Retinopathy and plasma growth hormone levels in idiopathic hemochromatosis with diabetes

Growth hormone and ocular dysfunction: Endocrine, paracrine or autocrine etiologies?

The eye is a target site for GH action and growth hormone has been implicated in diabetic retinopathy and other ocular dysfunctions. However, while this could reflect the hypersecretion of pituitary GH, the expression of the GH gene is now known to occur in ocular tissues and it could thus also reflect excess GH production within the eye itself. The possibility that ocular dysfunctions might arise from endocrine, autocrine or paracrine etiologies of GH overexpression is therefore the focus of this brief review.

Radial artery wall alterations in genetic hemochromatosis before and after iron depletion therapy

Iron overload is believed to have an adverse influence on the cardiovascular system and animal studies have shown that iron may be involved in the events that lead to atherosclerosis via an enhancement of smooth muscle cell proliferation, lipid oxidation, and free radical production. There are no data on the effect of iron overload on arterial structural and mechanical properties in humans. We measured wall thickness and distensibility (D) by ultrasonography of the radial artery in 12 patients with uncomplicated genetic hemochromatosis (GH) who were normotensive and without atherosclerotic plaques. Twelve age- and sex-matched patients were taken as controls. Nine patients were evaluated also after iron depletion. Wall thickness was greater in patients with GH than in controls (+50%, P <.01) whereas D was slightly reduced in the former group compared with the latter group, though the difference was not statistically significant. After iron depletion, a significant reduction of wall thickness and a significant increase in D were observed (-24% and +33%, P <.05 for both). Thus, in patients with hemochromatosis, arterial wall thickness is increased before the onset of cardiovascular complications. This alteration is reverted by iron depletion, which also can improve the initial and modest radial artery wall stiffening associated with this condition. Thus, functional and structural alterations in midsize muscle arteries may be an early abnormality of hemochromatosis.

Dual hormonal replacement therapy with insulin and recombinant human insulin-like growth factor (IGF)-I in insulin-dependent diabetes mellitus: effects on the growth hormone/IGF/IGF-binding protein system

Patients with insulin-dependent diabetes mellitus (IDDM) exhibit abnormalities in the GH/insulin-like growth factor (IGF) axis, including GH hypersecretion, low serum IGF-I and IGF-binding protein-3 (IGFBP-3) levels, and elevated IGFBP-1 levels. We recently demonstrated that in IDDM, dual hormonal replacement therapy with insulin plus recombinant human IGF-I (rhIGF-I) improves glycemic control better than insulin alone. To determine whether the addition of rhIGF-I therapy to insulin therapy also corrects GH/IGF/ IGFBP abnormalities, we examined the effects of chronic combined rhIGF-I/insulin therapy on key components of the somatotropin axis. Forty-three pediatric IDDM patients were randomly assigned to groups receiving daily, fasting subcutaneous injections of placebo or rhIGF-I (80 micrograms.kg.day) for 28 days, while continuing to receive splitmix insulin therapy and intensive outpatient management. rhIGF-I therapy corrected IGF-I deficiency, suppressed IGFBP-1 levels (P < 0.01), and induced a trend toward lower circulating GH levels throughout the study. rhIGF-I therapy also induced an approximate 50% decrease in IGF-II levels (P < 0.001) and an approximate 70% increase in IGFBP-2 levels (P < 0.05). Serum IGFBP-3 levels, normal before treatment, remained normal during rhIGF-I administration. All effects were apparent during the first week of rhIGF-I therapy and persisted throughout treatment. Because improvements in the GH/ IGF axis abnormalities and in glycemic control were greater in subjects receiving combined rhIGF-I and insulin, these data strongly support the concept that dual hormonal replacement in IDDM may offer distinct therapeutic advantages over insulin monotherapy.

Effect of a long-acting somatostatin analogue (BIM23014) on proliferative diabetic retinopathy: a pilot study

A pilot study on the use of a continuous infusion of somatostatin, by subcutaneous pumps in the management of proliferative diabetic retinopathy is reported. Two patients out of eight with proliferative retinopathy demonstrated improvement. One patient demonstrated regression of disc new vessels and the other a reduced area of retinal capillary non-perfusion, both demonstrated by fluorescein angiography. Control patients showed worsening of fluorescein leakage over the observation period of four to six weeks whereas the other six patients given the somatostatin infusion did not demonstrate any deterioration. The mechanism of action of somatostatin in this study is unknown but it is thought to have direct anti-angiogenic properties as well as inhibiting growth hormone secretion.

