Plasma growth hormone profile in acromegaly before and ten days after transsphenoidal surgery

Serum lipoproteins in acromegaly before and 6-15 months after transsphenoidal adenomectomy

OBJECTIVES

Acromegaly is a rare disorder characterized by over-secretion of GH, most often because of a pituitary adenoma. The disease is associated with disturbances in lipoprotein metabolism and an increased cardiovascular mortality. The aim of the present study was to investigate whether treatment of acromegaly results in changes in serum concentrations of lipids and apolipoproteins, including lipoprotein(a) (Lp(a)).

DESIGN

Fourteen patients with clinical features of acromegaly and increased GH secretion were studied 1-10 months before and 6-15 months after transsphenoidal adenomectomy in an open study.

PATIENTS

Three patients had diabetes mellitus before surgery and two of these patients had normalized serum glucose levels post-operatively. Mean and baseline plasma GH levels were determined from 24-hour GH profiles. Serum samples were taken in the morning after an overnight fast. All patients were normocholesterolaemic, and four patients were hypertriglyceridaemic before treatment.

RESULTS

Mean plasma GH levels decreased from 34.5 +/- 7.4 to 2.1 +/- 0.4 mU/l (mean +/- SEM). Serum IGF-I, insulin and free T3 levels decreased and serum SHBG concentrations increased post-operatively. There was no effect of treatment on serum cholesterol concentrations, but serum triglyceride concentrations decreased. Serum apolipoprotein (apo) B and apoE levels were unaffected by treatment. Serum apoA-I levels increased and Lp(a) levels decreased post-operatively.

CONCLUSIONS

Successful treatment of acromegaly, resulting in normal mean GH values (< 5 mU/l) and/or normal responsiveness to TRH, have beneficial effects on serum lipoproteins with increased serum apoA-I levels and decreased serum levels of triglycerides and Lp(a). These effects seem to be independent of improvement in glucose tolerance, since patients with diabetes mellitus before surgery and normal fasting blood glucose levels post-operatively had similar lipoprotein responses to treatment as those with normal fasting blood glucose levels before surgery.

Characterization of 24-hour growth hormone secretion in acromegaly: implications for diagnosis and therapy

OBJECTIVE

Early studies of acromegaly undertaken before the general availability of insulin-like growth factor I (IGF-I) assays have used arbitrary and varying growth hormone (GH) threshold levels for diagnosing and assessing outcome of treatment for this disease. We have undertaken a detailed study of GH secretion and its relationship to IGF-I levels to assess the usefulness of GH and IGF-I measurements in the assessment of acromegaly.

PATIENTS

Thirty acromegalic subjects (12 untreated and 16 previously treated) and 30 age and sex-matched normal subjects were studied.

MEASUREMENTS

Twenty-four-hour GH secretion was obtained from 20-minute sampling and serum IGF-I was measured. Comparisons were made of IGF-I, mean 24-hour GH concentration, and of the pulsatile and diurnal characteristics of GH secretion between the two groups.

RESULTS

IGF-I levels in untreated acromegaly were elevated and clearly separated from the normal range. Mean 24-hour GH concentrations in untreated and treated acromegalic subjects with elevated IGF-I (> 40 nmol/l) were greater than (P < 0.01), and showed good separation from, those of normal subjects only after age-matching. From the 24-hour profiles, nadir GH levels in normal subjects fell below the level of detectability while those in untreated acromegalic subjects did not. Pulse amplitude (P < 0.01), ratio of pulsatile to non-pulsatile GH release and the night to daytime GH ratio (P < 0.05) were significantly reduced in acromegaly. In the six patients who attained normal IGF-I levels after surgery, pulsatile characteristics remained abnormal in four. Mean 24-hour GH was significant related (r = 0.57) to IGF-I. A random GH concentration > 2.5 micrograms/l (5 mIU/l) has a sensitivity of 77% and specificity of 95% in identifying acromegalic patients who have biochemically active disease (elevated IGF-I) after treatment.

CONCLUSIONS

Patients with active acromegaly secrete more GH than age-matched normal controls. GH secretion in acromegaly is characterized by marked blunting of pulsatile secretion and, in contrast to normal subjects, the failure of GH to fall to undetectable levels at any time during the 24-hour day. IGF-I measurement is a more practical alternative in the diagnosis of acromegaly and in the assessment of therapeutic outcome. Since abnormalities of GH regulation may persist despite normalization of IGF-I, a distinction between remission and cure should be made. Detailed post-treatment evaluation of GH secretion is necessary to define the nature of underlying GH regulation and to evaluate the risk of disease recurrence.

Cardiovascular and renal effects of growth hormone

OBJECTIVE

With the advent of recombinant human GH (rhGH), it has become possible in controlled clinical studies to explore the effects of GH replacement in adults with GH deficiency. The objective of this study was to determine cardiovascular and renal effects of GH replacement in adults with GH deficiency.

PATIENTS

We studied ten patients (one woman and nine men), mean age 47 years, with GH deficiency.

DESIGN

The patients were given s.c. rhGH (Humatrope, Eli Lilly) 0.5 U/kg/week or placebo in a 6-month double blind cross-over study. Cardiac and renal function was measured before drug administration (baseline), before cross-over (i.e. after 6 months), and before termination of drug administration (after another 6 months). Analysis of variance was used to compare measurements during GH replacement with baseline and placebo measurements. One patient was excluded because of atrial fibrillation.

