCLUSION

Heterogeneous patterns of altered diurnal rhythmicity in skin temperature and melatonin secretion parameters were observed in the majority of patients treated for NFMAs. On a group level, both NFMA and craniopharyngioma patients showed a lower daytime proximal skin temperature than control subjects, but other group averages were not significantly different. The observations suggest altered function of central (or peripheral) clock machinery, possibly by disturbed entrainment or damage of the hypothalamic SCN by the suprasellar macroadenoma or its treatment.

A randomized controlled trial of oral melatonin supplementation and breast cancer biomarkers

We examined compliance with and the effects of melatonin supplementation on breast cancer biomarkers (estradiol, insulin-like growth factor I (IGF-1), insulin-like growth factor-binding protein 3 (IGFBP-3), and the IGF-1/IGFBP-3 ratio) in postmenopausal breast cancer survivors. In a double-blind, placebo-controlled study, postmenopausal women with a prior history of stages 0-III breast cancer who had completed active cancer treatment (including hormonal therapy) were randomly assigned to either 3 mg oral melatonin (n = 48) or placebo daily for 4 months. Plasma samples were collected at baseline and after the completion of the intervention. The primary endpoints were compliance and change in estradiol and IGF-1/IGFBP-3 levels. Ninety-five women were randomized (48 to melatonin and 47 to placebo). Eighty-six women (91%) completed the study and provided pre- and postintervention bloods. Melatonin was well tolerated without any grade 3/4 toxicity and compliance was high (89.5%). Overall, among postmenopausal women with a prior history of breast cancer, a 4-month course of 3 mg melatonin daily did not influence circulating estradiol, IGF-1, or IGFBP-3 levels. Compliance was comparable between the two groups. Short-term melatonin treatment did not influence the estradiol and IGF-1/IGBBP-3 levels. Effects of longer courses of melatonin among premenopausal women are unknown. Low baseline estradiol levels in our study population may have hindered the ability to detect any further estradiol-lowering effects of melatonin.

Increased melatonin concentrations in children with growth hormone deficiency

A relationship between melatonin and growth hormone (GH) is poorly understood. We compare circadian melatonin rhythms in short children with normal and decreased GH secretion. The analysis included 22 children (20 boys and 2 girls) aged 11.1-16.9 yr (mean +/- S.E.M. = 14.1 +/- 0.3 yr) with short stature (height SDS below -2.0). Based on the GH peak in stimulation tests patients were divided into two groups: idiopathic short stature (ISS, n = 11; GH peak > or = 10 ng/mL) and GH deficiency (GHD, n = 11; GH peak < 10 ng/mL). In all patients the circadian melatonin rhythm was assessed on the basis of nine blood samples, collected in 4-hr intervals during the daytime and 2-hr intervals at night, with dark period lasting from 22:00 to 06:00 hr. Magnetic resonance imaging examination excluded organic abnormalities in central nervous system in all patients. Melatonin concentration at 24:00, 02:00 and 04:00 hr as well as the area under curve of melatonin concentrations (AUC) were significantly higher in the patients with GHD than in individuals with ISS. Significant correlations between GH secretion and melatonin concentrations at 24:00, 02:00 and 04:00 hr, and AUC were also observed. On the basis of these data it seems that the assessment of nocturnal melatonin secretion might be a valuable diagnostic tool used for the improvement of the difficult diagnosis of short stature in children.

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.

The role of somatostatin (octreotide) in the regulation of melatonin secretion in healthy volunteers and in patients with primary hypothyroidism

Somatostatin has been found in the pineal gland of several animal species, which suggests that it may be involved in the regulation of melatonin secretion. Whether somatostatin has regulatory influence on melatonin secretion in man has never been unequivocally shown. We studied the nocturnal melatonin secretion in 8 healthy volunteers, and 6 women with untreated primary hypothyroidism, a disease state that is associated with increased nocturnal secretion of melatonin. The participants were given subcutaneous injections at 18:00 h and 23:00 h of either saline or octreotide (Sandostatin; each injection 50 microg). During the nights when the healthy volunteers were given octreotide, melatonin secretion was similar to that recorded during administration of saline. Also the urinary excretion of melatonin was of similar magnitude at these two occasions. By contrast, the GH secretion was significantly lower the nights the healthy controls were given octreotide (GH AUC 22.6+/-5.4 mU/l x h during octreotide and 126.6+/-21.9 mU/l x h during saline; p<0.01). The patients with hypothyroidism also showed similar nocturnal melatonin secretion during octreotide and saline. Urinary excretion of melatonin also remained unchanged, as did GH secretion. The total nocturnal secretion of TSH was, however, significantly reduced by octreotide (TSH AUC 562+/-136 mU/l x h during octreotide and 851+/-185 mU/l x h during saline; p<0.05), thus suggesting that 100 microg of octreotide should be sufficient to inhibit also the pinealocytes if their function were regulated by somatostatin. Since exogenous somatostatin--in the form of octreotide--fails to influence nocturnal secretion and urinary excretion of melatonin in normal subjects and in patients with primary hypothyroidism, it is reasonable to assume that endogenous somatostatin may not be an important regulator of melatonin secretion in man.