Hormonal responses to hypoglycemia in orthostatic hypotension patients with adrenergic insufficiency

Neuroendocrine responses to levodopa in multiple system atrophy (MSA)

Hypothalamic dopaminergic pathways are involved in the regulation of growth hormone and prolactin release from the anterior pituitary. Neuroendocrine studies in patients with multiple system atrophy (MSA), in whom there is a reported loss of hypothalamic dopamine, are few and contradictory. We therefore studied the neuroendocrine responses to 250 mg levodopa (plus 25 mg carbidopa) in subjects with MSA (n = 15), and compared them with age- and sex-matched healthy control subjects (n = 8). There were no significant differences in basal or post-levodopa levels of growth hormone (GH), growth hormone-releasing hormone (GHRH), glucose, insulin-like growth factor (IGF-1), or thyroid-stimulating hormone (TSH) between the groups. In patients with MSA, basal levels of prolactin were elevated (21.1 +/- 5.2 ng/mL [mean +/-standard error]) compared with control subjects (12.1 +/- 1.7, p <0.05), and after L-dopa there was increased variability in prolactin response with less suppression compared with control subjects. In conclusion, in patients with MSA, the GHRH and GH responses to L-dopa were preserved and were similar to responses in age-matched control subjects. In contrast, there was impaired dopaminergic suppression of prolactin secretion. In patients with MSA this may represent a selective dysfunction, rather than generalized loss, of tubero-infundibular dopaminergic neurones.

Autonomic involvement in Guillain-Barré syndrome: a review

Autonomic neuropathy is an important and common complication of Guillain-Barré syndrome (GBS). Manifestations be present in cardiovascular, sudomotor, gastrointestinal and other systems involving both sympathetic and parasympathetic fibers. Some apparently selective acute autonomic neuropathies may be subvarieties of GBS. Experimental work in animal models, pathological studies of GBS patients, and autonomic function studies have provided some help in the understanding of this complication. In managing GBS patients with autonomic dysfunction there are important practical considerations that can improve their care. In this article we review the literature on autonomic neuropathy in GBS and propose a management scheme to accommodate it in the overall treatment of the neuropathy.

The insulin tolerance test and the ovine corticotrophin-releasing hormone test in episodic cluster headache

Clinical observations indicate a central nervous system, probably hypothalamic, involvement in cluster headache pathogenesis. In order to investigate the supposed hypothalamic involvement in cluster headache, we followed the hypothalamic-pituitary-adrenal axis and autonomic responses to the insulin tolerance test and the ovine corticotrophin-releasing hormone test in episodic cluster headache patients, both during remission and during the cluster period. The study revealed increased basal cortisol levels in all cluster patients. A blunted cortisol response to ovine corticotrophin-releasing hormone, in spite of a normal ACTH surge, was subsequently found in both illness phases. These findings suggest hypothalamic-pituitary-adrenal axis hyperactivity in both cluster phases. Furthermore, reduced ACTH and cortisol responses after insulin challenge were also observed in both remission and cluster period patients; a reduced norepinephrine surge was seen only in the cluster period. Taken together, these results suggest a hypothalamic involvement in the altered neuroendocrinological and autonomic responses found in our patients.

Beta-endorphin, ACTH, and catecholamine responses in chronic autonomic failure

Plasma epinephrine (EPI), norepinephrine (NE), beta-endorphin, and corticotropin (ACTH) responses were measured during insulin-induced hypoglycemia in normal subjects and in patients with either multiple system atrophy (MSA) or idiopathic orthostatic hypotension (IOH). In normal subjects, there was a striking rise in EPI, NE, beta-endorphin, and ACTH following the nadir of hypoglycemia. Both beta-endorphin and ACTH responses were significantly lower than normal in patients with MSA, in contrast to normal levels in IOH patients. No correlation was observed between the degree of adrenergic insufficiency and the beta-endorphin and ACTH responses. The normal peptide responses in IOH are consistent with involvement limited to the peripheral sympathetic nervous system, whereas lesions in the central nervous system in MSA interfere with release of beta-endorphin and ACTH in response to hypoglycemia. The strong correlation between beta-endorphin and ACTH levels is consistent with their common origin. Peripheral adrenergic activity is not essential for beta-endorphin and ACTH release in humans.