MEASUREMENTS

Main outcome measures were glomerular filtration rate and Doppler-echocardiographic estimates of cardiac function and structure. Computerized exercise electrocardiogram, spirometry, and blood samples for analyses of plasma hormones were also obtained.

RESULTS

Left ventricular function was maintained during GH replacement. However, left ventricular mass increased from 211 to 249 g (P < 0.05) mainly due to increased left ventricular dimension since wall thicknesses did not increase. The left atrium increased from 38 to 41 mm (P < 0.05), possibly because stroke volume increased from 92 to 118 ml (P < 0.0001) and cardiac output increased from 5.29 to 7.58 l/min (P < 0.05). Total peripheral resistance decreased from 18.9 to 12.4 mmHg min/l (P < 0.05), and diastolic blood pressure from 79 to 72 mmHg (P < 0.05). Heart rate at rest increased from 58 to 70 beats/min. Systolic blood pressure at rest was unchanged, as was systolic blood pressure during dynamic exercise. GH replacement did not cause ST-abnormalities. Serum creatinine decreased from 91.4 to 85.3 mumol/l (P < 0.05) and glomerular filtration rate increased from 89.6 to 99.8 ml/min (P < 0.01).

CONCLUSIONS

Thus, GH replacement has favourable cardiovascular and renal effects including increase of stroke volume and glomerular filtration rate with reduction of peripheral resistance.

The influence of octreotide treatment on pulsatile growth hormone release in acromegaly

The pulsatile release of GH was investigated in eight active acromegalic patients before and during a subcutaneous infusion of 300 micrograms octreotide/24 h for 4 weeks. The number of GH pulses increased from a basal value of 14.4/24h to 16.3/24h during octreotide therapy. At the same time the mean GH concentration, valley concentration, peak height and amplitude decreased significantly. The inhibitory effect of octreotide on pulse characteristics did not depend on the time of day. IGF-I levels also decreased significantly; in five patients normal levels were reached. IGF-I levels correlated significantly with the mean GH level (r = 0.714, P less than 0.001), mean valley concentration (r = 0.697, P less than 0.001) and, to a lesser extent, area under the curve (r = 0.436, P = 0.033), but not the number of pulses. Plasma octreotide levels did not correlate with pulse parameters. In all but one patient a circadian rhythm was present during both the basal study and octreotide therapy. Compared with surgically treated acromegalics, the number of GH pulses was higher in untreated and octreotide-treated patients. This study demonstrates the pulsatile release of GH in active acromegaly both before and during octreotide therapy. This result suggests that endogenous GHRH is important for the generation of GH pulses in this disease.

Low-dose pituitary irradiation for acromegaly

External radiotherapy has been used as primary treatment for acromegaly in 29 patients and in combination with surgery in 41 patients in whom growth hormone levels remained elevated postoperatively. Fourteen further patients who did not receive radiotherapy have also been studied, four of whom had undergone surgical treatment. Radiotherapy schedules consisted of 20 Gy in eight fractions over 11 days (n = 23) or 35-40 Gy in 15 fractions over 21 days (n = 47). Growth hormone hypersecretion was either unchanged or increased with time in non-irradiated patients. In those patients who underwent radiotherapy, the likelihood of the mean GH level during GTT falling to less than 5 mU/l was unaffected by the total dose of radiation administered. However, patients with a pre-radiotherapy GH level of less than 30 mU/l showed a significantly increased probability of achieving a post- radiotherapy GH level less than 5 mU/l (P = 0.002). Previous surgery, initial serum prolactin and the age or sex of the patient did not predict the successful outcome of radiotherapy. In view of the known dose dependency of radiation-induced hypopituitarism, lower radiation dose schedules (20 Gy; eight fractions in 11 days) can be used in acromegaly with some benefit, especially in younger patients. However, all patients should undergo operative removal of as much GH-secreting tissue as possible, in order to lower GH levels and increase the probability of achieving a cure following radiotherapy.

Body composition in acromegaly: the effect of treatment

Total body water (TBW) and total potassium (TBK) were measured in patients participating in a follow-up investigation of all acromegalic patients seen between 1956 and 1984. The results were compared with population-based estimates of TBK and TBW calculated from height (BH), weight (BW) age and sex, using data from a large number of healthy subjects (n = 476). The findings were compared with values obtained at diagnosis and were also related to growth hormone (GH) and IGF-I/SmC concentrations at follow-up. BW at follow-up was unchanged compared to BW at diagnosis and was 9.7 and 10.0 kg higher in males and females, respectively, than in healthy subjects of the same BH (BWnorm). Growth hormone concentration at follow-up correlated directly with excess extracellular fluid volume (ECW%) (P less than 0.001) and inversely with the ratio observed/predicted body fat (BF%) (P less than 0.001) as well as with BW/BWnorm (P less than 0.05). On the other hand, GH concentration did not correlate with excess body cell mass (BCM%) estimated from TBK. IGF-I/SmC concentration correlated with GH concentration at follow-up (P less than 0.001) and with ECW% (P less than 0.01) but not with BCM% or BF%. In 39 patients, data on body composition were also available at diagnosis. Of these, three males had developed gonadal insufficiency and their BCM had decreased markedly. One patient had suffered from hemiplegia. Five patients had not received any treatment. In the remaining 30 treated patients, those with a post-treatment GH concentration below 5 mU/l were normalized with respect to ECW and BF. BCM, however, was unchanged. In contrast, patients with GH concentration greater than or equal to mU/l displayed unchanged body composition. Furthermore, BH decreased significantly in successfully treated patients.