Arginine induced growth hormone (hGH) response and paradoxical hGH secretion stimulated by TRH in diabetes mellitus

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

Distribution of thyrotrophin-releasing hormone receptor messenger RNA in rat pituitary and brain

The distribution sites of messenger RNA encoding for the thyrotrophin-releasing hormone receptor have been studied in rat pituitary and brain. A specific 35S-labelled riboprobe generated from a rat thyrotrophin-releasing hormone receptor complementary DNA clone was used to perform in situ hybridization experiments on brain and pituitary sections. A positive hybridization signal was found in the anterior lobe of the pituitary gland, the intermediate and posterior lobes were negative. Hybridization was also detected in different areas of the brain. These areas include distinct regions in the olfactory system, septal area, amygdaloid complex, cerebral cortex, hypothalamus, hippocampus, basal ganglia and the motor nuclei of cranial nerves in brainstem. This study has shown for the first time the exact site of thyrotrophin-releasing hormone receptor expression in the central nervous system. These results correlate well with regions thought to possess thyrotrophin-releasing hormone recognition sites.

Inappropriate growth-hormone (GH) response to thyrotropin-releasing hormone (TRH) occurs infrequently in well-regulated diabetes mellitus

We randomly administered thyrotropin-releasing hormone (200 micrograms, as an i.v. bolus) or control saline (in isovolumic amount) to 30 male diabetic subjects (23 IDDM, 7 NIDDM) in fair metabolic control (HbA1 9.7 +/- 0.3%, means +/- SEM) and to 12 healthy male controls on two different mornings. While GH in the basal state was similar in IDDM, NIDDM and normal subjects, TRH administration evoked a significant GH release only in a single IDDM individual. The only GH-responder to TRH was a newly-diagnosed (two weeks) IDDM patient, still with a high glycated hemoglobin level (HbA1 11.1%), despite normal plasma glucose levels. Saline infusion did not affect GH concentrations either in normals or in diabetics. Exaggerated GH responses to TRH are uncommon in diabetic patients in good metabolic conditions.

Growth hormone response to thyrotropin releasing hormone and placebo in a group of insulin dependent diabetic patients

In order to evaluate if the assessment of the paradoxical GH responses to TRH in diabetic subjects could be altered by the presence of spontaneous fluctuations in plasma GH levels, we compared GH responses to TRH and to saline injection in 19 insulin-dependent diabetic patients. We observed significant increments (greater than 5 ng/ml) in plasma GH levels after TRH iv administration in 5 of 19 patients (26%); on the other hand, a significant increase was also observed in 6 patients (31%) after saline. We conclude that, at least in some diabetics, spontaneous GH pulses might be misinterpreted as paradoxical GH responses after a nonspecific stimulus administration. Moreover, the real existence of the paradoxical GH response to TRH has to be assessed using the following strict criteria: a sufficient magnitude in GH increment (greater than 5 ng/ml), the comparison of the kinetics of GH secretion after TRH and saline in the same patient, the presence of a significant GH rise above basal levels within the first 30 min after TRH injection.