Growth hormone response to clonidine is impaired in patients with central sympathetic degeneration

Serum growth hormone (GH) levels before and after intravenous clonidine (1.5 mcg/Kg) were measured in normal subjects and patients with chronic idiopathic autonomic failure (AF) due to central sympathetic degeneration. Normal subjects showed a rise in plasma GH from 2 +/- 1 mU/l to 27 +/- 12 mU/l. Basal levels were similar but there was no rise in GH levels in the AF patients. There was no difference in sedation in the two groups, indicating similar central nervous system penetration of the drug. Systolic blood pressure fell in both groups. Diastolic blood pressure fell significantly in normals but not in the AF patients. Clonidine-induced growth hormone release may be a potentially useful neuroendocrine marker indicating derangement of certain components of the central alpha-adrenergic system in man.

Growth hormone, vasopressin, cortisol, and catecholamine responses to insulin hypoglycemia in alcoholics

The hormonal responses to insulin-induced hypoglycemia were studied in 15 abstinent alcoholics with varying degrees of central and peripheral nerve damage and in six normal controls. Blood samples were taken at intervals after the injection of soluble insulin (0.1 U/kg of body weight). Growth hormone responses were significantly depressed (p less than 0.05) in nine alcoholics with severe central nerve damage (Korsakoff's psychosis) as compared to other alcoholic subjects. The alcoholic subjects with Korsakoff's psychosis also showed significant depression (p less than 0.01) of glucose recovery from hypoglycemia as compared with controls. However, responses of vasopressin, cortisol, and catecholamines (epinephrine and norepinephrine) were generally normal in the Korsakoff patients. Our results do not support previous suggestions that impairment of memory in alcoholism may be related to altered vasopressin secretion, even though the reduced growth hormone secretion in brain-damaged alcoholics does indicate some hypothalamic-pituitary dysfunction.

Hormonal response to insulin-induced hypoglycemia in patients with Shy-Drager syndrome

We examined the response of plasma glucose concentration and glucose counterregulatory factors (eg, glucagon, epinephrine, growth hormone, cortisol, and norepinephrine) to insulin-induced hypoglycemia in four patients with Shy-Drager syndrome and in five control subjects to determine if glucose counterregulation occurred in the patients with sympathetic and parasympathetic nervous system defects. The recovery of plasma glucose from hypoglycemia in a slower phase in the patients appeared to be almost similar to that in the control subjects, along with the absence of an initial rapid recovery phase; that is, there was no significant difference in the plasma glucose levels observed at any point between the patients and the control subjects. Although the insulin-induced hypoglycemia in the control subjects provoked a rapid release of epinephrine, followed by an increase in the plasma glucagon, growth hormone, and cortisol levels, it did not cause a significant increase in any of the glucose counterregulatory factors in the patients. Our findings that the restoration of normoglycemia after insulin-induced hypoglycemia occurred despite no significant increase in the counterregulatory hormonal factors suggest that other glucose counterregulatory mechanisms (eg, increased glucose release from the liver by the intrinsic effect of hypoglycemia on the liver) than the hormonal glucose counterregulatory factors might play an important role in the recovery of plasma glucose from insulin-induced hypoglycemia in a state of chronic deficiency of hormonal factors.

Deficient catecholamine release as the basis of orthostatic hypotension in pernicious anaemia

A patient with peripheral neuropathy and orthostatic hypotension was found to have pernicious anaemia. Symptoms improved after vitamin B12 replacement therapy. Insulin tolerance testing showed that the patient lacked catecholamine, heart rate, and sweating responses to hypoglycaemia. This indicates that pernicious anaemia may cause orthostatic hypotension owing to failure of noradrenaline release.