Abnormalities in estrogen, androgen, and insulin metabolism in idiopathic hemochromatosis

Of 44 male patients with idiopathic hemochromatosis who were diagnosed at an early stage without morphological or biochemical evidence of liver disease, 25% suffered from impotence and 34% manifested glucose intolerance. Impotence was correlated with a 50% reduction in plasma testosterone, resulting from a 63% decrease in testosterone production. Testicular atrophy was caused by insufficient secretion of gonadotropins due to the selective accumulation of iron in gonadotropic cells of the pituitary gland. However, peripheral sexual hormone metabolism, in particular the conversion of androgens to estrogens, remained unaltered. It was therefore possible to employ substitution therapy successfully with testosterone in these men, and hyperestrogenism was not observed as a side effect. The pathogenetic factors in the development of diabetes mellitus in patients with idiopathic hemochromatosis include impaired insulin secretion caused by the selective deposition of iron in B-cells of the pancreas and insulin resistance due to iron accumulation in the liver. In particular, the insulin resistance is markedly improved after depletion of body iron stores by phlebotomy treatment, resulting in lower insulin requirements in patients with insulin-dependent diabetes as well as improvement of carbohydrate metabolisms in about half of the patients with non-insulin-dependent diabetes. We have concluded that hypogonadism and carbohydrate intolerance are caused by the specific distribution pattern of excess iron in the organism, accompanied by functional impairment of affected parenchymal cells.

Growth hormone, prolactin and thyrotrophin responses to thyrotrophin-releasing hormone in diabetic patients

Growth hormone (GH), prolactin (PRL) and thyrotrophin (TSH) responses to thyrotrophin-releasing hormone (TRH) were studied in 15 insulin-dependent diabetic patients. Basal plasma GH levels were raised above 5 mu./l in 6 patients and following the injection of TRH there was a significant rise in plasma GH levels in 9. The mean rise in plasma GH from basal to peak values was significant in the group as a whole (P < 0.01). Basal PRL and TSH levels were normal and rose normally in response to TRH. GH release may be qualitatively abnormal in some diabetics and any such loss of specificity of GH-releasing mechanisms would further contribute to the raised GH levels found in many diabetics which would be of importance if GH is a factor in the aetiology of diabetic microangiopathy.

The GnRH test in idiopathic hemochromatosis

In 10 patients, 8 males and 2 females, suffering from idiopathic hemochromatosis (IH), the gonadotropic function has been studied using the GnRH test (iv administration of 100 micrograms) to make precise the pathogenesis of their hypogonadism. The FSH and LH mean basal levels were low and almost unaffected by GnRH (p < 0.001 at each time value when compared to controls). The hypogonadism often observed during the course of IH seems to be hypogonadotropic. Various factors could be responsible for this disturbance. The exact site of the lesion, whether hypothalamic or hypophyseal, remains unknown.

Hormonal profile, blood sugar control and HLA patterns in long-term insulin dependent diabetes with and without vascular disease

Nineteen insulin dependent diabetics with onset at 30 years of age or less and duration of diabetes of greater than 25 years were divided into two groups on the basis of the presence or absence of clinically evident vascular disease. The patients without vascular disease were characterised by a later mean age of onset, lower fasting growth hormone concentration, and a lower frequency of the unusual HLA pattern B8 without A1 compared to the diabetics with vascular complications. The level of blood glucose control assessed over the last 15 years, insulin antibody titres, plasma glucagon levels and plasma cholesterol did not differ between the two groups. Residual beta cell activity was found in only one of the 19 patients. Although this study does not exclude an effect of the degree of blood glucose control or persistence of beta cell function in the early stages of diabetes on the subsequent development of vascular disease, it suggests that genetic factors, age of onset and plasma growth hormone levels may be more important.

Glucagon secretion in diabetic patients with idiopathic haemochromatosis

The aim of the present investigation was to determine in patients with idiopathic haemochromatosis whether diabetes is of the primary type or secondary to pancreatic injury due to iron deposition. For this purpose, plasma glucagon concentrations were determined following arginine infusion or an oral glucose load in eight patients with diabetes and idiopathic haemochromatosis. The enhanced glucagon response to arginine and the nonsuppressibility of glucagon secretion by oral glucose found in these patients were similar to the results found in the same tests performed in our previous series of patients with "idiopathic" diabetes and at variance with those reported by others in patients with chronic pancreatitis.