Receptors and sites of synthesis and storage of gamma-aminobutyric acid in human pituitary glands and in growth hormone adenomas.

gamma-Aminobutyric acid (GABA) is an important regulatory factor of pituitary gland function, which in addition to hypothalamic neurons, can be derived from intrapituitary sources, ie, growth hormone (GH) cells of rat and monkey. We report that human pituitary glands also express 2 isoforms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD 65; GAD 67), the vesicular GABA transporter (VGAT), and multiple subunits of GABA (A, B, and C) receptors. GABA production and storage occurs in GH cells, as demonstrated by cellular colocalization of immunoreactive GAD and VGAT in GH cells and by reverse transcription-polymerase chain reaction analysis of laser capture-microdissected immunostained GH cells.

Evidence for a GABAergic system in rodent and human testis: local GABA production and GABA receptors.

The major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known.

Molecular and physiological evidence for functional gamma-aminobutyric acid (GABA)-C receptors in growth hormone-secreting cells.

The neurotransmitter gamma-aminobutyric acid (GABA), released by hypothalamic neurons as well as by growth hormone- (GH) and adrenocorticotropin-producing cells, is a regulator of pituitary endocrine functions. Different classes of GABA receptors may be involved. In this study, we report that GH cells, isolated by laser microdissection from rat pituitary slices, possess the GABA-C receptor subunit rho2.

An autocrine role for pituitary GABA: activation of GABA-B receptors and regulation of growth hormone levels.

There is increasing evidence suggesting that the neurotransmitter gamma-aminobutyric acid (GABA) is a local factor involved in the regulation of endocrine organs. Examples of such functions are documented in the pancreas, but recent results suggest that GABA may act in a similar way in the pituitary, in which GABA receptors are expressed and pituitary growth hormone (GH) cells provide a source of GABA. We hypothesised that GABA secreted in somatotropes may act as an autoregulatory signaling molecule.