Selective defect in gonadotrophin secretion in patients with autonomic failure

Gonadotropin-Releasing Hormone and Its Role in the Enteric Nervous System

Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone, and luteinizing hormone orchestrate the reproduction cycle and regulate the sex steroid secretion from the gonads. In mammals, GnRH1 is secreted as a hormone from the hypothalamus, whereas both GnRH1 and GnRH2 are present as neurotransmitters/peptides in various tissues, where the peptides exert many different effects. mRNA coding for GnRH1 and GnRH2 have been described in the human gastrointestinal tract, and GnRH has been found in both submucosal and myenteric neurons. mRNA coding for GnRH and the fully expressed peptide have been found in rat enteric neurons by some researchers but not by others. mRNA coding for GnRH receptors, but not the fully expressed receptor, has been found in one rat study. GnRH influences gastrointestinal motility and secretion. GnRH analogs are clinically used in the treatment of sex hormone-dependent diseases, i.e., endometriosis and malignancies, and as pretreatment for in vitro fertilization. Reduced numbers of enteric neurons and IgM antibodies against GnRH and progonadoliberin-2 (precursor of GnRH2) have been observed after such treatment, with the clinical picture of gastrointestinal dysmotility. Similarly, a rat model of enteric neurodegeneration has been developed after administration of the GnRH analog buserelin. Serum IgM antibodies against GnRH1, progonadoliberin-2, and GnRH receptors have been described in patients with signs and symptoms of gastrointestinal dysmotility and/or autonomic dysfunction, such as irritable bowel syndrome, enteric dysmotility, diabetes mellitus, and primary Sjögren's syndrome. Thus, apart from regulation of reproduction and sex hormone secretion, GnRH also constitutes a part of enteric nervous system (ENS) and its functions during physiological and pathological conditions. This review aimed to describe the role of GnRH in the ENS.

Catecholaminergic axons innervate LH-releasing hormone immunoreactive neurons of the human diencephalon

Catecholamines have been shown to modulate gonadal functions via interactions with hypothalamic LH-releasing hormone (LHRH)-synthesizing neurons. To reveal the morphological background of this phenomenon, the distribution of LHRH neurons and tyrosine hydroxylase (TH)-immunoreactive (IR), catecholaminergic structures were mapped in the human diencephalon. First, the location of LHRH and TH-IR neuronal elements was analyzed, and then the relationship between the two different systems was examined. The LHRH-IR cell bodies were mainly present in the medial preoptic and infundibular areas. The TH-IR perikarya were located in the periventricular, paraventricular, and supraoptic hypothalamic nuclei and also in the median eminence. The TH-IR fibers were numerous in septal, infundibular, periventricular, and lateral hypothalamic regions. The brown, diaminobenzidine-labeled LHRH-containing perikarya were found to receive black, silver-intensified, TH-positive axon terminals in the infundibular and medial preoptic areas. However, in the preoptic and caudal parts of the diencephalon, only a few juxtapositions were noted. The present results indicate that hormone released from diencephalic LHRH-IR neurons in humans may be influenced by the central catecholaminergic system via direct synaptic mechanisms.

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.

Plasma profiles of adrenocorticotropic hormone, cortisol, growth hormone and prolactin in patients with untreated Parkinson's disease

Plasma profiles of prolactin, growth hormone, adrenocorticotropic hormone (ACTH) and cortisol were evaluated in a group of untreated patients with idiopathic Parkinson's disease and a group of healthy age-matched controls. Plasma integrated concentrations of all hormones except prolactin were significantly lower in the patients as compared with the controls; however, prolactin nocturnal peak concentration was significantly elevated in the patients; nocturnal growth hormone levels were significantly reduced in the Parkinson group; ACTH and cortisol plasma concentrations were also consistently lower during most of the day in the patients with Parkinson's disease. These data confirm the presence of a hypothalamic disturbance in patients with idiopathic Parkinson's disease, which can affect pituitary function.